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International Journal of Heat and Mass Transfer
Journal Prestige (SJR): 1.498
Citation Impact (citeScore): 4
Number of Followers: 350  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
Published by Elsevier Homepage  [3206 journals]
  • Thermo-hydrodynamic model and parametric optimization of a novel miniature
           closed oscillating heat pipe with periodic expansion-constriction
           condensers
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Wei-Wei Wang, Lei Wang, Yang Cai, Guo-Biao Yang, Fu-Yun Zhao, Di Liu, Qing-Hua YuAbstractIn order to promote the thermo-hydrodynamic performance of a single miniature loop pulsating heat pipe (PHP), the oscillatory behaviors and thermal transport capability of PHPs should be comprehensively and accurately analyzed. A novel closed PHP with periodic expansion-constriction condenser was proposed, where phase change and thermal transport processes could be reproduced by a comprehensive computational fluid dynamics (CFD) technique together with volume of fluid (VOF) methodology. Moreover, available experimental data were utilized in the validation of the model for the average deviations within 10%. Subsequently, a full numerical modeling for oscillating flows under different operating conditions was sensitively tested, varying thermal power and filling ratio, respectively from 18 W to 86 W and from 40% to 60%. Complicated fluid dynamical phenomena such as nuclear boiling, formation of slug, coalescence of vapor plug and flow patterns transformation have been analyzed inside the PHPs; CFD visualizations were also presented excellent agreements with flow behaviors from previous experimental photographs. Additionally, the effects of periodic expansion-constriction condenser on the flow regimes, pressure difference and thermal performance have been comprehensively analyzed. Numerical results demonstrate that 45% sharply increase in the thermal efficiency of the expansion condenser, and oscillation frequency of liquid/vapor slugs has been directly promoted for the constriction condenser. Present investigations could contribute to enhance overall performance of PHP, particularly employed for electronic cooling or heat recovery units.
       
  • Experimental and numerical investigation of natural convection heat
           transfer of W-type fin arrays
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Kai Zhang, Ming-Jia Li, Fei-Long Wang, Ya-Ling HeAbstractIn this paper, a W-type finned heat sink for natural convection is proposed based on the research of inclined-plate fins. As thermal radiation considered, the natural convective heat transfer performance of W-type fins on a vertical substrate was numerically studied with respect to the variations of geometry. The parallel-plate finned heat sink with and without the surface coating were experimentally studied, to validate the numerical results and the influence of radiation. Moreover, the W-type finned heat sink was experimentally investigated. Experimental results indicate that the W-type finned heat sink achieves the cooling effect of a maximum temperature drop of 4.6°C and an average temperature drop of 2.9°C. Compared to the optimized parallel-plate finned heat sink, the area of heat dissipation decreased by 10%. The optimization results indicate that the average temperature of the substrate tends to decrease first and then increase with the increment of the fin spacing, inclined angle and gap clearance. Meanwhile, there exist peak values for mean heat transfer coefficient of the whole heat sink with the fin spacing, the inclined angle and the gap clearance varied. Furthermore, a characteristic parameter coupled with a series of dimensionless variables is proposed, and the correlation for the inclined plate finned heat sink is suggested with deviation within 12%. It is concluded that for the W-type finned heat sink, the air input is effectively increased in the direction perpendicular to the substrate, leading to smaller thermal resistance. The thermal boundary layer is thinned. Synergy analysis shows that the intersection angle between the direction of velocity and the temperature gradient reduced.
       
  • Aluminum-doped calcium manganite particles for solar thermochemical energy
           storage: Reactor design, particle characterization, and heat and mass
           transfer modeling
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Andrew J. Schrader, H. Evan Bush, Devesh Ranjan, Peter G. LoutzenhiserAbstractA two-step cycle was considered for solar thermochemical energy storage based on particulate aluminum-doped calcium manganite reduction/oxidation reactions for direct integration into Air-Brayton cycles. The two steps encompass (1) the storage of concentrated solar irradiation within endothermic reduction of aluminum-doped calcium manganite and (2) the delivery of heat to an Air-Brayton cycle via exothermic re-oxidation of oxygen-deficient aluminum-doped calcium magnanite. A 5 kWth scale solar thermochemical reactor operating under vacuum was designed, modeled, and optimized to thermally reduce a continuous, gravity-driven flow of aluminum-doped calcium manganite particles. The granular flows were characterized in a tilt-flow rig, and particle image velocimetry was used to determine flow properties via frictional and velocity scaling relationships. Flow properties were integrated into a detailed heat and mass transfer model of the solar thermochemical reactor. A reactor design with 31° inclination angle, 230 g/min of particles, and 5.2 kWth radiative input from the high-flux solar simulator was found to produce an outlet flow temperature of 1158 K, with stoichiometric deviations of 0.076 and a storage efficiency of 0.628 while avoiding particle overheating and promoting longer particle residence times.
       
  • Experimental and numerical investigation of the latent heat thermal
           storage unit with PCM packing at the inner side of a tube
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Guijun Chen, Guoxuan Sun, Dongyue Jiang, Yunpeng SuAbstractLatent heat thermal storage systems (LHTS) are widely studied for solving the mismatch between the energy supply and demand in time and space. Most of the previous studies are focusing on the systems with the phase change material (PCM) packing outside the tube. The characteristics of a LHTS with the PCM packing at the inner side of a tube has been rarely reported. In this paper, a visible experiment with a horizontal circular tube filled with PCM has been presented. The phase interface as well as the temperature of the PCM could be monitored varying with time. The performance of the LHTS system with the PCM packed at the inner side or outer side of the tube are compared at different filling rates (40–90%). The results show that the tube with PCM packing inside has a better comprehensive performance when the filling rate is more than 62%, as compared to the tube with the PCM packing outside. Furthermore, an enthalpy-porosity method verified by the experimental data is adopted to simulate the charging and discharging processes of the LHTS systems with other different tube shapes. The horizontal and vertical ellipse units and triplex tube units with three different shapes of inner tube are simulated to enhance the performance of basic circular unit. The performance evaluation indicators including charging and discharging time and power per mass of PCM in charging (POC), discharging (POD) and circulation (POA) are chosen to compare the performance. The triplex tube with an inner horizontal ellipse shaped tube (TTHE) reveals the best performance with a 118.3% increased POA.
       
  • Modelling Knudsen number effects in suspension high velocity oxy fuel
           thermal spray
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): S. Chadha, R. Jefferson-Loveday, T. HussainAbstractSuspension high velocity oxy fuel thermal spray is a system characterized by supersonic velocities and length scales of particles of the order of nm – µm. As the effects of rarefication become significant the assumptions within the continuum models begin to collapse, the effects of rarefication can be evaluated through the flow Knudsen number. Modifications to the numerical modelling must be made to incorporate the effects of rarefaction. This study looks to include the effects of rarefication into the computational fluid dynamics (CFD) models for the suspension high velocity oxy-fuel (SHVOF) thermal spray process. A model for the heat transfer coefficient that take into account the Knudsen and Mach number effects is employed. Finally, the Ranz-Marshall correlation for the Nusselt number is compared to the Kavanau correlation and a compressible Nusselt number correlation. The model is validated through comparisons of particle temperatures which are obtained from two colour pyrometry measurements using a commercially available Accuraspray 4.0 diagnostic system. This study shows that there is a significant improvement in the prediction of inflight particle temperatures when accounting for the effects of compressibility and the effects of rarefication on the Nusselt number.
       
  • The effect of rotation on the thermal-solutal capillary-buoyancy flow in a
           shallow annular pool with various capillary ratios
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Cheng-Zhi Zhu, Lan PengAbstractIn order to understand the effect of pool rotation on the thermal-solutal capillary-buoyancy convection at various capillary ratios, a series of three-dimensional simulations are performed in a rotating shallow annular pool filled with silicon-germanium melt and subjected to radial temperature and solute concentration gradients under normal gravity. The capillary ratios are Rσ=−0.5, −0.8, −1.25 and −2, while Taylor number ranges from Ta = 0 to 1200. Three types of basic flows are obtained at different capillary ratios. The pool rotation diversely affects the structures of the basic flow and further varies the destabilization mechanisms. The pool rotation enhances the flow stability at Ta  400 with Rσ=−0.5 and −0.8, while it always stabilizes the basic flow at Rσ=−1.25 and −2. The evolution of flow pattern depends remarkably on the Taylor number and the capillary ratio. Multiple flow bifurcations occur at small capillary ratios or high Taylor numbers, which results from the coupling of various driven forces. The reverse transition process is observed at Rσ=−0.5 and −0.8 with Taylor numbers slightly larger than the turning point. Meanwhile, abundant oscillatory flow patterns are shown. The effects of pool rotation on their characteristics are discussed.
       
  • Solution of radiative intensity with high directional resolution in
           heterogeneous participating media and irregular geometries by the
           null-collision reverse Monte Carlo method
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Yong Cheng, Hongxu Li, Jie Zhang, Zhifeng HuangAbstractRadiative intensity with high directional resolution is very useful for many inverse analyses. In this work, the null-collision algorithm is combined with the reverse Monte Carlo method to calculate radiative intensity with high directional resolution in heterogeneous participating media and irregular geometries. A convergence criterion by monitoring the standard deviation of Monte Carlo weights is proposed to determine the required number of energy bundles and to estimate the accuracy of the Null-Collision Reverse Monte Carlo (NC-RMC) method. Then, directional radiative intensity in heterogeneous participating media of three-dimensional cubic and irregular geometries is calculated. Results show that the accuracy of the NC-RMC method is well predicted by the proposed convergence criterion and very good accuracy is achieved by setting strict convergence condition. Meanwhile, with the same obtained accuracy, the NC-RMC method has better computing efficiency than the standard reverse Monte Carlo method. For the radiative system with heterogeneous participating medium and irregular geometry, the NC-RMC method shows a distinct advantage in ease of programming and program portability. Results in this work show that the NC-RMC method is a good choice to solve radiative intensity in heterogeneous media and/or radiative systems with irregular geometries, which is very useful for inverse analysis in combustion systems.
       
