Similar Journals
|
Journal of Thermal Science
Journal Prestige (SJR): 0.316  Citation Impact (citeScore): 1 Number of Followers: 21  Hybrid journal (It can contain Open Access articles)ISSN (Print) 1993-033X - ISSN (Online) 1003-2169 Published by Springer-Verlag  [2468 journals]
|
- Experiment and Analysis of Compatibility between New Phase Change Mixed
Molten Salt and 316L Stainless Steel-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Molten salt is considered as a promising heat storage and heat transfer medium due to its efficient thermophysical properties. In order to study the compatibility of five new mixed molten salts obtained with KNO3, NaNO3, K2CO3, Ca(NO3)2 ·4H2O, ZnCl2, NaF, Na2CO3, NaCl and MgO as materials and 316L stainless steel, corrosion weight loss, scanning electron microscopy, elemental analysis and XRD were used to analyze the compatibility of 316L stainless steel in the new mixed molten salt at different time and temperatures. The corrosion behavior under the conditions was studied and characterized. Their compatibility data was obtained, and the corrosion mechanism of 316L stainless steel in mixed molten salts was explored. The results show that the corrosion weight of 316L stainless steel increases, and the corrosion degree of grain, crystal crack depth and oxidation degree increase gradually with the increase of temperature and time. The corrosion of molten salt on alloy is mainly caused by the selective diffusion loss and corrosion of Cr, Fe and other elements, and is accompanied by the formation of different metal oxides. The formation of metal oxides can slow down metal corrosion and loss to a certain extent. The corrosion results under different working conditions show that 316L stainless steel has good compatibility with the new mixed molten salt, and has certain application value in the field of heat transfer and energy storage.
PubDate: 2024-08-27
-
- Effect of Shape and Placement of Twisted Pin Fins in a Rectangular Channel
on Thermo-Hydraulic Performance-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract To enhance the thermo-hydraulic performance of cooling channels, this investigation examines the influence of distinct cross-sectional shapes (i.e., triangular, rectangular, and hexagonal) of twisted pin fins and their arrangements in straight and cross rows. An ambient air cooling test platform was established to numerically and experimentally investigate the flow and heat transfer characteristics of 360° twisted pin fins at Re=15 200–22 800. The findings reveal that straight rows exhibit higher Nu values than cross rows for triangular and rectangular twisted pin fins, and Nu increases with Re. In contrast, for hexagonal twisted pin fins, only straight rows at Re=19 000 exhibit superior overall thermal performance compared to cross rows. Notably, the heat transfer performance of the cooling channel with hexagonal twisted fins surpasses both triangular and rectangular configurations, especially at high Reynolds numbers (Re=22 800). Although the heat transfer coefficient of the cooling channel with hexagonal twisted fins is significantly enhanced by 132.71% compared to the flat channel, it also exhibits the highest thermal resistance and relative friction among the three types of twisted fins, the maximum of which are 2.14 and 16.55. Furthermore, the hydrothermal performance factor (HTPF) of the cooling channels with different types of twisted pin fins depends on the Reynolds number and arrangement modes. At Re=15 200, the highest HTPF achieved for the cross-row hexagonal twisted pin fins is 0.99.
PubDate: 2024-08-22
-
- Aerodynamic Design Method and Experimental Investigation of a High-Load
Supersonic Compressor Cascade-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The high-load compressor plays an important role in further improving the performance of aero-engine. However, the complex shock waves in the cascade channel also bring more aerodynamic losses. This paper proposes a supersonic compressor cascade modeling method based on the theory of unique inlet flow angle, and the aerodynamic design and optimization of a cascade with inlet Mach number 1.85 are studied by combining the numerical optimization method and planar cascade experiment. The results show that pressure increase can be achieved by multiple shock waves which are obtained by the reflection of the leading edge detached shock wave in the initial supersonic cascade channel at the design point, which verifies the feasibility of the design method. After optimization, the aerodynamic performance of the cascade has been improved to different degrees at the design point and off-design point. When the static pressure ratio is 3.285, the total pressure recovery coefficient reaches 86.82% at the design point, which is on the advanced level of the same type of cascade. The experimental results of planar cascade schlieren and surface pressure measurement also verify the correctness of the simulation method, which provides useful references for the subsequent compressor design.
