Condensation of sulfur hexafluoride in steady supersonic nozzle flow

Abstract

Condensation of SF6 carried in argon by homogeneous nucleation has been studied experimentally in two continuously operating supersonic wind tunnels. Condensation onset was detected by Rayleigh light scattering. Calibration of the nozzles by static pressure measurements, together with a solution of equations of motion allowing for the caloric nonideality of the vapor, permitted the determination of the thermodynamic state at the observed onset of condensation. The experiments covered conditions of condensation onset in a range 77<T<113 K, and 0.09<pSF6<4.6 torr, well below the triple point of SF6. The adiabatic supercooling ranged from 38 to 45 C and the results agree qualitatively with the classical theory of homogeneous nucleation.

Nucleation and growth of Mg condensate during supersonic gas quenching

“…Classical nucleation and growth theory has been applied extensively to modelling of condensate formation and growth under supersonic quenching conditions [3][4][5][6]. Classical nucleation is based on the notion that at above a certain level of supersaturation and a corresponding critical nuclei size, the growth of condensate will proceed by rates defined by mass and heat transfer.…”

Scaled models for nucleation

“…[5] But for temperatures far below the critical temperature, diffusion controlled growth is not in general applicable and the rate of formation of the new phase is primarily dictated by the birth (nucleation) of new phase embryos (that is by g(n*)). [4,10] In this low temperature region the classical kinetic prefactor for vapor-toliquid nucleation is proportional to the equilibrium vapor pressure squared and appears to be highly temperature and material dependent.…”

“…[4][5][6][7][8][9][10] In the classical theory, x o = 2/3 3/2 . However, τ o is less well defined for temperatures far below the critical point -and not independent of T .…”

“…[4][5][6][7][8][9][10]17] In predicting critical point phenomena the prefactor must account for diffusion controlled growth and the vanishing of the diffusion constant as T approaches T c . [5] But for temperatures far below the critical temperature, diffusion controlled growth is not in general applicable and the rate of formation of the new phase is primarily dictated by the birth (nucleation) of new phase embryos (that is by g(n*)).…”

“…Near the critical point, (at T ∼ T c ) such scaling of the nucleation rate has been considered extensively [4][5][6][7][8][9][10]. In particular, Binder [4] presented a scaled form for the (slightly modified) classical nucleation rate valid near T c .…”