  • Strong electron-phonon coupling induced anomalous phonon transport in
           ultrahigh temperature ceramics ZrB2 and TiB2
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Jia-Yue Yang, Wenjie Zhang, Chengying Xu, Jun Liu, Linhua Liu, Ming HuAbstractUltrahigh temperature ZrB2- and TiB2-based ceramics are widely used in extreme thermal environment. Yet, open questions remain pertaining to their lattice thermal conductivity (кph). In this work we investigate the phonon transport of ZrB2 and TiB2 by systematically evaluating the phonon-phonon interaction (PPI), electron-phonon interaction (EPI) and grain boundary scattering (GBS) from the atomistic level using first-principles. Upon including EPI, the room-temperature кph of ZrB2 and TiB2 is significantly reduced by 38.16% and 52.34%, respectively, and agrees excellently with experimental measurement. Such giant reduction arises from the strong EPI for the heat-carrying acoustic phonons due to phonon anomaly and the existence of Fermi nesting vectors along high symmetry line in the Brillouin zone. Following the Casimir model, the GBS further decreases кph of ZrB2 even by 49.27% for small grain boundary spacing of 50 nm and theoretical calculations agree well with experiments. Thus, GBS crucially influences phonon transport, which explains the large deviation of previous experimental measurements on кph for ZrB2-based ceramics. Moreover, the combined influence of EPI and GBS results in the anomalous phonon transport where кph is almost temperature-independent over a large temperature range, consistent with experimental observations. This work directly reveals the phonon transport mechanism for high temperature ceramics ZrB2 and TiB2, gains deep insight into the large variation in the previously reported кph and provides guidance to engineer it for practical applications.
       
  • Effects of impingement gap and hole arrangement on overall cooling
           effectiveness for impingement/effusion cooling
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Gang Xie, Cun-liang Liu, Lin Ye, Rui Wang, Jiajia Niu, Yingni ZhaiAbstractThe effects of geometrical parameters on overall cooling effectiveness were experimentally investigated on the flat plate with impingement/effusion cooling. Geometrical parameters investigated included two relative positions of impingement and effusion holes (staggered arrangement and overlapped arrangement) and three impingement gap distances (H/D = 2.5, 5 and 7.5). In addition, numerical simulation was employed to predict the effect of gap distance in a wider range. The results indicate that overall cooling effectiveness is significantly improved by adding impingement, while distribution of cooling effectiveness is mainly determined by film cooling and bore cooling. The comparison of cooling effectiveness between staggered and overlapped hole arrangement indicates that the former produces higher value at each blowing ratio and gap distance. At the same blowing ratio, the overall cooling effectiveness decreases as the increase of gap distance for staggered arrangement. For overlapped arrangement, the cooling effectiveness peaks at H/D = 10. Specific scaling principles of overall cooling effectiveness are experimentally validated by three cases with different temperature ratios. After matching mainstream side Reynolds number, Biot number, and the momentum flux ratio, the cooling effectiveness of case with lower temperature ratio agrees well with that of case with higher temperature ratio at each gap distance and hole arrangement.
       
  • Prediction of non-equilibrium homogeneous condensation in supersonic
           nozzle flows using Eulerian-Eulerian models
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Jabir Edathol, Dmitrii Brezgin, Konstantin Aronson, Heuy Dong KimAbstractSupersonic flows involving non-equilibrium condensation of steam can be numerically modelled by established Eulerian-Eulerian methods. In the present work, two such popular methods are studied and implemented in a commercial software package ANSYS Fluent, and compared for performance. The first method which is based on a density-based solver, modifies source terms of the governing equations to account for the effect of phase change. In the second approach, an Eulerian-Eulerian mixture model constructed over a pressure based solver, which is already available with the software is adapted and altered for the prediction of non-equilibrium flows. Both models incorporate additional transport equations to estimate the rate of liquid phase generation together with a well-structured sequence of operations comprising several assumptions and theories. The IAPWS-IF97 supplementary equation of state for the metastable-vapour region is used to describe the state of steam with additional empirical relations for the estimation of properties of condensed phase. The nucleation rate is calculated by the classical nucleation theory with non-isothermal/partial pressure corrections and Gyarmathy’s equation is used to compute droplet growth rate. The two models are developed, validated, studied and the capability of respective approaches to model non-equilibrium flows are discussed in detail.
       
  • Modeling and simulation of solid-containing droplet drying and
           different-structure particle formation
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Bo-Hsuang Wu, C.A. ChungAbstractThe formation of solid and hollow particles from solute precipitation of a liquid droplet was investigated using a simulative approach. The simulation model describes the evolution of the solute concentration, temperature gradient, and size change of the droplet and includes the vapor concentration and temperature gradient in the air surrounding the droplet. The volume of fluid (VOF) method was adopted to capture the gas–liquid–solid interface. The entire drying process was analyzed using a sodium chloride aqueous droplet as an example. The influence of ambient temperature on the final structure of the precipitate particle was studied. Two distinct particle structures were discussed. The droplet solidifies into a solid particle when the ambient temperature is low, and into a hollow shape when the ambient temperature is high. The mechanisms underlying these two particle structures were discussed.
       
  • Effects of longitudinal vortex generators on the heat transfer
           deterioration of supercritical CO2 in vertical tubes
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Zenan Yang, Xiaobo Luo, Wei Chen, Minking K. ChyuAbstractIn order to improve the safety performance of supercritical heat exchanger, vertical tubes with three kinds of longitudinal vortex generators (LVGs) are numerically investigated to understand the mechanism of mitigation effects on the HTD phenomenon. The results show that the thermal efficiency index η in tube with single-row LVG is increased by 15.2% and the maximum value of wall temperature is decreased by 8.7 K. It is concluded that the mitigation of wall temperature peak benefits from the reduction of the boundary layer thickness and enhancement of flow mixing in the downwash zone. Furthermore, the thermal efficiency index η in tube with single-row LVG is increased by 73.4% and the maximum value of wall temperature is decreased by 67.7 K, which fully demonstrates the potential of LVG for supercritical heat exchanger. When the vortex structure produced by LVG array covers only part of the inner wall, HTD cycles may occur and lead to the decrease of thermal efficiency. On the other hand, HTD cycle phenomenon is eliminated when the inner wall is fully covered by the vortex pairs.
       
  • The morphological effect of carbon fibers on the thermal conductive
           composites
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Guannan Wang, Mengyuan Gao, Bo Yang, Qiang ChenAbstractThe locally-exact homogenization theory (LEHT) with thermal conductive capability is developed to investigate the morphological effect of carbon/graphite fibers on the effective and localized thermal responses of periodic composites. Based on the orientations of basal planes, the material properties of carbon fibers can be transversely isotropic, radially orthotropic or circumferentially orthotropic, possibly influencing the microscopic behavior of thermal conductive composites. By taking fiber-fiber interactions into account, repeating unit cells (RUCs) of hexagonal and rectangular geometries are considered with large fiber volume fractions. The efficiency and stability of the LEHT are guaranteed by solving the complete internal eigenvalue functions, imposing point-wise continuity conditions, as well as implementing the generalized variational principle. It is demonstrated that the present theory exhibits good agreement with the independently developed Eshelby solutions and Hashin's formula. The morphological effects are also tested by generating effective coefficients over a wide range of fiber volume fractions and recovering the local thermal field concentrations within the composite microstructures. The results clearly indicate that even if the homogenized properties are not significantly affected by the morphologies of carbon fibers by satisfying the replacement scheme, the large heat-flux gradients within the orthotropic fibers could still lead to the split of carbon reinforcement.
       
  • Parametric investigation of the enhancing effects of finned tubes on the
           solidification of PCM
    • Abstract: Publication date: May 2020Source: International Journal of Heat and Mass Transfer, Volume 152Author(s): Felipe S dos Santos, Kamal A.R. Ismail, Fatima A.M. Lino, Ahmad Arabkoohsar, Taynara G.S. LagoAbstractThis paper presents the results of a study on the enhancement of solidification around finned tubes and the development of correlations to predict their thermal performance. The effects of the geometrical and operational parameters on the solidification process and thermal performance are investigated. A numerical code to predict the solidification around radial finned tubes based on pure conduction and the enthalpy method is developed and validated against experimental results showing good agreement. Results of additional experiments were also used to develop correlations for the interface position, interface velocity and the time for complete solidification. The fin diameter, and low tube wall temperature enhance the interface position and velocity, and reduce the time for complete solidification. Experiments showed that there is an optimum fin diameter for which the solidified phase change material (PCM) and stored energy are the highest. The proposed correlations for the interface position, interface velocity and the time for complete phase change seem to agree well with experimental results within maximum deviation of 4%, 7% and 1.03%, respectively. Hence, the correlations can be used for overall and quick estimates of solidification of PCM around radial finned tubes.
       
