Mass transfer and liquid hold-up determination in structured packing by CFD

Mass transfer and liquid hold-up in structured packing geometry are investigated using the volume of fluid method. Numerical simulations of two-dimensional co-current gas-liquid flow on structured packing with interfacial mass transfer are performed. The volume of fluid method is used to capture the gas-liquid interface motion. The mass transfer is computed by solving the concentration equation with an adapted modeling of the solubility (Haroun et al., 2010b). The liquid hold-up and the mass transfer are studied as function of liquid flow rate and structured packing geometry. Results show how the liquid flow rate and the complex geometry affect the liquid film flow topology and the interfacial mass transfer. For a specified packing geometry, it is demonstrated that for low liquid flow rate, the liquid film remains uniform and follow closely the profile of the structured wall. For uniform liquid film flow along packing wall, it is found that the liquid hold-up is in good agreement with the model proposed by Billet and Schultes (1999) and Raynal and Royon-Lebeaud (2007). When increasing the liquid flow rate, the liquid film does not follow the shape of the structured wall anymore, a static holdup (recirculation zone) form in the cavities and grows as the Reynolds number increases until covering most of the packing cavities. The present work gives the liquid hold-up evolution for each liquid film flow regime according to the Reynolds number and the dimensionless amplitude of the corrugation. Concerning the liquid side mass transfer, it is found that the liquid side mass transfer is well predicted by the Higbie (1935) theory provided that adequate velocity and length scales are considered for exposure time determination. The exposure time of fluid element at the interface corresponds to the ratio between the curvilinear distance between two periodic corrugation contact point and the interface velocity. An exposure time model is proposed taking into the account physical and geometric parameters. (C) 2012 Elsevier Ltd. All rights reserved.