Numerical Study on the Dominant Condensation Mechanism in the Cross-Flow Transport Membrane Condenser

Abstract

Abstract Interest in the use of transport membrane condenser (TMC) technology for heat and mass recovery from the flue gas of the power plant has been in an increase in recent years. TMC is based on using nanoporous ceramic membrane as a tube wall of the heat exchanger. The heat and mass transfer from the TMC tube bundle have been studied experimentally and numerically, and several models have been proposed to calculate the condensation rate. Researchers have reported that the transport of the flue gas through the membrane condenser involves two mechanisms: the wall condensation and the capillary condensation. However, the dominant condensation mechanism is still under debate and needs more investigation. In this study, a single-phase multi-species model coupled with mixed condensation model was used to investigate the dominant condensation mechanism at different membrane porosity and water vapor mass fraction. The Numerical simulation was executed using ANSYS/FLUENT 2021 R1 software. The mixed condensation model, which is based on the wall condensation and capillary condensation, was written in the user-defined functions (UDF). The flue gas turbulent was modeled using the shear stress transport SST k-ω turbulence model. The results showed that, at the same membrane porosity and water vapor mass fraction, the wall condensation mechanism is the dominant condensation mechanism. As the porosity increases from 0.15 to 0.50, the percentage of the capillary condensation increases from 17% to 50%, which impact in a decrease in the wall condensation percentage from 83% to 50%. Furthermore, about 69% to 87% of the total condensation rate was obtained from the wall condensation mechanism, as a result of an increase in the water vapor mass fraction from 8% to 21%. Consequently, the wall condensation was able to recover more latent heat than the capillary condensation mechanism. The convection Nusselt number decreases as the porosity increases, because of the significant reduction in the effective thermal conductivity of the nanoporous ceramic tubes.