PubDate: 2024-08-20
-
- Thermal-Economic Comparative Analysis and Optimization of the Maisotsenko
Gas Turbine Cycle under Different Configurations-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The widespread adoption of Maisotsenko gas turbine cycle (MGTC) is significantly constrained by the design and manufacturing complexity of the saturator. The proposition of innovative approaches to regulate the water carrying capacity and operational environment of the saturator, coupled with the performance and economic evaluation of systems under various configurations, can substantially facilitate its commercial implementation. Unlike the conventional two-stage MGTC system that solely comprises aftercooling and regenerative processes, this study proposes a three-stage MGTC system with an intercooling process (IMGTC), which considers the reuse of cooling water and energy recovery. The pricing allocation and energy depreciation characteristics of components are analyzed, and the impact of key variables is considered. Finally, economic optimization of the system is conducted using ISIGHT to identify the optimal parameter combination and results. The results indicate that the saturator price of IMGTC is lower and its exergy efficiency is higher than that of MGTC. The average water capacity of the IMGTC saturator is only 57.4% of that of the MGTC saturator, but the average exergy efficiency of IMGTC is 1.1% higher than that of MGTC. Moreover, external parameters all lead to the levelized cost of electricity (LCOE). Thermo-economic optimization shows that the optimal LCOE of IMGTC is 0.26% lower than that of MGTC. This study confirms the feasibility of IMGTC, as well as its thermodynamic and economic advantages over MGTC.
PubDate: 2024-08-20
-
- Comparison of Direct Pore-Scale and Volume-Averaging Methods for the
Performance Evaluation of Porous Volumetric Solar Receiver-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Direct pore-scale and volume-averaging numerical simulations are two methods for investigating the performance of porous volumetric solar receivers. To clarify the difference in the prediction of heat transfer processes, a direct comparison between these two methods was conducted at both steady state and transient state. The numerical models were established based on X-ray computed tomography scans and a local thermal non-equilibrium model, respectively. The empirical parameters, which are indispensable to the volume-averaging simulation, were determined by Monte Carlo ray tracing and direct pore-scale numerical simulations. The predicted outlet air temperature of the receiver by the volume-averaging simulation method corresponded satisfactorily to that in the direct pore-scale simulation. The largest discrepancies were observed when the receiver’s working temperature was elevated, with differences of 5.5% and 3.68% for the steady state and transient state simulations, respectively. However, the volume-averaging method is incapable of capturing the local temperature information of the air and porous skeleton. It underestimates the inlet temperature of the receiver, leading to an overestimation of the receiver’s thermal efficiency, with the largest difference being 6.51%. The comparison results show that the volume-averaging model is a good approximation to the pore-scale model when the empirical parameters are carefully selected.
PubDate: 2024-08-14
-
- Ignition and Lean Blowout Characteristics of a Reverse-Flow Combustor for
an Ultra-Compact Gas Turbine Engine-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The flame stability limit and propagation characteristics of a reverse-flow combustor without any flame-stabilized device were experimentally investigated under room temperature and pressure. The results indicate that it is feasible to stabilize the flame in the recirculation zones constructed by the impact jet flow from the primary holes and dilution holes. The flame projected area is mainly distributed in the recirculation zone upstream of the primary holes, whose presence and absence mark the ignition and extinction. During the ignition process, the growth rate and value of the flame projected area first increase and then decrease with the inlet velocity increasing from 9.4 m/s to 42.1 m/s. A rapid reduction followed by a slow reduction of ignition and lean blowout equivalence ratios is achieved by the increased inlet velocity. Then the non-reacting fluid structure in three sections was measured, and detailed velocity profiles were analyzed to improve the understanding of the flame stabilization mechanism. The results are conducive to the design of an ultra-compact combustor.