  • Professor James V. Beck on his 90th birthday
    • Abstract: Publication date: Available online 28 January 2020Source: International Journal of Heat and Mass TransferAuthor(s): Oleg M. Alifanov, Donald E. Amos, Jean-Pierre Bardon, Ben Blackwell, Kevin D. Cole, Filippo de Monte, Kirk D. Dolan, Kevin J. Dowding, A. Haji-Sheikh, Ned R. Keltner, Robert L. McMasters, Wally J. Minkowycz, Aleksey Nenarokomov, Elaine P. Scott, Keith A. Woodbury, Neil T. Wright, Tim S. Zhao, Dharmendra K. Mishra
       
  • Countermeasures combined with thermosyphons against the thermal
           instability of high-grade highways in permafrost regions
    • Abstract: Publication date: Available online 29 November 2019Source: International Journal of Heat and Mass TransferAuthor(s): Zhongrui Yan, Mingyi Zhang, Yuanming Lai, Wansheng Pei, Tao Luo, Fan Yu, Sheng YangAbstractPermafrost degradation caused by climate warming and human activities would result in the thermal instability of embankments in permafrost regions, which would increase the maintenance cost. Two-phase closed thermosyphon (TPCT) is a widely-accepted green countermeasure against the problem in permafrost regions. However, the combination of TPCT with other countermeasures is usually proposed when it comes to a high-grade highway with a wide pavement. In order to explore the ideal combination, four combinations are compared by the instrumented physical embankment models: 1) inclined TPCT and insulation; 2) inclined TPCT, insulation and crushed-rock revetment; 3) L-shaped TPCT and insulation and 4) L-shaped TPCT, insulation and crushed-rock revetment. The experimental results show that the TPCTs can effectively cool down the embankment center, the crushed-rock revetments can keep the soil slope and slope toe frozen during the whole freezing-thawing period, and the insulation can effectively prevent heat from entering into the embankment in warm seasons. After a thorough comparison of the thermal distribution and heat flux during seven freeze-thaw cycles, the embankment combined with L-shaped TPCT, insulation and crushed-rock revetment is proved to be the best way to keep the thermal stability of the wide-paved embankment. The results have potential to use for the future optimal construction against the thermal instability of high-grade highways in permafrost regions.
       
  • Simulation of pool boiling regimes for a sphere using a hydrogen evolving
           system
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Je-Young Moon, Bum-Jin ChungAbstractPool boiling phenomena for a sphere were simulated by electrical reduction of hydrogen in an aqueous solution of sulfuric acid (H2SO4), with copper and stainless steel(SUS316L) spheres used as the cathode. The cell potential and current density, which correspond to superheat and heat flux were controlled, respectively. The cell potential–current density curve from nucleate to transition bubble regimes was analogous to the typical boiling curve. In addition, the hydrogen bubble behaviors in each bubble regime, observed using a high-speed camera, were also similar to the vapor behaviors in boiling systems, except for the difference in bubble size. The critical current density (CCD) was determined similarly to the determination of critical heat flux (CHF). The calculated CHF values, based on the measured CCDs, were smaller than the CHF values of the boiling system due to the bubble volume. The CCD value increased with decreasing sphere diameter due to the increasing bubble frequency. In conclusion, the hydrogen evolving system can reasonably simulate the boiling regime for a sphere.
       
  • Theoretical analysis of filmwise condensation in inclined tubes with
           nondivergent and irrotational flow components
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Kaipo Kekaula, Yitung ChenAbstractThe present theoretical study investigates laminar film condensation of a saturated vapor in inclined circular tubes. Nusselt thin film assumptions are implemented to derive the governing differential equations for mass, momentum, and energy. The impact of both rotation and divergence of the nonconservative Nusselt velocity vector field on film growth and mass conservation are investigated and a new film thickness equation was introduced. A transformation for effective peripheral angle during stratification is derived based on the assumed linear liquid-vapor interface of Chato at the lower region of the tube. The optimal inclination angle for heat transfer is 28.2° from the horizontal for a tube of infinite length. For a finite tube the inclination angle decreases with length from 90° to 28.2° but for tubes of length L* > 2, optimal inclination angle is in the range of 28.2° and 46.6°. An expression for entrance length, Le* was introduced as a function of inclination angle. The results for heat transfer ratio have been compared with experimental data and an empirical correlation from literature and a good agreement is obtained and shown between them.
       
  • Dynamic thermal response modelling of turbulent fluid flow through
           pipelines with heat losses
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Saleh Salavati Meibodi, Simon ReesAbstractThe dynamic thermal behaviour of pipe systems is important in many heating, cooling and process systems and is further complicated where radial heat transfer and the thermal capacity of the pipe are significant. In this study, the ability of three forms of discretized one-dimensional models in prediction of the dynamic thermal response of pipelines considering the longitudinal dispersion of turbulent fluid flow were examined. Furthermore, a model is proposed combining features of plug-flow and discrete stirred tank representations that take into account the thermal capacitance of the pipe material as well as radial heat transfer. This combination enables the proposed model to simultaneously handle the simulation of momentum and energy balance as well as simulation of the longitudinal dispersion in pipelines. The proposed model is further compared to experimental measurements. The results elucidated that the proposed model is not only able to capture the outlet temperature changes due to a step change in the very good agreement against the measurement data but also offers advantages in reduced computational expense.
       
  • 3D CFD simulation of turbulent flow distribution and pressure drop in a
           dividing manifold system using openfoam
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Nitin Minocha, Jyeshtharaj B. JoshiAbstractThe flow distribution in a manifold system is a critical design parameter which affects the performance of majority of the chemical equipment. The flow mal-distribution may lead to serious issues such as (i) reduced heat or mass transfer (ii) enhanced pressure drop (iii) high energy dissipation and (iv) creation of dead zones or hot spots. The objective of the present investigation is to identify potential design strategies for attaining uniform fluid flow, reduced pressure drops and minimum energy dissipation inside dividing manifold system. 3D CFD simulations using OpenFoam have been performed to study the effect of eight different design strategies on the extent of non-uniformity (ENU) and pressure drop inside manifold system. The results reveal the dominance of momentum effect near the inlet which results in reverse flow through the branched tubes near the inlet whereas maximum discharge occurs through the tubes near the closed end. The turbulent kinetic energy (k) and dissipation rate (ε) are very high near the T junction, decreases as the flow precedes in the downstream direction and vanishes completely near the closed end of manifold. This study for the very first time reveals the roles of turbulent parameters (k and ε) in controlling the flow mal-distribution and pressure drop inside manifold systems. The most effective design strategies for achieving maximum flow uniformity and minimum energy dissipation are (i) inclusion of perforated baffle which reduces the vortex formation and results in 95% reduction in ENU¯ and (ii) converging header which results in 66% reduction in ENU¯.
       
  • Extended adsorbing surface reach and memory effects on the diffusive
           behavior of particles in confined systems
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): M.V. Recanello, E.K. Lenzi, A.F. Martins, Q. Li, R.S. ZolaAbstractThe adsorption-desorption phenomena play a pivotal role in several industrial and scientific processes, deserving attention from research groups across several fields of knowledge. In this article, we study adsorption-desorption of neutral particles scattered in a confined liquid when memory effects are present in both processes, the adsorption and desorption phenomenon. On contrary to previous studies, in which kernels representing memory effects were added to kinetic equations in the desorption term, resulting in considerable change in the dynamics of adsorbed particles, in this work we study the insertion of memory effects on the adsorption process. Such memory means that the preceding state of the particle in the bulk is relevant to the adsorption process, thus heavily affecting how particles are distributed in the bulk and making the reach of the surfaces far greater than when these effects are not considered. We firstly study a case where memory effect occurs only on the adsorption case, and then we analyze situations in which memory effects are included on both adsorption and desorption, and the distinct diffusion regimes in these systems. Our results could be potentially applied and easily adapted to model systems with complex geometries where diffusion and adsorption are present, such as occurs in slit pores.
       
  • Subcooled flow boiling in an expanding microgap with a hybrid
           microstructured surface
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Liaofei Yin, Aranya Chauhan, Alyssa Recinella, Li Jia, Satish G. KandlikarAbstractFlow boiling in microgap is attracting increasingly wide attention in heat transfer community due to its promising application potential for thermal management of electronic devices. In this study, an expanding microgap with a hybrid microstructured surface is proposed. It consists of a roughened inlet region followed by an array of staggered micro triangular pin-fins machined downstream. Subcooled flow boiling tests were conducted using distilled water as the working fluid with the inlet subcooling between 20 °C and 40 °C at different flow rates ranging from 80 to 480 mL/min over a heat flux range of 100.0–651.7 W/cm2. High-speed visualization was performed to explore the flow pattern transitions and the effects of operating conditions on heat transfer and pressure drop characteristics. A new flow pattern was observed in which the bubbles blanket the surface over both roughened upstream surface and the micro pin-fins downstream surface at higher flow rates and higher heat flux conditions. Combination of the increased bubble nucleation site density on the roughened surface and suppression of local dryout from the micro pin-fins due to their capillary effect jointly led to the high heat transfer performance in the bubble blanket pattern. In addition, the expanding configuration provides additional space downstream to facilitate bubble growth and two-phase flow in the direction of expansion with reduced resistance, resulting in a relatively low pressure drop in the present system.
       
  • The profiles of the local void fraction close to the heated wall in the
           subcooled flow boiling
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Il Woong Park, Sin Kim, Yeon-Gun LeeAbstractFlow boiling in the subcooled liquid condition is characterized by the complex interplay of phenomena such as bubble detachment from the wall, condensation in the flow, and the interaction between bubbles on which non-drag forces are exerted. However, the fundamental characteristics of the flow boiling in the subcooled liquid condition remain uncharted. In particular, a distribution of the bubbles close to the heated wall is not well understood. Here, we measure the void fraction in the steam-water mixture which is representing the distribution of bubbles by using a single sensor optical fiber probe with fine radial spacing in the close vicinity of the heated wall. We show that the profile of the void fraction along the radial direction of the flow channel is altered by the flow condition. In particular, the peak of the void fraction can be shifted towards the heated wall when there are fast bubbles close to the heated wall.
       
