Investigation Of A Scroll Compressor As An ORC Expander For IC Engine Waste Heat Recovery

In this thesis, a theoretical investigation on small- or micro-scale Organic Rankine Cycle(ORC) is done with focus on scroll expander. To improve the performance of Organic Rankine Cycle which works in low-temperature range besides the exhaust pipe of combustion engine, optimization of expander plays an important role. Firstly this point should be taken into account that which category of expander is more appropriate to use in ICE and after consideration, the scroll expander type which belongs to positive displacement group was selected to investigate.Scroll expanders are not available in the market in mass-production scale; however scroll compressors are used very massively in refrigeration and airconditioning applications. It means that the selected expander was a scroll compressor originally which used inversely as an expansion machine. This work was done to find out whether is it possible to use scroll compressor as an expander firstly. Hence the scroll expander was used without any geometrical modification and changes in interior and exterior parts. Based on the CFX simulation of this expansion machine, it is concluded that the efficiency of scroll expander is not as high as the compressor's. It was not out of estimation because the original geometry was designed and manufactured for compression application and belonged to compressor processes.According to computational fluid dynamic simulation when the efficiency of selected compressor for an experimental test was more than 40%, the isentropic efficiency of expander for R134 a was 15%. In spite of the fact that this geometry was designed especially for compression process, the results show that it can work inversely with an acceptable efficiency range. The main reason that it does not operate as well as compressor is due to not adapted built-in volume ratio. If it is still required to apply original geometry, the best option to enhance the performance is changing the working fluid from R134 a to R404 a. By use of this medium, scroll expander's performance reached to 20% approximately. Finally, as CFX results of scroll expander represents, it can be concluded that without any modification on scroll profiles, scroll compressor can work as an expander and the efficiency will increase when scroll profiles and interior geometry are modified and changed based on expander design procedure. As it is found out from CFX and FLUENT results, the position of suction and discharge ports should be changed and they have to be opened completely. With current arrangement of ports, scroll machine works as an expander with more limited operating ranges compared to compressor.