PubDate: 2024-08-13
-
- Numerical Investigation on Characteristics of Supercritical CO2 Heat
Transfer in Vertical Circular Tubes with Circumferentially Half-Side
Heating-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The design of heat exchangers in the advanced supercritical power conversion system cannot be separated from the study of heat transfer issues. Half-side heating mode is often encountered for solar receiver and supercritical boiler. Here, the characteristics of supercritical CO2 (sCO2) convection heat transfer in vertical tubes with circumferentially half-side heating was numerically investigated through the SST k-ω turbulent model which matches well with the experimental data. Then, heat transfer between sCO2 upflow and downflow was compared. Similar to film boiling heat transfer at subcritical pressure, numerical results were processed according to the supercritical pseudo-phase transition hypothesis, with liquid-like phase in the tube core region and vapor-like film in the region near the heated tube wall. The structure of two layers was demarcated by pseudo-critical temperature Tpc. Therefore, sCO2 heat transfer was assessed according to double thermal resistances caused by vapor-like film near the wall and core liquid-like phase. The findings suggest that wall temperature for upflow is higher than that for downflow, which is attributed to larger thermal resistance in the fluid domain for upflow than that for downflow. The difference guarantees the excellent heat transfer performance for downflow than upflow. It is also further concluded that the formation of vapor-like film near the wall due to pseudo-phase transition plays a key role in dominating wall temperature and inducing heat transfer deterioration in half-side heating tubes. The present contribution is significant to the design of supercritical heat exchanger under half-side heating mode.
PubDate: 2024-08-13
-
- Influence of Real Gas Properties on Aerodynamic Losses in a Supercritical
CO2 Centrifugal Compressor-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Supercritical carbon dioxide (SCO2) centrifugal compressor is a key component of a closed Brayton cycle system based on SCO2. A comprehensive understanding of the loss mechanism within the compressor is vital for its optimized design. However, the physical properties of SCO2 are highly nonlinear near the critical point, and the internal flow of the compressor is closely related to its properties, which inevitably influences the generation of aerodynamic losses within the compressor. This paper presents a comprehensive investigation of the compressor’s loss mechanism with an experimentally validated numerical method. The real gas model of CO2 embodied in the Reynolds-Averaged Navier-Stokes (RANS) model was used for the study. Firstly, the numerical simulation method was validated against the experimental results of Sandia SCO2 compressor. Secondly, performance and loss distribution of the compressor were compared among three fluids including SCO2, ideal CO2 (ICO2) and ideal air (IAir). The results showed that the performance of SCO2 was comparable to IAir under low flow coefficient, however markedly inferior to the other two fluids at near choke condition. Loss distribution among the three fluids was distinctive. In the impeller, SCO2 was the most inefficient, followed by ICO2 and IAir. The discrepancies were magnified as the flow coefficient increased. This is due to a stronger Blade-to-Blade pressure gradient that intensifies boundary layer accumulation on walls of the shroud/hub. Furthermore, owing to the reduced sonic speed of SCO2, a shock wave appears earlier at the throat region and SCO2 encounters more intense boundary layer separation.
