Publication

Transient liquid holdup and drainage variations in gravity dominated non-porous and porous packed beds

Ilankoon, I.M.S.K., Neethling, S.J., Chemical Engineering Science 116, 398-405, 2014

Transient liquid holdup effects are a crucial aspect of the behaviour of many unsaturated packed beds systems. This study examined both a model system consisting of spherical glass beads and a system containing slightly porous (about 5% water accessible porosity) rock particles. Experiments on different column heights show that the initial wetting front moving through the packed bed takes the form of a soliton or standing wave. The final drainage of the bed when the liquid addition is turned off shows slightly more complex behaviour than that of the initial wetting of the bed. It was demonstrated that if the behaviour of the liquid held around the particles is separated from that held within the particles, the same relatively simple model can be used to describe the drainage of both the model glass bead system and the slightly porous ore system despite the apparent differences in their behaviour, such as a much longer time to achieve the steady state, and a markedly different shape to the initial overall saturation versus time curve. This simple model assumed that for the liquid between the particles, gravity was the dominant force and that capillarity could be neglected. Neglecting capillarity probably accounts for the slight discrepancy between the experimental and simulated liquid holdup results in the porous ore system at intermediate drainage times.


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