Stochastic and related models for the residence time distribution in trickle flow in a packed bed

Mathematical models have been derived on the basis of the abstraction that material would flow uniformly, in plug flow, through a system were it not that elements have a chance of being delayed at all points of their passage; an element so delayed eventually rejoins the main stream. The models are mutually differentiated by their delay time distributions. A trickle flow packed bed system was used to test the concepts involved. Liquid side residence time distributions in a 1½ inch diameter column packed with 1/8 × 1/8 inch ceramic Raschig rings were determined by the method of injecting an impulse of a tracer into the liquid stream. For different delay time distributions, the model parameters were obtained by direct comparison of the experimental and model responses. It was possible to obtain a good fit of the experimental responses, the model parameters correlating well with the operating variables. The effect of varying the packed heights, the liquid and the gas flow rates, the liquid viscosity and the tracer diffusivity on the residence time distributions was investigated. The measured and calculated liquid holdup data fitted several published correlations very well, confirming the reliability of the experimental and processing procedures.