Numerical modeling and transient analysis of printed circuit heat exchangers in the supercritical CO2/propane mixture Brayton cycle

CO₂/propane mixtures benefit the safe operation of the supercritical Brayton cycle while improving economic efficiency and mitigating environmental impact. Due to the intermittency of energy resources, understanding the dynamic characteristics of the supercritical mixture Brayton cycle is essential. The transition time of the cycle depends on the total time of the unsteady-state heat transfer. As a typical heat exchanger, the transient analysis of the printed circuit heat exchanger (PCHE) is necessary and significant. In this paper, the dynamic response of the straight PCHE in the supercritical CO₂/propane mixture Brayton cycle is thoroughly studied. First, the dynamic behavior of the mixture-mixture PCHE is analyzed when the inlet temperature or mass flow rate abruptly changes. Furthermore, the equilibrium times of the mixture-mixture PCHE under different disturbances are compared. CO₂/propane mixtures are more favorable for the stability of the parameters (outlet temperature and pressure drop). The mixture-mixture PCHE exhibits better flow and heat transfer properties than the CO₂CO₂ PCHE. Compared to CO₂, CO₂/propane mixtures could reduce the equilibrium time by more than 32 % when the molar fraction of propane is equal to 0.5. However, the outlet temperature of the mixtures in the hot channel is higher than that of CO₂, because the energy is not fully utilized.