Siloxanes: A new class of candidate Bethe-Zel’dovich-Thompson fluids

Abstract

This paper presents a new class of Bethe-Zel’dovich-Thompson fluids, which are expected to exhibit nonclassical gasdynamic behavior in the single-phase vapor region. These are the linear and cyclic siloxanes, light silicon oils currently employed as working fluids in organic Rankine cycle turbines. State-of-the-art multiparameter equations of state are used to describe the thermodynamic properties of siloxanes and to compute the value of the fundamental derivative of gasdynamics Γ, whose negative sign is the herald of nonclassical gasdynamics. Siloxane fluids starting from D6 and cyclic siloxanes of greater complexity, and MD3M and linear siloxanes of greater complexity are predicted to exhibit a thermodynamic region in which Γ is negative and hence nonclassical wavefields are admissible. As an exemplary case, a nonclassical rarefaction shock wave propagating in fluid D6 is studied to demonstrate the possibility of using siloxane fluids in nonclassical gasdynamic applications and to experimentally verify the existence of nonclassical wavefields in the vapor phase. The sensitivity of the present results to the considered thermodynamic model of the fluid is also briefly discussed.