Comprehensive Heat Transfer Performance Research Articles

Thermal-hydraulic investigation of liquid metal cross flow different arrangements of tube bundles under pulsating

The topic of this paper is to couple the passive and active approaches to enhance the heat transfer performance in the inline tube bundle heat exchanger. Firstly, the k-kl-ω turbulence model and Kays turbulent Prandtl number model are validated by liquid metal cross flow tube bundle experiments and rectangular groove pulsating flow experimental results. Then the numerical studies were carried out for pulsating velocity amplitude of 0.5, frequency of 10, and Re of 20,000 with transverse and streamwise pitch-to-diameter ratios of 1.5, 1.65, and 1.8. The introduction of pulsating flow effectively improves the turbulence characteristics between the tube bundles, especially at the first three rows, where the velocity fluctuation is enhanced by about 1.5–2 times. The tube heat transfer performances are all improved. The performance evaluation criterion (PEC) variation ranges from 1.04 to 1.32, which signifies that the introduction of pulsating flow can enhance the comprehensive heat transfer performance. The per unit flow rate thermal entropy generation decreased by about 9.7–33.3 %, in addition, a phase difference between the transient thermal entropy production and pulsating velocity was found. The correlation equations about Nu and f factor within the scope of this paper are presented.

Numerical analysis on heat transfer performance of spiral elastic copper tube heat exchanger with helical defectors

Based on the flow-induced vibration mechanism, three kinds of spiral elastic copper tube heat exchangers were proposed to improve the comprehensive heat transfer performance, involving the spiral elastic copper tube heat exchanger with no defector, the spiral elastic copper tube heat exchanger with forward helical deflector and the spiral elastic copper tube heat exchanger with reverse helical deflector. A both-way fluid–structure coupling method was utilized to investigate the effects of helical defectors and their arrangements on the vibration-enhanced heat transfer performance of the spiral elastic copper tubes at different inlet velocities by numerical simulation. The results indicate that: when the inlet velocity ranges from 0.1 m/s to 0.7 m/s, the heat exchanger with reverse helical deflector possesses better heat transfer performance than the other two heat exchangers. For the heat exchangers with no defector and forward helical deflector, the flow-induced vibration always promotes the comprehensive heat transfer performance. Compared with the heat exchanger with no defector, the comprehensive heat transfer performance of the heat exchanger with reverse helical deflector is higher 4.02 % averagely, while that of the heat exchanger with forward helical deflector is lower 29.34 % averagely. Furthermore, a structural optimization is presented to improve the existing disadvantages of the heat exchanger with reverse helical deflector, after structural optimization, the average amplitude of the heat exchanger with forward helical deflector is decreased by 3.26 % averagely and the heat transfer performance is raised to a maximum of 26.24 %, which are of great significance to extend the service life and improve the energy efficiency of heat exchanger.

A novel method based on the calculus of variations to optimize the cooling passage configuration in thermal protection structure

A novel method based on the calculus of variations to obtain the optimization of cooling structure was developed in this work. The optimization of heat sink designs for better heat-dissipating effects has been researched substantially. However, the optimization of cooling passage configurations in thermal protection structures to improve the comprehensive heat transfer performance has remained a long-term interest and unsolved problem for researchers. Due to the intrinsic complexity, the laminar flow is usually considered before while the turbulent flow is seldom treated. It is valuable to provide timely and effective solutions to optimize the cooling structure, where the turbulent flow is involved, for practical use. A novel method to optimize cooling structure based on the calculus of variations has been developed to meet this need. The average temperature, temperature inhomogeneity, and coolant flow pressure drop were chosen as objective functions. The cooling channels can be established depending on the geometric and thermal boundary conditions of the structure, and then the quasi-three-dimensional simulation of the fluid/solid coupling field was calculated to get the temperature distribution of the cooling structure, the pressure drop, etc. Hence, this work explores the feasibility of combining coupled heat transfer and the calculus of variations to realize optimal cooling channels. By the novel method, the minimum objective function can be obtained.

