Subjects -> PHYSICS (Total: 857 journals)
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THERMODYNAMICS (30 journals)

Showing 1 - 28 of 28 Journals sorted alphabetically
Advances in Heat Transfer     Full-text available via subscription   (Followers: 27)
Applied Thermal Engineering     Hybrid Journal   (Followers: 38)
Araucaria. Revista Iberoamericana de Filosofía, Política y Humanidades     Open Access  
Archives of Thermodynamics     Open Access   (Followers: 11)
Chemical Thermodynamics and Thermal Analysis     Open Access   (Followers: 3)
Condensed Matter Physics     Open Access   (Followers: 2)
Diffusion Foundations     Full-text available via subscription   (Followers: 4)
European Journal of Mechanics - B/Fluids     Hybrid Journal   (Followers: 5)
Experimental Heat Transfer     Hybrid Journal   (Followers: 18)
Experimental Thermal and Fluid Science     Hybrid Journal   (Followers: 35)
Fluids     Open Access  
Heat and Mass Transfer     Hybrid Journal   (Followers: 28)
Heat Transfer Engineering     Hybrid Journal   (Followers: 38)
High Temperature     Hybrid Journal   (Followers: 2)
HTM Journal of Heat Treatment and Materials     Full-text available via subscription   (Followers: 3)
International Journal of Thermodynamics     Open Access   (Followers: 14)
International Journal of Thermophysics     Hybrid Journal   (Followers: 7)
Journal of Chemical Thermodynamics     Hybrid Journal   (Followers: 8)
Journal of Low Temperature Physics     Hybrid Journal   (Followers: 6)
Journal of Non-Newtonian Fluid Mechanics     Hybrid Journal   (Followers: 14)
Journal of Thermal Science     Hybrid Journal   (Followers: 22)
Journal of Thermal Spray Technology     Hybrid Journal   (Followers: 5)
Journal of Thermodynamics     Open Access   (Followers: 9)
Journal of Thermophysics and Heat Transfer     Hybrid Journal   (Followers: 95)
Low Temperature Physics     Hybrid Journal   (Followers: 6)
Metal Science and Heat Treatment     Hybrid Journal   (Followers: 36)
Quantitative InfraRed Thermography Journal     Hybrid Journal  
Thermophysics and Aeromechanics     Hybrid Journal   (Followers: 6)
Similar Journals
Journal Cover
Heat and Mass Transfer
Journal Prestige (SJR): 0.448
Citation Impact (citeScore): 1
Number of Followers: 28  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1432-1181 - ISSN (Online) 0947-7411
Published by Springer-Verlag Homepage  [2467 journals]
  • Experimental study of drying garlic slices (Allium sativum L.) using a
           fluidized-bed dryer

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      Abstract: Abstract The drying kinetics of garlic (Allium sativum L.) slices in a fluidized bed were investigated experimentally and modeled mathematically in this study. A pilot-scale fluidized bed dryer was set up for this purpose where it was used to study the behavior of garlic slices during the fluidization drying process. The fluidized bed dryer used flow rates of 0.034 kg s-1 and temperatures ranging from 45 °C to 60 °C. The maximum temperature of the garlic was set at 60 °C, as high temperatures can damage or reduce the final quality of the dried products. The results obtained showed that the optimal temperature for drying garlic is 50 °C. A predictive model was established to study the heat and mass transfer phenomenon in the fluidized bed. A good agreement was found between the experimental and predicted results obtained by the developed mathematical model.
      PubDate: 2023-02-01
       
  • Experimental study on the overall heat transfer capability of the thin
           liquid film at different positions in the three-phase contact line area

