The power flow topology of heat transfer systems at supercritical conditions for performance analysis and optimization

Heat transfer processes with supercritical fluids are more complex than those with ordinary fluids due to the drastic variation of physical properties. In this study, with consideration of the changes of specific heat and heat transfer coefficient, the power flow topology of a multi-loop heat exchanger network is developed to investigate heat transfer processes at supercritical conditions. Simulation of a cooling process with supercritical CO2 validates the newly proposed method, where the maximum relative error of heat transfer rate is −2.72%. Meanwhile, optimization of a heat exchanger network discovers several design criteria for the optimal heat transfer performance. For instance, the mass charge of CO2 in the heat exchanger network influences its supercritical heat transfer performance significantly, which has the optimal value. Furthermore, the optimal mass charge nearly keeps constant with the heat transfer rate and the temperature boundaries, and increases linearly with the rise of the total heat transfer area, which indicates the optimal average density keeps constant. Substituting this constant density into the state equation of CO2 establishes the matching relation of the temperature range and the pressure for the optimal heat transfer performance.