Multi-field coupling in designing embedded microchannels for three-dimensional integrated chip: A topology optimization approach

Topology optimization methods have shown promise in enhancing the heat transfer performance of microchannel structures. However, the thermal-electrical-force multi-field coupling effects in three-dimensional integrated chips present a complex heat generation scenario that necessitates their consideration in the design of embedded microchannel structures. Here, we perform topology optimization of embedded microchannels specifically tailored for three-dimensional integrated chip, with a specific focus on the multi-field coupling effects of through-silicon-via structures within the topology optimization process. A new and improved 2D microchannel structure that exhibits superior heat transfer performance was obtained by analyzing the effects of pressure drop constraints within the channel, as well as fixing the microfin diameter and local heat flux of through-silicon-via. Furthermore, the obtained topology optimization results were validated through rigorous three-dimensional numerical simulations. The findings demonstrate that the new microchannel structure, when compared to the original microfin model, yields a significant improvement in the comprehensive heat transfer performance coefficient, achieving a remarkable enhancement factor of 1.43. Furthermore, under identical flow conditions, the structural stress within the chip experiences a substantial reduction of 43.9%. These outcomes underscore the efficacy of the topology optimization approach in effectively addressing the thermal management challenges associated with three-dimensional integrated chip.

Experimental and Numerical Investigations on Thermal-Hydraulic Performance of Three-Dimensional Overall Jagged Internal Finned Tubes.

To satisfy the demand for efficient heat transfer, a novel three-dimensional overall jagged internal finned tube (3D-OJIFT) was fabricated, using the rolling-ploughing/extruding method. The thermal performance of the 3D-OJIFT were studied and compared in experiments and three-dimensional numerical simulations. The RNG k-ε turbulence model is well verified with the experimental results. By analyzing the distributions of velocity, temperature, and turbulence kinetic energy, it was found that the 3D-OJIFT destroyed the development of the velocity and thermal boundary layers, increased the turbulence disturbance, and reduced the temperature gradient, thus improving the heat transfer. The influences of the jagged height and jagged spiral angle of the 3D-OJIFT are discussed. The Nu and f increased as the jagged height of the 3D-OJIFT increased. The Nusselt number of the 3D-OJIFT was 1.67-2.04 times the value for the smooth tube. In addition, the comprehensive heat transfer performance of the 3D-OJIFT improved after increasing the jagged spiral angle. Compared with conventional internal helical-finned tubes and other reinforcement structures reported in the literature, the 3D-OJIFT demonstrated better comprehensive heat transfer performance. Finally, empirical correlations of the 3D-OJIFT were obtained.

Heat transfer performance study of Cu-ethanol/ethylene glycol/propylene glycol-water nanofluids in a wavy-walled tube heat exchanger

With the rapid consumption of nonrenewable energy sources, improving the heat transfer efficiency of conventional fixed tube plate heat exchangers, optimizing their structure, and finding more efficient coolants have become popular topics. In this paper, the cooling effect of ethanol/ethylene glycol/propylene glycol-water solution with a mass fraction of 50 % in a wavy-walled tube heat exchanger was investigated, while Cu nanoparticles with volume fractions of 1.5 % and 3.0 % were added to the cold working mass to form three different nanofluids. The effects of the three nanofluids at different volume fractions on the heat transfer performance of the wavy-walled tube heat exchanger were analyzed with numerical simulations, while the microscopic mechanism of the enhanced thermal conductivity of the nanofluids was investigated using molecular dynamics simulations. The results showed that the thermal conductivity of the nanofluids was greatly enhanced due to the formation of adsorption layers with different properties on the nanoparticle surfaces, and the Cu–ethylene glycol-water nanofluid showed the largest increase in thermal conductivity among the three nanofluids. It was also found that the shell-side pressure drop, convective heat transfer coefficient, and heat exchange quantity of the nanofluid in the wavy-walled tube heat exchanger significantly increased with an increase of volume fraction. The comprehensive heat transfer performance of the three nanofluids was found to be better compared to the base fluid. Cu-ethanol/EG/PG-water nanofluid with a volume fraction of 3.0 % increased the PEC of the heat exchanger by 10.4 %, 19.8 % and 27.6 %, respectively, at a volume flow rate of 1.53 m3/h. Therefore, the Cu-propylene glycol-water nanofluid had the best comprehensive heat transfer performance. Cu-ethanol-water nanofluid volume fraction of 3.0 % reaches a maximum PEC value of about 3.12 at Qv near about 2.0 m3/h, and Cu-EG-water nanofluid volume fraction of 3.0 % has a peak PEC value of about 4.07 at Qv of near about 2.0 m3/h. Therefore, the Cu-ethanol-water and Cu-ethylene glycol-water nanofluids are the optimal solutions for the combined heat transfer performance within the study.

