Thermal evaluation of heat exchanger and a dry-cooled supercritical CO2 mixture Brayton cycle based on three-dimensional and one-dimensional models: Key factors and potential applications

Abstract

High ambient temperatures in the desert environment and heat capacity mismatch of printed circuit heat exchanger (PCHE) are always main factors that limited cycle efficiency of supercritical CO2 Brayton cycle (SCBC). The SCBC was established to obtain the operating parameters of precooler, low temperature recuperator (LTR) and high temperature recuperator (HTR) in this paper. The performance evaluation factors were developed and applied. The findings demonstrated that the precooler total heat transfer coefficient (HTC) peaked near the pseudo-critical temperature. Smaller hot-side pressure, larger hot-side and cold-side mass flux could improve heat transfer performance (HTP) of the precooler. The CO2-H2S in the precooler had larger HTC and pressure drop (ΔP), the CO2-Propane in the LTR and HTR had larger total HTCs and ΔP for the same critical temperature. Heat transfer correlations about the precooler of pure CO2 and CO2 mixtures were proposed. A conclusion was drawn by analyzing the performance evaluation factors that the PCHE using CO2-H2S for the precooler and CO2-Propane for the LTR and HTR could achieve better HTP under the same ΔP, but had the smaller effectiveness under the same ΔP. The CO2-H2S had the potential for practical application because of the larger cycle thermal efficiency and relatively good tolerance to the change of critical temperature.