Research On Hybrid Liquid Cooling For Both High Flux And High Power Heat Dissipation

Along with the trend of miniaturization and lightweight of various satellite payloads,various types of optical/electronic devices are moving toward higher integration and higher power,which brings more stringent heat dissipation requirements to the thermal management system.Liquid cooling technologies such as microchannel cooling and jet impingement cooling have the advantages of good integration ability and high heat transfer efficiency.However,when applied to the cooling of large-scale heat sources,single-phase and two-phase heat transfer will face new challenges such as flow boiling instability in confined space,increase of non-uniformity in surface temperature,and excessive loss of total resistance loss due to large flow rate.This paper focuses on the“high heat flux,high power"heat dissipation requirements of heat flux ranging from 10 W/cm² to 100 W/cm²,and total heating power over 1 kW,and carries out related design and experimental research.Based on the good gas and liquid separation working characteristics of the axial grooved heat pipe structure,an?-shaped microchannel heatsink with a steam chamber was proposed and developed to solve high heat flux energy dissipation problem over a large area.It aims at solving the problems of flow boiling instability and heat transfer deterioration caused by"gas plug"and"backflow"phenomena,which in turn leads to problems of flow boiling instability and heat transfer deterioration.The heatsink contains 20?-shape parallel channels on the substrate,and the chamber connecting the top of the ribs and the bottom side of the quartz glass cover plate serves as a gas flow path for two-phase heat transfer.A heat sink test platform based on the closed pump fluid circuit was built to test the flow and heat transfer characteristics of anhydrous ethanol and HFE 7100 respectively.The experimental results show that:1)with the gradual increase of the heat flux,the flow and heat transfer between the heat sink and the fluid gradually changed from single phase forced convection,nucleate boiling to transitional boiling state,which allows successful realization of the separation of gas flow and liquid flow in high heat flux conditions.2)when the anhydrous ethanol flow rate was minimum v_f=5.48 mL/s,the critical heat flux?CHF?was q''=30.3 W/cm²?total heating power 762.3 W?,and the maximum heat transfer coefficient?HTC?was h=9494 W/?m²·K?.According to the"field synergy principle",the better the synergy between the velocity gradient direction and the heat flow fields,the higher the convective heat transfer performance theoretically.In order to further optimize the heat dissipation performance of the traditional microchannel cooling technology and combine the advantages of porous medium structure in promoting two-phase convection heat transfer,distributed hybrid jet impingement heatsinks?SL1³?with composite smooth/rough pin-finned surface structures were designed.The numerical calculation of heat sink rectification zone and distributed jet orifice plate were achieved using ANSYS FLUENT software.Four visualized jet cooling test sections were designed and a high-speed micro-imaging platform was built to verify the effectiveness of the above-mentioned surface strengthening structure in promoting phase transformation and increasing critical heat flux density.Distributed composite array jet cooling heat sinks for three composite different surface structures?flat plate surface SL1,smooth pin fin surface SL2,sintered porous layer?120¹50?m?coated rough pin fin surface SL3?that can be used for heat dissipation of 30×30 mm² heat source area.The effect of different inlet working fluid mass flow rates,inlet working temperatures and installation tilt angles on the heat sink performance under low Reynolds number conditions?Re<1200?was tested.Semi-empirical calculation formula for heat transfer performance of different inlet coolant flow rates,coolant temperatures and installation inclination angles was obtained with corresponding average absolute error less than 6.0%.The experiments on four kind of visualized jet cooling test sections?KS1^KS4?were carried out using anhydrous ethanol as working medium at same subcooling?T_sat=60±1 K,effective heating heat flux q''fixed at 82.5±2.5 W/cm²,and mass flow rate at 1.0⁷.5?±0.5 mL/s?.Results show that as the coolant flow rate gradually decreases,bubble flow,slug flow and annular flow gradually developed from stratified turbulence flow on the test sections KS2⁴ with pin-finned structure.The heat transfer mechanism between the coolant and surface changes from single-phase forced convection to nuclear boiling and film boiling.That demonstrates both types of pin-finned surfaces can effectively promote phase change.The test results of three distributed composite array jet cooling heat sinks?SL1³?show that:1)Using anhydrous ethanol as working medium,increasing the working fluid flow can effectively reduce the wall superheat,and increase the critical heat flux and the single-phase HTC?heat transfer coefficient?,but the temperature non-uniformity in the two-phase region and the resistance loss of the heat sink also increase.2)Increasing the inlet subcooling will increase CHF?critical heat flux?by a small amount,but the corresponding heat transfer coefficient will decrease,and the temperature uniformity will not be affected much.3)Compared with the result of horizontal installation,the CHF and HTC of the heat sink will be slightly attenuated in the vertical installation,but in general the heat sink performance is affected by the flow rate of the working fluid.4)According to the difference of amplitude-frequency characteristics of pressure drop oscillation with the increase of heat flux,the whole operation process can be divided into 4 typical regions,namely Part1⁴.Each region corresponds to single-phase forced convection heat transfer,stable nucleate boiling,transition boiling and saturated boiling,respectively.5)Comprehensive comparison of all experimental results,using the distributed composite jet cooling heat sink SL2 with smooth pin-finned surface with positive horizontal installation,the global maximum critical heat flux was obtained at the working inlet subcooling of 60 K and the coolant flow rate of 10.2 mL/s.The global maximum CHF was 160 W/cm²?total effective heating power 1440 W?,at which time?=17921W/?m²?K?.The global maximum HTC was obtained at inlet subcooling of 50 K and coolant flow rate of 12.7mL/s.The global maximum HTC was 18341W/?m²?K?when q''=140 W/cm².Compared with the optimized microchannel cooling heat sink described above,the hybrid jet cooling heat sink has better heat transfer performance.6)Considering the influence of supercooling in nuclear boiling heat transfer coefficient model has better universality.And clarifying the interaction of jet velocity,hole diameter and mass flow rate in the CHF correlation based on single-hole jet was further optimized on this study.