  • Numerical modeling of a benchmark experiment on equiaxed solidification of
           a Sn–Pb alloy with electromagnetic stirring and natural convection
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Tao Wang, Lakhdar Hachani, Yves Fautrelle, Yves Delannoy, Engang Wang, Xiaodong Wang, Olga BudenkovaA three-phase volume averaged equiaxed model is applied to simulation of an experiment on solidification of the binary alloy Sn-10 wt.% Pb subjected to the electromagnetic stirring. The experiment, whose description was published earlier, was performed in a parallelepiped cavity under controlled cooling conditions and with real-time two-dimensional temperature measurement over a lateral surface of the cavity co-planar with direction of solidification. Applied numerical model treats motion of the liquid and equiaxed grains whose growth kinetics is taken into account and uses a double time step scheme to accelerate solution. Growth of columnar dendrite is not considered. It is shown that electromagnetic force acting in a direction opposite to the natural convection flow creates moderately turbulent flow in pure liquid which is treated with a realizable kε−ε model. It is demonstrated that calculated temperature distribution in the cavity well reproduces temperature maps reconstructed from thermocouples measurements throughout the experiment. Final macrosegregation map and distribution of density grain number are qualitatively similar to those obtained in the experiment. Variation of intensity of electromagnetic stirring in numerical model shows that this affects shape and localization of positive segregation region at the bottom of the cavity.Graphical abstractGraphical abstract for this article
       
  • Investigation on forming defects and crystallization of plastic parts in
           combined in-mold decoration and microcellular injection molding based on a
           multiphase flow-solid coupled heat transfer model
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Qing Yang, Wei Guo, Zhenghua Meng, Huajie Mao, Lin Hua, Yanxiong LiuAbstractMicrocellular injection molding (MIM) combined with in-mold decoration (IMD) method can produce foamed parts with improved surface appearance by changing the heat transfer in the MIM mold. The temperature field has a significant effect on the forming defects and crystallization of the foamed parts. Based on finite volume method, a multiphase flow-solid coupled heat transfer model was established to calculate the temperature field in IMD/MIM process, and the implicit domain coupling algorithm (IDCA) was used to calculate the temperature field by taking the coupled heat transfer between the mold and the polymer melt into account. Compared with the experimental results, it is found that the established model can accurately predict the temperature field. The thermal response in IMD/MIM process was further analyzed. The effect of film on the forming defects of parts molded by IMD/MIM process was discovered by combining the simulation results with the experimental surface topography and warpage results, and the effect of film on the crystallization of parts molded by IMD/MIM process was also revealed.
       
  • In-flame spheroid formation from non-spherical slag particles – A
           numerical and experimental study
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): H. Gerhardter, M. Knoll, J. Raic, R. Prieler, M. Landfahrer, C. Hochenauer, P. Tomazic, H. SchroettnerAbstractIn order to identify the key factors for successful and efficient production, the formation of spherical particles from highly non-spherical coal slag grains was investigated within this work. The main focus was on precise drag and heat transfer calculations in order to obtain suitable criteria to predict the later product quality. State-of-the-art combustion, radiation and multiphase models in combination with specially adapted closure relations for drag and heat transfer were used for this purpose. The second objective was to investigate the relationship between particle temperature, viscosity, surface tension, shape and time required by the particles to obtain a smooth, round surface while passing through the burner chamber. In the first step, the process was investigated in experimental work. Slag particles were injected into an experimental furnace with a thermal input of 70 kW. The slag particles heated up which caused a reduction of slag viscosity by several orders of magnitude. While passing through the furnace, the sharp-edged powder grains transformed into smooth, highly spherical particles due to their surface tension. Numerical calculations were used to identify the main influence factors of in-flame spheroid formation. The effects of particle temperature, size, initial shape and residence time on the sphericity of the particle were studied using a Volume of Fluid (VOF) multiphase model and single-particle simulations which allowed calculations of the interface between an isothermal particle and the surrounding gas phase, as well as the interface deformation due to surface tension. The calculations have shown, that particles with volume-equivalent diameters in the range 420 µm-840 µm and an initial sphericity of 0.65 transform to spheroids in timescales in the order of 10−1 – 10° s when heated to temperatures above 1373 K. The critical particle temperature value of 1373 K was also confirmed by Euler-Lagrangian calculations of the reactive multiphase flow in the furnace. It has been shown that the particle peak temperature is a sufficient criterion for the formation of spheroids from highly non-spherical particles and that fluid temperature and particle residence time are the most important parameters of the later production process.
       
  • Evaporation heat transfer characteristics of R-245fa in a shell and plate
           heat exchanger for very-high-temperature heat pumps
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Kang Sub Song, Sungho Yun, DongChan Lee, Kibong Kim, Yongchan KimAbstractA shell and plate heat exchanger (SPHE) has been introduced for use in very-high-temperature heat pumps (VHTHPs). However, studies on the evaporation heat transfer characteristics of refrigerants in SPHEs for use in VHTHPs are very limited. In this study, the evaporation heat transfer characteristics of R-245fa in the SPHE are measured and analyzed by varying the saturation temperature, mass flux, heat flux, mean vapor quality, and fluid direction. Experiments are conducted under high temperatures of 60−80 °C for VHTHP applications. The evaporation heat transfer coefficient increases as the mass flux and mean vapor quality increase, whereas it decreases as the heat flux increases. The two-phase frictional pressure drop increases as the mass flux and mean vapor quality increase. The heat transfer performance of the upward flow in the SPHE is better than that of the downward flow. In addition, empirical correlations of the Nusselt number and two-phase friction factor of R-245fa in the SPHE are derived.
       
  • Acoustic field alteration in a 100 Hz dual acoustic driver straight tube
           travelling wave thermoacoustic heat pump for thermoacoustic heat transport
           control
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): A. Widyaparaga, T. Hiromatsu, Deendarlianto, M. Kohno, Y. TakataAbstractA dual acoustic driver thermoacoustic heat pump was constructed to investigate the effect of acoustic field control on travelling wave thermoacoustic heat transport at a frequency of 100 Hz. The acoustic field was controlled by varying the phase difference and magnitude between the two drivers. Variation of phase difference demonstrated the change of both acoustic power flow direction and standing-travelling wave characteristics. Maximum temperature differences obtained between the ends of the regenerator were 23 °C and 19 °C when the acoustic power was flowing in the negative and positive directions, respectively. It has been shown that matching impedances on the cold and hot side of the regenerator influence the thermoacoustic heat pumping characteristics. Where monodirectional acoustic flow was observed on both sides of the regenerator, the impedance angles also coincided well. Variation of magnitude displayed a trend in which activation of an opposing acoustic driver at weaker power enhanced acoustic power flow and heat transport. A maximum temperature difference between the hot and cold sections of 23 °C is obtained when the input electric power of the opposing acoustic driver was 17% of the power of the initial acoustic driver where the impedances and impedance angles on both ends of the regenerator are matched but the acoustic field travelling wave characteristics are still sufficient for travelling wave device operation.
       
  • In situ investigation of annealing effect on thermophysical properties of
           single carbon nanocoil
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Chenghao Deng, Tianze Cong, Yangsu Xie, Ridong Wang, Tianyu Wang, Lujun Pan, Xinwei WangAbstractIn reported high-temperature annealing of carbon nanocoils (CNCs), the samples studied before and after annealing are different ones. This significantly hinders annealing effect understanding due to unknown and remarkable sample-to-sample structure difference. Here using the transient electro-thermal technique (TET) and current-induced annealing, we report the first time in situ investigation of annealing effect on the thermophysical properties for the same individual CNC. Our dynamic annealing track uncovers an electrical resistance relation with annealing time as R∼−Rsln(t). The reaction rate (Rs) shows a normal distribution against the annealing power/temperature, proposing that the activation energy for structure reconstruction in CNCs follows a normal distribution. After annealing at 5–35€μA, the average thermal diffusivity (α) and electrical conductivity (σ) of CNCs show respective 50–160% and 100–170% increase. Normative linear relation between α and σ is discovered, which proposes axial-direction parallel structure in CNCs. The nonuniform temperature distribution along the sample during annealing creates different annealing levels and provides a great advantage to study the relation between structure and thermophysical properties. Our micro-scale Raman characterization reveals the nonuniform distribution of grain size along the length direction of CNCs after annealing and finds a rapid grain size increase from 4.0 to 7.8 nm near the sample's middle point. The middle point of the sample has the highest temperature rise (Tc), largest thermal conductivity (κ) increase, and the most dramatic structure improvement. Its κ shows a rapid improvement (8.7-fold maximum change) from 1200 K to 1800 K. A linear relation between κ−1 and Tc is observed and is attributed to the change of grain size during annealing. Using the concept of thermal reffusivity (Θ=1/α), a 1-fold increase of average grain size and a 197 K decrease of Debye temperature of CNCs after annealing are uncovered.
       
  • Computational study of nanoparticle assisted hyperthermia in tumors
           embedded with large blood vessels
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Behnaz Gheflati, Nadia NaghaviAbstractObjectiveThe use of nanostructures as factors that can accumulate exclusively in tumor cells and convert irradiated energy into heat, as energy converters, has been highly regarded in recent years. The purpose of this paper is to move towards a more realistic treatment planning model with investigating the effect of non-uniform distribution of gold nanoparticles within a tumor and also the cooling effect of large blood vessels, transiting through the tumor, on the temperature changes.MethodsThree-dimensional finite element based model was applied to simulate gold nanoparticle assisted laser-induced hyperthermia in the presence of large blood vessels. Assuming a specified initial location of nanoparticles at the center of the tumor, the mass equation was used to model the nanoparticle distribution. The laser heating was accounted for as a volumetric heat source and calculated using Beer–Lambert law. Furthermore, conjugate heat transfer equations in the tissues and blood were simultaneously solved to predict the temperature distribution.ResultsThe numerical model can predict the optimal laser intensity for a specified time interval between the diffusion of nanoparticles and laser irradiation.ConclusionWe show that the distribution of nanoparticles and the effect of large blood vessels embedded in the treatment region have a great influence on the distribution of heat and the degree of damage caused.SignificanceThis model by considering important aspects of hyperthermia treatment simultaneously, is more accurate and more complete than the existing ones in predicting the amount of injury and defining the optimal treatment parameters before the surgery.
       
  • Heat transfer and boundary layer analyses of laminar and turbulent natural
           convection in a cubical cavity with differently heated opposed walls
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Alexandre Fabregat, Jordi PallarèsAbstractThe buoyancy-driven flow in a cubical cavity with differently heated opposed walls has been chosen to investigate the laminar and turbulent heat transfer in enclosed domains. This type of configuration contains the essential physics existing in flows where transport between a fluid and an adjacent solid surface is controlled by the existence of boundary layers. The dependence of the wall heat transfer on the buoyancy force over the range Ra=105 to Ra=5.4×108 has been investigated, for air (Pr=0.7), using Direct Numerical Simulations. Under the assumption of mixed convection flow within the boundary layer produced by the combined effect of buoyancy and forced convection due to the large-scale flow, we assessed the validity of classical 2D boundary layer solutions in this flow configuration. The resulting characterization of the near-wall flow allows to derive new semi-analytical models for wall transfer applications in enclosed cavities.
       
