Experimental Study Of Jet Impingement Heat Transfer With Microencapsulated Phase Change Material Slurry

With the development of high-power electronic components towards miniaturization and high integration,the heat flux increases rapidly.How to design efficient and reliable cooling scheme is very important to ensure its safe operation.Jet impingement,as a highly efficient enhanced heat transfer technology,has a very high heat transfer coefficient and is one of the popular technologies to solve the problem of high heat flux in the future.The microencapsulated phase change material(MEPCM)slurry is a functional fluid that integrates heat storage,temperature control and enhanced heat transfer.Its phase change capsule core can absorb or release a lot of latent heat in the process of solid-liquid phase change,and has a large equivalent specific heat,which can significantly improve the convective heat transfer capacity of the fluid.Based on this,this paper combines the high-efficiency heat transfer performance of jet impingement and the enhanced heat transfer characteristics of the MEPCM slurry,and proposes a new jet impingement cooling method.The experimental study on the heat transfer mechanism of MEPCM slurry jet impingement is carried out by setting up a jet impact experimental device.The effects of working fluid parameters,jet structure and phase change characteristics of capsule core on jet impingement heat transfer are systematically analyzed.Meanwhile,the prediction model of physical parameters of MEPCM slurry and the melting time model of capsule monomer particles are established.The main achievements of this paper are as follows:The phase change properties of the MEPCM particles and the thermophysical properties of the MEPCM slurry are analyzed.The effects of several key parameters on the heat transfer and pressure drop of jet impingement are also discussed.Experimental results show that a 10%mass fraction of MEPCM slurry may enhance jet heat transfer by 32.8% compared with water because of the latent heat absorption of the PCM core.The heat transfer enhancement will be limited for higher mass fractions of slurry.And the pressure drop of the system increases rapidly with the increase of the flow rate of working medium,and the higher the concentration of slurry,the greater the pressure drop of the system.When the mass flow rate is constant,the smaller the diameter of the single nozzle,the higher the heat transfer coefficient,but at the same time the greater the pressure drop,which requires more pump power.With the increase of jet distance,the impact heat transfer effect of single hole jet increases first and then decreases.The slurry exhibits a high heat transfer efficiency when the jet distance is ΔL/D = 4～9.3.The heat transfer coefficient decreases with the decrease of the jet angle,and with the same amplitude of the jet angle,the decrease of the heat exchange effect gradually increases.The convective heat transfer coefficient of the slurry first increases and then decreases with the increase of the jet temperature.The optimal jet inlet temperature is about 12.1℃ lower than the melting peak temperature.If the inlet temperature is too high or too low,the heat transfer effect of the slurry will be worse.Only when it is within a suitable range,the convective heat transfer performance of the slurry will be better than that of water.The complete melting time of the phase change material is always less than the residence time of the particles on the heating surface,which can ensure that the phase change material is in the melting state.The heat exchange effect of the three array nozzles is significantly stronger than that of the single-hole nozzle,and the 19-hole array nozzle has the best heat exchange effect,followed by the 37-hole nozzle,and the 7-hole nozzle has the weakest heat exchange effect.The pressure drop increases rapidly with the increase of the number of holes in the array.The greater the flow rate,the greater the pressure drop increase.When the hole distance is constant,the heat transfer coefficient of array nozzle decreases with the increase of jet distance,and the optimal jet distance is smaller than that of single hole nozzle.In addition,the hole distance and jet distance affect the heat transfer effect together.When the jet distance is small,the smaller the hole distance is,the better the heat transfer effect is;On the contrary,with the increase of the jet distance,the larger the hole spacing,the better the heat transfer effect.The stability of the experiment is tested.Compared with the initial convective heat transfer coefficient,the heat transfer performance of the system can still reach more than 94% of the original after 1000 cycles.