Numerical and experimental analysis of thermodynamic properties of plate heat exchangers at high Reynolds number based on different single-phase fluid structures

The structural design of plate heat exchanger (PHE) is pivotal for overcoming the limitations of heat flux density. This study investigates the heat transfer mechanisms of single-phase and two-phase flows in different structures, revealing distinct heat transfer enhancement patterns. A numerical model of PHE was first established, in which the heat transfer area of the offset fin structure was approximately 1.5–2 times that of the dimple. Simulations of single-phase demonstrated that at Reynolds number (Re) between 2000 and 2500, the offset fin structure achieved Nusselt number (Nu) of 20, which was 1.4 times that of the dimple, with a comparable pressure drop of around 9 kPa. Subsequently, two PHEs were fabricated using brazing, and a performance test rig was constructed. Experimental results further validated the single-phase conclusions from the simulations. Moreover, for two-phase, Nu of the PHE with the offset fin structure reached 800 at Re above 5000, which was 1.2 times that of the dimple. The significant difference in heat transfer performance between single-phase and two-phase flows highlighted distinct enhancement mechanisms: the heat transfer area was the decisive factor for single-phase heat transfer performance, while the intense disruption of thermal boundary layer dominated the two-phase side. Finally, empirical correlations for heat transfer and pressure drop on both sides of the PHE were derived. Experimental data verified that over 95 % of the fitted Nu and f had errors of less than 20 %. Therefore, the findings on the key factors influencing PHE heat transfer provide significant engineering insights for breaking the heat flux limits in traditional PHE structural designs.