High Power Electronic Components Research Articles

Thermodynamic analysis of two-fluid, two-phase immersion cooling system for cooling of electronic components

Two-phase immersion cooling system is a specialized and increasingly popular method for cooling high-power density electronic components, such as CPUs, GPUs, and other server equipments. In a typical two-phase immersion cooling system, a dielectric fluid is employed for immersing electronic components. The challenge lies in the fact that the fluid chosen often has limited thermal conductivity, hindering effective heat transfer. In a two-fluid immersion cooling system, electronic components are submerged in a dielectric fluid known as the boiling fluid. Within the same tank, a separate condensing fluid is introduced, which is immiscible with the boiling fluid. The condensing fluid, characterized by its lower density and higher thermal conductivity compared to the boiling fluid, enhances heat transfer within the system. In the current study, Novec 7100 serves as the boiling fluid, while deionized water is employed as the condensing fluid. In this work, exergy analysis is conducted to assess and compare the efficiency of a two-fluid, two-phase immersion cooling system in contrast to a single-fluid, two-phase immersion cooling system. Additionally, a comparison is carried out to evaluate how the performance of the system varies under diverse operating conditions. The study is conducted for a maximum heat flux of 12.3 W/cm2 and performance of the system is evaluated at condenser inlet temperatures spanning from 5 to 25 °C. From the investigations carried out, it is seen that the exergy efficiency of the two-fluid system surpasses that of the single-fluid system by approximately 70% under same heat flux and condenser inlet temperature conditions.

Study on the structure and thermal properties of graphite/copper laminated composites assembled by Ti-containing active filler metals

The development of high-power and small-sized electronic components requires the emergence of heat management materials with high heat flux. Hence, Ti-containing filler was used to braze graphite film/Cu high heat flux composites. The microstructure and forming mechanism of joints were studied, the influence of temperature on joint formation was analyzed, and the influence of graphite volume fraction on the thermal properties of the composites were discussed. The results show that the main microstructure of graphite/copper joints are Cu(s,s), Ti6Sn5 and CuTi2. As the brazing temperature increases, the carbide layer (TiC) that affects the connection gradually thickens, from <0.5 μm at 800 °C to 3 μm at 850 °C, which deeply improve heat transfer of composite materials. The tensile properties of composites also increase with increasing temperature, maximum tensile strength 31.94 MPa can be obtained at 850 °C. Furthermore, the composites are proved to possess high heat flux during process of heat transfer, and the transfer rate was 1.77 times that of Cu, 3.72 times of Al. The temperature rise test carry out in hot bench intuitively demonstrating that the composites have faster heating rate. Al used 197 s to raise from 25 °C to 50.5 °C, Cu used 140 s, while 76.92 % graphite-contained composites only took 75 s in the same volume and experimental condition.

Development and experimental study of a 3-dimensional enhanced heat pipe radiator for cooling high-power electronic devices

A 3-dimensional enhanced heat pipe radiator (HPR) is developed to meet the requirements of heat dissipation and temperature uniformity in the cooling of high-power electronic components. The radiator is composed of a conventional flat heat pipe base and roll-bond flat heat pipe fins, which can enhance heat transfer in three dimensions. By means of experiments, the heat transfer characteristic is firstly studied under different filling ratios for a single roll bond flat heat pipe. Then, a comparison is performed of the heat transfer performance between the HPR and the conventional aluminum fin radiator (CAFR) under different heating powers and wind speed conditions experimentally. In this research, HPR demonstrates obvious advantages in the heat transfer. Results show that the optimum filling ratio is 35% for the roll-bond flat heat pipe. The start-up time of HPR is shorter (25 mins), and the start-up performance is not affected by power variation. HPR has a low thermal resistance of less than 0.48 °C/W compared with CAFR, which can effectively control the heat source temperature difference is about 1.7 °C–1.8 °C. The maximum heat dissipation of HPR and CAFR is almost the same under natural convection condition. But when the wind speed is 4 m/s, the maximum heat dissipation of HPR increased by 58.2% compared to the maximum heat dissipation of CAFR.

