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

The novel concept of improving organic Rankine cycle engines (ORCEs) by exp loiting the unusual fluid dynamic behavior of a special class of working fl uids known as Bethe-Zel'dovich-Thompson (BZT) fluids is explored. ORCEs are currently manufactured and used for numerous remote terrestrial applicatio ns requiring reliable, unattended power. One of the major loss mechanisms i n 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 dr ag from shocks as well as losses from boundary-layer separation due to shoc k reflections on the turbine blades. Two-dimensional flowfields through rea listic symmetric impulse turbine cascades are compared using a flux-limited , finite difference numerical scheme to assess differences in dow efficienc ies. Results show significant improvements in turbine efficiencies for BZT working fluids over conventional ORCE working fluids.