High Heat Flux Removal Research Articles

High Heat-Flux Removal From Topside-Cooled GaN Power Devices by Water-Jet Impingement Using 3-D-Printed Nozzles

High Heat-Flux Removal From Topside-Cooled GaN Power Devices by Water-Jet Impingement Using 3-D-Printed Nozzles

Nanoscale Thin-Film Boiling Processes on Heterogeneous Surfaces

Acquiring rapid and efficient boiling processes has been the focus of industry as they have the potential to improve the energy efficiency and reduce the carbon emissions of production processes. Here, we report nanoscale thin-film boiling on different heterogeneous surfaces. Through nonequilibrium molecular dynamics simulation, we captured the triple-phase interface details, visualized the bubble nucleation, and recorded the internal fluid flow and thermal characteristics. It is found that nanoscale thin-film boiling without the occurrence of bubble nucleation shows excellent heat and mass transfer performance, which differs from macroscale boiling. In general, rough structures advance the onset time of stable boiling and improve the efficiency. The heat transfer coefficient and heat flux on a rough hydrophilic surface respectively reach to 7.43 × 104 kW/(m2·K) and 1.3 × 106 kW/m2 at a surface temperature of 500 K, which are 100-fold higher than those of micrometer-scale thin-film boiling. However, due to the resultant vapor film trapped between the liquid and the surface, the rough hydrophobic surface leads to heat transfer deterioration instead. It is revealed that the underlying mechanism of regulatory effects resulting from surface physicochemical properties is originated from the variation of interfacial thermal resistance. It is available to reduce the overall interfacial resistance and further improve the heat and mass transfer efficiency through increasing surface roughness, enhancing surface wettability, and increasing the area proportion of the hydrophilic region. This work provides guidelines to achieve rapid and efficient thin-liquid-film boiling and serves as a reference for the optimized design of surfaces utilized for high-heat flux removal through vaporization processes.

Experimental Demonstration of Pressure-Driven Flash Boiling for Transient Two-Phase Cooling

This work demonstrates transient cooling for high-heat-flux electronics using pressure-controlled flash boiling. Many advanced electronics packages demand rapid, high-heat flux removal under stringent spatial and temporal constraints such as limited lateral heat spreading area, sharp power delivery transients, and heterogeneous power dissipation among dies. Flash cooling achieved by rapid depressurization of liquid coolant is inherently transient and provides high initial peak cooling that can be used for adaptive cooling demanded by these advanced packages. A coolant loop thermal testbed has been constructed to perform rapid transient thermo-fluid experiments of flash cooling with methanol. This work provides insights into depressurization-based flash incipience, thermodynamic analysis of flash cooling, and the ability to provide transient cooling in two application settings. First, a vapor chamber able to adapt to high initial transients applicable for short-burst applications. Second, a co-designed convective chamber that supports simultaneous power delivery and heat extraction for high-performance wafer-scale systems. A prototype vapor chamber was tested to obtain results for overall cooling and flash incipience experiments. The results demonstrate the efficacy of flash cooling for transient thermal management and highlight directions for further research and necessary data to exploit this technique for future electronics applications.

Prospects for using two-phase micro-size systems for high heat flux removal

Heat transfer in active systems for high heat removal based on the micro-channels and hybrid micro-channel/micro-jet is considered. The application of these systems allows significantly increasing the critical heat flux for a dense arrangement of the heat stressed equipment. The characteristics of heat transfer and critical heat flux during subcooled flow boiling of water in the micro-channel heat sink and during micro-jet impingement in narrow channel are obtained. The experiments are performed for the horizontal segmented microchannels with a cross section of 340×2000 μm2 made on the top of copper target and for impingement micro-jet cooling of the copper target in the gap of 1000 μm. It has been found that, compared with impingement micro-jet cooling in similar condition, the micro-channel cooling is more effective for high heat flux removal although it creates the considerably high wall temperature.

Determination of heat transfer and spray performances of isopropyl alcohol electrospray

Reducing the size of electronics to micro or even nanoscale and increasing capacity leads to an increase in heat flux density. Various cooling methods fall short of removing heat flux from the surface. Electrospray is a novel method that provides high heat flux removal with a small surface area. In the previous studies; the mean particle velocity and the mean particle diameter of isopropyl alcohol electrospray based on electrospray modes have not been adequately studied. In this study, the electrospray and heat transfer characteristics of isopropyl alcohol were characterized for varying voltage ranges, in addition to alterations in volumetric flow rate, nozzle diameters, and nozzle lengths. The electrospray modes, mean particle diameter and velocity were determined by digital image processing of the resulting images from spray characteristic experiments, and the Enhancement Ratio (ER) values were calculated from the surface temperatures obtained in the heat transfer experiments. A minimum mean particle diameter of 31 µm was measured for the 12.70 mm length 26 G nozzle with a 100 µl/min flow rate and 12 kV DC voltage. Maximum mean particle velocity was found to be 7 m/s for a 6.35 mm long 20 G nozzle at 100 µl/min flow rate and an applied voltage of 16 kV. Maximum ER was obtained 1.75 for a 12.70 mm length 26 G nozzle, 100 µl/min flow rate and a voltage of 16 kV. ER values increased in almost all experimental conditions with the increasing voltage and volumetric flow rate.

