Nature of Residual Liquid Holdup in Packed Beds of Spherical Particles

Abstract

The theoretical prediction of the residual liquid holdup in beds packed with nonporous spherical particles is tested by microscopic imaging of a bed of glass spheres wetted by water. The commonly used Young−Laplace equation accurately predicts the meniscus shapes of the pendular rings (Saez, A. E.; Carbonell, R. G. J. Colloid Interface Sci. 1990, 140, 408). The ring sizes are measured directly, and the minimum internal energy (Mao et al. Chem. Eng. Sci. 1993, 48, 2697) and critical percolation (Kramer, G. J. Chem. Eng. Sci. 1998, 53, 2985) boundary conditions proposed in the literature are shown to overpredict the average ring size. The summation of ring volumes over the bed yields a residual holdup smaller than that obtained through weighing. It is concluded that additional liquid is trapped through capillary action at locations where two or more particles are in close proximity. Photographic evidence of the existence of such liquid “globules” is presented.