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Annals of the Assembly for International Heat Transfer Conference 13

ISBN 1-56700-225-0 / CD 1-56700-226-9

Volumes per year:

various

Year 2006

DOI: 10.1615/IHTC13.p17

OPTIMAL WORKING FLUID AND ELECTRODE CONFIGURATION FOR EHD-ENHANCED SINGLE-PHASE HEAT TRANSFER

Walter Grassi
Low Gravity and Thermal Advanced Research Laboratory, Dipartimento di Energetica “L. Poggi,” Università di Pisa, Pisa, Italy

Daniele Testi
LOTHAR (LOw gravity and THermal Advanced Research laboratory), Department of Energetics "L. Poggi", University of Pisa, Italy

D. Della Vista
LOTHAR (LOw gravity and THermal Advanced Research laboratory), Department of Energetics "L. Poggi", University of Pisa, Italy

ABSTRACT

The application of a sufficiently high voltage to a sharp electrode immersed in a single-phase fluid can lead to the creation of ions, which are driven towards the opposite electrode, while dragging the fluid neutral molecules. The resulting induced electrohydrodynamic (EHD) flow, if impinging on a heat transfer surface, can become an extremely efficient means of heat exchange. In order to maximise the heat transfer enhancing effect and at the same time limiting the power consumption, an optimum combination of working fluid and electrode configuration was searched.
First of all, an array of points, properly spaced, was chosen as the high-voltage electrode, obtaining localised intensification of the electric field with known sources of injection. As for the point-electrode material, five metals were compared at the application of both polarities. Moreover, ambient air and three liquids with different electric permittivity and resistivity were examined. Among them, HFE-7100, a weakly polar hydro-fluoro-ether, was chosen for its best heat transfer performance with negligible Joule dissipation and its long-term stability.
Using the EHD technique, in its optimised configuration, it is possible to stably exchange heat at high rates, even at a low Reynolds number of the main forced flow, without significant power input. The utilization of the phenomenon to reduce size and pumping power of heat exchangers is in view.