Enhanced heat transfer in two-phase closed thermosyphons with external liquid-vapor separation

Two-phase closed thermosyphons (TPCTs) are highly efficient heat transfer devices that leverage natural convection to transport heat over substantial distances with minimal temperature gradients. This study investigates the thermal performance of a novel TPCT equipped with an external liquid-vapor separator, compared to a conventional TPCT. The innovative design incorporates an external pathway connecting the condenser and evaporator sections. A comprehensive evaluation was conducted using three working fluids (water, methyl acetate, and ethanol) across a spectrum of heat inputs (50 ≤ Q ≤ 300 W) and filling ratios (25 %, 40 %, 55 %, 70 %, and 85 %). Optimal performance was consistently observed at a 70 % filling ratio for all fluids tested. While the conventional TPCT exhibited superior performance with methyl acetate, the novel TPCT demonstrated enhanced thermal efficiency when charged with water or ethanol. Notably, the novel TPCT using water reduced thermal resistance by approximately 63 % and 60.5 % compared to ethanol and methyl acetate, respectively, at a 50 W heat input and the optimal filling ratio. These findings underscore the critical influence of working fluid selection and offer valuable insights into the thermal characteristics of the novel TPCT. The results contribute significantly to the optimization and design of TPCTs for diverse applications.