M.S. Thesis Presentation by Nathaniel R. Morgan
Friday, February 28, 2003

(Dr. Marc Smith, advisor)

"A Porous Medium for Structural Support and Multiphase Cooling of High-Frequency Conductors"

Abstract

Multiphase convection generates larger heat fluxes in comparison to single-phase convection. This technology currently is not used in applications requiring substantial structural support such as high-frequency electrical windings. A porous, dielectric material was created that will adequately support an element and have enough interconnected voids to sustain liquid-vapor transport for boiling heat transfer. The interconnected voids will allow a coolant to boil at the surface of a heat-generating element.

The porous medium was created from an understanding of the physical behavior of randomly packed sphere beds, transport behavior through porous beds, and how epoxy is deposited using a carrier. A sphere bed was injected with epoxy using a carrier to bond the spheres together. This generated a material with numerous interconnected channels for transport of liquid and vapor. The porous medium was also non-electrically conductive and non-magnetic, so it could be used in electrical applications. A technique was found for applying a binder ratio of epoxy and carrier to the sphere bed. Different binder ratios were investigated to find the optimum structural strength and heat transfer. For additional reinforcement, the porous material was combined with a standard composite material – NEMA G10. Structural properties were determined for the non-reinforced and composite reinforced configurations, corresponding to different interconnected void sizes.

A pool boiling test chamber was constructed to investigate the heat transfer characteristics of a high-frequency conductor encased in the porous medium. The conductor-porous media assembly was mounted horizontally on two conductor posts and submerged into a highly wetting perfluorinated coolant, FC-72. The tests were performed using support structures with different sized interconnected voids, and different outer diameters. Critical heat flux was captured and each assembly was evaluated for best performance in transferring heat. The results from these experiments will enhance the cooling technology used in many applications.