Experimental study of the thermal performance of an assisted-gravity heat pipe using two working fluids: Water and FC-72

Abstract

In this work, an assisted-gravity heat pipe has been designed and built to study the performance of a thermosyphon of 680 mm overall length of which the lengths of the evaporator and condenser zones are respectively of 41 and 190 mm. The parameters affecting the thermal hydraulic characteristics are the input power (10 to 200W), the working fluids, namely water and the FC-72, the filling rate of the working fluid varying from 7 to 161% (with regards to the volume of the evaporator) and an aspect ratio which is the ratio of the evaporator length to the overall heat pipe one, fixed at 0.06. The experimental results showed that the best performances of the thermosyphon are obtained for a power of 100 W, with a corresponding water heat transfer coefficient  reaching approximately a maximum of 3000 W/K.m2 for a filling rate of 161% while that of FC-72 does not exceed 1800 W/K.m2 whatever the filling rate is, except for 7%.

Keywords: Thermosyphon- Biphasic- Phase change- filling rate- Heat transfer coefficient- Thermal resistance