Microscale rarefied gas dynamics and surface interactions for EUVL and MEMS applications.

Abstract

A combined experimental/modeling study was conducted to better understand the critical role of gas-surface interactions in rarefied gas flows. An experimental chamber and supporting diagnostics were designed and assembled to allow simultaneous measurements of gas heat flux and inter-plate gas density profiles in an axisymmetric, parallel-plate geometry. Measurements of gas density profiles and heat flux are made under identical conditions, eliminating an important limitation of earlier studies. The use of in situ, electron-beam fluorescence is demonstrated as a means to measure gas density profiles although additional work is required to improve the accuracy of this technique. Heat flux is inferred from temperature-drop measurements using precision thermistors. The system can be operated with a variety of gases (monatomic, diatomic, polyatomic, mixtures) and carefully controlled, well-characterized surfaces of different types (metals, ceramics) and conditions (smooth, rough). The measurements reported here are for 304 stainless steel plates with a standard machined surface coupled with argon, helium, and nitrogen. The resulting heat-flux and gas-density-profile data are analyzed using analytic and computational models to show that a simple Maxwell gas-surface interaction model is adequate to represent all of the observations. Based on this analysis, thermal accommodation coefficients for 304 stainless steel coupled with argon, nitrogen, and helium are determined to be 0.88, 0.80, and 0.38, respectively, with an estimated uncertainty of ±0.02. 4 AcknowledgmentThis project, LDRD 04-1413, "Microscale Rarefied Gas Dynamics and Surface Interactions for EUVL and MEMS Applications," was funded by the Laboratory Directed Research and Development (LDRD) program at Sandia National Laboratories. The authors thank Jeremy Barney for his support in automating our data acquisition procedures. 5 Table of Contents List of Tables

Modeling rarefied gas-solid surface interactions for Couette flow with different wall temperatures using an unsupervised machine learning technique

“…Heat and momentum transfer of fluid flows in contact with surfaces in noncontinuum or rarefied conditions has been an active research topic in numerous modern engineering applications such as vacuum technology, micro or nanoelectromechanical systems (M/NEMS), astronautics, and particle sizing techniques used in the aerosol industry [1][2][3][4]. In these systems jump conditions for temperature and velocity, which manifest themselves mainly at the gas-solid interfaces, are of crucial importance in computing the drag force and heat transfer experienced at the solid surfaces.…”