Research On Heat Transfer Characteristics Of Spray Cooling And Droplet Depressurized Evaporation Based On Temperature Sensitive Paint

Spray cooling has good heat dissipation capacity and has been widely used in industrial fields such as electronic device cooling,energy chemical industry,and mechanical processing.Both atmospheric spray and flash spray involve droplet evaporation.This paper conducts an experimental study on the temperature distribution of the solid-liquid contact surface from two aspects of spray cooling and droplet depressurized evaporation.In this paper,an open spray cooling experiment platform was first built,using HFE7100 and n-pentane as spray working fluids,and temperature-sensitive paint temperature measurement technology was used to obtain temperature distribution changes on the solid-liquid contact surface.The results show that during the process of atmospheric spray cooling,the surface temperature can be divided into three stages:rapid cooling stage,vaporization stage and temperature rise stage.During the rapid cooling stage,the wall temperature drops the fastest;the wall temperature during the vaporization stage remains almost unchanged;then the wall temperature rises after the spray finished.Experiments have obtained the effects of spray height(10-30mm).initial substrate temperature(50-75~oC),spray working fluid,and spray flow rate(170-432m L/min)on the average wall temperature.The results show that the higher the spray height,the lower the average temperature of the substrate.The higher the initial temperature of the substrate,the faster the temperature drop rate during the cooling stage,but the surface temperature rises faster.The larger the spray flow rate,the impact on the liquid film on the wall surface is enhanced,the lower the average temperature of the substrate wall surface and the greater the temperature drop rate.On the basis of experimental research,a numerical simulation study was carried out on the temperature distribution of the substrate surface during the rapid cooling stage in the spray cooling.The average surface temperature change obtained by the simulation is compared with the experimental results,the results show the validity of the simulation results.Further theoretical analysis of the reasons for the uneven temperature distribution on the surface,the thickness distribution of the liquid film on the surface and the flow velocity distribution of the liquid film are the reasons for the uneven temperature distribution.Using temperature-sensitive paint temperature measurement technology,the effects of spray height(10-30mm)and spray flow rate(170-432 m L/min)on the wall temperature distribution and the maximum temperature difference are studied.The results show that the higher the spray height,the larger the spray impacting surface,and the surface temperature distribution has a larger ring area.For the spray working fluids of HFE7100 and n-pentane,n-pentane vaporizes more violently,and the probability of a ring-shaped area is smaller.In addition,the higher the spray height,the smaller the maximum temperature difference on the surface.The temperature distribution of the low-flow spray in the rapid cooling stage does not appear in the annular temperature distribution area,but the maximum temperature difference in the rapid cooling stage is larger.Finally,temperature-sensitive paint temperature measurement technology was used to experimentally study the temperature distribution of the solid-liquid contact surface of HFE7100 droplets and n-pentane droplets over time during the depressurized evaporation process.The results show that the lower the environmental pressure,the shorter the evaporation time of the droplets.The lower the latent heat of vaporization of the droplet working fluid,the lower the temperature of the contact surface.The lower the ambient pressure or the larger the droplet volume,the lower the average temperature of the contact surface.