A generalized multifluid optimal pressure for heat exchangers operating with supercritical fluid

Abstract

ABSTRACTDistinct thermophysical properties encountered in supercritical fluids operating near the critical point have made them strong candidates for working fluids in various engineering applications. Particularly due to the existence of heat capacity maxima near the critical point, heat transfer involving supercritical fluids and their employment in power generation systems have received special attention. In this paper, the existence of optimal operating pressures that maximize the global conductance of supercritical heat exchangers is demonstrated. Analysis of the behavior of the isobaric specific heat along the heat transfer process shows that optimal performance is achieved when the average isobaric specific heat is maximized. Consequently, optimal pressure maps can be created to assist heat exchanger design for various combinations of inlet temperatures and heat transfer rates. Furthermore, it is demonstrated that simple dimensionless groups can correlate—with a mean absolute error (MAE) of 0.0332—the optimal operating pressures of up to 122 different fluids. In addition, it is shown that the correlation is even stronger closer to the critical point and for separate classes of fluids, where MAE can be as low as 0.0103 for triatomic substances.