Geometric and operational analysis of a heat recuperator operating with s-CO2 near the pseudocritical region

Abstract

Heat recuperators are commonly used in numerous industrial processes, including power generation plants. Additionally, with interest in power cycles operating with supercritical fluids, such as carbon dioxide (s-CO2), a better understanding of heat exchangers operating with the hot and cold fluids near the pseudo critical points is needed. Therefore, this study models a printed circuit heat exchanger operating with s-CO2 on the hot and cold sides using a finite volume formulation. The model considers the convective resistances associated with the s-CO2 on both sides of the heat exchanger, as well as the conductive resistance due to the solid wall separating them. The recuperator’s behavior was analyzed while varying its geometrical (diameter, length and number of channels) and operational (inlet pressure and temperature on both sides) parameters. Thermal and hydraulic figures of merit were considered, such as the heat exchanger effectiveness, thermal conductance and pressure drop. The results showed that similarly to geometrical parameters, the operational conditions also had a significant effect on the figure of merits considered, especially near the pseudo critical line, a region characterized by major property changes. In addition, a multi-objective optimization process was implemented returning a series of optimal solutions, which were presented as a Pareto curve. Among the results obtained, it is worth mentioning that an optimum hot s-CO2 inlet temperature was obtained for the entire front at roughly 650 K, while there were a minimum number of channels and a cold s-CO2 inlet pressure, close to 155,000 and 15 MPa, respectively, limiting the Pareto front, which were related to the maximum effectiveness.