Experimental study on the influence of inlet and exhaust pressure loss on the performance of single screw expanders

Abstract

At present, the most prominent technical problems of small and medium capacity expanders are low internal efficiency and small expansion ratio. In order to promote the practical application of small and medium capacity Organic Rankine Cycle (ORC) system, improving the thermodynamic performance of the expander was a remarkable issue, and the systematic research on the irreversibility of expander's working process is the fundamental work to achieve this goal. Summarizing the related research on various small capacity volumetric expanders, the research on flow problem is lacked. For an atypical volumetric expander, the flow mechanism of single screw expanders (SSEs) is more complex. In this paper, we discussed the effect of the pressure loss in the inlet and exhaust passages on the performance of SSEs. We selected two SSE prototypes developed by our laboratory to carry out the experiment under variable working conditions. The internal volume ratios are 2.95 and 3.98 respectively. The pressure differences of inlet and exhaust passages were measured. In order to evaluate the effect of the flow losses on the performance, we defined two indexes: pressure loss rate (PLR) and pressure energy loss influence rate of shaft efficiency (PELRe). From the results, the pressure losses of inlet and exhaust passages for each SSE increase gradually, PLRin increases slightly and PLRout increases gradually. At the maximum point of shaft efficiency, the losses of the SSE with 2.95 are 28.06 kPa and 46.09 kPa, and the values of the SSE with 3.98 are 37.58 kPa and 33.79 kPa, respectively. It shows that the pressure losses are relatively high. The maximum values of internal and external expansion ratio for the SSE with 2.95 are 4.8 and 6 respectively, and the values of the SSE with 3.98 are 5.7 and 7 respectively. For ideal volume expansion, the internal expansion ratio of two prototypes should be 4.55 and 6.9, respectively. Summarizing the above results, how to enhance the pressure drop effect of leakage and reduce the flow resistance loss of inlet and exhaust passages simultaneously is an important technical premise to improve the expansion ratio by structural optimization. Meanwhile, PELRe of two prototypes are 16.01% and 13.59% respectively at the point. It shows that the flow losses of inlet and exhaust passages could significantly influence the performance of SSEs.