Capillary rise in porous, fibrous media during liquid immersion

The modified Washburn equation has been further developed in this work, to examine capillary rise in porous media which are being immersed in liquid at a continuous rate. The capillary rise rate and/or properties of the media can be determined by a series of differential equations which govern the processes. The model was applied to oleophillic and oleophobic porous, fibrous media with generally good results, however it was found that the model needed to be fitted separately to the initial rise phase and to the longer-term (near-constant slope) phase. It was also found that a good agreement between the theory and experiment could be found if the porous media was contained inside a glass tube so that inflow could only occur from below and not from the sides of the filter. In order to model the insertion of media without this tube, a combination of a horizontal and a vertical capillary model was needed. The model could not be easily fitted to very thin, oleophillic media, and reasons for this are discussed; one likely reason being the inflow of liquid from the sides of the media. However, good agreement between the model and experiment could be found for equivalent media with an oleophobic coating and the same oil.