Determination of density and concentration from fluorescent images of a gas flow

Abstract

A fluorescent image analysis procedure to determine the distribution of species concentration and density in a gas flow is proposed. The fluorescent emission is due to the excitation of atoms/molecules of a gas that is intercepted by an electron blade. The intensity of the fluorescent light is proportional to the local number density of the gas. When the gas flow is a mixture of different species, this proportionality can be exploited to extract the contribution associated to the species from the spectral superposition acquired by a digital camera. This yields a method that simultaneously reveals species concentrations and mass density of the mixture. The procedure is applied to two under-expanded sonic jets discharged into a different gas ambient -Helium into Argon and Argon into Helium -to measure the concentration and density distribution along the jet axis and across it. A comparison with experimental and numerical results obtained by other authors when observing under-expanded jets at different Mach numbers is made with the density distribution along the axis of the jet. This density distribution appears to be self-similar.

The hydrodynamics of astrophysical jets: scaled experiments and numerical simulations

“…Detailed information can be found in the work of Belan et al (2008Belan et al ( , 2010Belan et al ( , 2011Belan et al ( , 2012, including descriptions of the configurations and improvements adopted in different experiments. The jets under test in this work were obtained by means of suitable de Laval nozzles and were propagated along the longitudinal axis of a modular cylindrical vacuum vessel.…”

“…The constant k g was obtained from direct calibrations performed on each tested gas (Belan et al 2008). …”

An experimental setup for visualizations and measurements on free hypersonic jets

“…The distance of observation, as referred to the initial jet diameter, is far larger than any of the available experiment and is in the range of stellar jets, while it is not the only purpose of these facilities, as shown e.g. in [6]. Although real stellar jets are not generated in this way, the development of the jets and of the observed instabilities in form of "knots" are not related to boundary conditions but are part of the jet development itself.…”

“…The first version of this system was already employed to study the properties of highly underexpanded jets, making use of truncated nozzles and color CCD cameras, detailed information can be found in the works by Belan et al [4,5,6,7]. In present work the system was reconfigured, by adding and improving devices for the present purpose, i.e.…”

An investigation of the hydrodynamics of hypersonic jets in astrophysical conditions

“…The jets travel inside a modular vacuum vessel, with a maximum length of 5 m and a diameter of 0.5 m, much larger than the diameter of the jets, so that the lateral walls effects are limited (Belan et al 2008). The required ambient inside the vessel is obtained by means of a valves system that sets the ambient density, at pressures ranging from 1.5 to 100 Pa, using a gas in general different from the jet gas.…”