Numerical research of an internal and external-corrugated tube-in-tube helical coil heat exchanger

ABSTRACT To effectively enhance the heat transfer of a tube-in-tube helical coil heat exchanger, a novel internal and external-corrugated tube-in-tube helical coil was proposed by improving both the inner and outer tubes. The impact of the corrugation layout on the annular region’s heat transfer property was simulated. The effect of periodically distributed corrugations on flow patterns and the local Nusselt on the inner tube wall was explored. Furthermore, by comparing the fluid’s velocity and temperature field contour in traditional helical coil and novel helical coil, the enhanced heat transfer mechanism was discovered. Finally, the effects of Re, dimensionless depth H, and dimensionless pitch S of corrugations on the annular region’s heat transfer, flow resistance and entropy generation were analyzed. The results showed that annular region’s heat transfer could be improved due to the periodically distributed corrugations. The local Nu distribution on the corrugated inner tube wall was similar to that of ordinary inner tube, while changed periodically due to the continuous influence of corrugations. The number of Nu and f increased by 53% ~72% and 40% ~120% with the dimensionless corrugation depth and dimensionless pitch being 0.15 and 1.5, respectively. The comprehensive heat transfer performance PEC reached 1.2 ~ 1.6, and cross-arranged inner and outer tube corrugations were more favorable for heat transfer than the corresponding arrangement, when Re = 6000, H3 structure has the highest S t , S f and S gen , which are 0.934W/K, 0.379 W/K and 1.312W/K, respectively. Increasing H and decreasing S could enhance the Nu, f and entropy generation. The values of PEC decreased with increasing S, while with the increment of H, PEC increased and decreased, respectively when Re was in the range of (2000, 4000) and (4000, 6000). In the study range, changing H and S could increase Nu by 40.3%–97.3%, 31.7%–96.8%, and f by 11.7%–176.5%, 16.4%–180.9%, respectively. The final comprehensive heat transfer performance increased by 12.8%-65.9%. Finally, the prediction correlation formulas of Nu and f in NTTHC annular region with high correlation is proposed.

Study of flow and heat transfer performance of nanofluids in curved microchannels with different curvatures

This study focuses on investigating the flow and heat transfer characteristics of Copper-water nanofluids (Cu-H2O) and water in microchannels with varying curvatures. The results reveal that Cu-H2O nanofluids demonstrate superior heat transfer performance compared to pure water in all four microchannels. Moreover, curved microchannels exhibit higher heat transfer performance than straight microchannels, regardless of whether the flow is laminar or turbulent. The heat transfer performance improves with increasing channel curvature, volume fraction of nanoparticles, and decreasing particle size. During laminar flow, the impact of curvature on heat transfer performance is more significant. However, during turbulent flow, variations in volume fraction have a greater influence on heat transfer performance compared to changes in curvature and particle size reduction. While larger volume fractions and higher curvatures increase flow resistance, this relationship is less pronounced for turbulent flow as Reynolds number and volume fraction increase. It is worth noting that the comprehensive heat transfer performance index does not consistently improve with increasing curvature, and sometimes straight microchannels outperform curved microchannels with specific curvatures. Additionally, curved microchannels exhibit a smaller average field synergy angle (FSA) compared to straight microchannels, indicating better synergy between the flow field and temperature field. The FSA also shows a relatively uniform distribution of local field synergy angles throughout the flow region in curved microchannels. Furthermore, the FSA decreases as the curvature increases.

