Effect of frequency on two-phase flow regimes under high-voltage AC electric fields

The effect of high-voltage AC electric fields on two-phase flow regime redistribution for flowing refrigerant HFC-134a in a circular tube has been investigated. In particular, the effect of the frequency of an applied square wave between 0 and 8 kV was studied for frequencies in the range 4 Hz to 1 kHz. The electric field was applied through a central electrode along the centerline of the tube. The flow regime redistributions under the applied electric field were visualized using a high-speed camera at frame rates up to 2000 fps. The experiments were performed for a constant mass flux of 55 kg/m2 s and test-section outlet vapor quality of 30%. These flow conditions correspond to stratified flow with the liquid level below the electrode (without EHD). At the low-frequency range (4 Hz⩽f⩽10 Hz), the two-phase flow was able to respond to the repeated on/off action of the applied square-wave signals causing liquid extraction from the bottom stratum to the vapor phase. In the intermediate range of frequencies (10 Hz