Enhancing thermal performance of a heat-pipe module for air-cooled servers using self-rewetting fluids

This study experimentally investigates the performance of an air-cooled thermal module consisting of a fin stack integrated with six heat pipes charged with various self-rewetting fluids (SRWFs) for CPU cooling. Results show that thermal performance is strongly dependent on working fluid composition. Among the tested fluids, the 4 wt% 2-butanol solution delivers the most significant enhancement at high heat loads, achieving an optimal operating capacity of 500-550 W. This capacity is substantially higher than that inferred from single-pipe tests, despite the less favorable condenser boundary conditions in the air-cooled module. The improvement suggests an effective module-level enhancement, likely associated with heat sharing among multiple heat pipes and extended activation of inverse Marangoni convection. Dilute long-chain alcohol solutions (heptanol and octanol) reduce case temperature by up to 5.6°C at moderate heat loads but provide limited extension of the optimal operating capacity. Moreover, heat pipes located closest to the hotspot do not necessarily activate earlier or carry a dominant share. Instead, heat transport is uneven among different heat pipes at low heat loads. As the heat load increases, the contributions of individual heat pipe become more comparable, indicating more uniform utilization. Thermal resistance analysis reveals that the primary bottleneck resides in the condenser-to-ambient path governed by air-side convection, whereas the internal heat pipe and contact resistances are relatively minor. Nevertheless, with an optimized SRWF, the case temperature can still be maintained below 70°C at 500 W. These findings highlight the importance of jointly optimizing SRWF properties and module design for high-performance cooling.