Heat transfer enhancement of power-law fluid in a solar-driven pretreatment system for microalgae hydrothermal liquefaction

In this article, the flow and heat transfer performance of microalgae slurry in a solar-driven rectangular absorption tube with embedded vortex generators were studied by data optimization analysis and numerical simulation. The orthogonal test design method was used to establish an orthogonal test table by changing the shape, height, spacing, and fluid flow rate of the vortex generator to determine the optimal combination of various factors. Then the response surface analysis method was used for further optimization analysis. Eventually, the flow and heat transfer performance of microalgae slurry were studied numerically, and the optimal data were verified. The results show that the optimal comprehensive heat transfer performance (PEC) is delivered by the cylindrical vortex generator with height of 9 mm and spacing of 28 mm when the inlet velocity of microalgae slurry is 0.02 m/s. It can be seen that the data analysis method combined with numerical simulation can optimize the experimental process parameters and save the cost of the engineering design process, effectively and practically.

Numerical Study and Structural Optimization of Impinging Jet Heat Transfer Performance of Floatation Nozzle

A floatation nozzle can effectively transfer heat and dry without touching the substrate, and serves as a vital component for heat transfer to the substrate. Enhancing the heat transfer performance, and reducing its heat transfer unevenness to the substrate play an important role in improving product quality and reducing thermal stress. In this work, the effects of key structural parameters of the floatation nozzle on the heat transfer mechanism are systematically investigated by means of a numerical simulation of computational fluid dynamics. The findings demonstrate that the secondary vortex structure induced by the floatation nozzle with effusion holes increases heat transfer performance by 254.3% compared with the nozzle without effusion holes. The turbulent kinetic energy and temperature distribution between the jet and the target surface are affected by the jet angle and slit width respectively, which change the heat transfer performance of the float nozzle in different degrees. Furthermore, to improve the comprehensive heat transfer performance of the floatation nozzle structure, taking into account the average heat transfer capability and heat transfer uniformity, the floatation nozzle’s design is optimized by the application of the response surface method. The comprehensive heat transfer performance is increased by 26.48% with the optimized design parameters. Our work is of practical value for the design of floatation nozzles with high heat transfer performance to improve product quality in industrial systems.

Pore-scale numerical investigation on comprehensive heat transfer performance of homogeneous and graded metal foam heat sinks

In order to improve the heat dissipation efficiency of heat sinks, heat sinks filled with metal foam were proposed and numerically studied in this work. Different shapes, including the tetrakaidecahedron, triangular prism, and equivalent tetrahedron, were employed to develop geometries for the cells, ligaments, and nodes of the metal foam. Computational simulation was carried out to analyze the hydraulic and thermal performance of the homogeneous metal foam(HMF)-filled heat sinks and graded metal foam (GMF)-filled heat sinks. The study found that well-designed GMF-filled heat sinks can improve both hydraulic and thermal performance. A graded pores per inch (PPI) negative change along the X-axis direction can improve the comprehensive heat transfer performance (CHTP), and the positive change has a similar effect. Graded PPI negative change along the Y-axis direction can effectively improve the CHTP, while the positive change has no effect. Moreover, a greater thickness of the metal foam with a larger PPI leads to better performance. GMF-filled heat sinks can also effectively reduce the surface temperature of the bottom plane and enhance the convection performance.

