Modeling, Expander, Single-Screw, Overall Energy Balance
A comprehensive mechanistic model of an open-drive single-screw expander for waste heat recovery applications by means of an Organic Rankine Cycle (ORC) has been previously developed and validated by the authors. The model included sub-models of geometry, leakage flows, in-chamber heat transfer, simplified friction losses and a single-lumped temperature overall energy balance. Furthermore, a non-symmetric approach was also implemented to simulate the simultaneous expansion process occurring on both side of the central rotor. In this work, the mechanistic model has been extended to compute the loads on the starwheels bearings as well as the main rotor. Forces and moments analyses allowed integration of a more detailed friction loss analysis and identification of a thermal resistance network of the housing with multiple lumped temperatures. To the best of the author’s knowledge such a detailed integrated thermal model of a single-screw machine has not been reported in the available literature. The multi-lumped temperature overall energy balance (OEB) is validated with experimental data obtained from a dedicated ORC test stand. A comparison between single-lumped and multi-lumped temperature approaches on the performance predictions is provided along with a discussion about the losses distribution inside the machine.