Steady, isentropic flows of dense gases

Abstract

Steady isentropic flows of fluids in their dense gas regime are examined. It is shown that the Mach number may increase, rather than decrease, with density or pressure if the specific heats of the fluid are sufficiently large. Conditions are also reported under which isentropic expansions through converging–diverging nozzles are not possible, regardless of the imposed exit pressure. In such cases, the nozzle must be replaced with one having multiple throats. Applications to external transonic flows are briefly considered.

The influence of molecular complexity on expanding flows of ideal and dense gases

“…Only HMC fluids may possibly feature a nonmonotonous Mach number variation with density in a limited thermodynamic region. 25,26 This is not the case for the thermodynamic conditions considered here.…”

“…For HMC fluids also qualitative differences in fluid dynamic behavior can be observed in the dense-gas region, close to saturation. [25][26][27] Most notable is the increase in the speed of sound upon isentropic expansion, possibly leading to a local decrease in the Mach number, 11,27-29 which instead increases 33 may possibly occur, although no experimental evidence of these "exotic" wave fields is available yet. 34 In Ref.…”

Bayesian quantification of thermodynamic uncertainties in dense gas flows

“…In summary, the RKS model in non-dimensional form (5), (8) considered in the present work depends on three uncertain parameters, namely the acentric factor ω, the exponent n and the reduced ideal-gas constant-volume specific heat at the critical temperature c v,∞ (T c ).…”

“…Globally, the MAH thermodynamic model in reduced form, Eq. (11) and (8), requires the knowledge of six material-dependent parameters, namely, the critical pressure p c , the critical temperature T c , the critical compressibility factor Z c , the normal boiling temperature T b , the exponent n and the reduced ideal-gas constant-volume specific heat at the critical temperature c v,∞ (T c ). Nevertheless, previous results [13] show that Z c , T b and n have a relatively small impact on the results.…”

“…In thermodynamic regions close to the liquid-vapor coexistence curve, the thermodynamic behavior of fluids with high molecular complexities differs significantly from that of a perfect gas and can no longer be represented by the polytropic perfect gas law. The largest deviations are encountered in the so-called dense gas flows ( [7,8,9]) -for which a non-ideal dependence of the speed of sound on the fluid density is observed when the flow is submitted to isentropic perturbations-and most of all for a class of fluids known as the Bethe-Zel'dovich-Thompson (BZT) fluids ( [10,11,12]). Examples of gases exhibiting this special behavior are given by heavy hydro-and fluorocarbons and siloxanes, for which accurate and comprehensive thermodynamic data are scarce.…”