Experimental Study On Visualization And Heat Transfer Characteristics Of Liquid Nitrogen Flash Spray

With the development of high heat flux electronic devices and rapid freezing technology,the method of seeking rapid heat dissipation has become a focus of attention.Due to its unique evaporation mechanism,thin liquid film evaporation has higher evaporation heat transfer efficiency than ordinary evaporation heat transfer.The flash spray has a much higher heat transfer efficiency than ordinary sprays because it can perform rapid evaporation in a spray environment.Based on the principle of thin liquid film evaporation,combined with liquid nitrogen flash spray can create a rapid heat dissipation method.In this paper,the visual experiment of liquid nitrogen flash spray and liquid nitrogen evaporation on microstructure is carried out,and the heat transfer experiment is combined to explore its internal heat transfer mechanism,which provides a new idea for solving the problem of rapid heat dissipation.In this paper,the high-speed camera is used to visualize the spray process of liquid nitrogen flash spray and the evaporation process of liquid nitrogen on the surface of microstructure.It is found that as the spray pressure increases,the spray cone angle also increases,and the spray pattern changes more rapidly.When the spray pressure is small,the center point of the cooling surface is submerged by liquid nitrogen.Liquid nitrogen is sprayed onto the microstructure,which adsorbs well on the microstructure and forms a thin liquid film.It is also observed that the amount of liquid nitrogen on the microchannel has a great influence on the evaporation heat transfer phenomenon,and there is an optimum liquid nitrogen amount.In the heat transfer experiment of liquid nitrogen flash spray on microstructure,the microstructure surface with different feature sizes and types was processed by fiber laser etching machine,and their microstructure sizes were characterized.This paper mainly studies the heat transfer performance of flash spray on microstructures under different spray conditions and the effect of different microstructures on the heat transfer characteristics.It is found that when the injection distance is in the range of 1mm～30mm,the heat transfer performance first increases slowly and then decreases as the injection distance increases.There is an optimum spray distance.As the nozzle outlet temperature decreases,the heat transfer performance deteriorates.As the spray flow rate increases,the heat transfer performance generally improves,and the central rejion is greatly affected by the spray pattern.As the feature size decreases,the heat transfer performance becomes better,and the heat transfer performance of the microstructured surface is better than that of the smooth surface.The study found that the hexagonal microstructure has the best heat transfer performance.