Experimental investigation of QCM-derived sticking coefficients for use in molecular transport simulations

Lubos Brieda; Elana Helou; Tianxiang Zhao; Joseph Wang; Denisse Aranda; Vince Green; Syed Iqbal

doi:10.1117/12.2632195

3 October 2022 Experimental investigation of QCM-derived sticking coefficients for use in molecular transport simulations

Lubos Brieda, Elana Helou, Tianxiang Zhao, Joseph Wang, Denisse Aranda, Vince Green, Syed Iqbal

Author Affiliations +

Proceedings Volume 12224, Space Systems Contamination: Prediction, Control, and Performance 2022; 122240O (2022) https://doi.org/10.1117/12.2632195
Event: SPIE Optical Engineering + Applications, 2022, San Diego, California, United States

Abstract

This paper presents data from an experimental characterization of molecular transport in vacuum chambers. Specifically, our goal was to determine the applicability of a Quartz Crystal Microbalance (QCM)-derived sticking coefficients for modeling gray-body view factors. The testing was performed at Blue Origin and at USC, and consisted of performing a QCM thermogravimetric analysis (QTGA) to derive the sticking coefficient from a QCM with a direct line of sight to an outgassing sample. This sticking coefficient was then used in a numerical simulation of the chamber, which was used to compute deposition on a secondary QCM with no direct line of sight to the sample. The simulations were found to greatly under-predict the collection on the second QCM. This under-prediction is attributed to the sticking-coefficient based adhesion model reducing flux on each wall impact. In reality, the contaminant population is composed of a heterogeneous mixture of multiple chemical species. Lower vapor pressure gases collect on the first wall impact, while the remaining molecules continue to bounce around without additional sticking. A temperature-based sticking coefficient applies the reduction on each impacting, leading to an artificially low prediction for gray body deposition onto the final cold surface. For the two considered configurations, we found the model to underestimate the experimental measurements by a factor ranging from 7.2 to 1764.3.

Conference Presentation

Citation Download Citation

Lubos Brieda, Elana Helou, Tianxiang Zhao, Joseph Wang, Denisse Aranda, Vince Green, and Syed Iqbal "Experimental investigation of QCM-derived sticking coefficients for use in molecular transport simulations", Proc. SPIE 12224, Space Systems Contamination: Prediction, Control, and Performance 2022, 122240O (3 October 2022); https://doi.org/10.1117/12.2632195

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