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      Abstract: Abstract With the miniaturization and integration of electronic devices, the power density in electronic devices has increased significantly, putting forward higher requirements on the service life and stability of electronic devices. The micro-scale liquid cooling systems have played an essential role in the heat dissipation of microelectronic devices. In the micro-scale liquid cooling systems, when solid, liquid, and gas are in contact, a three-phase contact line area is formed. At the micro-nano scale, heat transfer in this area cannot be ignored. However, because of the small size of the three-phase contact line area, the experimental researches are mainly focused on the profile of the liquid thin film. Few experimental methods can easily measure the heat transfer capacity of the three-phase contact line area. In this study, we used the transient time-domain thermoreflectance (TDTR) technique, which has a satisfactory spatial and temporal resolution, to characterize the heat transfer capacity of the thin liquid film at different positions in the three-phase contact line area and established a heat transfer model for TDTR to measure the overall heat transfer coefficient of the thin liquid film. In addition, we used Wayner’s evaporation model of wetting film to verify the experimental results. The experimental results show that the overall heat transfer coefficient of the liquid film in the middle of the microgroove is much smaller than that at the edge, which has the same law as the theoretical calculation. The evaporating thin-film region’s measured overall heat transfer coefficient can reach ~ 650 kW/(m2·K). This study provides an idea for the experimental study of micro-nano-scale liquid film heat transfer and laid the foundation for revealing the heat and mass transport mechanism in the three-phase contact line area.
      PubDate: 2023-02-01
       
  • Characterization of thermal boundary resistance at solid–liquid
           interface based on continuous wave frequency domain thermal reflection
           method

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      Abstract: Abstract Thermal transport properties of the solid–liquid interface continue to be in urgent research need with the widespread use of nanoscale fluid cooling, particle-assisted therapy, and lubrication technologies. In this paper, we developed an experimental system of Continuous wave frequency domain thermal reflection for measuring the thermal conductivity of liquids and interfacial thermal conductance of the solid–liquid and a two-way heat transport model based on the transmission line theory model, and the thermal conductivity, the interfacial thermal conductance and the contact angle of liquids on the surface of the aluminum sensing layer were measured for water, ethanol and hexadecane. In addition, we simulated the thermal transport at the Al /water interface by molecular dynamics with simulation results agreeing with experimental results. The results show that solid/liquid interface thermal transport depends on the transverse mode coupling of liquid wettability, increase the force interaction between solid and liquid molecules which couples the energy of low-frequency phonons to the liquid, thus making the interfacial thermal conductance decrease.
      PubDate: 2023-02-01
       
  • Vapour-liquid rebalancing behaviour of free water evaporation kinetics:
           experimental investigation and modelling

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      Abstract: Abstract Drying and moisture evaporation are inextricably linked and major attention is focused on thermal conditions. But the non-thermal factors, especially the relative humidity and air distribution of wet air, also affects drying kinetics. Aiming to obtain the drying kinetic features of water evaporation under isothermal conditions, an experimental investigation was conducted using a variation of each single variable method. The experimental phenomena of non-thermal factors affecting evaporation kinetics under different isothermal process were presented. The results show that water evaporation rate is linear with vapor partial pressure difference under constant temperature condition, and nonlinear change in evaporation rate is caused by wet air flow hindering factors, i.e. the wall height above water surface. A vapour-liquid rebalancing behaviour hypothesis was concluded basing on the results, that water is dried by turning into saturated vapour then being transferred through convection and diffusion. The stronger capability to remove saturated water vapor from the liquid surface is associated with higher evaporation rate. A comprehensive evaporation kinetic model was obtained basing on experimental data and the prediction accuracy is verified by an out of sample experiment. The most probable physical reasons behind the thermal condition change caused parameter change rules were interpreted. This proposed vapor–liquid rebalancing hypothesis shows a consistent behavior with respect to drying theory.
      PubDate: 2023-02-01
       
  • Heat transfer in air-gap and thermal-fluid coupling field of a large-scale
           turbine generator

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      Abstract: Abstract With the capacities of large-scale turbine generators increase, higher electrical and thermal loads may cause higher risk of thermal faults. Especially, for those air cooling machines with single channel ventilation system, the comparatively poor thermal conductibility of air makes the air-gap become a critical part in thermal transmission network. Thus, the heat transfer in air-gap of large scale turbine generators is followed with interest. The investigation is performed on a 150 MW air cooling turbine generator with single channel ventilation cooling system, and realized via the thermal-fluid coupling field studying. A nonlinear numerical calculation model for fluid flowing and heat transfer within the machine is proposed, and solved by finite volume method (FVM). Then, the heat transfer in the air-gap is analyzed, whilst the temperature distributions in machine different parts, as windings, stator core, and rotor components, are investigated. In addition, the velocity vector distribution of coolant in the ventilation system is also studied, and the air motion track in the air-gap is analyzed while considering the influence of rotor rotation. Finally, the influence of flow in the air-gap on fluid flowing in the stator radial ventilation ducts is investigated.
      PubDate: 2023-02-01
       
