Effect of flow rate on condensation of CO2-water vapor mixture on a vertical flat plate

The presence of non-condensable gas significantly deteriorates the heat transfer of water vapor condensation, and the condensation process of a CO2-water vapor mixture is a key process for CO2 separation and purification. In this study, we fabricated an experimental system to investigate the heat transfer characteristics of the mixed vapor condensation using a CO2 mass fraction of 32-85 % at a flow rate of 0.4-1.2 m/s and surface subcooling of 3-70 K. Liquid film thickness, gas-phase diffusion layer thickness, and interface temperature were calculated based on the double boundary layer model. An increase in the flow rate (0.4-1.2 m/s) improved the mixed vapor heat transfer, especially at high CO2 concentrations, and increased the heat transfer coefficient by 177 % at a surface subcooling of 40 K. The lower the surface subcooling, the greater the effect of the flow rate. As the CO2 concentration increased, the liquid film thickness decreased, whereas the gas-phase diffusion layer thickness increased to 1.7 mm, which is tens and hundreds of times the liquid film thickness. Increasing the flow rate slightly changed the liquid film but significantly reduced the gas-phase diffusion layer thickness and afforded a better heat transfer performance. A new heat transfer correlation equation was fitted, and the error of the predicted value was within +/- 30 %. This study provides fundamental insights for the design of related heat exchangers.