Significance of loss correlations in performance prediction of small scale, highly loaded turbine stages working in Organic Rankine Cycles

The comparison is made between various turbine loss models from the point of view of small, highly loaded impulse turbines operating in ORC cycles. The focus is laid on the influence of the passage and partial admission loss models and their combinations. The paper discusses the limitations concerning the small turbine designs for ORC and takes them into account in the analysis. A case study is provided for an ORC operating with cyclopentane. The cycle output power is in the range of a few to a few hundred kW. The last part of the results includes more generalized maps of efficiency plotted in the expansion ratio-size parameter domain. The results yield qualitative similarities between the efficiency values obtained by different model combinations. For low specific speeds the differences exceed 15% and for high specific speeds they are within about 5%.