  • Moisture sorption characteristics and dynamic mechanical thermal analysis
           of dried petiole and rhizome of red water lily (Nymphaea x rubra)

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      Abstract: Abstract This research aimed to experimentally determine moisture sorption characteristics and mechanical thermal properties of different parts of red water lily (Nymphaea x rubra). The data obtained from dynamic vapor sorption (DVS) were modeled with six sorption isotherm models. The shape of sorption isotherms of dried petiole and rhizome was classified as Type III and II, respectively. Peleg model was the best fit with the experimental data. GAB and BET models were used to estimate monolayer moisture content (M0) of the samples and M0 of petiole ranged between 7.17 to 8.291% d.b. and 10.455 to 10.588% d.b. for GAB and BET models, respectively and M0 of rhizome ranged between 6.208 to 7.741% d.b. and 3.566 to 3.669% d.b. for GAB and BET models, respectively. Blahovec-Yanniotis model was used to describe the amount of bounded water and solution water in material and the contribution of solution water played an important role in both adsorption and desorption processes of dried petiole and rhizome. Dried red water lilies were equilibrated at different relative humidity levels. Dynamic mechanical thermal analysis (DMTA) was used to estimate the glass transition of the samples at different water activities. Increasing the solicitation frequency shifted the temperature of the relaxation to a higher temperature and Arrhenius equation described well the frequency dependency of the transition temperature. The apparent activation energies (Ea) of dried petiole and rhizome were in the range from 217.98 to 248.49 kJ/mol and 187.34 to 230.30 kJ/mol, respectively.
      PubDate: 2023-02-01
       
  • Experimental study of the performance of two water-based nanofluids in the
           thermal entrance region of a pipe

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      Abstract: Abstract In this study, the local Nusselt number and the convective heat transfer coefficient of water and two water-based nanofluids are determined in the thermal entrance region in a laminar pipe flow. The pressure drop and the friction factor are also measured. Three mass concentrations, up to 5%, of Al \(_2\) O \(_3\) -water and TiO \(_2\) -water nanofluids were prepared from commercial stock solutions. The results show that the non-dimensional relationships that relate the friction factor to the Reynolds number and the local Nusselt number to the Graetz number are still valid for these nanofluids. Both the local heat transfer coefficient and the pressure drop increase with mass concentration at a constant Reynolds number due to the enhancement of the thermal conductivity and the rise of the viscosity. However, at a constant pumping power, we demonstrate that the addition of these particles degrades heat transfer during the whole process of thermal development. This can be explained by the fact that the boundary layer grows faster for nanofluids than for water at a constant pumping power. A conservative criterion has been developed to assess the thermal performance of nanofluids in the thermal entrance region of a pipe. It suggests that it may not be possible to increase the thermal performance of water in this region by adding common solid particles.
      PubDate: 2023-02-01
       
  • Digital interferometric studies of jet impingement cooling system

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      Abstract: Abstract Currently large numbers of electronic components are packed closely together in semiconductor chips and the power densities of VLSI chips range up to 100 W/cm2. Jet impingement cooling is widely used in electronics cooling, as high convective heat transfer rates are required for effective heat dissipation. The jet impingement cooling depends on various parameters and the analysis of all possible combination requires huge cost and time. Various investigative studies have been conducted in the field of jet impingement cooling but the use of digital interferometric techniques has not been prominent. Mach Zehnder interferometric technique is a non-intrusive technique which is extensively used by many researchers to estimate the heat transfer from plates, fins in both air and fluid mediums. The present work focuses on the convective heat transfer studies of jet impingement cooling of a flat plate in air, using digital interferometric technique. The flat heater plate simulating the IC chip under operation was fabricated inhouse and is cooled by a vertical jet of air. Wedge fringe mode has been adopted for the estimation of the heat transfer from the deflection of fringe caused due to the temperature variation. The effect of various parameters on the rate of heat transfer rate was determined with the help of a Design of Experiments software. Computational fluid dynamic analysis of the impingement of an air jet on the flat plate of the experimental setup was done to compare it with the results obtained from experiments. A correlation between the significant parameters affecting jet impingement is proposed, from the experimental results.
      PubDate: 2023-02-01
       