Dynamic regulation of the thermal performance of the S–CO2 minichannel using a piezoelectric oscillating fin

It is difficult to alter the thermal performance of a minichannel heat sink with a fixed structure under constant operating conditions. In particular, if the local heat transfer of the substrate cannot be regulated in real time, the dynamic heat dissipation needs of high-power electronic components cannot be met in the electrical servo systems of flight vehicles. In this paper, a new minichannel heat sink structure based on the classical rectangular channel is proposed and a piezoelectric oscillating fin (POF) is introduced to replace the fixed fin. The thermal performance of the heat sink can then be regulated using the swing of the POF, with supercritical carbon dioxide (S–CO2) as the coolant. Transient numerical simulations are applied to investigate the influence of various POF operating parameters on the heat transfer of the channel, such as the oscillation amplitude and frequency. The results demonstrate that a channel with a POF can allow for dynamic and rapid adjustment of the thermal performance through control of the oscillation frequency and amplitude of the POF, with a constant channel configuration, coolant, and operating conditions. The heat transfer can be enhanced significantly by the swing of the POF, with the local Nusselt number growing up to 8.3 times and the overall one up to 1.14 times. Both the oscillation frequency and amplitude have a positive correlation with the intensity of heat transfer. The POF also contributes to a greater pressure drop and fluctuation in pumping power. A comprehensive evaluation coefficient shows that the POF is effective at improving the overall thermal performance with a low-frequency swing, while high-frequency operation enhances the local heat transfer and decreases the local temperature near the tail end of the POF. Finally, considering the effects of the frequency and amplitude of the POF, as well as the variable thermophysical properties of the supercritical coolant, a heat transfer correlation based on the Dittus–Boelter equation is established to predict the thermal performance of the channel with a POF. This prediction has a maximum error of ±0.56%.

High strain-rate driven nano-tubular architecture in NiMn alloy for supercapacitor electrodes

Electrochemical energy storage (EES) devices play a crucial role in our pursuit of non-polluting, green technologies. With the characteristic short ion-diffusion length, nano-scale materials are considered promising for the realization of high-performance EES. In contrast, existing nano-textured electrodes' inadequate ion-accessible surface area and laborious multi-step synthesis technology limits their overall performance. Herein, we provide the first demonstration of sub-homologous temperature solid-state nano-moulding in a crystalline alloy, resulting in a highly ordered hierarchical nano-tubular architecture with outstanding electrochemical energy storage. Benefitting from increased material fluidity at a high strain rate, a short burst of physical deformation facilitated the material flow into the nano-moulds. The chemically dealloyed nano-tubular electrode demonstrated excellent volumetric specific capacitance of ∼1000 F/cm3 at 5.5 A/cm3 current density. A symmetric supercapacitor device showcased an exceptional energy density of ∼90 Wh/L at a power density of ∼0.5 kW/L and excellent cyclic stability of 94% after 10,000 cycles. The device-level technology readiness is demonstrated by successfully integrating multiple small devices to operate high-power electronic components, setting the way forward for advanced energy storage applications.

Pool boiling heat transfer enhancement on the hybrid surfaces coupling capillary wick and minichannels