  • Numerical simulations of convection heat transfer in porous media using a
           cascaded lattice Boltzmann method
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Xiang-Bo Feng, Qing Liu, Ya-Ling HeAbstractConvection heat transfer in porous media is a universal phenomenon in nature, and it is also frequently encountered in scientific and engineering fields. An in-depth understanding of the fundamental mechanism of convection heat transfer in porous media requires efficient and powerful numerical tools. In this paper, a cascaded lattice Boltzmann (CLB) method for convection heat transfer in porous media at the representative elementary volume (REV) scale is presented. In the CLB method, the flow field is solved by an isothermal CLB model with the D2Q9 lattice based on the generalized non-Darcy model, while the temperature field is solved by a temperature-based CLB model with the D2Q5 lattice. The key point is to incorporate the influence of the porous media into the CLB method by introducing the porosity and heat capacity ratio into the shift matrices. The effectiveness and practicability of the present method are validated by numerical simulations of several heat transfer problems in porous media at the REV scale. It is shown that the present method for convection heat transfer in porous media is second-order accurate in space. Moreover, in comparison with the Bhatnagar-Gross-Krook lattice Boltzmann method, the present method has sufficient tunable parameters and possesses better numerical stability.
       
  • Second law assessment of nanofluid flow in a channel fitted with conical
           ribs for utilization in solar thermal applications: Effect of nanoparticle
           shape
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Mehdi Bahiraei, Ali Monavari, Hossein MoayediAbstractThis research tries to assess the second law characteristics of the water–boehmite alumina nanofluids in a rectangular channel enhanced with the conical ribs. The effects of different arrangements of the ribs and various shapes of the nanoparticles are evaluated. Shear Stress Transport (SST) k-ω model is implemented to perform the simulations. Based on the observations, the highest and lowest temperature gradients occur at the dead zones and the reattachment regions, respectively. For all the nanoparticle shapes, by the increase in the rib height and the reduction in the rib pitch, the entropy generated by the heat transfer diminishes while the entropy generated by the friction intensifies. Because of the dominance of the thermal entropy generation compared to the fractional one, the total irreversibility decreases by rising the rib height and reducing the rib pitch. The Oblate spheroid (Os)-shaped nanoparticles cause the highest thermal entropy generation followed by the brick-, blade-, cylinder-, and platelet-shaped nanoparticles, respectively. Moreover, the maximum frictional entropy generation belongs to the nanofluid having the platelet-shaped nanoparticles followed by respectively the cylinder-, blade-, brick-, and Os-shaped nanoparticles. The results also reveal that using the platelet-shaped nanoparticles besides greater rib heights and lower rib pitches are optimal based on the second law of thermodynamics causing the smaller total irreversibility. Furthermore, the Bejan number demonstrates the great values in all the cases under study.
       
  • Inversion of flow and heat transfer of the paramagnetic fluid in a
           differentially heated cube
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): S. Kenjereš, E. Fornalik-Wajs, W. Wrobel, J.S. SzmydAbstractThe present study addresses the detailed numerical analysis of the flow and heat transfer of a paramagnetic fluid inside a differentially heated cubical box and subjected to a strong non-uniform magnetic field. Two different heating scenarios are considered regarding an initial thermal stratification: unstable (heated from the bottom) and stable (heated from the top), both subjected to the same magnetic field. For a fixed value of the thermal Rayleigh number (Ra=1.4×105) integral heat transfer is measured over a range of imposed magnetic fields, 0 ≤  b0 max ≤ 10 T. To obtain detailed insights into local wall-heat transfer and its dependency on the flow patterns generated, numerical simulations of the experimental setup are performed. A relatively good agreement between experiments and numerical simulations is obtained in predicting the integral heat transfer (with an averaged ΔNu¯
       
  • Experimental study of heat transfer at the transition regime between the
           natural convection and nucleate boiling: Influence of the heated wall tilt
           
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Lounès Tadrist, Hervé Combeau, Mohammed Zamoum, Mohand KessalAbstractThe works carried out in this study aimed to get a better understanding of the heat transfer in natural convection and nucleate boiling as well as the transition between these two regimes. An experimental test set up was built to generate the liquid boiling on the wall using a boiling-meter. This sensor was developed in order to investigate the heat transfer and its dependence with time in well controlled conditions. Temperature, pressure and heat flux required for the measurements were implemented. Experiments were focused on determining the characteristic curves of heat transfer in the natural convection regime and the nucleate boiling regime. The influence of the orientation of the wall relative to the gravity on the heat transfer is investigated. Characteristic heat transfer curves were obtained in several operating conditions and wall orientation with regard to gravity.At the transition regime between natural convection and nucleate boiling regimes, it was highlighted a competition between these two regimes. It was found, that the transferred heat flux differs depending on the orientation of the wall and the degree of liquid superheat in the nucleate boiling regime. In the natural convection regime, the measured heat fluxes exhibited a slight variation with the tilt angle of the wall. While in the nucleate boiling regime, strong variations were observed on the onset of nucleate boiling as well as for the heat flux. At very low heat flux, the heat transfer increases with the tilt angle while it decreases for moderate heat flux. The onset of nucleate boiling (ONB) and the onset of dominant natural convection (ONC) were found to decrease as a function of the tilt angle of the wall with different variation laws. The wall superheats values for the ONB and ONC are getting closer when the tilt angle tends to 180°.
       
  • Direct numerical simulation of phase change in the presence of
           non-condensable gases
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Lubomír Bureš, Yohei SatoAbstractThis paper describes a new numerical method for the simulation of phase change phenomena between a liquid and a vapour in the presence of non-condensable gases. The method is based on an interface-tracking approach in the framework of single-fluid modelling. The principal innovative feature represented is the capability of simulating a mixture of the condensable gas (vapour) and non-condensable gases with different densities. The formulation and subsequent discretization of the governing equations for the species transport are discussed in detail. In particular, a volume-averaged velocity field is introduced into the species transport equation in combination with a mass-averaged velocity field approach for the momentum equations. The resulting algorithm has been implemented into the incompressible Navier–Stokes solver, PSI-BOIL, which features a finite-volume approach based on a fixed, rectangular, Cartesian grid. Several verification cases have been undertaken to ensure the code modifications have been correctly implemented. These include simulation of the Stefan problem, involving evaporation and condensation in a 1D configuration, and an evaporating droplet under forced convective flow. In all cases, very good agreement has been obtained with analytical solution. A simulation of direct-contact condensation of a practical application is also presented, which serves to demonstrate the potential capability of the new approach to a wider range of engineering problems, including pressure suppression pools in nuclear reactors.
       
  • Thermal-exergetic behavior of triangular vortex generators through the
           cylindrical tubes
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Samira Pourhedayat, Seyed Mehdi Pesteei, Hamed Ebrahimi Ghalinghie, Mehran Hashemian, Muhammad Aqeel AshrafAbstractIn this paper, new arrangements of triangular winglet as a turbulator are numerically studied through a cylindrical tube. Triangular winglets are commonly placed on one side of a rectangular plate and inserted inside the tube. However, in present work, the winglets are located on both sides of the rectangular plate to further enhance the thermal performance of the fluid flow through the tube. Both backward and forward configurations of the winglets are analysed. Moreover, despite the importance of “latitudinal pitch of the winglets” and “winglet-plate angle” no investigation has been evaluated these parameters which will be evaluated in this work. Moreover, as no exergetic evaluation has been performed for triangular vortex generator, exergetic behavior of the triangular winglet is analysed as well. The impacts of all said factors on thermal, frictional and exergetic specifications of fluid-flow under the constant wall-temperature are investigated. The results showed that forward configuration provides higher thermal performance. Moreover, smaller longitudinal pitch and aspect ratio can provide stronger heat transfer rate through the tube. However, latitudinal pitch showed an extremum point which means that the winglet should not be very close to the wall-side or central-side of the tube. Among the tested latitudinal pitches (among 0 and 40 mm), the pitch of 20 mm showed the maximum enhanced heat transfer. Besides, the behavior of Nu number for smaller aspect ratios (below the 60°) is different from higher degrees (more than 60°).
       
  • Multilayer in-plane graphene/hexagonal boron nitride heterostructures:
           Insights into the interfacial thermal transport properties
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Ting Liang, Man Zhou, Ping Zhang, Peng Yuan, Daoguo YangCombining both vertical and in-plane two-dimensional (2D) heterostructures opens up the possibility to create an unprecedented architecture using 2D atomic layer building blocks. The thermal transport properties of such multilayer-mixed heterostructures, critical to various applications in nanoelectronics, however, have not been thoroughly explored. Herein, we construct two configurations of multilayer in-plane graphene/hexagonal boron nitride (Gr/h-BN) heterostructures (i.e., mixed heterostructures) via weak van der Waals (vdW) interactions and systematically investigate the dependence of their interfacial thermal conductance (ITC) on the number of layers using non-equilibrium molecular dynamics (NEMD) simulations. The computational results show that the ITC of two configurations of multilayer in-plane Gr/h-BN heterostructures (MIGHHs) decrease with increasing layer number n and both saturate at n = 3. Surprisingly, we find that the MIGHH is more advantageous to interfacial thermal transport than the monolayer in-plane Gr/h-BN heterostructure, which is in strong contrast to the commonly held notion that the multilayer structures of Gr and h-BN suppress the phonon transmission. The underlying physical mechanisms for these puzzling phenomena are probed through the stress concentration factor, overlap of phonon vibrational spectra and phonon participation ratio. In particular, by changing the stacking angle of MIGHH, a higher ITC can be obtained because of the thermal rectification behavior. Furthermore, we find that the ITC in MIGHH can be well-regulated by controlling the coupling strength between layers. Our findings here are of significance for understanding the interfacial thermal transport behaviors of MIGHH, and are expected to attract extensive interest in exploring its new physics and applications.Graphical abstractImage, graphical abstract
       
  • Effect of heat exchanger design on seasonal performance of heat pump
           systems
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Shehryar Ishaque, Md Irfanul Haque Siddiqui, Man-Hoe KimAbstractThis paper presents the effect of heat exchanger design on heat pump performance based on partial load operating conditions. 3-D numerical analysis was conducted to calculate face velocity profiles for each outdoor heat exchanger design (rectangular, cylindrical, and trapezoidal) in 10 different operating conditions. Heat exchanger circuits were modified considering heat exchanger face velocity distributions, and seasonal heat pump performances were calculated with modified heat exchanger design. The maximum seasonal performance enhancement of 7.07% was achieved with a modified heat exchanger design. Air-side flow maldistribution could affect significantly refrigerant path design and heat exchanger performance as well as system performance. The analysis results also revealed that smaller refrigerant circuits at the upper part of the heat exchanger interacting with higher air velocity could further enhance the annual system performance.
       
