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Theory of the Greenspan viscometer
Keith A Gillis1, James B Mehl, Michael R Moldover
1Process Measurements Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8360, USA. keith.gillis@nist.gov
The Journal of the Acoustical Society of America
|July 26, 2003
Summary
This study details an acoustic model for a Greenspan viscometer, enabling accurate gas viscosity measurements. The prototype instrument achieved high precision, validating its effectiveness for reactive gases in semiconductor processing.
Area of Science:
- Acoustics
- Fluid Dynamics
- Physical Chemistry
Background:
- Accurate viscosity measurements are crucial for understanding gas behavior, especially in industrial processes like semiconductor manufacturing.
- Existing methods may lack precision or be unsuitable for reactive gases.
- The Greenspan acoustic viscometer offers a potential solution for precise gas viscosity determination.
Purpose of the Study:
- To develop and validate a detailed acoustic model for the Greenspan acoustic viscometer.
- To assess the instrument's capability for accurately measuring the viscosity of gases, including reactive ones.
- To refine the model's parameters for improved measurement accuracy.
Main Methods:
- Developed a comprehensive acoustic model of the Greenspan viscometer, treating it as a Helmholtz resonator.
- Represented the duct using a T-equivalent circuit and chambers as lumped impedances.
- Incorporated end effects and thermal dissipation into the model.
- Utilized a prototype instrument to measure gas viscosity at various pressures.
Main Results:
- The acoustic model accurately predicts the viscometer's behavior.
- The prototype instrument achieved viscosity measurements within +/-0.8% of reference values for surrogate gases.
- Excellent agreement was obtained across a pressure range of 0.2-3.2 MPa with minimal parameter adjustment.
Conclusions:
- The detailed acoustic model provides a robust framework for the Greenspan viscometer.
- The instrument demonstrates high accuracy and reliability for gas viscosity measurements.
- This technology is suitable for characterizing reactive gases in demanding applications like semiconductor processing.