Effect study of super-critical CO2 parameters on heat transfer performance of U-shaped double-pipe heat exchanger

Abstract

This paper presents a numerical study on the heat transfer performance of U-shaped double-pipe heat exchanger for the concentrated solar power system. The effects of the mass flow rate, temperature and pressure of inlet super-critical CO2 are evaluated. The results show that due to the effect of centrifugal force, temperature and flow velocity distribution divergences happen in the elbow part of the double-pipe. That can enhance the heat transfer performance. With the inlet super-critical CO2 mass flow rate increased, the convection heat transfer coefficient and Nusselt number of the super-critical CO2 both increase. When the inlet super-critical CO2 mass flow rate increases to 0.6 kg s−1, the maximum local average convection heat transfer coefficient and Nusselt number of the super-critical CO2 are 7120.0 W m−2K−1 and 1892.7. By increasing the inlet super-critical CO2 temperature or pressure, the convection heat transfer coefficient of the S–CO2 can be increased. With the inlet super-critical CO2 temperature increased from 700.0 K to 780.0 K, the maximum local average convection heat transfer coefficient of super-critical CO2 increases from 5034.5 W m−2K−1 to 5149.1 W m−2K−1. Compared with the other two parameters, the effect of inlet super-critical CO2 pressure on the heat transfer performance is relatively smaller.