VOLTAGE PULSES FOR THE ENHANCEMENT AND CONTROL OF HEAT TRANSFER IN FLUIDS

RECENT EXPERIMENTS IN GREAT BRITAIN AND JAPAN DEMONSTRATED A HUNDRED-FOLD ENHANCEMENT OF CONVECTIVE AND BOILING HEAT TRANSFER BY THE APPLICATION OF DC OR LOW FREQUENCY ELECTRIC FIELS. ALSO, IN THE CASE OF BOILING HEAT TRANSFER, THE MEAN BUBBLE DETACHMENT TIME WAS REDUCED AND BOILING HYSTERESIS ELIMINATED. HOWEVER, THE TECHNIQUE, AS IT HAS BEEN DEVELOPED, IS APPLICABLE ONLY TO INSULTATING FLUIDS, SINCE EXCESSIVE HEAT WOULD BE GENERATED BY THE ELECTRICAL FIELD IN LIQUIDS OF LOW OR MEDIUM RESISTIVITY. RESEARCHERS ARE APPLYING HIGH-FIELD GRADIENTS IN THE FORM OF PULSES. THE HEAT GENERATED IS SMALL BECAUSE OF THE LOW-DUTY CYCLE. BY APPLYING VOLTAGE IN PULSES, POTENTIAL GRADIENTS MANY TIMES HIGHER THAN FOR DC VOLTAGES ARE SUSTAINED. AS THE ELECTRIC FORCES ACTING ON FLUIDS INCREASE APPROXIMATELY BY THE SQUARE OF THE VOLTAGE GRADIENT, MUCH STRONGER FORCES ARE AVAILABLE TO INFLUENCE FLUID MOTION, BUBBLE DETACHMENT, OR INSTABILITIES ON THE VAPOR-LIQUID INTERFACE. THE METHOD IMPROVES ON THE REPORTED RESULTS FOR INSULATING FLUIDS AND EXTENDS THE TECHNIQUE TO MEDIUM RESISTIVITY LIQUIDS SUCH AS WATER. THE RESEARCH STUDIES THE PULSED CONCEPT IN ITS EFFECT ON CONVECTIVE AND BOILING HEAT TRANSFER IN LIQUIDS. THE INFLUENCE OF ELECTRICAL AND GEOMETRICAL PARAMETERS IS BEING INVESTIGATED, AND EXPERIMENTS PERFORMED IN WATER AND AN INSULATING LIQUID. A PROTOTYPE BOILER BASED ON THE PULSED CONCEPT IS BEING DESIGNED AND ITS COSTS ESTIMATED.