Thermal Performance of Embedded Oscillating Heat Pipe With Dielectric Fluid FC-72 and Direct Condenser Heat Output Measurement

Abstract Very few experimental studies on oscillating heat pipes (OHPs) have employed FC-72 as the working fluid, despite its demonstrated capability to initiate OHP operation at significantly lower heat inputs. Moreover, the thermal resistance of FC-72-charged OHPs has not been reliably characterized, as existing studies have not utilized direct measurements of the heat dissipated by the condenser. In this work, an embedded OHP is experimentally studied using the dielectric fluid FC-72. Experiments were conducted at a filling ratio (FR) of 0.62 and under dry conditions. The heat input at the evaporator was varied from 60 W to 200 W, while the heat output at the condenser was directly measured to characterize the thermal transfer capability of the OHP. Notably, this study uniquely provides direct experimental measurements of condenser heat output for OHPs charged with FC-72, an aspect not previously addressed in the existing literature. Heat transfer performance and fluid flow in the channel were examined during operation. The minimum thermal resistance of the OHP was found to be 0.139 K/W, representing a 28.7% reduction compared to the thermal resistance under dry conditions at the same heat input. Furthermore, the thermal resistance achieved in this study is the fourth lowest reported in the literature for OHPs using FC-72 as the working fluid.