UNCERTAINTY QUANTIFICATION OF PERFORMANCE PARAMETERS IN A SMALL SCALE ORC TEST RIG

Thermodynamic measurements are affected by a certain level of uncertainty due to the sensor/probe characteristics, installation, calibration procedure, and references. In power cycle for energy production, such as standard Rankine cycles and Organic Rankine Cycles (ORC), pressure, temperature, and mass flow rate are used as the basis for estimating the cycle performance, as well as, they are used for monitoring the entire cycle and its operating conditions. In the present work, a small-scale ORC system is taken as reference for performing the assessment of the uncertainty sources and their propagation in the estimation of the cycle performance. The analysis is referred to an ORC system that operates with a temperature of the hot source lower than 100 °C, a net electric power at the generator lower than 1 kW and the R134a as the working fluid. Since the accuracy of the performance estimation is related to the performance of measurement system and to its calibration, three different scenarios have been analyzed in relation to the sensor/probe performance, calibration process, and acquisition devices’ operating conditions. For the performance uncertainty estimation, temperature, pressure, and mass flow rate measurement uncertainties are taken into consideration, as well as the effect of the thermodynamic library used for calculating enthalpy values. The uncertainty values of performance parameters that characterize an ORC system such as expander work, expander power, and overall system efficiency have been assessed showing how the calibration process represents the mandatory step in the way of reducing the uncertainty band. Acquisition module and calibrator performance have to be assessed in comparison with the performance of the sensors and probes installed in the ORC system.