Electrohydrodynamic Condensation Heat Transfer Modulation under dc and ac Applied Voltages in a Horizontal Annular Channel

An experimental study of direct (dc) and alternating current (ac) EHD induced condensation heat transfer modulation for a single tube condenser has been conducted. A single-pass, counter-current heat exchanger with a rod electrode placed concentric to the tube was studied. Experiments were conducted for R.134a with inlet qualities of 50 - 90%, heat flux of 11 kW/m(2), mass fluxes from 75 kg/m(2), to 400 kg/m(2) s and applied voltages from 0 kV to 8 kV dc and 0 kV to 10 kV RMS ac (30 kV peak to peak) for low frequency (63 Hz) sinusoidal waveforms. The condensation results show that the average heat transfer coefficients and pressure drops can be modulated by as much as 3-fold using EHD. Through application of ac, as opposed to dc voltages, the pressure drop and heat transfer can be independently changed. This is not possible in traditional, passive heat exchangers. The differences are attributed to an oscillatory flow pattern, a function of frequency, hypothesized to be the continuous transition between flow regimes due to the approximate "on/off" effect of electric field applied under an ac voltage.