Research On Sublimation Cooling Characteristics Of Dry-ice In High Thermal Flux

Aerospace exploration and aerospace technology accelerate,Airborne equipment presents a trend of highly integrated and micro-modularization,which challenge traditional aerospace thermal control systems,the phase change cooling technology opens up the research direction for the cooling and efficient heat dissipation of the aerospace vehicle airborne equipment,and is an effective means of cooling and heat exchange for the next generation of high heat flux equipment.The sublimation phase change of dry-ice has a large latent heat and can achieve low temperature(-78.5℃)sublimation.It is very suitable for use as a coolant for the thermal control system of electronic equipment with high heat flux,it is an inevitable choice for space exploration and aviation equipment heat dissipation.In order to study the characteristics of dry-ice sublimation cooling under high thermal flux,the thesis designed and built a dry-ice sublimation cooling research experimental platform.The spray distance,dry-ice spray temperature and average temperature in the spray chamber were measured experimentally to verify the cooling ability of dry-ice spray sublimation phase change cooling;The effects of nozzle aperture,carbon dioxide mass flow rate and heating power on the performance of dry-ice sublimation phase change cooling are experimentally studied,and the heat transfer characteristics of dry-ice sublimation cooling are obtained;Numerical studies have obtained the variation of dry-ice spray velocity,the temperature distribution in the cavity and the temperature distribution of the heat exchange surface under different inlet pressures.The research on the sublimation cooling characteristics of dry-ice provides a theoretical basis for phase change cooling technology,and is the focus of research on high thermal flux thermal control systems.Experimental study on spray parameters of dry-ice sublimation cooling and heat transfer characteristics.Experiments were carried out in the range of mass flow rate of 2.85 g/s～13.56g/s and nozzle diameter of 0.8 mm～2.0 mm.The experiment measured the temperature change trend of dry-ice spray at different stages under different mass flow rates,as the flow of carbon dioxide increases,the nozzle inlet pressure continues to increase,and the temperature of the working fluid before and after the nozzle shows different degrees of temperature drop.The inlet temperature drops to-30.15°C and the outlet temperature drops to-70.82°C;After adding a dry-ice spray chamber,the temperature at the inlet and outlet of the nozzle does not change much,and the average temperature in the spray chamber is-58.29°C.The best spray height is determined to be 5 mm according to the cone angle of the dry-ice spray at the nozzle outlet.Experimental study on the heat transfer characteristics of dry-ice sublimation cooling with high heat flux.The experimental research on the effect of spray nozzle aperture,carbon dioxide mass flow rate and heating power on the heat transfer and cooling capacity of dry-ice has been systematically carried out.There are differences in the parameters of nozzles with different nozzle apertures to form dry-ice spray.A higher Reynolds number can promote the formation of dry-ice and improve the heat transfer capacity of the dry-ice sublimation cooling system,however,it will also affect the sublimation rate of dry-ice,cause the process cold energy of dry-ice to be dissipated,and impair cooling performance.While the high mass flow rate increases the pressure of the working fluid,the Reynolds number of the fluid increases,thereby increasing the proportion of dry-ice particles in the dry-ice spray.Compared with the heat flux density of small mass flow(4.85 g/s),the heat flux density of mass flow 7.92 g/s and 10.79 g/s increased by 16.32%and 32.04%,respectively,the corresponding heat transfer coefficients are reduced by 7.76%and 10.72%respectively.Although a higher mass flow has a high cooling heat flux density,it may cause damage to the heat transfer performance due to a lower spray temperature,and the same heat flux will result in a lower surface temperature.Dry-ice sublimation cooling is greatly affected by the characteristics of the heat source.Corresponding to the heat source cooling under different heating powers,it is necessary to adjust the relevant parameters of the dry-ice cooling system.The fixed spray form does not meet the cooling requirements under all heating powers.In the current study,the highest heat flux density of dry-ice spray cooling heat transfer is 105.26 W/cm~2,and the heat transfer surface temperature can be controlled at 79.86℃through dry-ice spray sublimation heat transfer,this is the best cooling and thermal control capability with a solid cone nozzle with a diameter of 1.5 mm at a carbon dioxide mass flow rate of 10.79 g/s and a spray height of 5 mm.Numerical study on spray characteristics of dry-ice spray.The spray characteristics of dry-ice spray under different pressure inlet conditions are numerically studied,and the change law of velocity field,pressure field,temperature field and spray center velocity are studied.The temperature of the dry-ice spray at the nozzle is significantly reduced,the pressure is significantly increased,and the fluid velocity gradient near the nozzle wall is larger;The flow rate of the working fluid reaches the maximum at the nozzle core,and the average flow rate of the working fluid at the nozzle outlet decreases steadily until it reaches the heat exchange surface and turns into a radial velocity;The obvious temperature laminar flow occurs during the dry-ice spraying process,which is the result of the heat exchange between the cone-shaped dry-ice spray edge and the surrounding environment and the heat exchange surface with the dry-ice spray.The flow pattern of dry-ice spray is an important influencing factor for enhancing heat transfer.The increase in the flushing speed of dry-ice spray and heat transfer surface can enhance cooling and heat dissipation and help improve the heat transfer performance of dry-ice sublimation cooling.This research provides theoretical basis and experimental methods for the development of sublimation phase change cooling in the field of thermal control of high thermal flux equipment and practical engineering applications.It has guiding significance and practical engineering application value for the research of aerospace equipment cooling and thermal control system.