Diffusive separation of binary mixtures of CO2–H2 in a sonic-orifice expansion

Abstract

The separation of binary gas mixtures of carbon dioxide and hydrogen in sonic-orifice-generated free jets is investigated over a source Reynolds number range of 100 to 3000 using the well-known electron beam fluorescence technique. The lighter species, hydrogen, is chosen as the minor species in order to examine the extent of the validity of Sherman’s first-order diffusive separation theory for large separation. The diffusive separation of mixtures containing approximately 2%, 5%, and 20% hydrogen in carbon dioxide is investigated by experimentally determining the relative number densities of the two species as a function of centerline axial distance within the free jets. Sherman’s diffusive separation theory is applied to the jets using axial Mach number profiles which were a combination of experimental and analytical results for γ=1.40 expansions. The γ=1.40 expansion is shown to approximate the CO2–H2 expansion quite well, and the calculated separation agrees remarkably well with the experimentally determined values.

Nonequilibrium Processes in Supersonic Jets of N2, H2, and N2 + H2 Mixtures: (I) Zone of Silence

“…The inaccuracy of the Mach number near the nozzle yields an uncertainty of about 10% in the calculated enrichment for z/D > 1. 10 The present experimental values of N 2 enrichment are higher than the predicted ones (see Figure 5a), as in other works with such high Re 0 , 13 in qualitative agreement with the theory.…”

“…The firstorder approximation, applied to the central streamline of an axisymmetric flow, gives the mole fraction X of the heavy component along the axis as a function of the Mach number and of some parameters which depend on the mixture. 11 This theory is in good agreement with the experimental enrichment of the heavy component along the jet axis of He + Ar 11 and CO 2 + H 2 13 expansions, over the ranges 100 < Re 0 < 10000 and 100 < Re 0 < 3000, respectively. Most of the reported enrichment takes place over a distance z/D < 10 for molecular mixtures, being faster for mixtures of monatomic gases.…”

“…10 Since then, it has been employed to explain the experimental separation of binary mixtures. [11][12][13] The spatial and kinetic energy distribution of species within the jet, due to this effect as well as to aerodynamic focusing 14 or velocity slip, 15 are of particular interest in film deposition technology and in the generation of nanoparticles. 16 In the present work, we have studied the N 2 + H 2 system, focusing our attention on the nonequilibrium between degrees of freedom and on the diffusive separation of species.…”

Quadrupole mass spectrometry of reactive plasmas

“…F (γ, x/d) is a function of the distance and reaches its final value of 13, 16, or 18 for γ = 5/3, 7/5 , or 9/7 at a distance of x/d = 3, respectively. The validity of this formula was demonstrated by McCay et al [173] in H 2 /CO 2 mixture. The concentration of the heavier CO 2 in the mixture has been enhanced as much as five-fold for their experimental conditions, in very good agreement with calculated enrichment factors.…”

The effect of cluster formation on mass separation in binary molecular beams

“…This effect has been ascribed to pressure gradients in the rapidly expanding gas jet in the stagnation pressure region before free molecular flow is achieved. 4,12,13 This so-called diffusive separation results in a concentration of the heavier species near the center line of the beam. Following this region there is an increase in the ratio of neon to xenon up to a stagnation pressure of about 700 Torr.…”