Simulation of Pseudo-Critical Line Based on Different Equation of State and Definition of Pseudo-Critical Region

The thermophysical properties of supercritical fluids (SCF) will change drastically in the narrow range of thermodynamic conditions near the pseudo-critical line, and this narrow region of thermodynamic parameters is named the pseudo-critical region. The complex fluctuation of thermophysical properties in the pseudo-critical region makes SCF’s thermal-hydraulic characteristics very different from that of subcritical fluids. Therefore, the normal flow and heat transfer prediction models are no longer applicable among this region. From the perspective of engineering application, it is very necessary to determine the pseudo-critical line and pseudo-critical region as a reference point for adjusting thermodynamic parameters and improving the processing efficiency in the application of SCF. In the paper, supercritical carbon dioxide is taken as the research object. First, the pseudo-critical lines were obtained respectively according to three different equations of state. Then, based on the continuous phase transition theory, the pseudo-critical region was determined by the Ehrenfest equation. Finally, the occurrence area of heat transfer deterioration was in alignment with the proposed pseudo-critical region, and the mechanism that affects the heat transfer deterioration behavior was analyzed.