Journal
ENERGY
Volume 217, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.energy.2020.119339
Keywords
High-expansion radial inflow turbines; ORC power systems; stator-rotor unsteady interaction; Three-dimensional simulations
Categories
Funding
- Netherlands Organization for Scientific Research (NWO) [14711]
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Organic Rankine cycle (ORC) systems have low thermal performance due to the low temperature of heat sources and the inefficiency of the expanders used. Designing turboexpanders is challenging because of the highly supersonic and unsteady flow field.
Organic Rankine cycle (ORC) systems are a readily available technology to convert thermal energy from renewable- and waste heat sources into electricity. However, their thermal performance is relatively low due to the low temperature of the available heat sources, but more importantly, due to the low efficiency of the employed expander. Designing the turboexpander is exceptionally challenging, because the flow field is highly supersonic and unsteady, and since the expansion takes place in the highly non-ideal dense-vapor region. In this work, we perform unprecedented three-dimensional unsteady simulations of several high-expansion cantilever ORC turbines to highlight distinctive loss mechanisms. The simulations indicate strong unsteady effects in the rotor blade passage, as a result of unsteady propagating shock waves interacting with viscous wakes and boundary layers. Moreover, the flow field in the rotor blade passage is strongly affected by three-dimensional secondary flow features and a sharp expansion in the shroud region at the inlet of the rotor blade. These span-wise mechanisms and unsteady flow interactions introduce irreversible losses which must be taken into account for designing highly efficient ORC expanders. (C) 2020 The Authors. Published by Elsevier Ltd.
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