Numerical Study of Convection Heat Transfer of Supercritical CO_2 in a Vertical Mini-tube

Convection heat transfer of CO2 at supercritical pressures during cooling in vertical circular mini-tube with inner diameter of 0.4 mm was studied numerically using Realizable turbulent model.The effects of pressure,cooling water mass flux,CO2 mass flow rate and CO2 inlet temperature on the heat transfer coefficient were investigated.The simulated results indicate that cooling water mass flow rate and CO2 inlet temperature have little influence on convection heat transfer of supercritical CO2,but CO2 inlet mass flow rate and inlet pressure affect significantly.With the increasing of CO2 mass flow rate,coefficient of heat transfer improves dramatically.The inlet pressure is closer to the critical pressure,the change of coefficient of heat transfer near critical point is more drastically,and the peak value is higher.