Pietro Congedo,
National Institute of Aerospace
Introduction to dense gas flows: exploitation of non-classical
properties for energy applications
Abstract: 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.
Advisor: Bernie Grossman (NIA)