Simulation And Application Of An Organic Rankine Cycle Scroll Expander And Its Power Generation System

Organic rankine cycle (ORC) is a crucial technology to convert and utilize low-grade thermal energy. Focused on the key component of an ORC system, this thesis studied the volumetric efficiency and isentropic efficiency of a scroll expander, and further simulated the ORC system performance. The detailed work and results are highlighted below: With a scroll of 28.6m3/h volume flow and 2.85 volume ratio being selected as the expander, this work thoroughly analyzed its internal and external irreversible factors. Efforts have been made to model the scroll expander and its ORC auxiliary components. Deviation analysis has been carried out for the scroll expander model using the experimental results. Simulation has been performed for the performance of R245fa and R124 ORC systems with different expansion ratio and condensing temperature. An ORC test bench of 6kW generating capacity has been designed and set up using biomass boiler to provide 70?150? low-grade heat.The following results and innovations have been obtained from this paper:(1) Compared with the experimental data, the deviation of the scroll expander model has been carried out with the accuracy as following:The absolute error of working fluid outlet temperature is lower than 3K, the relative error is less than 1%; The absolute error of mass flow rate is less than 0.004kg/s, the maximum relative error is less than 1%; The absolute error of electric power is lower than 81W, the relative error is less than 5%. The deviation analysis of ORC test bench indicates that the maximum uncertainty of electricalefficiency is less than 5%.(2) Based on the experimental results, the polynomials of volumetric efficiency and isentropic efficiency have been developed using curve fitting methods. Both polynomials are defined as ternary quadratic of rotation speed, expansion ratio and the inlet pressure of working fluid.(3) The simulation results for ORC systems are as following:For R245fa system, the net power per unit mass of hot fluid reaches a maximum 2.13kW/(kg/s) when the expansion ratio is 8 and condensing temperature is 45?; The cycle efficiency reaches a maximum 6.89% with 4.3 expansion ratio and 45? condensing temperature; The exergy efficiency reaches a maximum 45.9% with the 3.1 expansion ratio and 25? condensing temperature. For R124 system, the net power per unit mass of hot fluid reaches a maximum 2.55kW/(kg/s) when the expansion ratio is 5.6 and condensing temperature is 35?; The cycle efficiency reaches a maximum 7.36% with 4.1 expansion ratio and 25? condensing temperature; The exergy efficiency reaches a maximum 47.35% with 2.6 expansion ratio and 25? condensing temperature.(4) The influence of superheat on ORC system performance has been carried out:For R245fa system, the impact of superheating is negligible. For R124 system, the cycle efficiency and exergy efficiency are improved with higher superheating temperature and the effect of superheating increases with higher expansion ratio.The results of this paper can be useful for research and development of ORC heat engine system.