Rotary machines have played an important role for many years in refrigeration and air compression applications because of their inherent simplicity and reliability. They are also very attractive machines since as positive displacement devices; they are more suitable for low flow rates (low specific speeds). In this paper, the thermodynamic and fluid mechanic characteristics of a rotary-vane air-motor are analyzed. The optimum geometrical and operational characteristics of the machine are presented. Experiments are conducted to understand the working principles and operational constraints of the machine. This study also helps formulate design procedures that can be utilized to modify air-motors into optimized expanders for single-phase flow applications. The model has been used to evaluate geometrical parameters such as the optimum intake and exhaust port locations, their spreads and the geometric volume ratio, as well as evaluating performance parameters such as the work produced and the mechanical, isentropic and total efficiencies of the machine. It is anticipated in a follow-up study that the model developed will be the basis for an expander design tool that uses two-phase working fluids in relevant industrial applications.

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