Effect of Dropwise Condensation on the Thermal Performance of a Two-Phase Closed Thermosyphon

This study investigates the enhancement of thermal performance in a two-phase closed thermosyphon (TPCT) by promoting stable dropwise condensation on the condenser surface. Conventional TPCTs rely on filmwise condensation, which results in additional thermal resistance and degrades overall heat transfer efficiency. To address this, we developed a robust and hydrophobic ceria/PDMS/Teflon composite coating that maintains dropwise condensation even under high heat flux conditions without flooding or coating degradation. A custom-built, half-cylindrical visualization setup allowed in-situ visualization of internal two-phase flow and revealed the influence of condensation mode on system behavior. While dropwise condensation significantly improved local heat transfer coefficients at the condenser, the condensate was returned to the evaporator as a form of discrete droplets rather than a continuous film, resulting in decreased evaporation performance and increased overall thermal resistance. These findings highlight the complex interdependence between condensation and evaporation processes in TPCTs and suggest that surface modification of both sections is essential for overall system optimization.