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

Abstract

The downstream composition of a skimmed supersonic binary molecular beam originally consisting of a 20% neon/80% xenon mixture before expansion has been studied as a function of nozzle stagnation pressure. We have found that the neon to xenon ratio dropped dramatically as the stagnation pressure was increased at low nozzle temperature ͑303 K͒, a drop which cannot be well described by existing theory. Time-of-flight ͑TOF͒ measurements indicate that Xe clustering occurs as the stagnation pressure is increased. This clustering coincides with the additional Ne depletion we observe. At a higher nozzle temperature where Xe clustering does not occur ͑573 K͒, this measured mass separation phenomenon is absent. Similar experiments have been done for another binary mixture, 20% O 2 /80% Xe. Similar anomalous mass separation is observed with this mixture, confirming the attribution of this phenomenon to clustering of the more massive component of the mixture. These findings have implications for novel methods of gas-dynamics-based mass separation potentially including isotope enrichment.

Quantitative study of cluster growth in free-jet expansions ofCO2by Rayleigh and Raman scattering

“…A slightly faster drop of the total density with distance is observed the higher is the stagnation pressure P 0 . This effect may be attributed in part to a depletion of the lighter free molecules from the jet axis [48]. The Rayleigh intensities I R are shown in the upper part of Fig.…”

Probing Phase Transitions with Supersonic Beams – A Joint Experimental and Theoretical Study

“…Also, the macroscopic description using a "beam temperature" as a basis assumes the equalization of internal and kinetic energies of all particles. This requirement is considerably more difficult to warrant in experiments; customarily, non-compliance is reflected in artifacts such as an incomplete relaxation of rotational or vibrational excitations [27,[47][48][49][50] or the appearance of a "velocity slip" between lighter and heavier species [51][52][53][54][55][56][57][58][59][60][61]. In many cases these effects can be ascribed to an insufficient number of particle-particle collisions caused by low source densities.…”

Numerical study of gas mixture separation in curved nozzles

“…Li et al [12] proposed that the aerodynamic separation of species can be enhanced by the formation of clusters. To model such cases, the continuum mechanical description should be complemented by appropriate particle descriptions.…”