Conceptual design and heat transfer performance of a flat-tile water-cooled divertor target

The divertor target components for the Chinese fusion engineering test reactor (CFETR) and the future experimental advanced superconducting tokamak (EAST) need to remove a heat flux of up to ∼20 MW m−2. In view of such a high heat flux removal requirement, this study proposes a conceptual design for a flat-tile divertor target based on explosive welding and brazing technology. Rectangular water-cooled channels with a special thermal transfer structure (TTS) are designed in the heat sink to improve the flat-tile divertor target’s heat transfer performance (HTP). The parametric design and optimization methods are applied to study the influence of the TTS variation parameters, including height (H), width (W*), thickness (T), and spacing (L), on the HTP. The research results show that the flat-tile divertor target’s HTP is sensitive to the TTS parameter changes, and the sensitivity is T > L > W* > H. The HTP first increases and then decreases with the increase of T, L, and W* and gradually increases with the increase of H. The optimal design parameters are as follows: H = 5.5 mm, W* = 25.8 mm, T = 2.2 mm, and L = 9.7 mm. The HTP of the optimized flat-tile divertor target at different flow speeds and tungsten tile thicknesses is studied using the numerical simulation method. A flat-tile divertor mock-up is developed according to the optimized parameters. In addition, high heat flux (HHF) tests are performed on an electron beam facility to further investigate the mock-up HTP. The numerical simulation calculation results show that the optimized flat-tile divertor target has great potential for handling the steady-state heat load of 20 MW m−2 under the tungsten tile thickness <5 mm and the flow speed ≥7 m s−1. The heat transfer efficiency of the flat-tile divertor target with rectangular cooling channels improves by ∼13% and ∼30% compared to that of the flat-tile divertor target with circular cooling channels and the ITER-like monoblock, respectively. The HHF tests indicate that the flat-tile divertor mock-up can successfully withstand 1000 cycles of 20 MW m−2 of heat load without visible deformation, damage, and HTP degradation. The surface temperature of the flat-tile divertor mock-up at the 1000th cycle is only ∼930 °C. The flat-tile divertor target’s HTP is greatly improved by the parametric design and optimization method, and is better than the ITER-like monoblock and the flat-tile mock-up for the WEST divertor. This conceptual design is currently being applied to the engineering design of the CFETR and EAST flat-tile divertors.

Investigation of the Thermal Characteristics of a Flat Bifacial Evaporator Loop Heat Pipe

The realization of a high heat flux removal with a flat loop heat pipe at ambient temperature is of great importance for achieving thermal control within spacecraft electronic equipment. In this article, a flat bifacial evaporator loop heat pipe with two flat thermo-contact surfaces has been proposed, fabricated, and investigated. The shell of the flat evaporator was made of stainless steel, and ammonia was selected as the working fluid. The startup and operating characteristics of the single side, both sides, and switching working modes were analyzed, as well as the influence of heat consumption, orientation, wind speed, and environmental temperature. The experimental studies indicated that this novel loop heat pipe can start up and run successfully under different working modes, and that the heat dissipation capacity of a set of loop heat pipes can reach 250 W at room temperature. Based on this, a light-weight and small electronic device has been developed using a multi-functional (efficient ‘heat collection-heat dissipation-structural support’) flat bifacial loop heat pipe to realize a kilowatt level heat dissipation capacity. This work can provide reference for the future design of high heat flux, light-weight, and small payload for use in spacecraft.

Fast Capillary Wicking on Hierarchical Copper Nanowired Surfaces with Interconnected V-Grooves: Implications for Thermal Management

Evaporation and boiling heat transfer on micro/nanostructured surfaces with superior wicking capability is an efficient cooling approach for high heat flux removal. The enhancement of the wicking c...

