Numerical modelling and performance maps of a printed circuit heat exchanger for use as recuperator in supercritical CO2 power cycles

Abstract

In heat to power systems with CO2 as working fluid in the supercritical state (sCO2), heat exchangers account for nearly 80% of the capital expenditure. Therefore, improved design, materials and manufacturing methodologies are required to enable the economic feasibility of the sCO2 technology. In this study, a comparison of different modelling methodologies for Printed Circuit Heat Exchangers (PCHE) is proposed to identify strengths and weaknesses of both the approaches. The elementary heat transfer unit of a PCHE recuperator for sCO2 applications is firstly modelled using 1D and 3D CFD methodologies respectively; implemented in GT-SUITE and ANSYS FLUENT software. After the comparison in terms of heat transfer performance and pressure drops, the 1D approach is used to model a 630kW PCHE recuperator. The PCHE model calibration on the design point, followed by its validation against off-design operating points provided by the manufacturer, eventually enabled to broaden the simulation spectrum and retrieve performance maps of the device. The CFD models comparison shows a good agreement between temperature profiles. However, the local heat transfer coefficient, modelled in the 1D approach through the Dittus-Boelter correlation, experiences a +10% offset on the hot side and a -20% on the cold one with respect to the 3D CFD calculations. Besides, the performance maps of the full scale PCHE recuperator show that the maximum temperature of the hot stream impose a greater influence than the maximum pressure of the cold one in terms of overall heat transfer coefficient. Nonetheless, both these operating parameters contribute to affect the heat exchanger effectiveness.