Research On Heat Transfer Of Microchannel Heat Sinks Using Phase Change Emulsion For Chip Cooling

The development of microelectronic components toward integration and high power leads to the heat released by the chip has reached 100 W/cm~2,which not only affects the normal operation of electronic devices,but also reduces its service life.Phase change material cooling not only uses sensible heat but also makes full use of the latent heat of phase change during phase change,storing and transferring large amounts of heat energy.Compared with single-phase fluids or with boiling(two-phase flow)coolants,phase change emulsion as a new type of phase change material can remove more heat from the surface of the electronic device,which has the advantages of reducing the transmission flow,reducing the power consumption of the pump and shortening the pipelines to reduce the operation and investment costs.Compared with the microencapsulated phase change material slurry(MPCM slurry),it has the advantages of easy to prepare and use and it has a wide range of applications in chip cooling.At present,researches on the preparation of phase change emulsion and its physical properties have been extensively studied.However,it is very scarce on the research about the use of microchannel heat sinks for cooling chip.Therefore,phase change emulsion is used as cooling media to study the heat transfer performance of microchannel heat sinks in this paper.First,the heat transfer performance of the microchannel heat sink is investigated using MPCM slurry as a cooling medium.The analytical results of the temperature variation in the microchannel heat sink are obtained using the porous medium method under constant heat flow conditions.Compared with the data reported in the literature,the results are in good agreement.The reasonability of the hypothesis and the correctness of the analytical solution are proved.It is found that the thermal conductivity,volume concentration of the phase change material,and porosity of the microchannel heat sink are the main parameters affecting the heat transfer characteristics.While the diameter of the phase change particle has almost no effect on its heat transfer characteristics.When the volume concentration of the MPCM slurry is 0-25%,the optimal porosity of the microchannel heat sinks is between 0.69-0.73.Under the same conditions,it is analyzed that the use of a phase change emulsion with a volume concentration of 15%can increase the heat transfer performance of the microchannel heat sink by 20%than using the single-phase fluid.The analytical results are used to optimize the design value of the porosity of the microchannel heat sinks(taken as 0.71),and a six-layer rectangular microchannel heat sink is designed.A heating plate is used to simulate the heating of the chip and the copper plate is used to connect the heating plate with the microchannel heat sinks to determine the actual amount of heat.A phase change medium microchannel heat sink is used as a heating device to build a closed loop thermosyphon system test bench to test the heat transfer performance of the microchannel heat sinks.At the same time,by investigating different preparation methods,a stable phase change emulsion can be prepared under the conditions of 10000r rotation speed,HLB value(hydrophobic equilibrium value)of 9,emulsification temperature of 60?,emulsifier content of 10%and rotation time of 2 hours.Based on the closed-loop thermosyphon system bench,the actual heating amount and temperature are tested under phase change emulsion with different mass concentrations and different heating powers.By comparison with the thermal resistance of the empty tube,it is found that the start-up exhibits intermittent characteristics with 1%mass concentration phase change emulsion at 5 W.When the heating power is increased to 8.5 W or the phase change emulsion mass concentration increases,a greater density difference can be generated and the height difference is used together to increase the power of the automatic circulation of the fluid and shorten the time reaching the steady state of the system.Compared with the deionized water as the cooling medium,a phase change emulsion with a mass concentration of 2%can increase the heat transfer capacity by 17.1%.The relative error between the experimental and the analytical value of the outlet temperature of the microchannel heat sinks and the temperature of chip is within 15%,so that the validity of the assumption conditions and the correctness of the analytical solution are verified.