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An experimental assembly for precise measurement of thermal accommodation coefficients
Wayne M Trott1, Jaime N Castañeda, John R Torczynski
1Engineering Sciences Center, Sandia National Laboratories, Albuquerque, New Mexico 87185-0826, USA. wmtrott@comcast.net
The Review of Scientific Instruments
|April 5, 2011
Summary
Researchers developed a new system to measure thermal accommodation coefficients for various gas-surface interactions. Results show typical coefficients for argon, nitrogen, and helium, with cleaning procedures impacting values.
Area of Science:
- Materials Science
- Thermodynamics
- Surface Physics
Background:
- Thermal accommodation coefficients (TACs) are crucial for understanding gas-surface interactions in micro/nanoscale heat transfer.
- Accurate experimental determination of TACs is challenging due to complex surface conditions and measurement techniques.
Purpose of the Study:
- To develop and validate an experimental apparatus for precise measurement of TACs across diverse gas-surface combinations.
- To investigate the influence of surface properties (material, roughness, contamination) and gas composition on TACs.
Main Methods:
- Utilized a custom apparatus measuring pressure-dependent conductive heat flux between parallel plates.
- Employed Direct Simulation Monte Carlo (DSMC) simulations to derive TACs from heat flux data.
- Incorporated electron-beam fluorescence for in-situ gas density measurements.
Main Results:
- Determined baseline TACs: ~0.95 (argon), ~0.85 (nitrogen), ~0.45 (helium) for common materials without special cleaning.
- Observed reductions in TACs after in situ argon-plasma cleaning (up to 0.10 for helium, ~0.05 for nitrogen/argon).
- Investigated effects of surface materials (stainless steel, gold, Al, Pt, Si, SiN, polysilicon), gas mixtures, roughness, and contamination.
Conclusions:
- The developed system provides reliable TAC measurements for various gas-surface systems.
- Surface condition significantly impacts TACs, with plasma cleaning altering values.
- Experimental results align well with DSMC simulations, validating the methodology.
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