PubDate: 2024-08-13
-
- Experimental Study of Fuel-Air Mixing and Dilution Jets on Outlet
Temperature Distribution in a Small Gas Turbine Combustor-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Experimental analysis was conducted to study the impact of fuel-air mixing and dilution jet on the temperature distribution in a small gas turbine combustor using various optical diagnostic techniques. The strength and velocity of the swirler at the venturi exit were adjusted to modify the fuel-air mixture, which is presumed to dominate the heat release of the main combustion zone. Additionally, the dilution hole configuration, including the number and size of the holes, was varied to investigate the dilution effect on outlet temperature distribution. Various optical diagnostic techniques, such as particle image velocimetry, planar Mie scattering, and OH* chemiluminescence, were used to measure the flow field, fuel spray distribution, and flame structure, respectively. A reduction in swirling strength led to a decrease in the average flow rate in the throat, which improved the structure and symmetry of the axial vortex system in the sleeve, enhanced the mixing of fuel and gas in the dome swirling air, and ultimately, improved the temperature uniformity of the heat release zone. Compared to larger and sparse dilution jets, smaller and dense dilution jets tended to generate hot spots shifted towards the radial middle area.
PubDate: 2024-08-09
-
- Effect of Operation Parameters on the Thermal Characteristics in a Planar
Solid Oxide Fuel Cell-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Effective operation strategies in the solid oxide fuel cell (SOFC) can adjust the spatial distribution of temperature gradient favoring the long-term stability. To investigate the effects of different operating conditions on the thermal behavior inside SOFC, a three-dimensional model is developed in this study. The model is verified by comparing it with the experimental data. The heat generation rate and its variation under different operating conditions are analyzed. The combined effects of operating voltage and gas temperature are considered to be the key factor influencing the temperature gradient. Compared to the original case, the temperature of SOFC decreases by 21.4 K when the fuel velocity reaches 5 m/s. But the maximum temperature gradient increases by 21.2%. Meanwhile, higher fuel velocities can eliminate about 32% of the area with higher temperature gradient. And when the oxidant velocity reaches 7.5 m/s, the peak temperature gradient effectively decreases by 16.59%. Simultaneous adjustment of the oxidant and fuel velocities can effectively reduce the peak temperature gradient and increase the safety zone. The effects of operation conditions on the temperature gradient of the cell are clarified in this study, which can be a reference for further research on the reliability of SOFCs.
PubDate: 2024-08-09
-
- Experimental Data-Driven Flow Field Prediction for Compressor Cascade
based on Deep Learning and ℓ1 Regularization-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract For complex flows in compressors containing flow separations and adverse pressure gradients, the numerical simulation results based on Reynolds-averaged Navier-Stokes (RANS) models often deviate from experimental measurements more or less. To improve the prediction accuracy and reduce the difference between the RANS prediction results and experimental measurements, an experimental data-driven flow field prediction method based on deep learning and ℓ1 regularization is proposed and applied to a compressor cascade flow field. The inlet boundary conditions and turbulence model parameters are calibrated to obtain the high-fidelity flow fields. The Saplart-Allmaras and SST turbulence models are used independently for mutual validation. The contributions of key modified parameters are also analyzed via sensitivity analysis. The results show that the prediction error can be reduced by nearly 70% based on the proposed algorithm. The flow fields predicted by the two calibrated turbulence models are almost the same and nearly independent of the turbulence models. The corrections of the inlet boundary conditions reduce the error in the first half of the chord. The turbulence model calibrations fix the overprediction of flow separation on the suction surface near the tail edge.
PubDate: 2024-08-08
-
- Modelling and Temperature Control of Liquid Cooling Process for
Lithium-Ion Battery-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Efficient thermal management of lithium-ion battery, working under extremely rapid charging-discharging, is of widespread interest to avoid the battery degradation due to temperature rise, resulting in the enhanced lifespan. Herein, thermal management of lithium-ion battery has been performed via a liquid cooling theoretical model integrated with thermoelectric model of battery packs and single-phase heat transfer. Aiming to alleviate the battery temperature fluctuation by automatically manipulating the flow rate of working fluid, a nominal model-free controller, i.e., fuzzy logic controller is designed. An optimized on-off controller based on pump speed optimization is introduced to serve as the comparative controller. Thermal control simulations are conducted under regular operating and extreme operating conditions, and two controllers are applied to control battery temperature with proper intervals which is conducive to enhance the battery charge-discharge efficiency. The results indicate that, for any operating condition, the fuzzy logic controller shows excellence in terms of the tracking accuracy of set-point of battery temperature. Thanks to the establishment of fuzzy set and fuzzy behavioral rules, the battery temperature has been throughout maintained near the set point, and the temperature fluctuation amplitude is highly reduced, with better temperature control accuracy of ∼0.2°C (regular condition) and ∼0.5°C (extreme condition) compared with ∼1.1°C (regular condition) and ∼1.6°C (extreme condition) of optimized on-off controller. While in the case of extreme operating condition, the proposed optimized on-off controller manifests the hysteresis in temperature fluctuation, which is ascribed to the set of dead-band for the feedback temperature. The simulation results cast new light on the utilization and development of model-free temperature controller for the thermal management of lithium-ion battery.