Pool boiling heat transfer can fully utilize the latent heat of the vaporization, to meet the heat dissipation needs of high-power electronic components. In this study, several enhanced hybrid surfaces were designed and processed by sintering spherical copper powder on the minichannels in different ways. The coupled effects of various parameters of capillary wick and minichannels were considered to enhance the pool boiling heat transfer performance of these hybrid surfaces using HFE-7100 as the working fluid. The bubble dynamic behaviors were captured and analyzed by the high-speed camera. The results indicate that the ring groove around the minichannels and the capillary wick have a significant impact on the boiling heat transfer of these hybrid surfaces. This is because the capillary wick provide a large number of nucleation sites and large specific surface area, which can greatly reduce the contact thermal resistance between the capillary wick and the minichannels. At ΔTsub = 30 K, the critical heat flux (CHF) of hybrid surfaces coupling capillary wick and minichannels is up to 147.4 W/cm2, and its maximum heat transfer coefficient (HTC) is 2.69 W/(cm2·K). Compared with minichannels without capillary wick covered, the CHF and HTC are increase by 86.8% and 192.0%, respectively. Furthermore, a correlation for predicting CHF on these hybrid surfaces covered capillary-wick is proposed. Dimensionless parameters such as the subcooled Jakob coefficient (Jasub), the outer surface area enhancement ratio (AER), the particle distribution coefficient (PDC) and the ratio of inner to outer surface area of capillary wick (IOR) are defined to estimate the effect of different factors on the CHF.

Investigation of Flow and Heat Transfer Performance of Double-Layer Pin-Fin Manifold Microchannel Heat Sinks

The manifold microchannel (MMC) heat sink is characterized by high heat transfer efficiency, high compactness, and low flow resistance. It can be an effective method for the high-flux removal of high-power electronic components. To further enhance the performance of the MMC, a double-layer pin–fin MMC structure was designed. The thermodynamic properties, including the flow and heat transfer characteristics, were numerically investigated using ANSYS Fluent with deionized water as the working liquid. Compared with the single-layer MMC, the temperature uniformity is better, the pressure drop is lower, and the comprehensive performance is improved at the cost of slightly larger thermal resistance for the double-layer MMC. The geometric effects on the thermodynamic performance were also analyzed. The results show that among the pin–fin structures with round, diamond-shaped, and rectangular cross-sections, the round pin–fins demonstrate the best comprehensive performance and the minimal thermal resistance. Under the same inlet velocity, the thermal resistance is decreased, and the comprehensive performance is first increased and then decreased as the pin–fin size increases. In addition, it is recommended to adopt a larger height ratio for low inlet velocity and a smaller height ratio for high inlet velocity.

Experimental study on the heat transfer performance and dimensionless correlations for R134a spray cooling system

Spray cooling is a promising and effective cooling method, which may be used to solve the heat dissipation problem of high-power electronic components. In this paper, the influences of flow rate, sub-cooling degree, and refrigerant charge on the spray cooling heat transfer performance with R134a as the working fluid were experimentally studied. Results showed that the enhancement effect of the increase of sub-cooling degree on the heat transfer performance is very limited in this experiment. When the sub-cooling degree rises from 5 to 8 K, the heat transfer coefficient increases by 2.6% on average at lower heat flux (45.93–72.55 W/cm2). The increase of refrigerant charge can effectively improve the heat transfer performance, especially at higher heat flux (84.02–105.25 W/cm2). However, the Jacobian number decreases with the increase of the refrigerant charge, which hinders the improvement of heat transfer performance at higher heat flux. Therefore, there is an optimal refrigerant charge of 1.05 kg in this experiment. In addition, based on the experimental data, a Nusselt number dimensionless correlation of R134a solution with higher prediction accuracy was proposed.

Mechanical performances of AlN/Al metallized ceramic substrates fabricated by transient liquid phase bonding and pre-oxidation treatment

