Interaction of a millimeter sized droplet on the powder substrates and study of capillarity in porous media flow

A.G. Avhad, H. Tan
Washington State University,
United States

Keywords: absorption, droplet, millimeter size, nylon powder substrate


Droplet impact on powder materials is a ubiquitous phenomenon in nature and engineering technologies including powder-binder based 3D printing, wet granulation, spray drying, powder coating, agricultural sprays, water erosion of soil, and raindrops landing on sand or soil. An important aspect of droplet-powder interaction is the absorption of liquid droplet by powder substrates due to capillary force. Fundamental understanding of this phenomenon is crucial to achieve the desirable outcomes in engineering technologies. Therefore, it is necessary to determine the parameters affecting droplet absorption by powder materials. In this study, we have investigated the phenomenon of absorption of a multiple solutions into the substrate material of nylon powder PA2200, mainly used in 3D printing process, in this experiment. The focus of this research is to put forward that surface tension variation of the fluid affects the absorption for the given substrate of different porosity values. With the help of contact angle results for test liquid solutions and the substrate, it is possible to calculate the critical parameter of the substrate for the fluid to get absorbed. Furthermore, the effect of the porosity of the substrate material on the absorption of the fluid is discussed. To support our experimental results with the analytical solutions, Darcy’s equation for flow through porous medium is discussed and a derived equation for fluid absorption into the porous medium is employed to substantiate our experimental results. These results are further going to contribute in the selection of correct solution in order to achieve absorption. This research has been conducted on the millimeter sized drops and the results would further be used for comparison with micron sized drops when similar experimental study will be conducted soon. The final objective of this research is to study the behavior of droplets when used in millimeter size and when used in micron sized.