Determining the mean size and density of clusters, formed in super sonic jets, by Rayleigh scattering and Mach-Zehnder interferometer

Abstract

In this work, the formation of clusters in a supersonic jet expansion has been investigated. Clusters of argon, carbon-dioxide, nitrogen, and oxygen have been generated in the gas jet with three different types of nozzles (0.5 mm diameter, 0.8 mm diameter, and a conical nozzle with 0.8 mm diameter aperture). The mean size and density of the clusters have been measured as a function of backing pressure. Here, density of clusters refers to the density of the cluster collection. Rayleigh scattering experimental data and Mach-Zehnder interferometer data have been combined to estimate the average size and density of clusters. CO2 and Ar clusters form easily at about a backing pressure of 2 bars, while N2 and O2 clusters do not form easily. N2 and O2 begin to cluster at a backing pressure of about 18–24 bars. The mean cluster radius of Ar varies from 6.6 Å to 24 Å and the cluster radius of CO2 varies from about 8.8 Å to 35 Å as the backing pressure increases from 3 bars to 14 bars. In the same range of backing pressures, the average cluster gas density changes from 37.3 × 1015 cm−3 to 1.6 × 1015 cm−3 for Ar clusters and changes from 10.52 × 1015 cm−3 to 0.22 × 1015 cm−3 for CO2 clusters. It is assumed that the condensation into clusters is total. The mean cluster radius of N2 is smaller and varies approximately from 4.2 Å to 8.6 Å and the cluster radius of O2 varies from about 4.9 Å to 12.4 Å as the backing pressure increases in the range of 18 bars to 35 bars. In the same range of backing pressures, the average cluster density changes from 48.2 × 1016 cm−3 to 3.7 × 1016 cm−3 for N2 clusters and from 21.5 × 1016 cm−3 to 1.3 × 1016 cm−3 for O2 clusters.

The optical measurement of large cluster tracks in a gas jet

“…The parameter q has commonly been fixed at 0.85 in the scaling law of Hagena 13 17 . The exponent r is the function of q and γ, where γ is the specific heat ratio of the gas which is 5/3 for monatomic gas and 7/5 for diatomic gas respectively 18 19 .…”

Spatial mapping of low pressure cluster jets using Rayleigh scattering

“…The well-known Hagena parameter 10 and its modified version 11 are simple empirical relations used to predict the cluster size for a particular nozzle operating at particular reservoir density and temperature. However, its predictions often differ from the experimental measurements 12 which indicates further scope of including more parameters which are responsible for cluster growth. It is well known that the size of the cluster ( ) increases with the reservoir pressure ( ) according to power law , where for Argon 13 – 15 .…”

Diagnostics of Gas Cluster Flows by Transverse Intensity Profile of Molecular Beam

“…Известные экспериментальные методы диагностики газоструйных кластерных потоков позволяют определять только один из указанных параметров. Поэтому для более полного описания обычно используют комбинацию взаимодополняющих методов, чаще всего оптических: Рэлеевское и Рамановское рассеяние [15; 16], Рэлеевское рассеяние и интерферометрия [17], рассеяние и поглощение лазерного излучения [18]. При этом малые абсолютные значения сечений рассеяния и локальной плотности кластеров вынуждают использовать в этих экспериментальных методах комплекс высокочувствительного оборудования.…”