Dynamics Of Sessile-drop In The Presence Of Contact Angle Hysteresis On The Heated Surface

The movement of drops is a common phenomenon in nature.Factors such as contact angle hysteresis(CAH),sensitivity of interfacial tension to temperature,wettability gradient surface,and the inclination angle of substrate have an important influence on drop movement.Further study on the internal mechanism of these factors affecting drop movement is helpful to realize the regulation and control of drop movement,thereby improving the production process,which is beneficial to industrial production and life.Therefore,present study adopts the method of numerical simulation to conduct further study on the dynamics of a drop on the heating surface in the presence of CAH.The main results are as follows:For drops that evaporate on a uniformly heated solid surface,a model of contact angle hysteresis is introduced,and a two-dimensional evolution equation of the drop thickness is established based on lubrication theory and Navier slip boundary conditions.A numerical simulation is conducted to examine the dynamic behaviors of an evaporating drop in the cases of without and with CAH(indicating with ?? =0,and ?0),the characteristic parameters of drop evaporation under different hysteresis angles(??)is analyzed.The influence of temperature sensitivity of different gas-liquid interfacial tension on drop evaporation dynamics is discussed.And the evaporation experiments are carried out to compare with the numerical simulation results.Numerical results show that the CAH and the sensitivity of gas-liquid interfacial tension to temperature have important effects on droplet evaporation,and both ca n accelerate the drop evaporation process.The increase in the hysteresis angle prolongs the pinning time of the contact line,shortens the duration of the spreading stage and the de-pinning stage,and reduces the contact angle during the de-pinning phase.A flatter shape emerges and the contact area of the gas-liquid interface increases when depinning,thereby enhancing the heat transfer ability and accelerating evaporation.Besides,increasing the temperature-sensitivity coefficient of the gas-liquid interfacial tension can improve the wettability of the drops on the wall by reducing the contact angle,thereby enhancing the heat transfer and accelerating the evaporation.The comparison shows that our experimental results are consistent with the present simulation of CAH,that is,the theoretical model with CAH could accurately reflect the typical characteristics of the drop movement.Based on the mathematical model built in the above study,the drop migration on an inclined surface with wettability gradient is numerically simulated.The effects of contact hysteresis,wetting gradient(wettability difference)and the inclination angle of substrate on the dynamics of drop migration were explored.The results of the study indicate that the drops tend to migrate to the more hydrophilic side(good wettability)on the wettability gradient surface.With the increase of the hysteresis angle,the spreading ability of the drops decreases,and the migration of the drop to the direction of good wettability tends to be in hibited.Increasing wettability gradient makes the drop more inclined to migrate to the side with good wettability,and the migration speed of the contact line accelerates when moving to the side with good wettability.The enhancement of the inclination an gle results in the drop sliding downward along the wall instead of climbing upward.This i s because the gravity component force of the drop along the parallel wall gradually increases,prompting the drop to overcome the influence of the wettability gradien t and gradually move towards the side with low wettability.