Effect of symmetrical and asymmetrical structures of transverse tube on heat transfer performance of nanofluids in a solar collector system

AbstractIn an effort to enhance the heat transfer performance of solar collectors, this paper proposed to replace the smooth tube with symmetrical and asymmetrical transversely corrugated tubes, and to couple with SiO2‐H2O nanofluids for heat transfer of solar collectors. Effects of nanofluids mass fraction (w = .0%, .1%, .3%, and .5%), Reynolds number (3000, 4000, 5000, 6000, and 7000), and groove radius (1.5, 2, and 2.5 mm) on the flow and heat transfer properties of nanofluids in solar collectors were studied. The comprehensive evaluation index was used to consider the heat transfer property and flow resistance of fluid flow at the same time. Results showed that with the augment of nanofluids mass fraction, Reynolds number, and groove radius, the heat transfer enhancement performance of the collector becomes better. Among them, when the Reynolds number is 4000, the asymmetric transversely corrugated tube with a nanofluids mass fraction of .5% and a groove depth of 2.5 mm has the best comprehensive flow and heat transfer performance, and the comprehensive evaluation index can reach 1.62. The study results in this paper are beneficial to the coupling of nanofluids and transversely corrugated tubes and their application in the domain of enhanced heat transfer of solar collectors.

Optimization of microchannel heat sink based on multi-objective particle swarm optimization algorithm for integrated circuit chips cooling

The microchannel heat sink is an effective way to solve the heat dissipation problem in integrated circuit chips. In order to obtain the high efficiency and low resistance microchannel heat sink, the three variables (△h, f, g) were selected as the design variables, and the thermal resistance and pumping power were selected as objective functions. Then, the RSM, multi-objective particle swarm optimization algorithm and K-means clustering method were comprehensively applied to the multi-objective optimization of the microchannel heat sink with turbulence to obtain the five representative solutions (Case A–Case E), and the results were verified by CFD. The research shows that the maximum relative errors between Pareto optimization values and numerical simulation values of thermal resistance and pumping power of the five groups representative solutions are 0.637% and 1.187%, respectively. The Pareto optimization values are in good agreement with the numerical simulation values, and there is an effective tradeoff point between the five representative solutions of the Pareto optimal solution to make both the pumping power and thermal resistance within the optimal range. Compared with before optimization and the research results of Han Wang et al. [Appl. Therm. Eng. 2022;215:118849], the comprehensive heat transfer performance of the optimized microchannel heat sink has been improved, where the comprehensive heat transfer performance of the Case B ( Δ h = 0.0400 mm, f = 0.0979 mm, g = 0.5000 mm) is the best. The maximum temperature and pressure drop of the optimized microchannel heat sink can be reduced by 3.045% and 7.659%, respectively. Compared with the research results of Han Wang et al. [Appl. Therm. Eng. 2022;215:118849], the temperature distribution more uniform and the pressure drop of the microchannel heat sink after optimization (Case B) decreased by 7.058%. This optimization method can provide a reference for the optimization design of the microchannel heat sink structure parameters for integrated circuit chips cooling.

Numerical study on the effect of baffle structure on the heat transfer performance of elastic tube bundle heat exchanger

To make up for the research gaps in the existing literature on the effect of baffle structural parameters on the vibration and heat transfer of elastic tube bundle (ETB) heat exchangers, and improve the comprehensive heat transfer performance (HTP) of heat exchangers, based on an improved elastic tube bundle (I-ETB) heat exchanger used in previous studies, using the bi-directional fluid-structure interaction calculation method, the effects of the baffle structure improvement (height and curvature) on the comprehensive HTP of the I-ETB heat exchanger at different inlet velocities (Uin) were numerically studied. The results show that: while the height factor increases from 0.70 to 0.80, the vibration amplitude of I-ETBs decreases maximum by 10.05 %, and the heat transfer coefficient (h) of I-ETB increases maximum by 5.50 %. Increasing the baffle height improves the comprehensive HTP while suppressing the vibration of the I-ETBs. While the baffle curvature is 10°, the vibration of I-ETBs is the most intense, with the amplitude of the I-ETBs improving maximum by 10.79 %. The Nusselt number per unit pressure drop Nu/ΔP and performance evaluation criteria PEC and JF (a dimensionless number related to Colburn factor j and Fanning friction factor f) values of the heat exchanger all reach the maximum while the baffle curvature is 10°. The increase of baffle curvature has a positive effect on the vibration-enhanced HTP of the I-ETBs, and when the curvature is 10°, the comprehensive HTP of the heat exchanger is better.

