Heat Transfer Characteristic And Application Of Spray Cooling On Mirostructure Surface

As a high-efficiency phase change heat transfer method,Flash spray cooling(FSC)has high surface evaporation heat transfer coefficient.It uses liquid nitrogen as a refrigerant and can be used to explore the unsteady acyclic heat transfer mechanism under large superheat.The use of modern micro-nano processing technology on surface micro-machining of the capillary structure of the frozen carrier helps to strengthen the phase-change heat transfer.Besides,it has many applications in these fields like the ship’s precision air-conditioning system,fishery vitrification and preservation,IGBT high-power original heat dissipation,marine engineering energy-saving.Based on the theory of thin film evaporation,a vitrification experiment platform was built by means of liquid nitrogen flash spray.The experimental study on the heat transfer characteristics of liquid nitrogen on the heat transfer surface of the frozen carrier with microstructure was carried out.According to the result,the new structure combines the advantages of both the porous structure and the copper mesh,thus increasing the heat transfer coefficient and contributing to high heat flux study.Then,it was applied to cell vitrification experimental study,which provided technical support for the practical application of this new ultra-high-speed vitrification method.Firstly,the frozen carrier with microstructure was sintered by transient liquid phase bonding technique(TLP),and the contact angle and porosity of the frozen carrier were characterized.The surface wettability was improved by reducing the contact angle and porosity,thereby enhancing heat transfer.Experimental results show that under the conditions of sintering temperature of 800 0C,holding time of 120 min and pressure of 0.2 MPa,the sample’s evaporation heat transfer characteristics are the best,and the average cooling rate of the frozen carrier can reach 83570.18℃/min.Then,the vitrification cell experiment system was used to study the effects of superheat,sintering temperature and capillary morphology on the heat transfer characteristics of liquid nitrogen on the surface of the frozen carrier.The data processing method is the classical analysis of unsteady heat transfer-the lumped heat capacity method,and the variation law of each heat transfer parameter with the superheat degree is obtained.It is found that the silicon-copper sintering method has the best effect on the heat transfer enhancement of the microstructure surface.Under the same conditions,the parameters such as evaporation heat transfer coefficient and surface heat flux of the microstructure of the sintered copper mesh are better than those of the other two structures.The frozen carrier was then applied to the vitrified cell experiment,and the low temperature protective agent concentration was found to be 5%DMSO,and the cell survival rate was the highest.The evaporation heat transfer rate decreases with the increase of the cryoprotectant concentration,and the cell survival rate increases first and then decreases.There exists the optimal value.