Experimental study of heat transfer performance of wettability controlled Multi-Tube Thermosyphon Heat Sink

Abstract

This study investigates the thermal performance of a multi-tube thermosyphon heat sink that integrates a vapor chamber with multiple thermosyphons operating via phase-change heat transfer. The effects of surface wettability on boiling and condensation heat transfer characteristics were systematically analyzed for both the boiling and condensing surfaces. For the condensing surface, a hydrophilic surface disrupted the return of condensate to the boiling section, thereby reducing thermal performance. In contrast, a hydrophobic condensing surface facilitated condensate departure and improved liquid return, resulting in a 6.81% reduction in thermal resistance compared to the bare surface. For the boiling surface, a hydrophobic surface enhanced thermal performance at low heat fluxes by promoting early nucleate boiling. However, at higher heat fluxes, rapid film boiling decreased the critical heat flux (CHF) and degraded performance. Conversely, a hydrophilic boiling surface exhibited delayed boiling initiation at low heat flux but delivered superior performance at higher heat fluxes due to improved liquid supply through enhanced wettability. Among the configurations tested, a boiling surface combining hydrophobic and hydrophilic regions demonstrated the best performance. At low heat fluxes, hydrophobic regions promoted rapid nucleate boiling, while at high heat fluxes, hydrophilic regions ensured effective liquid supply, enabling efficient heat transfer over a wide operating range. To optimize the design of bi-philic surfaces, surfaces featuring pattern sizes of 5.2 mm, 2.6 mm, 3.5 mm, and 2 mm, and pitches of 8.64 mm, 4.51 mm, 8.3 mm, and 5 mm were fabricated and tested. The pattern with a 2 mm size and 5 mm pitch yielded the lowest thermal resistance, achieving a 12.64% reduction compared to the bare surface. Additionally, external plate fins were attached to the condenser to evaluate the effect of fin structures on heat transfer performance. The thermal resistance was reduced by up to 39.4% through the application of fins and further reduced by up to 43.7% by additionally controlling the wettability of the internal boiling and condensing surfaces. In addition, the MTTHS, which includes a vapor chamber, exhibits significantly lower spreading resistance compared to heat sinks without a vapor chamber, thereby maintaining excellent heat transfer performance even as the heat source size decreases.