Numerical Investigation Of Droplet Migration Under Thermal Capillary Force Or Gravity

The controlled migration of droplet migration is of great significance to the application of microfluidics in industrial application and scientific investigation.In this study the numerical simulation is carried out for the droplet migration on the substrate under thermocapillary force or gravity.Firstly,with the Level Set method for gas-liquid interface capture,the transient three-dimensional numerical model is established for migration of sessile droplet on the substrate,the contact angle between the droplet and substrate is implemented under three-dimensional coordinate.The numerical results are compared with the theoretical analysis,and the reliability of current numerical model is proved.Secondly,the spontaneous migration of sessile droplet is investigated under the thermocapillary effect due to the temperature gradient on the substrate,the effect of Ohnesorge number,Marangoni number,contact angle and the gas-liquid property ratio on the droplet migration in provided.It is found that under the thermocapillary force,at low contact angle the droplet can migrate spontaneously from the hot region to the cold region,while at high contact angle,the droplet can migrate from the cold region to hot region.The difference in migration direction comes from the inner vortex and stagnation points induced by the thermocapillary flow.The viscosity ratio of gas over liquid can also affect the droplet migration direction.With the increasing viscosity ratio,the droplet tends to migrate from towards cold region to towards hot region.Finally,the droplet migration in inclined plate is investigated under gravity,the effect of Froude number,Reynolds number and inclination angle on the droplet migration is studied.It is found that under the gravity the migration velocity will increase rapidly first and then approach to a constant value.The time for velocity to reach constant will increase with the increasing Reynolds number.Furthermore,the steady migration velocity will decrease with increasing Froude number,and will increase with increasing Reynolds number and inclination angle.These findings are helpful for the controlled spontaneous droplet migration and the application of microfluidics in industrial application and scientific analysis.