Numerical investigation of thermal and hydraulic characteristics of sCO2-water printed circuit heat exchangers with zigzag channels

Abstract

Since the precooler and the recuperator are the largest components of a supercritical carbon dioxide Brayton cycle, their design can substantially affect the performance and size of the whole system. Although the design of a precooler with zigzag channel geometry as an alternative to straight channels can reduce its size significantly, the applicability of available correlations (e.g. 0.7 < Pr<2.2) for the zigzag channel geometries is limited to the operational range of recuperators only. The current study, therefore, aims to develop correlations and understating of the complex flow and heat transfer characteristics in the zigzag channel printed circuit heat exchangers (PCHEs) operating under precooler conditions (2.2<Pr<13) of supercritical carbon dioxide Brayton cycle(sCO2-BC). Thermal and hydraulic characteristics of the PCHEs are computed numerically for a wide range of Reynolds numbers (5000<Re<7000) and Prandtl number (2.2<Pr<13). Also, a new data reduction method based on segmental averaged values has been proposed to handle adverse variations in the thermophysical properties of CO2 under precooler conditions. To ensure accurate evaluations, steep variations in the thermophysical properties of CO2 are implemented by supplying high-resolution real gas (RGP) property tables. Results suggest that thermal and hydraulic characteristics associated with zigzag channel vary substantially along the length of heat exchanger thus the conventional data reduction methods based on the channel average values cannot be used for true evaluations. Instead, segmental average values are used to develop pressure drop and heat transfer correlations for a broader range of Reynolds number and Prandtl number. The proposed correlations should be useful in the design of compact heat exchanger systems using zigzag channels for a wider range of cooling loads.