Experimental investigation of a new hybrid structured surface for subcooled flow boiling heat transfer enhancement

A new scheme with hybrid submillimetre/micro/nano-structured surfaces providing both high subcooled flow boiling performance and relatively low flow resistance was proposed to develop highly efficient and reliable water cooling schemes for plasma facing components (PFCs) in future nuclear fusion engineering. Both comparative microscopic surface structure pattern observations and macroscopic mockup subcooled flow boiling experiments under fusion reactor like heat flux conditions were conducted. The proposed technique can create hybrid structures favourable for subcooled flow boiling enhancement: including increasing bubble generation sites and multiscale instability etc. We demonstrated that the heat transfer coefficients of manipulated surfaces in the subcooled flow boiling state were almost doubled and that the critical heat flux (CHF) values were promoted by 80–200% under the tested flow conditions compared with under smooth surface conditions, with the flow path pressure drop deteriorating by less than 12%, indicating better capacities of high heat flux removal and low flow path resistance than those of existing PFC cooling schemes. The results encourage further optimization and development of this new scheme for practical application in nuclear fusion engineering.

Numerical study and experimental verification on spray cooling with nanoencapsulated phase-change material slurry (NPCMS)

Spray cooling is an efficient cooling method with high heatflux removal capability. In this study, we propose a spray cooling regime with nanoencapsulated phase-change material slurry (NPCMS), aiming to improve the coolant's heat capacity. We develop a three-dimensional model of spray cooling of NPCMS based on DPM and Lagrangian Wall Film (LWF) models. Also, the equivalent heat capacity method is integrated in LWF model to characterize the solid-liquid phase change of NPCMS. In addition, the experiment of spray cooling of NPCMS is conducted to verify our model. The influences of initial temperature of NPCMS and dynamic properties on flow and heat transfer of NPCMS are discussed. The results show that NPCMS greatly improves the heat transfer coefficient within the phase-change temperature range, especially the coefficient at the stagnation point of heated surface, but reduces the uniformity of heat transfer. The optimal heat transfer performance occurs when the initial temperature of NPCMS is 301 K, 0.9 K lower than the peak temperature of phase change. The heat transfer coefficient at the center of wall is almost twice of that of the water due to latent heat absorption. Lower surface tension and viscosity are beneficial to improving spray cooling performance.

A Highly Efficient Integrated Silicon-Microchannel Cooler for Multi-Module Electronic Microsystems: Model Design, Optimization, and Performance Validation

Abstract Recently, the development trend of multi-module and multi-function in electronic microsystems makes the ever-increasing heat flux problem more serious. In this study, a highly efficient integrated single-phase microchannel cooler with four heat sources is presented for handling the challenges from both workings independently of all electronic modules and the high heat flux. Both numerical and experimental studies are conducted. By optimizing the structural design and the fabricated process, the presented microchannel cooler has outstanding cooling performance, which contains desired fluid flow distribution, pressure drop, heat transfer, and combination thereof. Results reveal uniform coolant flow dissipates four individual heaters independently, and their maximal temperature difference below 4 °C. Beyond this, high heat flux removal (707.6 W/cm2) is realized with an extremely low coolant flowrate (45 ml/min), and the maximum temperature rise is less than 60 °C. This study provides a referable solution for the thermal management of multi-module heat sources and high heat flux in compact electronic microsystems.

Numerical Assessment of Nanofluids in Recharging Microchannel: Thermo-Hydrodynamic and Entropy Generation Analysis

Abstract Three-dimensional numerical study is presented in this work that deals with thermo-hydrodynamic and entropy generation analysis of water-based nanofluids in recharging microchannel (RMC). Four different water-based nanofluids (Al2O3, CuO, SiO2, and ZnO) are considered with volume concentrations of 1–5% and nanoparticle diameters of 10–50 nm to understand their effect on thermo-hydrodynamic performance and entropy generation. Substrate bottom surface is subjected to a constant wall heat flux of 100 W/cm2 while coolant with Reynolds number range of 100–500 flows through the RMC. It is revealed that among all the nanofluids under investigation, water/Al2O3 provides enhanced thermal performance with higher effectiveness parameter (η), and it also shows reduced entropy generation. With increasing volume concentration of water/Al2O3 nanofluid, heat transfer coefficient increases, effectiveness parameter increases, and entropy generation reduces. Water/Al2O3 nanofluid with smaller nanoparticle diameter shows enhanced heat transfer coefficient and reduced entropy generation, whereas it shows decreased effectiveness parameter. This is attributed to increased pressure drop with decreasing particle diameter. This study suggests that an optimized combination of particle diameter and volume concentration should be chosen for using nanofluid-based coolants for high heat flux removal.

