Effect of Working Fluid-Filling Ratio Combination on Thermosyphon Performance as Add-In Enhancer for Indoor Air Conditioning Devices

Abstract

An experimental study is presented to account for the implementation of a two-phase closed thermosyphon pipe, for energy-saving purposes, in air conditioning systems in the context of COVID-19. The experimental setup consisted of a 0.5 m × 0.0127 m type L copper pipe which was employed as the body of the heat exchanger; an electric resistance heater of 0.1 m length located at the bottom; and a 0.25 m length water-cooled concentric condenser located at the top. The evaluation was conducted employing acetone, ethanol, and distilled water as working fluids; ranging the heat supplied at the evaporator from 25 to 125 W and the filling ratio from 20% to 40% of the total inner volume of the thermosyphon. From the data obtained, it was found that ethanol is the working fluid most susceptible to changes in operation conditions. Contrarily, distilled water was found to deliver consistent performance, up to a point that, for the analysed setup, it is considered to be independent of both, heat flow supplied at the evaporator and thermosyphon filling ratio. Meanwhile, acetone was found to be the only fluid tested that displays a directly proportional behaviour between heat absorption and dissipation. From compiling experimental data, response surfaces were constructed and used as direct and rough optimization tools. The information provided by this approach is considered to be particularly useful and is introduced for modelling and design purposes. Based on the results, it was found that acetone, within operation ranges of 34%<ϕ<40% and 75 W<Q˙Evap<125 W, was the most suitable working fluid to use in a two-phase closed thermosyphon for energy-saving purposes in air conditioning applications.