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Keith A. Gillis

Dr. Keith Gillis has major roles in three projects that exploit his expertise in physics and physical acoustics:

  1. developing a long-wavelength acoustic flowmeter to measure the flow of flue gas in the exhaust stacks of coal-burning power plants. Accurate emission measurements will be required by any regulations that put a price on carbon dioxide emissions. In contrast with existing pitot-tube based measurements, the acoustic flow meter is insensitive to turbulence and swirl that are present in most stacks.
  2. developing reliable, self-calibrating photoacoustic spectrometers that will be deployed in a network to monitor the concentrations of greenhouse gases and aerosols. In contrast with other systems that measure molecular optical absorption, the response of these spectrometers is calculated from fundamental physical principles. Also, these spectrometers have fewer components and are less expensive than other systems.
  3. participating in an international collaboration using acoustic techniques to measure the thermodynamic temperature up to 1350 K and measuring the Boltzmann constant. This project led Gillis to extend the theory and modeling of acoustic resonators and the propagation of sound in waveguides.

In earlier research at NIST, Gillis developed acoustic techniques for accurately measuring the thermodynamic and transport properties of gases over wide ranges of temperature and pressure. He developed an all-metal cylindrical acoustic resonator with remote transducers to measure the speed of sound, the ideal-gas heat capacity, and the equation of state of refrigerants that were candidate replacements for chlorofluorocarbons. This setup had acoustic transducers at room temperature and acoustic waveguides that transmitted sound to and from the resonator through metal diaphragms and was used between 240 K and 400 K and pressures up to 1 MPa. Gillis perfected the Greenspan acoustic viscometer for accurate measurements of the shear viscosity of gases. These instruments were also used to characterize hazardous gases used by the semiconductor industry. With NASA sponsorship, Gillis developed an acoustic resonator optimized to measure the bulk viscosity and speed-of-sound dispersion in xenon near its liquid-vapor critical point. This resonator spanned a factor of 50 in frequency from 100 Hz to 5000 Hz. Before joining NIST, Gillis studied third sound in thin superfluid helium films and the heat capacity anomaly at the superfluid transition in helium confined within porous glass.


Sensor Science Division
Fluid Metrology Group

Phone: 301-975-2468
Email: keith.gillis@nist.gov