Influence of surfactants on thermal performance of Al2O3/water nanofluids in a two-phase closed thermosyphon

An experimental study was conducted to investigate the effect of surface tension and thermal conductivity of distilled water (DW) and 0.5 wt% alumina nanofluid with or without 1.5 wt% SDBS on a two-phase closed thermosyphon (TPCT). The TPCT thermal performance test was performed under varying conditions of filling ratio (30%, 50%, and 70%) and heat input power (5, 10, and 15 W). The surface tension and thermal conductivity of the working fluids were compared to confirm the effect of adding 1.5 wt% SDBS to DW and 0.5 wt% alumina nanofluid at 298 and 293 K, respectively. The surface tension of the DW decreased by approximately 58.7%, while the thermal conductivity decreased by approximately 2.1%. When the thermal conductivities of the DW and alumina nanofluids were almost the same, the decrease in the surface tension of the working fluids, approximately 6.7%, could reduce the thermal resistance. Even with a 58.7% decrease in surface tension and 2.1% decrease in thermal conductivity, the thermal resistance of the TPCT decreased. However, with a 58.3% decrease in surface tension and 5.6% decrease in thermal conductivity, the thermal resistance increased.