Forced convection cooling of additively manufactured single and double layer enhanced microchannels

Metal based additive manufacturing (AM) is gaining increasing attention in the thermal management community due to the ability to fabricate intricate internal cooling features with acceptable accuracy. The non-traditional designs possible with AM can be leveraged to fabricate enhanced microchannel geometries which allow removal of high heat fluxes from power electronic devices. This study thereby explores the marriage of additive manufacturing and microchannel cooling where microchannels are fabricated using Direct Metal Laser Sintering (DMLS). Microchannels arranged in single layer and double layer configurations are evaluated for their heat transfer and pressure drop performance over Reynolds number, based on channel hydraulic diameter, ranging from 200 - 900 with water as the coolant. The double layer microchannels present a more complex geometry, with two layers of microchannels stacked one on top of the other which promises improved thermal performance based on literature. Enhancement features in the form of periodic oblique and alternating oblique secondary channels, known to augment fluid mixing and disrupt boundary layer growth are incorporated in both configurations aimed at augmenting the overall performance. Seven AM microchannel geometries, three in single and four in double layer configurations are tested. AM parts analyzed for their surface roughness and dimensional accuracy exhibit high surface roughness and deviation from design intent dimensions. Straight microchannel, fabricated using conventional manufacturing where the channel walls exhibit lower roughness levels serves as the baseline case. Comparing the performance of straight microchannels fabricated via conventional and additive methods reveal roughness induced augmentation in heat transfer and pressure drop of about 10-15%. Incorporation of secondary flow channels results in enhanced thermal hydraulic performance in both single and double layer configurations. Microchannels ranked based on thermal-hydraulic performance show double layer microchannel featuring oblique secondary channels offering the best performance with ~60% higher performance than baseline. The findings from this study highlight the potential of AM in developing sophisticated microchannels.

Estimation of Oil Spray Cooling Heat Transfer Coefficients on Hairpin Windings With Reduced-Parameter Models

Hairpin windings and spray cooling are becoming an increasingly popular combination in the field of high-performance electrical machine design. Machines adopting hairpin windings can achieve higher torque and power densities while enabling them to be manufactured automatically on a large scale to meet the rapid market growth of electric transport. Spray cooling is an effective way for high heat flux removal, which has shown great potentials in electrical machine applications. Although spray cooling has been studied for decades in different engineering applications, the focus had been on investigating its performance on regular surfaces using low-viscosity liquids, such as water. In addition, many existing models for spray cooling heat transfer were built on spray parameters that are difficult to obtain without specialist equipment. Thus, most results from previous studies are difficult to be interpreted and directly applied to electrical machine applications. Practical and economical approaches for estimating the heat transfer coefficients (HTCs) of spray cooling on hairpin windings are needed. This article proposes and validates an experimental approach based on reduced-parameter models that can be applied to predict the HTC of spray cooling setups on hairpin windings.

A review of the state-of-the-art nanofluid spray and jet impingement cooling

Nanofluid spray/jet impingement cooling is widespread and finds applications in many scientific and industrial paradigms. Because of these ubiquities of nanofluid spray/jet impingement cooling, this branch of fluid dynamics has attracted great attention from the scientific community. The performance of nanofluid spray/jet impingement cooling very often depends on the nanoparticle concentration, shape, and size of the nanoparticle, as well as the mass flow rate of the nanofluid. These aspects lead to interesting variants of the thermo-hydrodynamic analysis of the nanofluid, which are studied meticulously, and some new functionalities are established such as high heat flux removal capacity, temperature uniformity, lower flow rate demand, and no thermal resistance to the heated test surface. We provide an overview of nanofluid spray/jet impingement cooling with an emphasis on the parametric effects, such as the Reynolds number, jet to test surface distance, the Prandtl number, the confinement of the jets, test plate inclination, and the roughness of the test surface, on the underlying phenomenon. Also, we aptly discuss the essential features of the nanofluid spray/jet impingement cooling, which includes spray properties, cooling fluid properties, substrate properties, and environmental conditions, which affect the heat transfer of spray cooling.

Capillary hydrodynamics and heat transfer in two-phase gas-liquid microscale systems

This paper aims at discussing the hydrodynamics and heat transfer in gas-liquid microscale systems. A new approach for the determination of the flow pattern, based on measuring the statistical characteristics of gas-liquid flow is proposed that can be used for flow pattern map design. The characteristics of heat transfer during upflow boiling in microchannel heat exchangers that operate at low wall superheat are discussed. A novel method for prediction of the flow boiling heat transfer which accounts the heat transfer enhancement due to formation of the thin curved liquid film and surface waves is presented. The characteristics of heat transfer during subcooled flow boiling in microchannel heat sink designed for high heat flux removal are discussed and method for heat transfer prediction is proposed.