  • Drying performance of limonite pellets in the hot air-assisted microwave

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      Abstract: Abstract The limonite acted as the raw material for iron smelting should be pre-dried due to its high initial moisture content. Based on a lab-scale setup, the drying performance of limonite pellets (diameter: 15 mm) was evaluated in terms of the influence of the hot air (100–200 °C), microwave power (100–600 W) and microwave combined with hot air drying. As the temperature of hot air rose from 100 to 200 °C, the drying time of limonite during the hot air drying alone saved by 54%. The effective moisture diffusivities (Deff) of limonite in the hot air were between 2.07 × 10–9 and 4.78 × 10–8 m2/s. With lifting the microwave power from 100 to 600 W, the time in the microwave heating alone saved by 80%. The values for Deff of the limonite in the microwave drying were between 1.71 × 10–8 and 1.23 × 10–7 m2/s. The apparent activation energy (Ea) of the limonite in the hot air drying was 12.3 kJ/mol. Ea for the microwave drying was 37.4 W/g, while that after adding 0.6% Na2CO3 was about 56% lower than that of the pellet without Na2CO3. In the combined drying, the hot air temperature of 145 °C, the air velocity of 0.5 m/s and microwave power of 500 W were determined as optimized parameters regarding the minimum drying time integrated with energy consumption according to the response surface methodology. Increasing the feed sources and hot air assisted drying could all improve the microwave heating uniformity.
      PubDate: 2023-02-01
       
  • 3D simulation of momentum, heat and mass transfer in potato cubes during
           intermittent microwave-convective hot air drying

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      Abstract: Abstract Simultaneous use of convective hot air and continuous microwave is a new method for drying of agricultural products. This study indicated the effect of different drying methods (Convective Hot Air 45 °C at a speed of 1 m/s (CHA), Microwave 540 W (MIC), simultaneous Convective Hot Air and continuous Microwave (HA-MIC)) on the drying kinetics of potato cubes (moisture ratio, effective moisture diffusion coefficient and energy consumption). In addition, modeling of momentum, heat and mass transfer, along with changes in chemical composition and thermophysical properties of potato (at the same time with temperature change and moisture exit) during HA-MIC drying method was performed. Considering to results, the lowest energy consumption was related to the MIC method. The results of the modeling section showed that, by reducing the mass and volume fraction of water, the ratio of other components (carbohydrates, proteins, fats, ash, and fibre) increases in the total solid. In addition, with decreasing the mass fraction of water along with increasing temperature, total density (kg/m3) and the density of potato constituents increased and decreased, respectively. Total specific heat (J/kg.K) and total heat conductivity (W/m.K) of potato also decreased with decreasing the mass and volume fraction of water; while in specific heat and thermal conductivity of potato constituents, an increasing trend was observed. Finally, a high correlation was obtained between the results of experimental data and numerical modeling for moisture distribution (R2 = 0.9589) and temperature distribution (R2 = 0.9961).
      PubDate: 2023-02-01
       
  • Stripping of carbon dioxide from ethanol solution of PAMAM dendrimer using
           hollow Fibre membrane contactor

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      Abstract: Separation of carbon dioxide was studied in microporous fiber (HF) membranes using the ethanol solution of PAMAM dendrimers. PAMAM dendrimers (Generations 0–4) are embedded in three membrane contactors called polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC) and polypropylene (PP) separately and responsive. With higher flow rates in the dendrimer fluid, a faster chemical reaction occurs that can accelerate the transfer of carbon dioxide to the alcoholic solution. Flow rate and efficiency increase with increasing fluid flow rates. The emission rate was controlled by the distribution in the liquid section at moderate flow rates. The maximum acquisition flow is achieved at a flow rate in liquids and gases of approximately 0.5 mL / s. Empty fiber membranes can replace columns full of carbon dioxide removal from industrial packing power applications, greater connections between the shell side and the tube side with greater driving force, ease of sealing and easy retrieval, less expensive and smaller space requirement compared to other separation techniques. Graphical abstract
      PubDate: 2023-02-01
       
  • Characterization of heat transfer and frictional pressure drops for water
           flows through micro tubes

