Numerical simulation of H2O with a large amount of CO2 condensation heat transfer characteristics outside horizontal tubes buddle under sub-atmospheric pressure

Abstract The outlet mixture gas of CCS and coal supercritical water gasification systems after turbine is H2O and CO2, whose pressure is around 7 to 20 kPa. While, the condensation heat transfer of H2O with a large amount of CO2 before the outlet of condenser is not well studied. The fluid flow, heat transfer and condensation transfer for H2O/CO2 mixtures has been studied in this paper. Volume of fluid model, species transport model and a phase change model written by User Design Function for energy, mass and component source terms were used to study H2O/CO2 condensation outside a horizontal tubes buddle. The results show that the predicted heat transfer coefficients agree well with previous experimental data. The variation of liquid film on tube wall surface with the time elapsing and the distribution of streamlines, velocity vector, liquid volume fraction and temperature near the liquid-vapor interface region has also been investigated. The effects of pressure, velocity, surface subcooling, and non-condensable gas mole fraction on the liquid and diffusion gas film thickness, heat transfer coefficient and latent heat transfer coefficient of CO2/H2O distribution along the circumferential direction of tubes have also been studied. The liquid film thermal resistance is decreased by the growth of non-condensable gas, velocity and pressure, on the contrary, increased by the rise of surface subcooling. Meanwhile, the total heat transfer coefficient is decreased with the increasing of CO2 fraction and surface subcooling, while increased with the augment of pressure and velocity.