Enhanced heat flux in non-uniform electric fields

Abstract

Heat transfer by convection from a thin wire to a liquid was very appreciably increased by the application of a non-uniform electric field of several hundred kilovolts per centimetre which was confocal with the temperature field. This enhancement of the heat flux was much larger in a polar, slightly conducting liquid than in a practically ion-free liquid; the behaviour of a non-polar liquid which contained traces of a polar impurity was intermediate between the two. The polarity of the electric field affected the magnitude of the enhancement of the heat flux in the polar liquid and to a lesser extent also in the non-polar liquid which had a slight content of a polar contamination, but the direction of the field had no influence what­-soever on the enhancement of the heat flux in the ion-free liquid. With each of these three liquids the electrostatic field delayed and even suppressed the transition to nucleate boiling and therefore reduced the risk of ‘burn-out'. It appears that dielectrophoresis is primarily responsible for the increased convection, but that an ion transport phenomenon can make a further significant contribution. The observed polarity effects, in the presence of a minute concentration of ions, suggest that this could be an ion wind. For large values of the elec­trical number ( El ) the incremental increase of the Nusselt number ( Nu ) by dielectrophoresis can be of the order of one hundred.