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      Abstract: Abstract The heat transfer and pressure drops characterization of water through round micro tubes is investigated experimentally. Nine tube diameters in the range of 50 µm, 80 µm, 100 µm, 250 µm, 300 µm, 400 µm, 800 µm, 900 µm, and 950 µm and over a wide range of Reynolds numbers are tested to characterize the friction factor, the pressure drops, heat transfer coefficient, fully developed heat transfer, thermal developing heat transfer, the effect of viscous heating, and evaluating the surface temperature on the wall of the micro tubes. It is observed that the fully developed HTCs and friction factors in micro tubes agree well with the predicted conventional heat transfer correlations for laminar and turbulent flow, Poiseuille’ (f = 16/ReD) theory, Blasius’ (f = 0.079ReD−0.25) equation [1], and Filonenko [2]. It is also observed that the transition takes place at (Re = 2288 ~ 2989), which corresponds to that in the conventional sizes of tubes. It is also observed that the thermal entrance length in the laminar region for the test micro tubes is longer than that of the conventional sizes of tubes predicted by the empirical correlations. Moreover, since the specific heat of water is very high and the velocity is very low, there is no significant effect of the viscous heating.
      PubDate: 2023-02-01
       
  • Optimization of heat and fluid flow over curved trapezoidal winglet pair
           type vortex generators with one-row and three-row

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      Abstract: Abstract Passive heat transfer enhancement methods are frequently chosen to achieve higher thermo-hydraulic performances in engineering applications because they do not require external energy. One of the most popular passive methods for increasing heat transfer and improving the cooling effects of heat transfer surfaces is the use of vortex generators (VGs). However, the pressure drop generated by the usage of VGs must be controlled. This work is interested in the number (one, three) and geometric dimensions of VGs in the rectangular channel. Numerical optimization studies are carried out for heat and fluid flow over curved trapezoidal winglet pair (CTWP) type VGs for one-row and three-row to obtain optimum geometric dimensions of one-row and three-row of CTWP types VGs in the rectangular channel under incompressible and turbulent flow and conjugate heat transfer assumptions. Heat transfer and pressure drop values are compared in terms of \(j/{j}_{0}\) (the ratio of Colburn factor with CTWP to without it) and \(f/{f}_{0}\) (the ratio of friction factor with CTWP to without it), respectively. The optimization problems are solved with no constraints in the workflows. Multi-Objective Genetic Algorithm (MOGA) is used for the computations where the maximization of \(j/{j}_{0}\) and minimization of \(f/{f}_{0}\) are the two objective functions. Thermo-hydraulic performances ( \(R=(j/{j}_{0})/(f/{f}_{0})\) ) of the studied cases are also compared. The optimization variables are inclination angle (α), attack angle (β), width / length ratio (b / a), height of the VG (h), interval between VG pair’s front edges ( \({S}_{1}\) ) for both one-row and three-row cases, also longitudinal spacing between each VG pair ( \({S}_{L}\) ) is added as an optimization variable for three-row case. It is found that three-row of CTWP type VGs can increase \(j/{j}_{0}\) also increase \(f/{f}_{0}\) , i.e., heat transfer enhancement is obtained with a pressure drop increment disadvantage and it is possible to achieve 24.05% heat transfer enhancement with the penalty of 17.27% pressure drop increment as compared to one-row of CTWP type VGs. Furthermore, the fact that the pressure drop has the maximum value does not mean that the heat transfer value is the maximum.
      PubDate: 2023-01-27
       
  • Synthesis, characterization and application of SiO2 and CuO nanofluid in
           spray cooling of hot steel plate

