Experimental Study On Isolated Liquid Film Flow In Spray Cooling

With the development of science and technology,the size of the microchip is getting smaller and smaller,and the power is bigger.Heat flux is increasing,too.The large amount of heat generated by the microchip can damage electronic components if not transferred in time.The traditional cooling method is limited by insufficient heat exchange,which can’t be effectively applied to the cooling of electronic devices.Spray cooling has become an effective choice for cooling of electronic devices due to its advantages of heat flux removal capability and uniform heat transfer.Previous experimental studies have fully research about the characteristics of spray cooling and its influencing factors.There has also been great progress in the simulation research of the single-phase cooling zone.However,there are few studies on liquid film that play a key role in heat transfer.The lack of research on the dynamic characteristics of the liquid film leads to incomplete research on the heat transfer of spray cooling.The surface characteristics of the liquid film are deeply studied by building a spray cooling visualization experiment bench in this paper.Firstly,droplet velocity in spray cooling is measured by experiment.The distribution of droplet velocity with spray radius under different nozzle heights,different inlet pressures,different working medium subcooling degrees and different heat flow conditions are measured respectively for water,HFE-7000 and HFE-7100.And the experimental correlations of droplet velocity are obtained,too.The experimental results show that the droplet velocity distributions of the three coolants at different heights all show a trend of increasing and then decreasing with increasing radius.The liquid film images of the surface under different pressures,different heat flows and other working conditions are obtained by building a spray cooling experimental bench.And the image is analyzed by programming.The image is processed by MATLAB software programming.And the image area and speed are solved quantitatively.The definition of the isolated liquid film is given,and the shape change and speed change of a single liquid film from its generation to move to the heat exchange boundary are analyzed.The liquid film area gradually increases with time,and the liquid film speed increases in general.Sometimes they are mutated due to fusion with other liquid films or being crushed by droplets.It is found that with the increase of heat flow,the liquid film changes from continuous to dispersed by analyzing the influence of heat flux on the isolated liquid film.As the pressure increases,the liquid film tends to be continuous.And in this process,the velocity of the isolated liquid film keep increasing.Finally,the droplet velocity is related to the velocity of the isolated liquid film,and the surface average Re number is used to represent the initial momentum of the isolated liquid film.and an experimental correlation was performed on the average velocity of the isolated liquid film in combination with the Ja number.