BEHAVIOR OF A WATER DROP IMPINGING ON POROUS SUBSTRATES-EXAMINATION OF CONTACT-LINE DRAG EFFECT

Abstract

In the present study, spreading and permeation behavior of a water drop impinging on the surface of the porous media was investigated both experimentally and numerically. In order to examine the effect of the three-phase contact-line drag on the drop motion, a numerical simulation solver was developed based on OpenFOAM, an open source code. The governing equations were modified from the conventional VOF solver (porousInterFoam) taking account of the effects of the porosity on the motion of the liquid-vapor interface and on the capillary wicking force. Also, a preliminary contactline drag model was proposed based on the dynamic contact-angle model by Kistler, and was adapted to the numerical solver; thereby the effect of the contact-line drag could be tested numerically by varying an adjusting parameter. The behavior of the drop was predicted and the results were compared with the experimental data. By selecting an appropriate adjusting parameter, the solver could predict the time evolution of the drop shape and the maximum spreading diameter with reasonable accuracy.