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      Abstract: Abstract The current work uses SiO2 and CuO mono, mixed nanofluid to improve very-high mass-flux spray cooling performance. At first, the modified sol–gel method based SiO2 and wet-chemical method based CuO nanoparticles are prepared. The prepared nanoparticles' density, crystalline/amorphous nature, functional groups, compositions, morphology, and particle size are characterized. The SiO2 and CuO nanofluid are prepared using one-step and two-step methods, respectively. The nanofluid thermophysical properties, particle size distribution, and stability are determined. The heat transfer performance of applied nanofluid is assessed in terms of parameters cooling rate, heat flux, and heat transfer coefficient, which are estimated using inverse heat conduction analysis. The cooling performance improvement is observed with concentration enhancement for all nanofluids. However, for mono CuO and mixed SiO2-CuO nanofluid at their highest concentration, the cooling enhancement percent decreases compared to their second highest concentration. The highest cooling rate of 164 °C/s is observed for mixed nanofluid at the highest concentration. The average surface heat flux, critical heat flux, and average heat transfer coefficient improvement are maximum at 1.80 MW/m2, 2.36 MW/m2, and 2.67 kW/m2K, respectively, for mixed nanofluid highest concentration. Therefore, nanofluid inclusion leads to spray cooling performance improvement, with slight performance reduction after nanoparticle loading enhancement in some cases.
      PubDate: 2023-01-27
       
  • Physical gas absorption into a stirred liquid: a new kinetic model and
           experimental studies

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      Abstract: Abstract We presented a new analytic model of physical gas absorption into a stirred liquid. This model is based on the assumption that the gas absorption/desorption process can be considered as a reversible chemical reaction that occurs at the gas–liquid interface. In addition, in this model, there is no assumption about the distribution of the concentration of the dissolved gas inside the liquid during its intensive stirring. In the framework of the presented model, it is shown that the physical absorption coefficient is the rate constant of the desorption reaction. This quantity is individual for each specific gas–liquid system, it does not depend on concentrations, and its temperature dependence obeys the Arrhenius equation. Experiments were carried out to study the kinetics of physical absorption of methane into stirred water at different temperatures and methane pressures. Experiments were also carried out to study the kinetics of physical absorption of carbon dioxide into stirred water at different temperatures and carbon dioxide pressures. The obtained experimental data fully confirmed the validity of the proposed model. The dependences of the rate constant of the desorption reaction (physical absorption coefficient) on temperature for the methane–water and carbon dioxide–water systems were determined.
      PubDate: 2023-01-26
       
  • Experimental investigation of convective heat transfer inside tube with
           stable plasmonic TiN nanofluid and twisted tape combination for solar
           thermal applications

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      Abstract: Abstract The present experimental study involves a convective heat transfer performance analysis of the fully developed laminar flow of TiN nanofluid through a uniformly heated U pipe with and without twisted tape (H/D = 5) combination. The TiN nanofluid, with its enormous thermophysical properties, opens up a new dimension in solar thermal applications. TiN nanofluid pretends to have photoabsorption properties (localized surface plasmon resonance). The preparation of stable, efficient, low-cost TiN nanofluid and its application is an emerging area of research. Titanium nitride (TiN) nanoparticles with sizes of 40–50 nm were used to make distilled water-based nanofluid at concentrations of 0%, 0.025%, 0.05%, 0.075%, and 0.1%. The two-step preparation method is preferred to prepare a stable nanofluid. The thermophysical properties are evaluated experimentally over a wide temperature range. The experiments were performed at flow rate (0.25–1.25 LPM), volume concentration (0–0.1%), inclination angle (35 degree), and heat flux (1000 W/m2). The nusselt number, convective heat transfer coefficient, and friction factor were evaluated at a bulk mean temperature. The convective heat transfer performance increases with volume concentration and Reynolds number. The friction factor decreases with a rise in volume concentration and Reynolds number. The nusselt number of the entire test section increased by 30.04% for a 0.1% volume concentration of TiN nanofluid and 42.8% for 0.1% of TiN nanofluid with twisted tape (H/D = 5) combination. The convective heat transfer performance enhancement is obtained at a cost of 2% pressure drop. The correlation has been developed to estimate the nusselt number and friction factor.
      PubDate: 2023-01-23
       
  • Thermal performance improvement of multilayer insulation technique

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      Abstract: Abstract Multilayer insulation (MLI) technique has provided a reliable thermal protection mechanism for cryostat’s cold wall boundary against the ambient heat load, in particular, the thermal radiation heat load. The aim of the current work is to attain an improved thermal performance from MLI technique by scrutinizing its insulation potential in terms of the heat load. The intervening medium in this investigation is made up of three suitable spacer and radiation shield materials: perforated Double Aluminized Mylar (DAM) with Dacron, perforated DAM with Glass−tissue, and unperforated DAM with Silk−net. The thermal performance of MLI system is evaluated by exploring the impact of associated physical parameters such as emissivity and residual gas pressure, geometry of the radiation shields (perforation styles of radiation shields), and analyzing the effect of the radiation shield’s arrangement on the heat load. We have observed that for perforated DAM with Dacron, the radiation heat load is the lowest. A medium vacuum level < 0.01 Torr, perforation style PS \(_{\mathrm {A}}\) in the radiation shield (in low−temperature region), and positioning radiation shields with decreasing spacing from the cold to hot wall boundary region facilitates a significant reduction in the heat load.
      PubDate: 2023-01-20
       
