Remote gas sampling with a swirl air stream

One of the promising techniques of remote gas sampling from the surface or from the inside of an object involves the use of a swirl air stream. The case in which a swirl sampling stream produces a vortex core of a composite swirl is of most interest. But a practical implementation of a vortex sampling faces major problems due to the fact that the majority of the available gas analyzers feature a low analytical flow. This offers limitations on sampling distance and reduced pressure created at the object surface. This paper deals with the problem of adjusting vortex and sampling flows for a mass-spectrometer with atmospheric pressure ionization used for remote sampling of diethylanyline vapors. It is shown experimentally that additional sampling flow (Qadd) that coaxially envelops an analytical channel allows one to achieve conditions required for the formation of a vortex core, which is characterized by an increased tangential component of the flow velocity at its boundary and abnormally low pressure on the core axis. A satisfactory agreement between the calculations by the composite vortex model and the experiment is obtained. The studies performed have shown that the optimal relationship between vortex (Qvortex) and additional flows is Qvortex/Qadd = 1.3 and is symbate in terms of both gas dynamic parameters (minimal diameter of a backflow core) and sampling efficiency. It is shown that both the sampling distance and sampling area depend mainly on geometric sampler parameters. The experiments performed have revealed the unique ability of a vortex sampling flow in the form of a composite vortex to focus the sample inside the vortex core, thus preventing its dilution over the backflow.