Performance evaluation of header pipe in heat pipe evacuated tube solar collector by dimpled condensers

Among different solar water heaters, heat pipe-based solar water heaters foster potential solutions to alleviate water scarcity. However, a lower outlet temperature at the outlet section of their header pipe reveals low system efficiency due to limited heat transfer between the flowing fluid and the heat pipe condenser walls. The main aim of this study is to investigate a model manifold header pipe having five condenser sections with a dimple pattern to replicate internal features of heat pipe condensers within an evacuated tube solar collector, and its significance is to provide a comprehensive understanding of flow and thermal behaviour in the header pipe. To conduct research for this purpose, laminar flow simulations alongside Particle Image Velocimetry (PIV) experiments spanning Reynold numbers ( Re ) of 424 and 848 are performed, whereas the flow field and thermal effects for the dimpled configuration are then compared with the benchmark case (without dimples). Results of this research indicate that the dimple pattern affects the shape of the recirculation zone formed downstream of condensers as compared to the benchmark case at both Re . Moreover, the dimple pattern exhibits approximately 1.3% and 4.5% higher vorticity for all five condensers when compared with the benchmark case, at Re = 424 and Re = 848, respectively, which intensifies flow separation and hinders fluid-condenser wall interaction. Furthermore, dimples lead to about 13.3% and 11.4% lower wall shear stress over the surface of all condensers at Re = 424 and Re = 848, respectively, in comparison with the benchmark case, which results in acceleration of flow to maintain mass continuity of fluid. Consequently, the convective heat transfer coefficient over the surface of all condensers decreases by approximately 7.6% and 7.7% at Re = 424 and Re = 848, respectively, in the dimple case when compared to the benchmark case. Contrary to many heat-transfer enhancement studies, dimples are found to reduce thermal performance under the present HP-ETSC operating conditions relative to dimple-related studies in the literature.