Modelling of CO2 absorption via hollow fiber membrane contactors: Comparison of pore gas diffusivity models

This paper discusses the modelling of CO2 absorption in water as an absorbent via a hollow fiber membrane contactor to predict the performance of the absorption process under various operational conditions. The governing equations are two dimensional. Since, the gas diffusion along the pores is responsible for the mass transfer across the membrane thickness, i.e. both the skin layer and the membrane bulk, how to estimate the effective gas diffusivity has a vital degree of importance. When small pores combined with low pressures are dealt with, a challenging issue appears, i.e. the effective gas diffusivity is a contributive phenomenon, in which, several mechanisms are cooperated. Selecting an inappropriate model, inevitably leads to unrealistic values for the tuning parameters. Conventionally, the Bosanquet equation has been widely used for modelling the gas diffusivity through the membrane pores. In the current paper, it is intended to prove that the Bosanquet model is a limiting form of Wakao et al. model, when we are far enough from the continuum region. The modelling results are compared with six sets of different membranes from the open literature including high and low pressures. The results show that, ignoring the viscous flow contribution in Dg,eff (the Bosanquet gas diffusivity model) causes underestimation of the absorption flux. Based on the observations, there is a meaningful consistency between the model and the experimental data once the contribution of the viscous flow in Deff (the Wakao et al. gas diffusivity model) is considered.