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A free jet of high Prandtl number fluid impinging perpendicularly on a solid substrate of finite thickness containing small discrete heat sources on the opposite surface has been analyzed. Both solid and fluid regions have been modeled and solved as a conjugate problem. Computed results included the velocity, temperature, and pressure distributions in the fluid, and the local and average heat transfer coefficients at the solid-fluid interface. Numerical results were validated with available experimental data. It was found that the thickness of the disk as well as the location of the discrete sources showed strong influence on the maximum temperature and the average heat transfer coefficient.

Rotating Heat Pipe (RHP) technolog y is being developed for high speed (>20 krpm) regimes of electric motor/generator cooling. The motivation for this research is the potential application of the high speed RHPs for the thermal management of advanced rotating electrical machines. The passive nature and relatively simple features of this device are attractive for the removal of waste heat from the rotors of electric machines. Interesting air-cooling experimental results of two high speed RHPs designed, fabricated and tested at AFRL are presented here. Emphasis is made on external heat removal concepts useful for cooling the RHP condenser in order to be successful in promoting this technology to real world problems.

In recent years, the Air Force has been developing rotating heat pipe(RHP) technology for potential use in advanced aircraft systems. The major interest has been to investigate the high speed operating regime(15-60 krpm) of the RHP with targeted application to the more-electric systems such as the integrated power unit and integral starter/generator. Towards this goal, a 2000 W, stainless steel-water, high speed RHP was manufactured and successfully tested up to 30 krpm for the first time. Also, a newly patented RHP design was incorporated in the rotor of an existing permanent magnet alternator presently used in aircraft. Commercial production of this alternator is in progress.

The rotating heat pipe (RHP) technology is revisited in the context of finding a suitable thermal management solution for the advanced electrical machines such as switched reluctance and permanent magnet types. These machines, with potential applications involving direct mounting to gas turbine main shaft, have very high operating speeds and rotor thermal loads requiring new research studies on the use of RHP technology. The RHP literature data of the 1970's and 1980's are mostly limited to low speeds and off-axis mode tests. In this paper, results of a stainless steel - water on-axis RHP are presented. Also, potential application areas are identified.

A cooling technique is devised which will maintain the electronics within their thermal operating limits when the power output of currently used VSCFs is augmented to 65 kVA from 40 kVA. This study suggests that the use of jet impingement cooling selectively applied in regions of high heat flux will support the enhancement in performance desired. Experiments were run to determine the forced convective cooling of the current VSCF design. Experiments were then run to determine the submerged jet impingement cooling characteristics. Finally a FEA numerical model of the SCR module mounted on the tube flange with forced convection and jet impingement cooling was set up. The FE analysis indicates that at 65 kVA submerged jet impingement cooling will mitigate the temperatures of the SCRs sufficiently to maintain them within their operating envelope.