Mathematical modeling of pulsing flow in large trickle beds

A crossflow model for pulsing flow in a trickle bed of large cross section is presented. The trickle bed is idealized as being made up of pulses and the trickling flow region surrounding these pulses. Assuming the macroscopic gas flow around the pulses to be irrotational and the pulses to contain only liquid, the model equations are derived. An analysis of the model and comparison with the experimental results of Christensen (1986) reveals that the irrotational flow model underestimates the pulse velocity for realistic pulse shapes. This can be attributed to the underestimation by the model of the drag exerted by the trickling region on the pulses. By dropping the irrotational flow assumption and viewing the model as semiempirical, a single parameter characterizing the magnitude of this drag is estimated from the pulse velocity data. When this estimated value for this parameter is employed, the model predicts the average pressure gradient data reasonably well.