Predictive modelling of supercritical CO2 dewatering of capillary tubes

Abstract

Supercritical CO2 can be used to mechanically dewater porous materials by expelling moisture via gas bubble pressure and buoyancy during depressurisation. We have developed an Ansys Fluent™ fluid dynamics model to predict the behaviour of the supercritical CO2 dewatering process. This complex model combines the Multiphase Euler-VOF solution method with Interfacial-Area Species-Transport mechanism and user defined functions for non-linear Henry’s law and mixture density. We have effectively modelled dewatering as a series of 40 mm long, water-filled capillary tubes, with internal diameters ranging from 0.1 to 10 mm. The model predicts experimental results well. The mass transfer coefficient required an additional empirical dispersion term, approximately 80 times that of diffusion, when the characteristic Bond number is greater than unity and viscous forces are greater than surface tension forces. The model will contribute to the understanding of fundamental dewatering behaviour and assist with supercritical dewatering plant design.