PubDate: 2024-08-03
-
- Regulating Melting Process in the Energy Storage of Solid-Liquid PCM based
on Double MRT-LBM Simulation-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The melting process of solid-liquid phase change materials (PCM) has a significant impact on their energy storage performance. To more effectively apply solid-liquid PCM for energy storage, it is crucial to study the regulation of melting process of solid-liquid PCM, which is numerically investigated based on double multiple relaxation time lattice Boltzmann method (MRT-LBM) in this work. In this work we pay more attention to the effects of different Stefan numbers (Ste) and Rayleigh numbers (Ra) on the melting process. The results indicate that the PCM melting is greatly influenced by the Ste number and Ra number, which can be divided into the heat conduction dominant stage and the convection dominant stage, according to the onset time of convection FoC. In order to describe the contribution of the heat conduction dominant stage to the whole melting process quantitatively, we firstly propose the ratio of the heat conduction dominant stage Rpc, which can be defined as the ratio of FoC to the complete melting time FoM. Rpc gradually decreases as the Ra number increases, and when the Ste number rises: Rpc=90.0% when Ste=1.0 and Ra=1×105, Rpc=39.6% when Ste=0.1 and Ra=1×105, and Rpc=14.0% when Ste=1.0 and Ra=1×107. A regime map about the effects of different Ste numbers and Ra numbers on Rpc has been further summarized. The discovered findings would be helpful in regulating melting process in the energy storage of solid-liquid PCM.
PubDate: 2024-08-03
-
- Performance Enhancement of Single-Phase Immersion Liquid-Cooled Data
Center Servers-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract As the promising cooling method for the next generation of data centers, the internal heat transport mechanism and enhancement mechanism of single-phase immersion liquid-cooled (SPILC) systems are not yet well understood. To address this, a steady-state three-dimensional numerical model is constructed herein to analyze flow and thermal transport capacities in servers using SPILC and traditional air-cooling methods. Moreover, this paper emphasizes the influence of component positioning, and underscores the benefits of optimizing coolant flow distribution using baffles. The results indicate that the SPILC system outperforms the traditional air-cooling approach at the same inlet Reynolds number (Re). When Re=10 000, the SPILC method reduces the maximum temperature by up to 70.13%, increases the average convective heat transfer coefficient by 287.5%, and provides better overall thermal uniformity in data center servers. Moreover, placing devices downstream of high-power components creates “thermal barriers” and degrades thermal transport for upstream devices due to increased flow resistance. Excessive spacing between high-power devices can lead to the formation of bypass channels, further deteriorating heat transfer. Additionally, the addition of baffles in the inlet section of SPILC systems effectively enhances heat dissipation performance. To maximize the heat dissipation capacity, minimizing bypass channels and optimizing the flow distribution of coolants are crucial.
