Experimental results of a small-scale organic Rankine cycle: Steady state identification and application to off-design model validation

This paper presents experimental results from a prototype of an 11 kWe organic Rankine cycle (ORC). Special attention has been paid to detecting reliable steady state data points. This has been achieved by application of a novel steady state detection algorithm. This method also allows evaluating the performance of the sensors in relation to remaining steady state fluctuations. The reliability of the experimental data is evaluated by investigating the heat balances over the heat exchangers and through error propagation of the measurement uncertainties. In addition, the experimental data from the setup is used for validating an off-design ORC model. The proposed simulation model solely requires the pump and expander speed as inputs besides the given heat source and sink conditions while subcooling is assumed to be constant. The important dependent model outputs are the evaporation pressure, the condensation pressure and the working fluid mass flow rate. All three predicted outputs show a maximum deviation of less than ±1% from the measured values. The modelled net power output deviates less than ±2% from the measured values. In general, this is a satisfactory result that gives confidence in using these models in future off-design simulations.