Development of a sliding vane expander in a micro-scale ORC system for utilizing low-grade heat

Abstract

In power generation unit, the steam Rankine cycle is usually used to generate electricity. At the temperature below 300°C (low-grade heat), the steam Rankine cycle is not efficient to operate. To utilize low-grade heat, Organic Rankine Cycle (ORC) is introduced for producing mechanical work. However, its system performance relies heavily on the design of the expander. This present work aims to propose the development of the sliding vane expander for a micro-scale ORC system. The air motor, which is commercially available, is modified in an attempt to prevent leakage and to consistently use with ORC system. The experimental test rig is constructed to demonstrate performance of the sliding vane expander. It is driven by a 15kW boiler. The condenser is a water cooled plate heat exchanger at which the cooling water temperature is regulated by the chiller. R141b (1, 1-Dichloro-1-fluoroethane), which is a kind of HCFC, is used as the working fluid. The torque of the expander is measured by means of the Prony Brake method, and later used to determine shaft power of the expander. The preliminary test to demonstrate the performance of the expander is implemented. The tested condition is set at boiler and condenser temperature of 90°C and 34°C, respectively. It is found that the sliding vane expander is workable steadily without leakage of working fluid. Also, it provides an acceptable performance. The ORC operated with the sliding vane expander can produce approximately 200W of shaft power while the system efficiency is about 1.5%.