Study On Droplet Evaporation On The Substrate Under Electric Field By Numerical Simulation

The phenomenon of droplet evaporation on solid substrate is common in nature and industry,and strengthening the droplet evaporation could be widely applied in industrial and agricultural production and worth researching.The electric field can change the surface charge distribution and morphology of the droplet on the substrate,change the internal flow morphology of the droplet,accelerate the internal flow of the droplet,and strengthen the heat exchange at the interface of the droplet,thereby promote evaporation and mass transfer of droplets.The evaporation of the droplet on substrate is affected by many factors,such as electric field,temperature field,internal flow field and dielectric conductivity.At present,the mechanism of electric field strengthening the evaporation of basal surface droplets is not very clear.A systematic mathematical and physical model is needed to explain this effect.In this thesis,based on the finite element method,the numerical model of the evaporation process of droplets on the solid substrate under the external electric field is established,and the simulation and analysis of the evaporation process of single droplet are carried out.The main work and research conclusions are as follows:Firstly,the charged droplets evaporation process is simulated,and the simulation result is verified with the experimental result.Comparing the evaporation process of droplets with different conductivity,the effect of electric field on droplet evaporation rate,droplet shape and internal flow and its genesis are analyzed.The relationship between internal flow and droplet heat and mass transfer under electric field is obtained.The results show that the electric field force can significantly change the morphology parameters of the droplet,increase the flow rate in the droplet and heat flux on the droplet surface,promoting the heat and mass transfer of the droplet.Secondly,the process of droplet evaporation under the coupling of electric field and temperature field is simulated.Under different substrate temperature conditions,the effect of droplet evaporation rate,droplet shape and internal flow are analyzed.It is found that temperature has obvious effect on electric field enhanced droplet evaporation.For the pure water droplet with low conductivity,when the electric field intensity is lower than and higher than the critical value 6k V/cm,the effect of temperature on the internal flow and evaporation of electric field enhanced droplets is different,and for the HCl droplet with high conductivity,temperature has great influence on electric field enhanced droplet influx and evaporation.Finally,the influence of the wettability of different substrates on the evaporation of droplets under electric field is studied by simulation.It is found that substrate wettability is also an important factor for droplet evaporation to be strengthened by electric field.Compared with the hydrophobic substrate,the internal flow of droplet on the hydrophilic substrate is less affected by the electric field intensity,but the morphology of the droplet is greatly affected by the electric field intensity,and the effect of droplet deformation on evaporation is larger with the increase of the electric field intensity.Therefore,the enhancement of electric field on droplet evaporation is stronger than that on the substrate with weak hydrophilicity.