ORC, charge-sensitive, experimental, mass, off-design
This paper presents an experimental investigation of the working fluid charge repartition in a 2kWe ORC (organic Rankine cycle) test bench. To this end, an online measurement apparatus is built and fully calibrated to evaluate the charge enclosed in the three heat exchangers and the liquid receiver of the ORC unit. By changing all the system boundary conditions (including the charge enclosed in the test rig), an experimental database of 304 steady-state points is gathered and post-treated. The charge inventories obtained by online measurements demonstrate promising results on average but experience high uncertainties when considering each point individually (i.e. the uncertainty on the global inventory is around ± 2.5 kg for a total charge of 31.2 kg). Deviations of the evaporator mass measurements are identified at high temperature of the heat source and discussed in details. A reconciliation method is applied to the raw measurements in order to retrieve consistent charge inventories while accounting for the different sources of uncertainty. Ultimately, the paper analyses the impact of increasing the charge in the ORC and how this parameter influences the thermodynamic state of the system.