Performances of multi-vane expanders

Multi-vane expanders possess many advantages as prime movers for organic Rankine-cycle power systems utilising low grade energy as the heat inputs, particularly for low power outputs (i.e. <10kW). The performances of these devices can be improved considerably by optimising their design parameters and by controlling their operating conditions. To achieve this, mathematical models were developed and computer codes composed for predicting the performance characteristics of multi-vane expanders, as functions of their design and operating variables. The constructed computer programs were applied to two existing designs. Also, a series of tests was carried out on the two considered expanders, using the low grade energy organic Rankine-cycle test rig at Cranfield Institute of Technology. The testing of the expanders was conducted in parallel with the theoretical analysis in order to determine the operational constraints and practical coefficients required for the computer simulation and to verify the validity of the models developed. The analytical predictions of the performance characteristics of the expanders have been compared with experimentally obtained observations. Due to the nature of the simplifying assumptions, a power correction factor was needed to match the analytical predictions with the experimental results to within a ±22 per cent relative deviation zone, over the investigated range of operating conditions.