Optimal design of liquid cooling structures for superfast charging cable cores under a high current load

Superchargers have become a focus of much research into new-energy vehicles, for which the cooling of high-current cable cores is a key problem that needs to be solved. To estimate influences of different core structures of liquid-cooled cables on the fluid flow and heat transfer characteristics in circular pipes, nine helical cable core structures with insertion of smooth pipes were designed taking dimethyl silicone oil as the coolant. The fluid flow and heat transfer in the pipes were studied through computational fluid dynamics (CFD) numerical simulation at different inlet velocities (0.2–2.0 m/s), and the models were verified by building an experimental platform. Numerical calculation results show that under conditions of the same Re and pitch of cable cores, the average surface temperature of three-core cables is lower than those of single-core and double-core cables. Moreover, the mean flow velocity v in pipes, heat transfer performance Nu, resistance factor f, evaluation factor for comprehensive heat transfer performance (PEC), and field synergy number Fc all increase with the decrease in the pitch of cable cores. This finding indicates that the heat transfer effect is gradually enhanced. The research implies that when the pitch p is 22.4 mm (cable C6), the velocity field is the most synergetic with the temperature field and the comprehensive heat transfer performance is optimal. This research provides an excellent cooling scheme for cable cores in superchargers under a high current load.

Numerical investigation of air–steam condensation in a vertically enhanced tube with dimples and protrusions

The thermo-hydraulic performance of air–steam condensation in a vertically enhanced tube with dimples and protrusions is investigated numerically. A forming experiment is conducted to test the validity of the physical model establishment. The heat transfer enhancement mechanism is investigated. In addition, the effects of inlet air mole fraction, the depth and pitch of the dimples on thermo-hydraulic performance are presented and discussed. The results showed that the error between the actual manufacture and mechanical simulation geometric model is less than 15 %. The structure of interlaced dimples and protrusions can disrupt the air concentration layer, promote fluid mixing, and eventually enhance the heat transfer between steam and condensing walls. The lower inlet air mole fraction, greater dimple depth, and longer dimple pitch of the enhanced tube, the better thermo-hydraulic performance is obtained. Among all the cases, the best design of geometric parameters occurs when the inlet air mole fraction, the dimple depth, and the pitch are 10 %, 4 mm, and 25 mm respectively. In addition, the comprehensive heat transfer performance is compared among different enhanced tubes and the results show that the enhanced tube with dimples and protrusions has better comprehensive heat transfer performance.

Numerical simulation and structure optimization of spiral wound heat exchanger with novel spacing bars

AbstractSpiral wound heat exchangers are widely used in industrial production for their advantages, such as large heat transfer areas and compact structures. However, their compact design also poses significant difficulties for numerical simulation and experimental research. The spacing bar between tube bundles has an essential impact on the performance of wound tube heat exchangers. This paper presents a new type of spacing bar vertically installed on the core barrel of the spiral wound heat exchanger to enhance the comprehensive heat transfer performance. A numerical model of a new type of wrapped tube heat exchanger has been constructed, which agrees with experimental results. Under the same working conditions, the comprehensive heat transfer performance on the shell side of the spiral wound heat exchanger with new spacing bars is increased by 7.4%–10.5% compared with the traditional structure. On this basis, the influence of the new spacing bar's structural parameters on the heat exchanger's performance was studied, and the empirical correlation between the structural parameters and operating conditions of the new spacing bar and the performance of the heat exchanger was fitted. The research results have guiding significance for the design of spiral wound heat exchangers.

