Research On Heat Transfer Performance Of Immersion System Based On SiC/white Mineral Oil Composite Nano-working Fluid

At present,the thermal management problem of high power density and heat generation in the data center has become the main bottleneck of the high integration of equipment.Finding an efficient and energy-saving thermal management method is an effective means to solve the problem of thermal accumulation in the data center.However,due to the high energy consumption and low efficiency of the traditional air-conditioning cooling system in the data center,the energy consumption of the data center remains high.Therefore,the research on the cooling system with low energy consumption and heat dissipation for highly integrated electronic devices has become a key issue.Immersion direct contact cooling,as a high energy density,low energy consumption,simple system and integrated thermal management method for electronic equipment,can transfer heat directly to the solution without passing through other thermal resistances.However,due to the small number of immersion solutions and the low thermal conductivity,its development in practical applications is limited.In order to solve the problem of low thermal conductivity of immersed solutions,this paper proposes a silicon carbide/white mineral oil-based nanofluid as a new type of immersed working fluid.Three-part study of thermophysical parameter characterization,concentration optimization and heat transfer performance in application scenarios,to explore the heat transfer of the new immersed working fluid under different heat loads and heat dissipation methods of the heat source and the influence of the temperature distribution of the immersed system.The specific research contents and conclusions are as follows:（1）The SiC/white mineral oil composite nano-working fluid was prepared by a two-step method,and the physical properties of the new working fluid at 0.1-10.3 vol% were characterized for its stability,thermal conductivity,constant pressure specific heat capacity and dynamic viscosity.The results of the study show that the dispersant can help the solution maintain overall stability for about 30 days.The volume fraction and temperature can improve the thermal conductivity.Compared with the base liquid,the thermal conductivity of 10.37vol% nanofluid can be improved by up to 25%.When the temperature rises from 30 to 70 ℃,the thermal conductivity of 0.3 vol% nanofluid can be improved by 15.5%.With the increase of the volume fraction,the specific heat capacity at constant pressure of the nanofluid decreases sharply;and the increase in temperature also increases the specific heat capacity at constant pressure.Conversely,with the increase of nanoparticles,the dynamic viscosity of the nanofluid increases;while the temperature increases,the viscosity decreases.（2）Using a fluid-structure coupled heat transfer numerical model,the comprehensive effects of the concentration parameters of silicon carbide oil-based nanofluids for immersion cooling were studied,including thermal conductivity,constant pressure specific heat capacity and dynamic viscosity.The results show that the optimal concentration is 0.3vol% at 250 Reynolds number.The maximum surface heat transfer coefficient is increased by 11.3%.And3.7vol% nanofluid performs better when the Reynolds number is higher than 1000.After comprehensively considering the flow rate range of the application,a 0.3vol% new working fluid was selected as the experimental object for the subsequent experimental exploration.（3）In view of the problem of low heat transfer performance of the immersion cooling working fluid,the method of experimental exploration is used to compare the experimental heat transfer capacity of the traditional working fluid and the new working fluid,and the application effect of the new working fluid in the immersion cooling.research.The results show that the new working fluid can not only significantly reduce the junction temperature of the heat source,but also improve the temperature uniformity of the heat source.Under the bare heat source,the maximum temperature drop is 13.7°C,the average temperature drop is6.5°C,and the temperature uniformity is increased by 7.2-29.1%.The maximum temperature drop under auxiliary cooling is 2.2°C and 2.6°C,and the maximum temperature uniformity is improved by 6.3%.（4）Through the research on the heat transfer performance of the new working fluid under different heat loads,its heat transfer capacity in different application scenarios is explored.The results based on the simulation calculation show that the maximum increase of the heat transfer coefficient of the bare heat source surface under the new working fluid is 11.3% at100 W.The maximum surface heat transfer coefficient increases of 11.7% and 10.7%respectively when the heat source is 300 W heating power under the auxiliary heat dissipation of the heat sink and the heat pipe.It can be seen from the cloud map that the high temperature area on the surface of the heat sink and the heat pipe is significantly reduced,and the internal temperature is also significantly reduced.Then,compared with the commercial fluorination liquid FC3283,the surface heat transfer coefficient of the new immersed working fluid is326.60-538.03 W/m·k,while that of FC3283 is only 101.93-159.86 W/m·k.Finally,the economic and reliability analysis of the new working fluid shows that the PUE after the new working fluid is only increased by 0.068-0.03%,which is negligible.After three months of repeated experiments,the average temperature increase is 0.1-2.3%,that is,the new working fluid has good stability and reliability,which proves that the new working fluid has a good application prospect in the immersion cooling system.