Local Flow and Heat Transfer of Supercritical CO2 in Semicircular Zigzag Channels of Printed Circuit Heat Exchanger during Cooling

Abstract

Understanding and predictions of the local thermal-hydraulic performance of supercritical CO2 in channels of printed circuit heat exchanger geometries are of great importance to the design and optimization of the pre-cooler and recuperators in supercritical CO2 cycle. The local flow and heat transfer of supercritical CO2 in horizontal semicircular zigzag channel during cooling near the critical or pseudo-critical point have been numerically investigated in this paper. The effects of thermophysical property variations, mass flux, and the channel geometrical parameters on the flow and heat transfer are discussed. It is found that the extrude angle in the zigzag channel impedes the bulk flow and generates secondary flow, which induces asymmetric flow and temperature distribution, and enhances fluid mixing and mitigates the temperature stratification. A dimensionless secondary flow velocity is adopted to evaluate the influence of secondary flow on the heat transfer, which is more enhanced for cases with relatively large mass flux and in channels with relatively large inclined angle and small pitch length, however, the pressure drop increases meanwhile. Finally, pitch-averaged local flow and heat transfer correlations have been developed based on the numerical results and mechanism analysis accounting for the thermophysical property variations and the channel geometrical parameters.