Numerical Analysis of the Thermal-hydraulic Performance of Supercritical LNG in Airfoil Fin PCHEs

Abstract As a novel, compact, and efficient plate-fin heat exchanger, the Printed Circuit Heat Exchanger (PCHE) is a prospective candidate for liquefied natural gas (LNG) vaporization at low-temperature and high pressure. Generally, the airfoil fin PCHE has better thermal-hydraulic performance than the zigzag channel PCHE. In this study, the thermal-hydraulic performance of supercritical LNG in PCHEs with different airfoil fin types and arrangements is investigated by numerical simulations. First, the effects of six different airfoil fin types, NACA0010, NACA0020, NACA0025, NACA0030, NACA 0040, and NACA 0050, on the thermal-hydraulic performances were studied. The results show that NACA0025 has the best comprehensive heat transfer performance. Then, the effects of staggered, vertical, and horizontal pitch of the airfoil fin arrangement on thermal-hydraulic performance were investigated. The results show that the optimal values of the dimensionless number for staggered and vertical arrangements are 1 and 4, respectively. The comprehensive performance does not change much when the dimensionless horizontal pitch number exceeds 3.0. Finally, the thermal-hydraulic performance of uniformly distributed, three front sparse and rear dense, and three front dense and rear sparse distributed airfoil fins was investigated. The results show that the front dense and rear sparse airfoil fins enhance and the front sparse and rear dense airfoil fins reduce the comprehensive performance compared to the uniform arrangement. The results show that a denser arrangement of airfoil fins near the quasi-critical point can improve the comprehensive performance while keeping the number of airfoil fins constant.

Experimental investigation into flow boiling heat transfer and pressure drop in porous coated microchannels

The flow boiling heat transfer and pressure drop in porous coated micro-channels were experimentally investigated at four porous coating particle sizes (i.e. 75 μm, 48 μm, 25 μm, and 13 μm), three mass flow rates (150 kg/m2s, 275 kg/m2s, and 400 kg/m2s), and a range of wall heat fluxes (0–1285 kW/m2). The comprehensive heat transfer (CHT) performance in the porous micro-channels was obtained and compared to the smooth micro-channel. The flow patterns in the micro-channels were visualized to analyze the flow boiling heat transfer characteristics near wall region. The results show that the heat transfer coefficient and critical heat flux were significantly enhanced and the pressure drop was increased in porous coating micro-channels as compared to the smooth micro-channel. As the size of sintered particle increases, the heat transfer coefficient on porous coating surface is increased, while the pressure drop in the micro-channel is increased. Due to its good liquid storage and re-wetting ability, the porous coating surface has a higher hydrophilicity, resulting in a higher critical heat flux in the porous micro-channel than the smooth channel. However, the CHT performance of the porous coating surface is not always better than the smooth surface. Among the studied porous-coating surfaces, the micro-channel with the averaged sintered particle size 13 μm has the best CHT, while the surface with 75 μm sintered particles has the highest critical heat flux and heat transfer coefficient. Compared to the smooth surface, the critical heat flux and heat transfer coefficient on the 75 μm porous coating surface were enhanced by 53.2 % and 114.5 %, respectively.

The enhanced heat transfer characteristics of trapezoidal channel heat exchangers under different inclination angles and fin parameters

The study of the heat exchangers in the trapezoidal channels and the rectangular channels were carried out. The trapezoidal channel has smaller friction resistance than the rectangular channel with equal section, and the friction factor (f) decreases gradually with the increase of inclination angle, when β= 25 °, the f is the smallest, which is reduced by nearly 22.6% compared to the rectangular channel with equal cross-section; when , the heat transfer factor (j) and comprehensive heat transfer performance of the trapezoidal channel are greater than those of the rectangular channel with the same section, and when , those increase by 8% and 20%, respectively. The height and length of fins have a significant impact on heat transfer performance, increased by 17.65% and 20.85% respectively; By analyzing the comprehensive performance of the trapezoidal channel, the # 8 structure (Fh=10.5mm, β=5°, Sf=3mm, Lf=45mm, tf=0.3mm) has the optimal performance.