Darcy's law-based models for liquid absorption in polymer wicks

Wicking of liquids in polymer wicks made of sintered polymer beads is studied experimentally where three different polymer wicks (made from polycarbonate, polyethylene, and polypropylene) and three different well-characterized liquids (hexadecane, decane, and dodecane) are used to plot the mass of wicked liquid as a function of time. The experimental results are compared with the Predictions from the Wash-burn equation as well as a Darcy's law-based formulation. The suction pressure needed to pull the liquid up a wick in the formulation is modeled using a new energy balance (EB) method and a capillary method. In the former, the released surface energy during wetting is equated to the viscous losses during liquid motion; in the latter, the suction pressure is obtained by treating the wick pore-space as a bundle of capillary tubes. The Darcy's law-based formulation also considers the effect of gravity in its predictions. The newly proposed EB method in conjunction with gravity yields the most satisfying predictions. All parameters used in the proposed model were measured independently and no fitting parameters were used. The success of this method is especially notable for a large-pore polypropylene wick where it was the only model to predict the final steady-state height for the liquid column. (C) 2007 American Institute of Chemical Engineers.