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It is shown that an indirect cooling system based on the venturi principle enhances the convective heat transfer many-folds as compared to a simple pipe-flow. Such enhancement results from the acceleration of the coolant in a variable cross-section annulus, created by a concentrically placed bi-conical obstruction inside a circular pipe. The heat-source is placed on the outer-wall of the pipe, at a location corresponding to the venturi-throat. The effect of different pipe materials on the thermal performance of the new cooling system are explored. Numerical results are presented for six Reynolds numbers (based on the pipe diameter) covering the range of about 3200 to 32000, and for a single, circular, ring-type heat-load of 273.5 W / cm2. The coolant used is water, at an inlet temperature of 20 °C. The materials considered are copper, aluminium and stainless-steel (AISI 304).

A detailed numerical investigation of the conjugate heat transfer problem in an annular-type venturi-flow cooling system, meant for removal of heat from localized, high power heat sources, has been carried out for a wide range of Reynolds numbers. Comparison with experiments show qualitative agreements for all quantities of interest, but there are some quantitative differences. Possible reasons are given. Results for the venturi- and simple pipe- flows are also compared to assess the relative merits of these two systems.

Advanced electrical machines such as permanent magnet and switched reluctance types are very compact and have high power densities, usually 2 - 5 kW/lb. Nearly 20% of the rated power capacity is dissipated as heat within the machine. Thermal stress, deterioration of magnetic and insulation properties, and loss of power are caused by the overheating of the machine resulting from poor cooling. Because of the enclosed and rotating nature of the rotors in these machines, it becomes increasingly difficult to cool. In this paper, a thorough literature review on this subject is presented. A general description of the thermal management issues and some possible solutions are discussed. Rotating heat pipe rotor shaft and spray cooling heat exchanger solution is suggested. This study was conducted in support of the Air Force more-electric aircraft technology development.