CFD Modelling and Calculation of Dynamic Two-Phase Flow in Columns Equipped with Structured Packing

Corrugated structured packings feature strong preferential flow directions due to their geometry of crossing triangular channels. This leads to good radial spreading, but causes stronger susceptibility to maldistribution of the phases. Detailed CFD calculations reflecting the exact packing structure are only feasible for very small sections of packing. However, effects like large scale maldistribution and instabilities in the flow field can only be modelled, if the hydrodynamics of the entire column are taken into account. In the present study, the macroscopic gas-liquid two-phase flow field of an entire column is modelled and numerically calculated. Both steady-state and dynamic cases are treated for counter-current operating conditions below the loading point. The model is based on the elementary cell model. It is extended to be used on anisotropic porous structures like corrugated structured packings. For the elementary cell model, flow field variables (velocity, phase volume fraction, pressure, and so on) and packing properties (void fraction, momentum exerted by the packing on the fluids, and so on) are averaged over the volume of one elementary cell. An elementary cell is the smallest periodically recurring structure of the porous material. For the gas phase, measurements of the pressure drop are conducted in different directions to model an anisotropic gas flow resistance tensor. The physically homogeneous liquid phase is split up for modelling purposes into two liquid phases, each of them representing film flow along one preferential flow direction. The numerical results are tested against X-ray radiographic measurements on a quasi two-dimensional segment of structured packing.