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NIA Seminar by Pietro Congedo |
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Date: August 18, 2006
Time: 10:30am
Location: NIA, Rm 137
Introduction to Dense Gas Flows:
Exploitation of Non-Classical Properties for Energy Applications
Pietro Congedo, University of Lecce, Italy
In recent years, great attention has been paid to a class of fluids of the retro-grade type (i.e. fluids that superheat when expanded), known as the
Bethe- Zel'dovich-Thompson (BZT) fluids, which exhibit in the vapor phase, above the upper saturation curve, a region of negative values of the Fundamental Derivative of Gas-dynamics. In the transonic and supersonic regimes, this leads to non-classical gas-dynamic behaviors, such as expansion shocks and mixed waves. An appealing application of BZT fluids is efficiency enhancement for Organic Rankine Cycles (ORCs). ORCs' working fluids are heavy organic compounds with large heat capacities: interestingly, several of these fluids possess BZT properties. One major source of losses in ORC turbines is wave drag, since they usually operate in the transonic/supersonic regime: the use of a BZT fluid could avoid shock formation and, ideally, allow isentropic turbine expansion.
This talk gives an introduction to the non-classical behavior of BZT fluids, and the complex equations of state that must be used in order to deal with.
Great benefits derived from using this kind of fluids are underlined through two numerical applications: first, the analysis of the aerodynamic performance of transonic BZT flows past an airfoil; secondly, a parametric investigation of transonic BZT flows through linear transonic turbine cascades.
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