Experimental Study On Enhanced Liquid Nitrogen Spray Cooling Heat Transfer With Micro-structured Surface

With the advancement of technology and the improvement of component performance,the heating power consumption of the equipment continues to increase,and the heat dissipation efficiency seriously affects stability,performance and service life of the device.As the temperature decreases,the performance of some semiconductor devices will increase.Spray cooling has the characteristics of high heat transfer coefficient,low contact thermal resistance,and small flow demand;therefore,it has good application prospects in high heat flux components.Among the spray cooling fluids,liquid nitrogen has the advantages of low viscosity,low evaporation temperature,high safety and stability,etc.This thesis designs,builds and debugs a set of experimental systems for the study of enhanced heat transfer on the surface of microstructures in the liquid nitrogen temperature zone.On this basis,several groups of liquid nitrogen spray cooling experiments with different microstructure surfaces and spray conditions were carried out,and the heat transfer characteristics of spray cooling with liquid nitrogen under different microstructure surfaces were obtained.The main conclusions are as follows:(1)After the liquid nitrogen is atomized by the solid cone nozzle jet,the overall shape is spindle.As the spray pressure increases,the spray cone angle first increases and then decreases,and the spray cone angle varies from 31°to 58°.When the spray pressure is0.65MPa,the best spray cone angle is 58°.(2)The experimental results of heat transfer on a smooth surface show that the reduction of the spray height of liquid nitrogen is conducive to the increase of the heat exchange heat flux density,but the uniformity of surface temperature will be worse.When the spray height is 15mm and 25mm,the maximum heat flux of smooth surface can reach to 86.63 W/cm~2 and 80.79 W/cm~2 respectively.(3)Compared with the smooth surface,the straight-finned microstructured surface of different depths can effectively enhance the heat transfer effect of spray cooling with liquid nitrogen,but it will result in the deterioration of the surface temperature uniformity.As the groove depth increases from 0.45mm to 1.1mm,the heat transfer effect increases first and then decreases.(4)Straight-finned and composite micro-structured surfaces can significantly enhance the heat transfer performance of liquid nitrogen spray cooling.Among them,the straight-finned microstructure surface with groove width of 0.5mm and groove depth of 0.7mm can achieve the largest heat flux density.Compared with a smooth surface,the maximum heat flux density is increased by 20.18%,and the heat transfer coefficient is increased by 64.2%.The heat transfer performance of the straight-fined microstructure surface of different sizes is better than that of the composite microstructure surface,but the temperature uniformity of the heat transfer surface is poor.