  • Analysis of bubble growth and motion dynamics in superheated liquid during
           flash evaporation
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Liang HaoAbstractThis study proposes a mathematical model for studying the growth and rise of a bubble in a superheated liquid during flash evaporation. The motion of the bubble is simulated based on force balance by considering various forces acting on the bubble, especially including the history force and the pressure force from a decreasing pressure field. The transformation of the rising bubble and its effect on interfacial heat and mass transfer are considered. Using this model, bubble growth and motion characteristics in the superheated liquid are analyzed in detail, and the effects of history and depressurization forces on both bubble motion and growth are examined. The results present a strong coupling of bubble growth with motion. A slow rise velocity of bubble at the late transition stage can significantly promote bubble growth, and the bubble growth even contributes more to the deceleration of bubble rise compared with the drag force. The history force is found insignificant for bubble rise and growth if the bubble has a relatively high growth rate in water at a superheated degree greater than 3.9 K in this study. The additional force from rapid depressurization provides a large pulse acceleration on the bubble. However, the bubble rise and growth are only sensitive to the depressurization rate for slow depressurizations. As the depressurization rate increases, the growth and rise curves of the bubble gradually converge to the case of instantaneous depressurization. In addition, the bubble rise velocity is lower for a higher overall pressure drop owing to a higher bubble growth rate. The proposed model is finally extended to simulate bubble growth and rise in superheated NaCl solution by revising the thermodynamic conditions at the bubble/solution interface based on the two-characteristic-parameter correlation model.
       
  • Thermal modeling with diffusion for dropwise condensation of humid air
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Brian Frymyer, Nasser Vahedi, Sudhakar Neti, Alparslan OztekinGraphical abstractImage, graphical abstract
       
  • Numerical modeling of vapor condensation over a wide range of
           non-condensable gas concentrations
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Ali Alshehri, Sahar Andalib, H. Pirouz KavehpourAbstractThis paper presents a numerical model to study the process of vapor condensation on surfaces characterized by film-wise condensation with the presence of Non-condensable gases (NCG). State variables in both the condensate film and the diffusion layer were solved separately and the condensation interface was used to couple the two solutions. The solution of the condensate film was obtained using well-established solutions of laminar film condensation of pure vapor. In contrast to other models surveyed, this work provides a inexpensive and accurate predictions of heat and mass transfer characteristics. We validated the work against two classical condensation problems. The model was first validated against empirical correlations and experimental work, resulting in a very good agreement. We then assessed the applicability of ignoring the condensate film effect, as performed in previous models, on the condensation processes by observing the thermal resistances of both the condensate film and diffusion layer. Results indicated that for the studied cases of NCG mass fractions above 20%, the condensate thermal resistance was at least an order of magnitude lower than that of the diffusion layer. However, the two thermal resistances seem to approach each other as NCG mass fraction becomes smaller. On another front, we observed that models that ignore the condensate film thermal resistance underestimate the interfacial temperature albeit accurately predicting the overall heat transfer rate. To simulate even lower NCG mass fractions, we validated our model to the classical analytical work of Sparrow and co-workers. Results showed a striking agreement between the two solutions at different NCG mass fractions (0.5%–10%) and subcooling degrees (5∘F–40∘F). Finally, we found a good agreement between results of our model and the heat/mass transfer analogy. The heat/mass transfer analogy is a semi-empirical method therefore, is limited to the existing correlations and their uncertainties. On the other hand, our model does not use any empiricism and relies on the available solutions of laminar condensate film of pure vapor in predicting the liquid side heat transfer coefficient.
       
  • On a simple and effective thermal open boundary condition for convective
           heat transfer problems
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Xiaoyu Liu, Zhi Xie, Suchuan DongAbstractWe present an effective thermal open boundary condition for convective heat transfer problems on domains involving outflow/open boundaries. This boundary condition is energy-stable, and it ensures that the contribution of the open boundary will not cause an “energy-like” temperature functional to increase over time, irrespective of the state of flow on the open boundary. It is effective in coping with thermal open boundaries even in flow regimes where strong vortices or backflows are prevalent on such boundaries, and it is straightforward to implement. Extensive numerical simulations are presented to demonstrate the stability and effectiveness of our method for heat transfer problems with strong vortices and backflows occurring on the open boundaries. Simulation results are compared with previous works to demonstrate the accuracy of the presented method.
       
  • Meso-scale investigations on the effective thermal conductivity of
           multi-phase materials using the finite element method
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Kai-Qi Li, Dian-Qing Li, Yong LiuAbstractMany materials (e.g. soil) are multi-phase composites in engineering, and the thermal conductivity of mixtures is a critical parameter for analyzing the temperature field. Owing to its heterogeneity, the effective thermal conductivity of multi-phase materials is also not deterministic. The prediction of the thermal properties of a multi-phase material remains a challenging task. In this study, soil is considered to be a typical multi-phase material. A numerical simulation model is established by the finite element method to predict the meso-scale effective thermal conductivity of soil. Monte Carlo simulation is employed to account for the random distribution of voids. Comparisons among numerical, experimental and empirical results suggest that the proposed model can predict reasonably accurate results. In addition, the effective thermal conductivity of unfrozen soil, partially frozen soil and fully frozen soil is calculated. The effects of soil type, porosity and saturation degree on effective thermal conductivity are considered via parametric studies. The proposed numerical method can be used as an effective supplement to empirical model and experimental tests for evaluating the thermal conductivity of multi-phase materials.
       
  • Experimental and numerical heat transfer study of turbulent tube flow
           through discrete V-winglets
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Pongjet Promvonge, Pitak Promthaisong, Sompol SkullongAbstractThe article presents an experimental and numerical investigation on heat transfer augmentation in a tubular heat exchanger inserted with discrete-V-winglet (DW) tape. Air entered the DW-inserted tube having a uniform wall heat flux in a turbulent flow regime, Reynolds number from 4200 to 25,800. Two arrangements of DWs: V-tip pointing upstream (V-up) and downstream (V-down) were introduced with three relative winglet heights (RB=b/D = 0.1, 0.15 and 0.2) and four relative winglet-pitches (RP=P/D = 0.5, 1.0, 1.5 and 2.0), all at a single angle of attack, α = 30°. Effects of those parameters on the heat transfer/Nusselt number (Nu) and friction factor (f) were examined. Also, a novel thermal-performance enhancement factor (TEF) was put forward. The experimental result has shown that at a given RB, the smallest pitch length (RP=0.5) yields the highest f and Nu. The DW with RB=0.2 and RP=0.5 has the maximum Nu and f of about 3.8 times and 18.8 times, respectively whereas the one with RB=0.15 and RP=1.0 gives the highest TEF of about 1.99 and 2.02 for the V-up and V-down, respectively. Moreover, the DW provides higher TEF than the typical V-winglet as expected. To explore the mechanism of heat transfer, a numerical model of the inserted-tube flow was carried out and the numerical result was validated and found in favorable agreement with available measurement. Flow structures and heat transfer patterns from the simulation such as temperature contours and streamlines including the Nusselt number contours were also proposed.
       
  • Modeling of wall condensation in the presence of noncondensable light gas
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): S. Benteboula, F. DabbeneAbstractDuring a loss of coolant accident in nuclear reactor, significant amounts of steam and hydrogen can be released in the containment. Condensation of steam in the presence of noncondensable gases on the containment walls and structures is a key issue because of its role in removing heat from the atmosphere. Extensive experimental and theoretical studies have been carried out for a better understanding of this complex phenomenon which involves several physical processes and parameters. When condensation takes place in the presence of noncondensable gases a liquid film is formed and noncondensable gases accumulate at the interface. The diffusion of steam through the gaseous layer depends on the gas composition, velocity, temperature and pressure. The formation of a gaseous layer leads to a significant reduction of heat transfer. Simulations based on CFD or lumped parameter (LP) approaches use correlations to estimate heat and mass transfer due to condensation. In this work, we are interested in theoretical correlations based on the diffusion layer theory using heat and mass transfer analogy. Among the variables and parameters affecting wall condensation, the effect of the gas mixture properties in particular the diffusion coefficient modeling is investigated. Test cases of steam injection into an enclosure filled with air or air-hydrogen mixture are simulated with a LP code using two different correlations for the evaluation of heat and mass transfer. Each correlation is based on different formulations of the effective diffusion coefficient. The ISP47 test performed in the MISTRA facility was used for validation purpose. The results showed that the addressed heat and mass transfer correlations underestimate the condensation rate in the steady state. Furthermore, the impact of the effective diffusion coefficient modeling on the heat and mass transfer turned out to be significant compared to the effect of the heat and mass transfer correlation.
       
