Multiscale coupling mechanisms of flow and phase‐change dynamics mediated by geometric curvature in heat pipe condensers

Abstract This study uses a validated 3D transient Volume of Fluid ‐ Continuous Surface Force (VOF‐CSF) model to elucidate curvature effects on phase‐change dynamics in gravity‐assisted heat pipes (GAHPs) condensers. Simulations of cone angles (15°–85°) reveal the condenser‐side heat‐transfer coefficient (HTC) has a non‐monotonic relationship with curvature, peaking at 65°: experimentally, HTC rises from 838 to 1370 W m −2 K −1 (15°–65°, ~63.5% enhancement), while simulated HTC increases from 1025 to 1569 W m −2 K −1 (~53.1% gain). Optimal performance comes from curvature‐induced turbulence with interfacial renewal; angles >65° cause vapor entrapment and liquid‐film thickening, increasing thermal resistance. Velocity fields transition from laminar to multiscale recirculation; temperature gradients shift from unidirectional to coupled. Experimental validation confirms model accuracy, with discrepancies from contact resistance and non‐condensable gases. Based on the 65° optimum, a modular GAHP heat exchanger is designed for medium‐low temp waste‐heat recovery, providing insights and design principles for heat‐pipe systems.