For the miniaturization of high-power electronic components, AlN/Al is a promising metallized ceramic substrate due to its superior mechanical and thermal performances. Numerous bonding processes have been proposed for fabricating the metallized ceramic substrate. Unfortunately, the influences of various bonding techniques on the mechanical performance of AlN/Al metallized ceramic substrate remain undetermined to date. The objective of this study was thus to investigate the effects of the transient liquid phase (TLP) technique and pre-oxidation treatment on the bonding, microstructure, and mechanical strength of the AlN/Al metallized ceramic substrate.The results indicated that the three-layered AlN/Al/AlN specimen could be effectively bonded by the TLP process and pre-oxidation treatment. However, the bending strengths of the specimens fabricated by the two techniques were obviously divergent. The bending strength of raw AlN substrate was 333 MPa. In contrast, the bending strengths of the three-layered specimens with AlN substrates pre-oxidized at 1050 °C, 1150 °C, and 1250 °C were 292 MPa, 250 MPa, and 224 MPa, respectively. Raising the pre-oxidation temperature of the AlN substrate from 1050 °C to 1250 °C obviously increased the thickness of the Al2O3 layer and deteriorated the bending strength, for the fracture propagated along the Al2O3 layer and the Al2O3/AlN interface. For the TLP bonding, the Cu film deposited on the AlN substrate contributed to the generation of Al–Cu transient liquid and to bonding. The bending strength of the three-layered specimens fabricated by TLP at 650 °C was 417 MPa, which was 25% and 43% better than those of the raw AlN substrate and the three-layered specimens prepared by the pre-oxidation treatment, respectively.

Arduino based temperature controlled sample holder using a power transistor and its application to measure the band gap of a silicon p–n diode

This experiment is developed with the aim of designing a temperature-controlled sample holder by using a commonly available power transistor as the heating element. Most temperature-controlled sample holders use commonplace heaters, which are made of high resistance materials like nichrome 80/20 (80% nickel, 20% chromium) wire and similar materials. The fabrication of this temperature-controlled sample holder also leads to the usage of high power electronic components, like power transistors and power resistors which are, otherwise, neglected in most laboratory experiments. Moreover, to develop this system, Arduino Uno Rev3 and resistance temperature detector (RTD) were used for the purposes of data acquisition and temperature measurement, respectively. Arduino is a single board micro-controller and RTD functions as a temperature sensor. This experiment serves as a good example of application and unification of basic concepts of electronics, heat and thermodynamics and offers an insight into data acquisition. The experiment is non-proprietary, and the apparatus is entirely made from off-the-shelf items. Thus, reconstruction and use will be simple and inexpensive. The power transistor, along with the power resistors, generates enough heat to raise the temperature of the sample holder by about 100 K. Also, to exhibit the working of the sample-holder, the energy band gap of the material of a p–n junction diode (silicon) has been determined experimentally using the setup.

Investigation of thermal characteristics of an LHP evaporator with heat sources having different heating surface areas

The paper presents the results of investigation of thermal characteristics of a flat evaporator 10 mm thick with an active zone of 27 cm2 that is part of a copper–water loop heat pipe (LHP) intended for cooling systems of high-power electronic components. The investigation of the device was conducted in a horizontal position with heat sources having thermocontact surfaces of 9 cm2, 16 cm2 and 25 cm2 at heat load from 20 to 900 W. It is shown that the evaporator thermal resistance and the heat flux depend considerably on the value of the thermocontact surface of the heat sources. The minimum values of thermal resistance were, respectively, 0.033, 0.021 and 0.016 °C/W at heat fluxes of 100, 56.2 and 36 W/cm2. The temperature distribution over the evaporator surface with different heat sources has been obtained in analytical way.

Smart microchannel heat exchanger based on the adaptive deformation effect of shape memory alloys

