Effect of flow curvature on the thermal-hydraulic performance of zigzag minichannels in printed circuit heat exchangers (PCHEs)

This study investigates the effect of flow curvature on the thermal–hydraulic performance of zigzag minichannels in printed circuit heat exchangers (PCHEs) using supercritical helium as the working fluid. A dimensionless bending number (β) is introduced as a geometric parameter to characterize channel curvature and to provide a basis for analyzing the development of curvature-induced flow structures and associated transport behavior. Three-dimensional CFD simulations are performed over Reynolds numbers of 1000–2000 and curvature ratios (rb/dh = 1.309–3.273) to evaluate heat transfer (Nusselt number, Nu) and hydraulic losses (friction factor, f). All configurations are compared under identical Reynolds number conditions to isolate geometry-induced effects. In addition to the classical performance evaluation criterion, a thermal–friction performance index (TFPI = Nu/f) is employed to examine performance under friction-limited operating conditions typical of compact PCHE systems. The results indicate that increasing geometric curvature intensifies secondary vortical structures, enhancing convective heat transfer while simultaneously increasing pressure losses. A curvature-dependent transition region (β ≈ 0.4–0.6) is identified, where thermal enhancement begins to plateau while frictional penalties increase more rapidly. This behavior reflects the emergence of curvature-induced transport regimes rather than a single optimal geometry. New correlations for the Nusselt number and friction factor are developed as functions of Reynolds number and geometric parameters. The findings provide both physical insight and practical design guidance for compact PCHE systems operating under constrained-flow conditions where hydraulic losses significantly influence performance.