Application of Bethe-Zel'dovich-Thompson fluids in organic Rankine cycle engines

The novel concept of improving organic Rankine cycle engines (ORCEs) by exploiting the unusual fluid dynamic behavior of a special class of working fluids known as Bethe-Zel'dovich-Thompson (BZT) fluids is explored. ORCEs are currently manufactured and used for numerous remote terrestrial applications requiring reliable, unattended power. One of the major loss mechanisms in ORCEs is shock waves generated in the turbine stage. Operating under the proper thermodynamic conditions, a BZT working fluid can potentially weaken or eliminate shock waves. This would reduce losses due to both the wave drag from shocks as well as losses from boundary-layer separation due to shock reflections on the turbine blades. Two-dimensional flowfields through realistic symmetric impulse turbine cascades are compared using a flux-limited, finite difference numerical scheme to assess differences in dow efficiencies. Results show significant improvements in turbine efficiencies for BZT working fluids over conventional ORCE working fluids.