Microchannel heat exchangers that are compact and have high efficiency have significant application value in the cooling of high-power electronic components. In this study, a smart microchannel heat exchanger with a shape memory alloy vortex generator (SMA-VG) was proposed to address the challenges associated with complex working conditions and random hotspots of electronic components. Owing to the shape memory effect, the structure of the SMA-VG can automatically adjust to change the flow characteristics of the microchannel, such that the cooling capacity and heat dissipation demand can be matched intelligently without external control. Herein, the principle underlying smart microchannel heat exchangers is analyzed, and a relationship between coil deformation and the Nusselt number (Nu) is proposed. Subsequently, the responses of the SMA-VG to different heat fluxes and Reynolds numbers are revealed, and a SMA-VG of three unequal lengths is proposed. The performance of microchannel heat exchangers with SMA-VG was investigated by combining experimental and numerical methods. The results showed that the SMA-VG adaptively adjusted its pitch configuration with changes in heat flux, improving the overall heat transfer performance of the channel in comparison to the non-deformed vortex generator (NDF-VG). The channel with the SMA-VG exhibited a stronger localized disturbance performance. When the heat flow density was 100 000 W/m2, Nu increased by 112% relative to that of the channel without a vortex generator, which was 9% higher than that of the channel with NDF-VG. Therefore, this novel heat exchanger resolves the challenges of poor automatability that are associated with traditional microchannel heat exchangers, in addition to removing random hotspots. Moreover, it facilitates the achievement of different levels of heat dissipation demands without external control, and it has potential for application in fields involving the usage of high-heat-flux chips.

(Invited) Low-Temperature Plasma-ALD of Wide and Ultra-Wide Bandgap Semiconductors: Accomplishments and Hurdles to Overcome

III-nitride and III-oxide based wide (GaN, InGaN, AlGaN) and ultra-wide bandgap (Ga2O3, AlN, BN) semiconductors play critical roles in high-power, high-frequency, and harsh-environment electronic components utilized in wireless communications, power grids, homeland security, and space applications. While GaN-based wide bandgap (WBG) devices have reached a certain degree of maturity, the emerging ultra-wide bandgap (UWBG) alloys are still in their early stage of technology development. Conventional chemical vapor deposition (CVD) based crystal growth processes for these materials are carried out at elevated substrate temperatures, reaching over 1000 °C. In an effort to substantially reduce this synthesis temperature, plasma-assisted CVD techniques are of particular interest. Owing to its unique features including pinhole-free synthesis, precision film thickness control, large-area uniformity, and ultimate 3D conformality, plasma-assisted atomic layer deposition (plasma-ALD) offers significant opportunities for electronic device layers at reduced substrate temperatures.Relatively limited number of research groups have targeted this challenging opportunity by using different types of plasma sources integrated into various plasma-ALD reactors. In addition, different metal precursors and plasma gas mixtures have been utilized and the resulting material properties are studied on different substrates. While mostly polycrystalline WBG and UWBG films are reported, recently several groups have reported epitaxial relationship of plasma-ALD grown III-nitride and Ga2O3 films on sapphire and SiC substrates, which hints the potential for success. However, there still exist critical technology barriers for the adoption of plasma-ALD as an alternative low-temperature materials synthesis technique for device layers. Reliable electron mobility values are lacking and atomic layer doping efforts are barely investigated.In this presentation, we would like to provide and updated overview of the field including the latest reports and achievements. In addition, we would like to present our own efforts and recent advances in developing crystalline III-nitride and Ga2O3 films by using the hollow-cathode plasma (HCP) source, which demonstrated its advantages for reducing the oxygen impurities in III-nitride layers. By incorporating a multi-wavelength ellipsometer for in-situ monitoring, unit-cycle growth behavior of WBG and UWBG films were analyzed and correlated with the obtained material properties. Moreover, real-time in-situ monitoring allowed the realization of the saturation curve experiments on a single sample, without the need for breaking the vacuum and using multiple samples necessitating individual ex-situ thickness measurements. The growth parameters studied include the substrate temperature, rf-power applied to the remote HCP source, and plasma gas mixtures (N2/H2/Ar and O2/Ar with different flow ratios for III-nitrides and Ga2O3, respectively). Structural, chemical, optical, and electrical properties of the grown WBG and UWBG films have been characterized and correlated with the growth conditions. One of the main results obtained for these films is the different behavior each binary compound shows for similar synthesis parameter variations. A roadmap towards overcoming the current limitations will be discussed with an outlook for potential device applications of these low-temperature plasma-ALD grown films.

