CFD aided design and analysis of a precooler with zigzag channels for supercritical [formula omitted] power cycle

Abstract

Printed circuit heat exchangers (PCHEs) with zigzag channel geometry have frequently been investigated under recuperator conditions (0.7<Pr<2.2) of the supercritical carbon dioxide Brayton Cycle (sCO2-BC). However, the characteristics of the zigzag channel under precooler conditions (1<Pr<20) of sCO2-BC are still unclear. For this reason, a 3D Reynolds Averaged Navier–Stokes (RANS) model is developed and validated to scrutinize the impact of various parameters on the design of precooler of sCO2-BC using zigzag channels. To ensure the accuracy of the numerical model, sharp variations in the thermo-physical properties of carbon dioxide are incorporated by providing high-resolution real gas property (RGP) tables to the solver. Additionally, a new data reduction method is devised and implemented to account for the adverse variations in carbon dioxide's thermophysical properties. Obtained results suggest that choosing smaller design point values for channel mass flow rates of CO2 reduce the pressure losses significantly; however, the consequent temperature profiles can draw the undesirable pinch point location inside the heat exchanger. Although pinch points can be avoided for precooler using higher channel mass flow rates, such designs are incredibly compact and exhibit poor hydraulic performance. Furthermore, it was found that pressure losses at the cold side were significantly higher in comparison with the hot side. However, it is shown that the hydraulic performance of the cold side can be improved substantially using sandwiched channel configuration without compromising the thermal characteristics of the precooler.