  • Migration dynamics for liquid/solid interface during levitation melting of
           metallic materials
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): X. Cai, H.P. Wang, B. WeiAbstractThe migration dynamics of liquid/solid interface for bulk metallic materials under the electromagnetic levitation (EML) condition were investigated by the combination of numerical simulation and related EML experiments. Based on the apparent heat capacity method and the Carman–Kozeny relationship, a thermo-electromagnetic-hydrodynamic model was established to explore the phase transition including the migration of liquid/solid interface, the evolution of melt flow and the temperature distribution. The details of migration process were quantitatively analyzed under different levitation conditions. The space and time evolutions of liquid/solid interface migration features were strongly correlated with the electromagnetic field in levitation space. In addition, the correlation between the heat transfer characteristics and the levitation conditions was explored by the levitated sample with a preset deformation shape. In heating process, the sample reached the lowest equilibrium temperature and the minimum melting rate when it was levitated in the middle of the levitation zone. A defined number related to sample properties D2ρσ−1k−1 was proposed to quantitatively describe the temperature difference of levitated solid sample. The migration details were validated by EML experiment that an oval molten pool formed near the lower sample surface firstly. Then, the liquid/solid interface gradually moved up to sample top. The migration behaviors under extreme conditions were predicted by simulation that molten pools formed simultaneously on the upper and lower surfaces when the sample was balanced near the levitation ceiling.
       
  • Ultrafast dynamics modeling via fractional Brownian motion run with
           Mittag-Leffler clock in porous media
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Wei Xu, Yingjie Liang, John H. Cushman, Wen ChenAbstractUltrafast diffusion process characterized by unusually large diffusivities is often occurs on porous media and the mean square displacement grows exponentially in time. This paper clarifies the characteristics of ultrafast diffusion and tackles this perplexing problem using the fractional Brownian motion run with a nonlinear clock model. We employ the Mittag-Leffler function as the nonlinear clock, the increments are dependent and obey Gaussian distribution, and the derived corresponding mean square displacement is more widely than the exponential function. A comparison between the power law model and the proposed model with respect to available experimental data verifies that the proposed model is more effective and accurate. Ultraslow diffusion is also studied with the inverse Mittag-Leffler function as the nonlinear clock. The results show that it can capture the ultraslow diffusion process better than the case of the logarithmic model. As the generalization of fractional Brownian motion, fractional Brownian motion run with a nonlinear clock is an alternative model method for extreme anomalous diffusion in complex systems.
       
  • NH3 condensation in a plate heat exchanger: Experimental investigation on
           flow patterns, heat transfer and frictional pressure drop
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Xuan Tao, Elias Dahlgren, Maaike Leichsenring, Carlos A. Infante FerreiraAbstractThis paper investigates NH3 condensation in a plate heat exchanger by visualizing the flow patterns and measuring heat transfer coefficients and frictional pressure drop. Visualization experiments were conducted between 20 and 100 kgm−2s−1. Full film flow takes place at large mass fluxes and intermediate mass fluxes of low vapor qualities, while partial film flow occurs at small mass fluxes and intermediate mass fluxes at high vapor qualities. The heat transfer and frictional pressure drop experiments cover the mass fluxes of 21~78 kgm−2s−1, the averaged vapor qualities of 0.05~0.65 and the saturated pressure of 630 to 930 kPa. Vapor qualities have significant influences on heat transfer and frictional pressure drop. In the tested ranges, the effect of mass fluxes is noticeable on frictional pressure drop, but is moderate on heat transfer. The impact of saturated pressure is small. The heat transfer reflects the change of flow patterns. The frictional pressure drop shows the characteristics of separated flow.
       
  • Irreversibility characteristics of a modified microchannel heat sink
           operated with nanofluid considering different shapes of nanoparticles
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Mehdi Bahiraei, Ali Monavari, Mohammad Naseri, Hossein MoayediAbstractIn the current paper, the influences of the water–Al2O3 nanofluid with various nanoparticle shapes on the second law attributes in the microchannel heat sink are analyzed. This assessment is carried out for five nanoparticle shapes (i.e., platelet, cylinder, blade, brick, and oblate spheroid) at four Reynolds numbers (i.e., Re = 300, Re = 800, Re = 1300, and Re=1800). Furthermore, the concentration is considered constant equal to 1% for all the modes. For all the nanoparticle shapes, the thermal entropy generation is diminished and frictional entropy generation is augmented by rising the Re. The oblate spheroid nanoparticles result in the highest entropy generation followed by the brick, blade, cylinder, and platelet nanoparticle shapes, respectively. By the changes of the Re, the variations of the thermal entropy generation are low, but the frictional entropy generation has significant changes. The greater Re numbers and the nanofluid with the platelet-shaped nanoparticles are optimal because result in the lowest irreversibility. In the nanofluid having the platelet-shaped nanoparticles, the total entropy generation decreases 17.4% by rising the Re from 300 to 1800. Besides, the Bejan number declines by the increase of the Re, and has its smallest value for the platelet nanoparticles-based nanofluid. Besides, the difference among the Bejan numbers of the various nanoparticle shapes is more noticeable at larger Re numbers.
       
  • Thermal performance investigation of the miniature revolving heat pipes
           using artificial neural networks and genetic algorithms
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Feng Liang, Jianmin Gao, Liang XuAbstractThe miniature revolving heat pipes (MRVHPs) are promising candidates for the cooling structure design of rotating machines, however, the relation between the thermal performance of MRVHPs and their thermophysical properties is still absent. Therefore, MRVHPs are tested in various operational conditions firstly. And then, a power-law empirical correlation is developed based on experimental data, Ku, Ja, Pr, Bo and Fr are determined as main effective dimensionless parameters, while the structural parameters of MRVHPs Di/R, Le/Lc, Le/Leff and filling ratio φ are considered as well. However, the prediction accuracy is not satisfactory enough. Considering ANNs have been widely used in varied applications and demonstrated to be particularly credible in system modeling and identification, therefore, a BPNN model which parameterized by GA is developed for thermal performance prediction of the MRVHPs. The experimental data are divided into training data set and testing data set. Ja, Pr, Bo, Fr and φ are regarded as inputs, while Ku is output. The results show that the established GA-BPNN model could predict thermal performance of MRVHPs with a very good accuracy. Comparing with the predicted results of semi-empirical correlation, the square of correlation coefficient (R2) is increased by 13.265%. Meanwhile, the evaluation method for the optimal filling ratio of the MRVHPs under specified working conditions is developed and an acceptable accuracy is obtained.
       
  • Experimental investigation on pool boiling heat transfer on
           untreated/super-hydrophilic metal foam under microgravity
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Juan Shi, Dongyang Feng, Zhenqian ChenAbstractFor improving the cooling efficiency of electronic devices in aerospace projects, pool boiling heat transfer on untreated/super-hydrophilic metal foam under short-term microgravity is experimentally investigated. The metal foam has a thickness of 5 mm and a diameter of 20 mm. The pore density of the metal foam is 50 PPI (pores per inch). The super-hydrophilic metal foam surface is created by surface oxidation method. FC-72 is used as the working fluid and the subcooling is controlled at 10 °C. Bubble dynamic behavior during pool boiling under microgravity is studied using high-speed camera. Visualization results show that the bubble departure diameter increases and the bubble departure frequency decreases under microgravity condition. Compared with the smooth brass surface, the untreated metal foam surface owns a better vapor release performance under microgravity, while the super-hydrophilic metal foam surface shows a superior ability in vapor release. Meanwhile, the temperature measurement results indicate that the test block temperature increases evidently at q> 11 W/cm2 after entering the microgravity condition. The wall superheat and heat flux of the heated surface under microgravity are derived by interpolation method. By the end of microgravity condition, the heat transfer coefficient on untreated metal foam surface is 86.1% higher than that on the smooth brass surface at q ≈ 11 W/cm2. The super-hydrophilic metal foam surface could improve the heat transfer performance by 12.9% compared with the untreated metal foam surface at q ≈ 15 W/cm2, showing the prime heat transfer performance in the present study.
       
  • Experimental investigation on flow boiling characteristics of radial
           expanding minichannel heat sinks applied for two-phase flow inlet
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Sihui Hong, Chaobin Dang, Eiji HiharaAbstractGenerally, two-phase (TP) flow inlet condition is not allowed for conventional microchannel heat exchangers, and a certain subcooled degree of liquid is strictly required to guarantee the efficient operation of system. To solve multi-heat sources cooling issue, a type of circular radial expanding minichannels heat sink (REMHS) utilizing flow boiling of deionized water is proposed in present work. Flow boiling heat transfer of REMHS is investigated with the inlet vapor mass qualities in the range of 0.01–0.53. Under TP flow inlet, slug-annular and annular flows are the main flow patterns observed in REMHS in this work, where the low-medium mass flux (22–132 kg/m2s) and medium-high heat flux (33.1–176.4 kW/m2) conditions are applied. The experimental results illustrate that the proposed REMHS under TP flow inlet maintains a stable and high flow boiling heat transfer performance without occurring heat deterioration. When xin increases from 0.04 to 0.53, the maximum local heat transfer coefficient increases by 22% from 42.5 to 51.9 kW/m2K. The flow distribution among the expanding channel array is relatively uniform and the heat transfer capability in the REMHS displays a good symmetry under TP flow inlet. The maximum discrepancy in heat transfer coefficient is below 19% within our experimental range. Six classic flow boiling heat transfer correlations are compared with the experimental results, and Li & Wu's correlation gives a good prediction on all the measured data with MAE of 21.1%. Besides, the thermal independence of REMHS connected in series is also examined, and the mutual interaction in heat transfer between the REMHS in series is trivial, the proposed REMHS is expected to be applied to multi-heat source cooling.
       
