Heat transfer enhancement by an impinging ionic jet in a viscous transformer coolant

The heat transfer performance of an ionic jet impinging on the upper surface of a heated plate is investigated. Ions are injected by a point, set at high voltage. The working fluid is the viscous dielectric ester MIDEL 7131, a refrigerant for power transformers. Different tests are performed on the working fluid, varying the composition, the shape and the polarity of the point, the applied voltage, the point-to-plane distance, and the imposed heat flux. Heat transfer coefficients are augmented up to 310% with respect to natural convection, a higher enhancement than the one obtained with traditional transformer oil. The electrohydrodynamic flow can be generated without significant power input (<0.01 W in these experiments). Cooling of power transformers can be greatly enhanced by this technique.