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Investigation of the flow field inside a mass spectrometer using Particle Image Velocimetry

Davradou Agapi

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Summary

The area of low pressure gas dynamics has received significant attention as part of a greater effort to enhance the sensitivity of modern Atmospheric Pressure Ionization Mass Spectrometry (API-MS) systems. In this thesis, an experimental visualization of the under-expanded jet, formed in the fore vacuum region of a mass spectrometer, is realized using the Particle Image Velocimetry (PIV) technique. The investigation of the under-expanded flow field is achieved during a free jet expansion as well as inside AerolensTM, a novel ion optical device designed to suppress turbulence and laminarize the supersonic flow. Aluminum polydisperse distributions of 10-100 nm, created by a Spark Discharge Source (SDG), are used to seed the flow transferred through a capillary in the low pressure vacuum chamber operated at 20 and 5 mbar respectively. A Scanning Mobility Particle Sizer (SMPS) system was used for the characterization of the spark source. The implementation of a Differential Mobility Analyzer (DMA) for accurate size selection during the PIV experiments was also tested. Fluorescent particles of ~100 nm size, using an Electrospray source, were also employed to test their applicability in such applications. Finally, a Particle Tracking Code available in the literature and developed for data post processing of captured images, was modified to be applied in experimental data obtained at elevated background noise levels, such as those established inside the AerolensTM or close to the capillary outlet.

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