  • Effects of surface wettability on two-phase flow in the compressed gas
           diffusion layer microstructures
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Xia Zhou, Lizhen Wu, Zhiqiang Niu, Zhiming Bao, Xiaoyan Sun, Zhanrui Liu, Yanan Li, Kui Jiao, Zhi Liu, Qing DuAbstractThe surface wettability plays a significant role in two-phase flow in the gas diffusion layer (GDL). However, few reported researches have considered directional single gradient polytetrafluoroethylene (PTFE) distribution, PTFE immersion depth, and the GDL compression. In this study, effects of various surface wettability distribution schemes on two-phase flow in the GDL microstructures are investigated. In addition, the GDL deformation is also considered via clamping pressure simulation based on the finite element method (FEM). Two-phase flow in the compressed GDL microstructures is modeled using the volume of fluid (VOF) model. The results show that the direction of single gradient of the surface wettability is influential in two-phase flow, especially for the compressed GDL. Moreover, thicker PTFE immersion depth contributes to water removal from the GDL. Finally, novel surface wettability distribution schemes are first proposed, and they are demonstrated as important references for controllable water transport in the GDL.
       
  • Correcting for tube curvature effects on condensation in the presence of a
           noncondensable gas in laminar regimes
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): A. DehbiAbstractFilmwise vapor condensation in the presence of noncondensable gases (NCG) continues to attract interest due to its widespread range of applications. In studies of NCG effects on condensation over external surfaces, experimentalists and analysts alike usually employ correction factors to transfer tube condensation rates to flat plate equivalents or vice-versa. For laminar flows over vertical cylinders, these factors are estimated from pure convection correlations as a function of the Grashof number and tube curvature only. We show that this procedure is not rigorous and leads to significant errors, especially at low NCG fractions and small tube radii. Indeed, the usual way of correcting for curvature is strictly valid only in the limit where the NCG fraction is so large that convection heat transfer dominates condensation. On the other hand, as the NCG fraction becomes vanishingly small, the vapor condensation rates should tend to values predicted by the Nusselt film theory, and no enhancement due to tube curvature is to be expected.This paper focuses on vapor condensation as the gas mixture moves along a vertical tube in the laminar free convection regime. The gas and liquid film boundary layer equations are coupled at the gas/film interface and a marching solution procedure using local non-similarity is adopted. The methodology is first verified for near pure free convection flows as well as previous analyses of condensation over a flat surface. The model is subsequently validated against data on steam condensation on a square plate in the presence of air. Finally, a correlation is deduced from the parametric numerical results to allow a proper correction for curvature effects when vapor condenses in the presence of a NCG. The proposed correction spans the whole range of NCG fractions, and displays the expected behavior at the extremes of this range.
       
  • Surface roughness variation effects on copper tubes in pool boiling of
           water
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Mario R. Mata Arenales, Sujith Kumar C.S., Long-Sheng Kuo, Ping-Hei ChenResults showing the effects of varying the surface roughness on copper tubes in pool boiling of water are presented in this study. To obtain different surface roughness values of each sample, the copper tubes were rotated with an electric rotor and sanded using sandpaper of different grit sizes. The average surface roughness values of the plain copper tubes were in the range 0.032–0.544 µm. All experimental samples were horizontally oriented, and experiments were carried out in ambient conditions up to a moderate heat flux regime (450 kW/m2). Moreover, for a comparative analysis, a sample with a rough surface and hydrophobic patterns was included in this study. Compared with the smoothest surface, the aforementioned rough sample exhibited a heat transfer coefficient that was up to a factor 1.5 higher for the highest evaluated heat flux. These findings show that even small increments in the surface roughness along with the addition of hydrophobic patterns can significantly lower the wall superheat temperature and increase the heat transfer coefficient of copper tubes. Furthermore, supported by high-speed imaging of the experiment, it was observed that increasing the surface roughness caused bubbles to depart when their diameter was larger, and the nucleation site density and bubble departure frequency increased. In contrast, the rough surface with hydrophobic patterns exhibited the best overall enhancement, including the characteristics mentioned above of the rough surfaces along with a uniform distribution of the bubbles around the surface.Graphical abstractImage, graphical abstract
       
  • Cooling performance evaluation for double-layer configuration of
           air-cooled heat exchanger
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Weijia Wang, Lei Chen, Yanqiang Kong, Lijun Yang, Yuguang Niu, Xiaoze DuAbstractFor large-scale natural draft dry cooling system in thermal power plants, the double-layer air-cooled heat exchanger is recommended thanks to its lower water flow resistance, while the cooling performance is rarely reported so far. Based on the typical natural draft dry cooling system with double-layer air-cooled heat exchanger, the numerical modeling and solution apporaches are developed, by which the representative variable fields and overall cooling performance are obtained and compared with the conventional system. The results show that at the wind speeds of 4 m/s and 8 m/s, the frontal and middle sectors of lower layer show better heat transfer performances than upper layer, especially for the middle sector. At high wind speeds, the frontal sector of upper layer presents a better performance than that of lower layer, but the cooling performances of the middle sectors for both layers get worse with the lower layer showing a slight recovery. The rear sector of lower layer has a much superior cooling performance to upper layer. With increased wind speed, the cooling performance difference of both layers varies little for the middle front sector. As for the middle and middle rear sectors, the performance gap between two layers increases greatly from 4 m/s to 8 m/s, but changes little at high wind speeds. For the rear sector, the difference between both layers stands always prominent at all wind speeds. Compared with the conventional system, the cooling performance gets improved in the absence of winds and at the wind speeds of 4 m/s and 8 m/s, but deteriorated a little at high wind speeds, so this innovative system could be recommended for power plants in arid places with weak wind all year round.
       
  • Effect of the heat transfer liquid fin on critical heat flux enhancement
           under ERVC condition
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Min Ho Lee, Hyo Heo, In Cheol BangAbstractSeveral critical heat flux (CHF) enhancement methods for in-vessel retention through external reactor vessel cooling (IVR-ERVC) have been researched. However, they have some limitations for practical applications. In the present study, heat transfer liquid fin concept was suggested to address the issue of CHF by spreading focusing effect of the heat flux. The liquid fin was located outside of the reactor pressure vessel; it is activated by filling under the accident situations. Liquid metal and oil were selected as the fin materials as they are characterized by significantly different Prandtl numbers; this property helps to clearly distinguish the heat transfer mechanisms involved. Analysis were conducted based on both experimental and numerical methods. As expected, conduction and natural circulation were the dominant heat transfer mechanisms in the case of liquid metal fin and the oil fin, respectively. Regardless of the Prandtl number of the fin, safety margin for the CHF was significantly increased in both fin cases. The heat flux profile of the conduction dominant liquid metal fin showed a moderately flattened shaped. However, for the oil fin, heat flux was mitigated and upwardly shifted (natural circulation as the primary heat transfer mechanism). Although both materials exhibited good performance in terms of securing a margin for CHF, temperature increment by the liquid fin was much higher in the oil case because of the relative lower thermal conductivity of the latter. Thus, the use of low thermal conductivity fins requires the temperature limit to be taken into consideration.
       
  • Numerical modeling of electromagnetic-based thermal recovery techniques
           combined with solvent injection
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Asghar Sadeghi, Hassan Hassanzadeh, Thomas G. Harding, Bill MacFarlane, Shima Bashti, Parnian HaghighatAbstractElectromagnetic heating (EMH) has been the focus of ever-increasing theoretical and experimental studies to examine if it can be used to heat geomaterials at the field scale. Bitumen recovery process using EMH technique assisted by solvent injection, such as that used in Enhanced Solvent Extraction Incorporating Electromagnetic Heating (ESEIEH®) pilot in currently being conducted in the Athabasca oil sands, utilizes radiofrequency waves to generate a moderate amount of heat in the reservoir. In conjunction with dilution effect of solvent the generated thermal energy reduces the viscosity of highly viscous bitumen leading to its mobilization.Electromagnetic (EM) wave propagation in a reservoir is a coupled multiphysics process that involves not only the heat transfer and fluid flow, but also EM field distribution. Currently, a coupled approach is followed by industry using a commercial reservoir simulator (CMG-STARS) and another commercial software (ANSYS-HFSS) or in-house electromagnetic wave solver with different gridding system where both are linked through a property mapping interface (CEMRS or AxHeat). The coupled scheme utilizes the interface to map parameters from two different gridding structures which causes an additional computational load on the simulation process and could be a source of error. This study presents an alternative integrated compositional numerical modeling approach to explore the EM heating phenomena pertinent to fluid flow and heat generation and transfer in oil sand reservoirs in the same grid structure. Energy balance and EM wave propagation are derived using Maxwell's equations in the frequency domain. Then, the newly developed numerical simulator is validated using benchmark problems and used to demonstrate the physics of EM-induced volumetric heat generation in multi-phase oil sand reservoirs. Finally, the developed numerical model is applied in a case study of propane injection along the antenna to achieve oil recovery and the results are compared with the analogous Steam Assisted Gravity Drainage (SAGD).
       
  • Pressure drop and heat transfer of flow boiling R134a in a dimpled flat
           duct
    • Abstract: Publication date: April 2020Source: International Journal of Heat and Mass Transfer, Volume 151Author(s): Ke Tang, Yuping Gao, Ye Feng, Pega HrnjakAbstractA test facility has been built up to investigate the pressure drop and heat transfer of flow boiling R134a in a dimpled flat duct. The experiments are conducted at mass flux from 102.2 to 205.0 kg m−2 s−1, heat flux from 2.3 to 9.3 kW m−2, pressure from 349.8 to 488.4 kPa and vapor quality from 0.05 to 0.95. The results show that the frictional pressure gradient increases with increasing vapor quality and mass flux, while decreases with a rise in pressure. The heat flux has little impact on the frictional pressure gradient. The flow boiling heat transfer coefficient decreases slightly first and then increases significantly with an increase in vapor quality, which is attributed to the combined contributions of nucleate boiling heat transfer and convective evaporation heat transfer. No dryout has been observed in the tested vapor quality region. The flow boiling heat transfer coefficient visibly increases with increasing mass flux and heat flux, while the rise in pressure just slightly increases the flow boiling heat transfer coefficient in low vapor quality region only. The comparisons with correlations for regular channels show that the dimpled flat duct has 3.9 to 8.3 times frictional pressure gradient and 1.3 to 3.0 times heat transfer coefficient.
       
 
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