PubDate: 2024-08-03
-
- Experimental Investigation of Thermal Performance of Novel Finned
Radiators for Automotive Cooling System-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract This research investigates innovative fin-type radiators for automobile engine cooling system. Micro-channel and helical radiators, along with straight type, were analyzed for heat transfer characteristics under various conditions. The uniqueness of this study is evident in the design of microchannel and helical radiators. For helical radiators, the inner rod features 4/8 helical-shaped water galleries, while the outer tube frame with embedded fins remains consistent. In contrast, the microchannel radiators have compact trapezoidal-shaped water galleries with separate fin strips. Furthermore, the novelty of the research is enhanced by the utilization of 3D printing technology in the manufacturing process. In constant fin height analysis at varied water and air flow rate, Microchannel Water Air Radiator with fin height 10.5 mm (MCWAR10.5) depicted a higher heat transfer rate amongst the radiators. In comparison to Straight Water Air Radiator with fin height 9.5 mm (SWAR9.5), the heat transfer rate is 30.3% and 1.3 times higher. However, in constant fin surface area analysis, microchannel radiator (MCWAR3.2) illustrates lower heat dissipation than Helical radiator (HWAR138) but higher than HWAR134 and Straight radiator (SWAR6). The examination of pumping loss indicated that the Micro-channel radiator outperformed helical radiators due to its lower pressure loss. The average pressure loss for Micro-channel radiators was 0.74 kPa, making it 1.2 times higher than that of a straight radiator (0.62 kPa), indicating a better trade-off.
PubDate: 2024-07-22
-
- Thermal Decomposition and Oxidative Decomposition Mechanism of HFC-134a by
Experimental and DFT Method-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract In response to the Kigali Amendment to the Montreal Protocol and global low-carbon emission environmental requirements, the phase-out and decomposition of numerous HFC refrigerants have become urgent, necessitating efficient and mild decomposition methods. This study investigates the thermal decomposition and oxidative thermal decomposition pathways of the typical hydrofluorocarbon refrigerant HFC-134a, employing a combination of experimental and quantum chemical DFT simulation methods. Quantum chemical simulations reveal that the initial reaction bond cleavage serves as the rate-determining step during the thermal decomposition process, with the most easily detectable closed-shell products including CF2=CHF, HF, CH3F, CHF3, CH2F2, and CF4. Reactive oxygen species can significantly reduce the Gibbs free energy barrier for HFC-134a decomposition. To achieve efficient degradation of HFC-134a, appropriate catalysts should be developed and selected to increase the level of reactive oxygen species in the reaction system. Experimental studies further corroborate that HFC-134a may undergo degradation through distinct reaction pathways under varying temperature (240°C to 360°C) and pressure (0.1 MPa to 4.5 MPa) conditions, in agreement with simulation predictions.
PubDate: 2024-07-19
-
- Experimental Investigation on Heat Transfer and Combustion of a Stirling
Engine Combustor Fueled by Reformed Gas and Diesel Fuel-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Thermochemical recuperation heat recovery is an advanced waste heat utilization technology that can effectively recover exhaust waste heat from oxy-fuel Stirling engines. The novel combustor of a Stirling engine with thermochemical recuperation heat recovery system is expected to utilize both reformed gas and diesel fuels as sources of combustion. In this research, the effects of various factors, including the H2O addition, fuel distribution ratio (FDR), excess oxygen coefficient, and cyclone structure on the temperature distribution in the combustor, combustion emissions, and external combustion system efficiency of the Stirling engine were experimentally investigated. With the increase of steam-to-carbon ratio (S/C), the temperature difference between the upper and lower heating tubes reduces and the circumferential temperature fluctuation decreases, and the combustion of diesel and reformed gas remains close to complete combustion. At S/C=2, the external combustion efficiency is 80.6%, indicating a 1.6% decrease compared to conventional combustion. With the increase of FDR, the temperature uniformity of the heater tube is improved, and the CO and HC emissions decrease. However, the impact of the FDR on the maximum temperature difference and temperature fluctuation across the heater is insignificant. When the FDR rises from 21% to 38%, the external combustion efficiency increases from 87.4% to 92.3%. The excess oxygen coefficient plays a secondary role in influencing temperature uniformity and temperature difference, and the reformed gas and diesel fuel can be burned efficiently at a low excess oxygen coefficient of 1.04. With an increase in the cyclone angle, the heater tube temperature increases, while the maximum temperature difference at the lower part decreases, and the temperature fluctuation increases. Simultaneously, the CO and HC emissions increase, and the external combustion efficiency experiences a decrease. A cyclone angle of 30° is found to be an appropriate value for achieving optimal mixing between reformed gas and diesel fuel. The research findings present valuable new insights that can be utilized to enhance the performance optimization of Stirling engines.
