Thermal and flow characteristics of an electrohydrodynamically enhanced capillary evaporator

Abstract

<p> Experimental investigations have been conducted for an Electrohydrodynamically enhanced capillary evaporator (EHD-ECE) for enhancement of liquid evaporation, hence the flow rate. A capillary evaporator has a liquid channel inlet and a vapour channel exit. Inside the evaporator is a porous media that separates the liquid and vapour, which is also responsible for the capillary action. When an external electric field is applied inside the liquid side of the evaporator, the capillary action may be enhanced due to external body forces. Voltage was applied to the 3.lmm electrode, in the centre axis of the evaporator liquid channel. The environmentally friendly HFC-134a is used as the working fluid. The coaxial cylindrical evaporator centre is liquid filled and surrounded by a porous polyethylene wick, where the vapour channels are located on the other side of the wick. Heat is applied to the outer diameter of the evaporator. Experiments were conducted for applied heat loads from 0 to 80W and applied electric fields of de voltages from 0 to -5kV and 5kV, as well as frequencies ranging from 5-200Hz with applied pulse voltages of -IOkV and 5kV. Thermal temperatures of the liquid inlet, vapour exit, and evaporator wall, pressure difference across the evaporator, system pressure and liquid flow rates are measured and analysed. </p> <p> The experimental results show that the vapour flow rate increases with increasing applied voltages and enhancement up to a maximum of 202% was achieved when 5kV de was applied with a heat input of 80W. The polarity of the applied voltage had only a slight effect as slightly higher flow rate enhancements were observed. The vapour flow rate was also enhanced for applied pulse voltage, where the vapour flow rate increased with increasing frequencies between 50Hz to 200Hz. </p> <p> With the application of de and pulsed electric fields, the vapour flow rate due to the external body forces acting on the liquid-vapour interface are enhanced. Future work is required to fully understand the phenomena and more optimization studies are required for the EHD-CPL. </p>