Cooling of electronic components on the LTCC module with an embedded flat heat pipe

The results of the experimental investigations of a ceramic circuit board sample with an embedded flat heat pipe are presented. The sample was made based on the technology of low temperature co-fired ceramic (LTCC). The flat heat pipe is formed at the bottom side of a ceramic substrate using a capillary structure made of sintered copper powder. The developed prototype of the LTCC module was used for the investigation of removing and spreading of high heat fluxes from high power electronic components mounted on the module. The embedded flat heat pipe filled with acetone provides 40 W/cm2 of heat flux removal from the heat source with the heat dissipation area of 1 cm2. The measured value of the thermal resistance between the heat source and cooler surface under the module is 0.8 °C/W.

Numerical Study of Fluid Flow and Heat Transfer Characteristics in a Cone-Column Combined Heat Sink

Temperature has a great influence on the normal operation and service life of high-power electronic components. To cope with the increasingly severe heat problems in integrated circuits, an enhanced heat transfer factor E is introduced to evaluate the comprehensive heat transfer performance of microchannel heat sinks (MCHS). The computational fluid dynamics (CFD) software was used to numerically study the fluid flow and heat transfer characteristics in the cone-column combined heat sink. The research results obtained the velocity field and pressure field distribution of the heat sink structure in the range of 100 ≤ Re ≤ 700. When Re changes, the change law of pressure drop ΔP, friction factor f, average Nussel number Nuave, average substrate temperature T, and enhanced heat transfer factor E, are compared with the circular MCHS. The results show that the uniform arrangement of the cones inside the cone-column combined heat sink can change the flow state of the cooling medium in the microchannel and enhance the heat transfer. In the range of 100 ≤ Re ≤ 700, the base temperature of the cone-column combined heat sink is always lower than the base temperature of the circular MCHS, and the average Nusselt number Nuave is as high as 2.13 times that of the circular microchannel. The enhanced heat factor E is 1.75 times that of the circular MCHS, indicating that the comprehensive heat transfer performance of the cone-column combined heat sink is significantly better than that of the circular microchannel.

An Overview of Thermal and Mechanical Design, Control, and Testing of the World's Most Powerful and Fastest Supercomputer

Abstract A new era of computing has begun with the development of high-performance computing (HPC), artificial intelligence (AI), machine learning (ML), and cognitive systems. Dramatic increases in the power density of the electronic components have led to the design and architecture of efficient thermal management technologies on these systems. IBM designed and delivered in 2018 the most powerful and fastest supercomputers of the world known as Summit and Sierra having 200 petaflops peak computing performance through LINPACK benchmarks. These systems which are called as IBM POWER AC922 are both air and liquid cooled, where water is employed in liquid-cooled systems to cool the high-power electronic components including IBM POWER9 processors and NVIDIA graphics processing units (GPUs). In this paper, we highlight the overview of the thermal and mechanical design strategies applied to these systems. Testing and experimental analysis with comparison to computational modeling is provided. Thermal control strategies are investigated for the optimization of overall system efficiency. In air cooled systems, we discuss the fan and heat sink designs, as well as the preheating effect on the PCIe section. In liquid-cooled systems, which have a unique cold plate design cooling the processors and the GPUs with water, we examine the water flow path design for the central processing units (CPUs), the GPUs, and the thermal performance of the cold plate. An overview of the cooling assemblies such as TIMs and air baffles in these systems is discussed. Unit and rack manifolds and rear door heat exchanger (RDHx) are investigated. Water flow and pressure distribution at the node and rack-level are provided.