PubDate: 2024-07-19
-
- Comprehensive Assessment of STGSA Generated Skeletal Mechanism for the
Application in Flame-Wall Interaction and Flame-Flow Interaction-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract In this study, we conduct a thorough evaluation of the STGSA-generated skeletal mechanism for C2H4/air. Two STGSA-reduced mechanisms are taken into account, incorporating basic combustion models such as the homogeneous reactor model, one-dimensional flat premixed flame, and non-premixed counterflow flame. Subsequently, these models are applied to more complex combustion systems, considering factors like flame-flow interaction and flame-wall interaction. These considerations take into account additional physical parameters and processes such as mixing frequency and quenching. The results indicate that the skeletal mechanism adeptly captures the behavior of these complex combustion systems. However, it is suggested to incorporate strain rate considerations in generating the skeletal mechanism, especially when the combustion system operates under high turbulent intensity.
PubDate: 2024-07-15
-
- Using Longitudinal Fins to Improve the Melting Performance of Stearic Acid
in Thermal Energy Storage Devices-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The heat transfer efficiency of a thermal energy storage unit (TESU) can be improved by the addition of novel longitudinal fins. A series of TESUs are analyzed using the finite volume method (FVM) to determine the effect of fin angle on the heat transfer performance. As the fin angle increases, the TES rate first increases, then decreases, reaching a maximum rate at 60°, where the melting time is less by 30.9%, 28.58%, 21.99%, 9.02%, and 18.1% than at 0°, 15°, 30°, 45°, and 80°, respectively. In addition, it is found that the melting time of the phase change material is significantly greater at the bottom of the TESU. The time percentage of this stage decreases as the fin angle increases through these percentages by 7%, 14%, 23%, 33%, and 20%, respectively. Further, the response surface methodology (RSM) is applied to optimize the longitudinal fin by minimizing the total melting time. The analysis concludes that a fin angle of 58.68° reduces the complete melting time of the stearic acid by 44% below the time at 0°. These findings fill a gap in knowledge of the effect on melting performance of the design angle of longitudinal fins and provide a reference for the design of horizontally placed longitudinal finned thermal energy storage units.
PubDate: 2024-07-11
-
- Effects of Heat Transfer on Laminar-to-Turbulent Transition over a
Compressor Blade Operating at Low Reynolds Number-
Free pre-print version: Loading...Rate this result: What is this?Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract To control the transition process in a laminar separation bubble (LSB) over an ultra-high load compressor blade at a Re of 1.5×105, the effects of wall heat transfer were considered and numerically investigated by large eddy simulations (LES). Compared with the adiabatic wall condition, the local kinematic viscosity of airflow was reduced by wall cooling; thus the effects of turbulent dissipation on the growth of fluctuations were weakened. As such, the transition occurred much earlier, and the size of LSB became smaller. On the cooled surface, the spanwise vortices deformed much more rapidly and the size of hairpin vortex structures was decreased. Furthermore, the rolling-up of 3D hairpin vortices and the ejection and sweeping process very close to the blade surface was weakened. Correspondingly, the aerodynamic losses of the compressor blade were reduced by 18.2% and 38.4% for the two cooled wall conditions. The results demonstrated the feasibility of wall cooling in controlling the transition within an LSB and reducing the aerodynamic loss of an ultra-highly loaded compressor blade.
PubDate: 2024-07-11
-
