To realize higher performance in heat pump systems utilising nonazeotropic mixtures, an EHD (electrohydrodynamic) evaporator has been installed. Conventional manufactured surfaces have not been effective for nonazeotropic mixtures because of the accumulation of the less evaporative component of the mixture around the heat transfer surface. By setting a perforated coaxial cylindrical electrode inside the 3.75-m-long evaporator tube, the evaporative and boiling heat transfer of the nonazeotropic mixture of HCFC123 and HFC134a on the inner surface of the tube has been enhanced by a factor of about 3 over a wide range of quality with the application of 7 kV at an electrode distance of 2.5 mm. Furthermore, by using electrically conducting transparent glass, it was clear that the flow pattern has been changed, and some EHD phenomena, such as EHD surface instability, have been observed.

KEYWORDS: experiment, evaporators, non azeotropic, mixtures, refrigerants, R123, R134a, heat pumps, surfaces, performance, fouling, heat flow, electrodes, coaxial, cylindrical, tubes, boiling, fluid flow, stability