Advanced Cooling Technique for Generator Rotor in Auxiliary Power Unit (APU) Application

Auxiliary Power Unit of military and commercial aircraft use permanent magnet generator to provide electrical power for key systems such as a full authority digital electronic control (FADEC) system and vital sensor systems. The rotor of this generator is made of samarium-cobalt magnets and generates core heating due to eddy and hysterisis losses. Cooling of the rotor to a safe operating temperature is essential to maintain the required efficiency. Conventional forced air or oil jet cooling of the hollow rotor shaft has been found to yield poor results. This proposal addresses a novel cooling concept to efficiently cool the rotor. The rotating heat pipe principle is used here. A set of radial fin-like vapor chambers attached to an external condenser through the extended hollow shaft. The condenser can be conveniently cooled by liquid spray cooling externally. As an operating temperature < 200oC is preferred for the generators, water or alcohol can be used as working fluid. The objectives of Phase I effort are to design a representative APU rotor thermal model and analyze its thermal characteristics incorporating the proposed cooling technique for demonstrating the feasibility. Anticipated Benefits: Efficient cooling of generator rotor prevents machine overheating and premature failures. APUs can be built very reliably, minimizing aircraft engine repair or down time. A well-cooled rotor design will result in weight reduction. Potential commercial applications include ground carts, portable generators, environmental control equipment and motors for electric transportation vehicles.