The effect of electrode polarity on EHD enhancement of boiling heat transfer in a vertical tube

The effect of the electrode polarity on EHD enhancement of boiling heat transfer for R-123 in a vertical tube was investigated experimentally by using a concentric wire/cylinder test section. Either positive or negative high voltage was applied to the cylindrical brass electrode, with the stainless steel tube grounded. It was demonstrated that the positive high voltage gave much greater enhancements and require lower average electric field strength to obtain a maximum enhancement factor than the negative high voltage. A maximum enhancement factor of 2.1 for the positive polarity was obtained at the heat flux of 1.5 kW/m2 with an average electric field strength of 1333 kV/m. The electric field breakdown strength for both polarities was also tested. The results showed that the breakdown strength of negative polarity was slightly higher than that of positive polarity. The experimental phenomena were discussed.