A Reynolds mass flux model for gas separation process simulation: I. Modeling and validation

Separation process undertaken in packed columns often displays anisotropic turbulent mass diffusion. The anisotropic turbulent mass diffusion can be characterized rigorously by using the Reynolds mass flux (RMF) model. With the RMF model, the concentration and temperature as well as the velocity distributions can be simulated numerically. The modeled Reynolds mass flux equation is adopted to close the turbulent mass transfer equation, while the modeled Reynolds heat flux and Reynolds stress equations are used to close the turbulent heat and momentum transfer equations, so that the Boussinesq postulate and the isotropic assumption are abandoned. To validate the presented RMF model, simulation is carried out for CO2 absorption into aqueous NaOH solutions in a packed column (0.1 m id, packed with 12.7 mm Berl saddles up to a height of 6.55 m). The simulated results are compared with the experimental data and satisfactory agreement is found both in concentration and temperature distributions. The sequel Part II extends the model application to the simulation of an unsteady state adsorption process in a packed column.

Anisotropic turbulent mass diffusivity in a steady-state absorption process of CO2 into aqueous NaOH solutions is characterized (see figure) by using the proposed Reynolds mass flux model. Distributions of the OH− concentration are obtained, which show the details of the behaviors of the absorption process in a packed column. The agreement between the simulations and experimental measurements for OH− concentration distribution is satisfactory, thereby confirming the validity of the proposed Reynolds mass flux model. It also demonstrates that more precise simulation can be obtained if the anisotropy of turbulent mass diffusivity is taken into account.Figure optionsDownload as PowerPoint slide