Structural Optimization and Heat Transfer Performance Analysis of a Cone-Column Combined Heat Sink

Abstract To address the impact of temperature on the normal operation and service life of high-power electronic components, a circular microchannel heat sink with cones has been designed. The cones are evenly arranged inside circular microchannels, which can change the flow state of the cooling medium in the microchannels and enhance the heat transfer performance. The experimental scheme of the heat transfer performance of microchannel heat sink was designed by an orthogonal test method, and the numerical simulation was carried out by ansys thermal-fluid–solid coupling. Within the test parameters, the inlet pore size, the split outer diameter, and the number of cone columns have effect the temperature of the heat sink base. Further, the inlet pore size and the number of cone columns have a heightened effect on the test results: the base temperature of the heat sink decreases rapidly with the increase in the inlet pore size and the number of cone columns. According to the orthogonal test analysis, the structural parameters of the heat sink were optimized. Under the condition that the other boundary conditions are the same, the temperature of the heat sink substrate obtained by the new factor levels combination is 27.87 °C.

Research on a Simplified Model of an Aluminum Vapor Chamber in a Heat Dissipation System.

With the rapid increase of power densities of electronic components, the traditional heat dissipation method of air forced convection has reached a heat transfer limit. As efficient phase change heat exchangers, vapor chambers have become an important guarantee for the development of high-power electronic components. Aluminum vapor chambers have become the future development trend because they are more lightweight and less expensive. In order to study the suitable simplified model of the aluminum vapor chamber in the radiating system, the testing system is established to test the thermal characteristics of the vapor chamber. First, six simplified models of the vapor chamber are proposed. Then, the thermal characteristics of the simplified models are simulated by STAR CCM+ software. Next, the error of the thermal resistance of the simplified model and the real vapor chamber is analyzed. Finally, a most suitable simplified model is obtained in the cooling system.

Effects of particles deposition on thermal performance of a convective-radiative heat sink porous fin of an electronic component

The advent of high-power electronic system components and slim margin errors require the proper understanding of particle deposition characteristics and its effects on the thermal performance of electronic heat sinks of electronic devices. In this work, we investigate the effects of particle deposition on the thermal performance of convective-radiative porous fin heat sink of an electronic component using Chebyshev spectral collocation method. The numerical solutions from the developed thermal models are also used to study the influence of thermal conductivity, porosity, convection, and radiation parameter on the temperature distribution and overall fin efficiency. The analysis establishes that presence of particles or thermal fouling on the surface of the fin increases the temperature distribution and temperature uniformity of the fin whilst decreasing the heat transfer rate from the fin. The study also establishes that decrease in heat transfer rate from the fin is due to the particle deposition on the fin, which depends on the particle size, particle density and cooling air flow rate. Moreover, the fin efficiency decreases with an increasing value of the fouled Biot, Darcy and radiation numbers, and thermo-geometric parameter. The study further shows that the efficiency of the fouled porous fin is always greater than the efficiency of the clean porous fin. The analysis established that the result of Chebyshev spectral collocation method is in good agreement with that of the convectional numerical method using Runge-Kutta coupled with shooting method.

Improved correlations of the thermal-hydraulic performance of large size multi-louvered fin arrays for condensers of high power electronic component cooling by numerical simulation

In view of a good thermal performance of the multi-louvered fin arrays, it is intended to introduce the special fin structure into the design of condensers for high power electricity converter cooling on the CRH (China Railway High-speed) trains in order to improve the security of normal running for the high-speed trains. The geometrical size of the multi-louvered fin arrays needed for the high power condensers is relatively larger than that of the conventional louvered fin arrays and the flow state within the large size multi-louvered fin arrays is different as well, with the Reynolds numbers based on the louver pitch over the range of 2850–11,000 in the present study. Flow and heat transfer characteristics of the large size multi-louvered fin arrays with various structural parameters are numerically simulated using Large Eddy Simulation (LES). More reasonable parameters correlated with the thermal-hydraulic performance of the large size multi-louvered fin arrays are identified compared to the conventional characteristic parameters employed in the published work. Finally, improved correlations for the Fanning friction f factor and the Colburn-j factor representing the flow and heat transfer characteristics, respectively, are put forward in terms of the identified parameters with special interval bounds for the condenser design of high power electronic cooling.