Research On The Influence Factors Of Bubble Growth Process During Depressurization

Bubble growth due to rapid depressurization in a single droplet plays an important role in many industrial processes.There are two kinds of bubble growth mechanism.The first is heat transfer,and the other is mass transfer.In this paper,the mechanism of bubble growth in a single droplet during rapid depressurization is experimentally and theoretically studied.During the experiment,a experimental system including a test vessel,a vacuum system,a photography system and a data acquisition system is built.A distilled water droplet is suspended on a thermocouplea which is spread with thin hydrophilic coating.It is also used to measure the droplet temperature.A high speed camera is applied to record the bubble expansion.In the theoretical research,reasonable simplifying assumptions are adopted.The mass transfer model,the heat transfer model and the improved heat transfer model are established.The first model couples bubble growth momentum equation with mass transfer equation.The second model couples bubble growth momentum equation with heat transfer equation.The third model considers the effect of the thermocouple.Comparing the simulation results with the experimental results,it is found that the mechanism of bubble growth is heat transfer.The calculation results show that the process of bubble growth can be divided into initial stage,transition stage and accelerating stage.Pressure difference accelerates bubble growth,while surface tension and viscous stress and friction resistance inhibit bubble expansion.The pressure is lower,the initial stage is longer.The droplet surface temperature is unchanged due to the whole process of bubble growth is in a relatively short time.While the bubble surface temperature gradually drops after the initial stage,because the bubble growth needs heat.The degree of superheat is bigger,the bubble grows faster when the environment pressure is same.The environment pressure is higher,the bubble grows faster when the degree of superheat is same.Because the environmental pressure is higher in the same degree of superheat,the bigger pressure difference promotes the bubble growth.The environmental pressure is bigger,the bubble grows slower when the pressure difference is same.