  • Parametric variation studies of experimental flow boiling heat transfer
           phenomena using R407c inside an enhanced tube

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      Abstract: Abstract An experimental investigation examines the flow boiling heat transfer phenomena of a vapour compression refrigeration system employing R-407c refrigerant inside a newly configured enhanced horizontally oriented tube with a 20° helix angle and 52° apex angle at ambient pressure. Experiments were conducted on a 1000 mm enhanced tube of copper at saturation temperatures of 15 – 45 °C with input refrigerant heat fluxes of 5—85 kW/m2 and mass fluxes of 100–250 kg/m2s. The heat transfer coefficients for different configurations are obtained and compared with the established correlations for the heat transport phenomena. The experimental Nusselt number defining the convective heat transfer coefficient captured the established correlations with a mean error of 10%. A Nondimensional Jacob number is introduced to signify the sensible heat transfer effects. Local Nusselt varying with location and Jakob subcooling numbers are also introduced. The area ratio is 1.83 for the enhanced tubes concerning the smooth tube specification. Results predicted the 1.45 times enhancement of heat transfer coefficient for the enhanced tubes. Parametric variation is also incorporated to analyse the experimental nature more comprehensively.
      PubDate: 2023-01-20
       
  • Heat and mass transfer of countercurrent air-water flow in a vertical tube

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      Abstract: Abstract The paper deals with the classification and the design features of direct contact heat exchangers used in various technological processes. It describes the existing two-phase flow regimes and the methods for heat and mass transfer prediction in heat exchangers with the direct contact of fluids in a vertical tube. The authors carried out the measurements of heat and mass transfer coefficients during the liquid film flow under the action of gravity towards the air flow in a vertical tube. The range of experimental variables is set to be the following: air mass flow rate is 1·10-3-4·10-3 kg/s, air inlet temperature is 26-28 °C, air inlet humidity is 38-50 %, water mass flow rate is 1.5·10-2 -4·10-2 kg/s, and water inlet temperature is 55-58 °C. It is shown that an increase in the fluid flow rate leads to the heat and mass transfer intensification due to an increase of waves on the film surface. The authors obtained new empirical correlations for calculating convective heat and mass transfer coefficients. These equations consider the influence of the water flow rate for the film Reynolds number. The described methods are recommended to be used in the range of air Reynolds numbers from 2300 to 6700 and film Reynolds numbers from 600 to 1300.
      PubDate: 2023-01-19
       
  • Numerical simulations of mass transfer in turbulent pipe flow at high
           schmidt numbers

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      Abstract: Abstract Numerical simulations for the wall mass transfer in a turbulent pipe flow were performed at Reynolds numbers (Re) of 40,000, 70,000 and 100,000 and Schmidt number (Sc) of 100, 200, 400 and 1280. Six versions of Low Reynolds Number (LRN) k-ε turbulence models were evaluated by examining the variation of the turbulent viscosity and diffusivity in the wall-normal direction. The predicted values of the turbulent viscosity and diffusivity from the AKN Low Reynolds Number model closely follow the cubic dependence in the near-wall region and found suitable for mass transfer simulations at high Schmidt numbers. The near-wall region was resolved down to y+=0.14 for Reynolds number of 100,000, which allowed the mass transfer to be obtained from the near-wall concentration profile. The exponent of the Schmidt number dependence on the Sherwood number was approximately 0.333 and in agreement with existing mass transfer correlations and experimental data for smooth pipe flow. The predicted mass transfer coefficient was in good agreement with pipe flow results and with experimental and numerical mass transfer results that yielded different Schmidt number dependences over the range considered.
      PubDate: 2023-01-07
       
 
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