IN-TUBE CONVECTIVE CONDENSATION UNDER AC HIGH VOLTAGE ELECTRIC FIELDS

The effects of alternating high voltage electric fields on heat transfer and pressure drop for tube-side condensation of flowing refrigerant HFC-134a have been investigated. Experiments were performed in a horizontal, single-pass, counter-current heat exchanger with a rod electrode placed along the centre of the tube. Tests were performed with a sine and square wave voltage signals over a range of frequencies, peak-to-peak voltages and DC offset voltage, for a fixed mass flux of 100 kg/m²s, inlet quality of %, and heat flux of 10 kW/m². The heat transfer coefficient was enhanced by a factor up to 2.7 with a similar increase in the pressure drop. An increase in the DC offset voltage and/or the peak-to-peak voltage increased the effective voltage of the applied AC signal, with a consequent increase in both heat transfer and pressure drop. The effect of frequency on heat transfer and pressure drop is strongly influenced by the DC offset voltage and the peak-to-peak voltage of the applied signal. In general, the heat transfer enhancement and pressure drop penalty increased with an increase of frequency at the low frequency range. The effect of frequency is less prominent as the frequency is increased and has a little effect in the high frequency range.