Printed circuit heat exchanger design and performance analysis near the CO2 critical point for S-CO2 power cycle applications

Abstract

The supercritical carbon dioxide (S-CO2) power cycle has been investigated as the next generation power conversion cycle to replace conventional steam Rankine cycles. The S-CO2 power cycle has a large potential to be a highly efficient and compact system due to the small compression work and remarkable transport properties of the supercritical state of CO2. Also, the S-CO2 power cycle can achieve high thermal efficiency at moderate turbine inlet temperature (450~650℃), and therefore it can be applied to various heat sources including nuclear. However, one of the engineering issues in S-CO2 technology is designing a system component which operates near the CO2 critical point (30.98℃, 7.38MPa). Because the thermo-dynamic properties change dramatically in vicinity of the critical point, conventional design methods based on constant property assumptions are not applicable. Furthermore computational analysis can be sensitive due to the non-linear property changes. Recently, KAIST research team focused on identifying the engineering issues of compact heat exchanger and optimized design for the S-CO2 cycle. To predict the thermal hydraulic performance of a heat exchanger, an one-dimensional printed circuit heat exchanger (PCHE) design and analysis code was developed; namely KAIST_HXD. A lab-scale PCHE, which was designed by the developed code, was tested under various conditions including the critical point of CO2. The heat transfer performance and the pressure drop of a heat exchanger are verified by experiments, and CFD analysis was conducted to modify the related correlations.