Effects of Inlet/Outlet Manifold Configuration on the Thermo-Hydrodynamic Performance of Recharging Microchannel Heat Sink

Abstract Thermal performance of microchannel heat sink can be augmented by designing inlet/outlet manifolds such that fluid flow distribution is uniform across microchannels. In this work, the effect of inlet/outlet manifold configurations on the thermo-hydrodynamic performance of recharging microchannel heat sink (RMCHS) is investigated numerically. For this purpose branched, rectangular, trapezoidal, and triangular manifold configurations are considered. All the numerical simulations are performed for channel Reynolds number of 50–300 and constant heat flux of 10 W/cm2 applied on the substrate bottom surface of the RMCHS. The results reveal that branched manifold configuration shows uniform fluid flow distribution across all the microchannels of heat sink and also shows uniform temperature distribution on the substrate bottom surface of RMCHS. Branched manifold configuration reduces thermal resistance by 16% and enhances average Nusselt number by 9.5% compared to rectangular manifold configuration. However, branched manifold configuration shows higher pressure drop in spite of enhancements in thermal performance and flow distribution uniformity. Overall performance analysis indicates that RMCHS with branched manifold configuration can be advantageous for high heat flux removal applications if there is no restriction on pumping power requirement.

Thermo-hydraulic and entropy generation analysis of recharging microchannel using water-based graphene–silver hybrid nanofluid

This work numerically investigates thermo-hydraulic and entropy generation characteristics of water-based graphene–silver (Gr–Ag) hybrid nanofluid with temperature-dependent properties in recharging microchannel (RMC). The thermal, hydraulic, and entropy generation characteristics in recharging microchannel are examined for different nanofluid volume concentrations and inlet velocity. The outcome of this study reveals that the utilization of Gr–Ag hybrid nanofluid in recharging microchannel enhances heat transfer performance. With an increase in both nanofluid volume concentration and fluid inlet velocity, substrate maximum temperature and thermal resistance decrease, whereas the uniformity in temperature distribution and average heat transfer coefficient enhanced. Moreover, the use of hybrid nanofluid in recharging microchannel shows higher pressure drop and requires more pumping power. Recharging microchannel (RMC) exhibits better overall performance compared to simple microchannel (SMC) with maximum performance factor value of 1.72. Further, frictional entropy generation increases, and thermal entropy generation decreases with increasing nanofluid volume concentration and inlet velocity. Both total entropy generation and Bejan number decrease with nanofluid volume concentration. Overall, the use of recharging microchannel (RMC) can be beneficial for high heat flux removal applications from both first and second law of thermodynamics perspective. Second, the utilization of water-based Gr–Ag hybrid nanofluid is beneficial when pumping power is not a constraint.

An Elaborate Review for Micro-Fin Heat Sink

Heat sinks are low cost, the process of manufacturing reliability, and design simplicity which leads to taking into consideration various cutting-edge applications for heat transfer. Like stationary, fuel cells, automotive electronic devices also PV panels cooling and other various applications to improve the heat sinks thermal performance. The aim is to focus on some countless fundamental issues in domains such as; mechanics of fluids and heat transfer, sophisticated prediction for temperature distribution, high heat flux removal, and thermal resistance reduction. The outcome of this survey concluded that the best configuration of heat sinks has a thermal resistance about (0.140 K/W to 0.250 K/W) along with a drop of pressure less than (90.0 KPa) with a temperature gradient about 2 °C/mm. Heat sinks with square pin fins lead to enhance the effectiveness of heat dissipation than heat sinks with microcolumn pin fins. While other researches recommend the use of high conductive coating contains nano-particles. The present survey focuses on the researches about future heat sink with micro fin and the development to resolve the fundamental issues. The main benefits and boundaries of micro fins heat sink briefed.

Effect of hydrophilic coating on mesh wicks used in heat pipes

ABSTRACTHeat pipes are efficient heat transfer devices which utilize two-phase flow for high heat flux removal and finds applications in many industries. Copper meshes are extensively used in heat pipes and their performance primarily depends on the wettability which is an important design criterion. The wettability and hence the thermal performance can be improved by providing a hydrophilic coating using sol–gel technique. The effect of the binder additive, namely, polyethylene glycolconcentrations, dipping time and dipping frequency on wettability and thermal performance are investigated in this study. It is found that coating on mesh reduces the contact angle and the wettability is improved by 32%. The results indicate that dipping frequency has significant effects on thermal performance due to the existence of hair-like microstructures. The coating is found to offer good thermal performance and reduces the surface temperature of heat pipe by 23 K at 180 W.