ELECTROHYDRODYNAMIC ENHANCEMENT OF FALLING FILM EVAPORATION HEAT-TRANSFER AND ITS LONG-TERM EFFECT ON HEAT-EXCHANGERS

Electrohydrodynamic (EHD) enhancement of vertical falling film evapora tion heat transfer has been experimentally studied using HCFC123, whic h is an alternative working fluid for CFCs. This research verified tha t EHD enhancement of HCFC123 condensation was as effective as that of conventional working fluids. The electrodes used for EHD enhancement o f vertical falling film evaporation utilized the following two EHD phe nomena: extracting the liquid by a nonuniform electric field, and surf ace granulation by a nearly uniform electric field. As a result, an el ectrode with vertically arrayed offset-slits that is suitable for indu strial applications has been developed that showed a six-fold enhancem ent of evaporation hear transfer over that for a smooth tube. The long -term effects of the high voltages associated with EHD on heat exchang er performance have been evaluated. Operation of EHD heat exchangers f or 1000 hours indicates they do not sustain serious damage, and are, t herefore, suitable for industrial applications.