Characteristics Of Heat Transfer In Evaporative Cooling Process Of High Heat Flow Density On The Microstructure Surface

Thin film evaporation is an efficient way of heat transfer with phase change,being applied to ship refrigeration,cooling of integrated chip,cryogenic engineering and so on.Using thin film evaporation to solve heat transfer problems of high heat flux density on the surface has become a research focus in the heat transfer.Based on liquid nitrogen evaporative cooling system,this paper conducts experimental study about heat transfer characteristics of liquid nitrogen on the surface of microstructure and analysis temperature distribution of frozen carrier in the cooling process by numerical simulation.In the evaporative cooling experiments on the surface of microstructure,the lumped capacity method is used to analyze the unsteady heat transfer process,researching heat transfer parameters changing with superheat,discovering that evaporation heat transfer coefficient of liquid nitrogen change as a parabolic trend that first it increases then decreases with the superheat decreasing;liquid nitrogen with five different flow rate evaporation cooling on the surface of microstructure,discover that heat transfer performance on the microstructure surface is not always good with the increase of liquid nitrogen flow rate and when flow rate is 3.48 g/s,the heat transfer performance is best;comparing two different microstructure shape of frozen carrier,square column and cylindrical,discover that square column of frozen carrier has a better heat transfer performance on the microstructure surface;to analysis heat transfer characteristics by changing microstructure spacing,the results show that heat transfer performance of liquid nitrogen improve with decreasing of microstructure spacing;comparing evaporative cooling effect under different exit distances,5mm,10mm and 15mm,it reveals that cooling rate of frozen carrier with 5mm exit distance is the best and its average cooling rate is 76386.88℃/min in the cooling process from 0℃ to-60℃.When giving a simulation of the unsteady heat transfer process on the microstructure surface,there are two different boundary conditions,constant heat transfer coefficient and instantaneous heat transfer coefficient.The method of using instantaneous heat transfer coefficient has a smaller error comparing with the experimental results.Simulating the cooling process of frozen carrier with different microstructure spacing,the results indicate that the smaller spacing between microstructures,the better temperature uniformity of frozen carrier in the cooling process.