The development of CO<SUB align=right><SMALL>2</SMALL></SUB> expander technology in CO<SUB align=right><SMALL>2</SMALL></SUB> transcritical cycles

In this study, the CO<SUB align="right"><SMALL>2</SMALL></SUB> expansion process in CO<SUB align="right"><SMALL>2</SMALL></SUB> transcritical cycles is analysed by taking a typical operation condition as an example. The expansion work is divided into two parts: the first is the work done mainly by pressure potential energy without the phase change, and the second is the work done mainly through the volume expansion of the two-phase fluid. According to the process, the ideal expander requirement was given. By the comparison and evaluation of many types of expander, the rolling piston was identified for our initial development due to its low cost, wide application, and reasonable efficiency. The rolling piston efficiency was analysed and the inlet fluid control methods were discussed.