Study of geometrical influence on heat transfer characteristics in a cross-wavy primary surface heat exchanger regarding thermal resistance method

The flow and heat transfer performance of primary surface heat exchangers (PSHEs) with cross-wavy (CW) structures is numerically investigated in this study. The influence of cross-sectional shape, amplitude, and period on thermohydraulic characteristics is assessed, while the local convective thermal resistance and temperature gradient layer thickness are evaluated. Results reveal that the circular channel with moderate amplitude and period demonstrates the best heat transfer rate. Moreover, the L is crucial for both friction and heat transfer performances in PSHEs, whereas the cross-sectional shape significantly influences the comprehensive performance. The optimal case 10 achieves a maximum average Nu of 29.1 at Re = 2471, corresponding 93.3 % enhancement compared with case 4 (Nu = 15.1). The local thermal resistance is reduced from 5.784 m2 K·W−1 to 0.591 m2 K·W−1. It is also found that narrow geometries contribute to higher local thermal resistance, thicker temperature gradient layers, implying that geometric optimization in such regions can further improve heat transfer. Moreover, empirical correlations for the Nusselt number and Darcy friction factor are developed as functions of Reynolds number and the La/L ratio based on the analysis of local convective thermal resistance and temperature gradient layer.