Experimental Investigation of Wicking Flow Through a Porous Medium as a Validation Approach for Numerical Simulations

Wicking flow through a porous medium with nearly-spherical interconnected pores was investigated experimentally for validation of numerical simulations of multiphase flow through a porous structure. The experimental setup was designed to eliminate the effects of pressure gradient and gravity. The porous structure is a commercial graphite foam (PocoFoam® with an average pore size of 400 μm and porosity of 75%) and the penetrating liquid is cyclohexane. The penetration of the liquid into the foam sample is unidirectional. The liquid originates from a side reservoir toward an empty reservoir on the opposite side, with the porous sample between the reservoirs. The level of the liquid was kept constant on the fluid source side of the sample, i.e. in the reservoir full of liquid. Since the top side of the experimental setup is exposed to the ambient, there is no pressure gradient effect. Thus, penetration of the liquid occurs only as a result of interfacial effects (i.e. surface tension and contact angle) while pressure gradient and gravity play negligible roles. The instantaneous liquid penetration length (i.e. the average position of liquid interface) versus time was measured experimentally using video frame analysis of the tests recorded with a digital camera aligned with the experimental setup and observing from the top. The experiments were repeated several times to ensure their repeatability and the variations of the liquid interface position were obtained at different time instants. The results exhibit agreement with the theoretical Washburn equation for the liquid penetration length for horizontal wicking along cylindrical capillaries. Moreover, the possible causes of deviations from the Washburn equation were studied. Furthermore, the experimental results are in good agreement with numerical results of the liquid penetration through a series of pores. The numerical analysis was performed for a two-dimensional model that is based on the geometric features of the graphite foam sample and using the multiphase Volume-of-Fluid (VOF) method.