FLOW AND HEAT TRANSFER CHARACTERISTICS OF HIGH PRESSURE NATURAL GAS IN THE GAPS OF HIGH-SPEED MOTORS WITH A HIGH RADIUS RATIO

A motor stator-gap-rotor model is established based on the numerical heat transfer theory by using the finite volume method. The flow evolution of high-pressure natural gas in the gap with a radius ratio of 0.971 is investigated. The results demonstrate that the flow patterns of high pressure natural gas in the motor gap can be categorized into turbulent, spiral Taylor-Couette, and turbulent TaylorCouette flow. The flow ranges are determined based on the Ta/Re2. 2 . Then, the flow and heat transfer characteristics of the cooling medium in the gap under different flow regimes as well as the mechanism of locally enhanced heat transfer in the gap by the Taylor-Couette flow are explored. Finally, the mathematical expressions for the Nusselt number of motor gap are determined in terms of the Reynolds number, Taylor number, and Prandtl number by fitting using the Levenberg-Marquardt and global optimization methods. Using these expressions, the flow and heat transfer characteristics in the motor gap can be predicted. Overall, this study provides useful and novel insights on the design of cooling systems for high-speed motors.