Integration of Scroll-expanders into Combined Absorption Cycles for Power and Refrigeration Applications

摘要

A semi-empirical model for a scroll expander using ammonia (and ammonia/water mixture with high concentration of ammonia) as a working fluid is developed. This model is validated with experimental data obtained in a test bench and is able to predict the main outputs with an accuracy: of ±4% for mass flow rate, ±8% for the shaft power and ±4 K for exhaust temperature. It is scaled-up to predict the performance of other scroll expanders, with higher swept volume, in the same family series. These semi-empirical models are integrated into a combined absorption power and refrigeration cycle global model for the purpose of representing the real performance of the expansion device in the cycle. The energetic analysis of the combined absorption system shows that it can achieve 14.8-17.8% effective first law efficiency with an overall isentropic efficiency of the expander in the range of about 61-71% for the operating conditions considered in this study (expander inlet temperature and pressure of 105-130 °C and 857-1554 kPa respectively). The expander rotational speed of 5000 rpm, absorber and evaporator exit temperatures of 30 °C and -5 °C, respectively, were kept constant in the energetic analysis of the system.