Gas Physical Property Measurements

Department Publications


Technical Publications

Contact Information

Brandon L. Ridens
Research Engineer
Pipeline Simulation
(210) 522-3459

Turbomachinery Research Facility

SwRI's Turbomachinery Research Facility

Machine to Determine Density

Determination of density based on highly precise mass measurements at constant volume under controlled pressure and temperature conditions

Machine to Determine Speed of Sound

Determination of speed of sound using half-wave resonant frequency

Machine to Determine Specific Heat

Determination of specific heat based on temperature rise measurements from the addition of heat energy within a constant volume

Compressor design optimization focuses on reducing entropy-generated losses and achieving an optimum Mach number at each inlet stage. The mechanical design of the compressor relies on calculation of relative gas velocity, temperature rise and flow rate for the state-to-stage geometry and material selection. Effective design requires prediction of gas density, compressibility, speed of sound, and specific heats. While a large body of work is available comparing the results from various equation-of-state (EOS) models, little to no data is available to verify the results from the various EOS calculations for the ranges of pressures, temperatures and gas compositions relevant to compressor and pipeline operations. Accurate gas property prediction is a necessary component for proper design, improving overall efficiency, and making accurate predictions, and reducing operating costs.

Southwest Research Institute (SwRI) has developed high-accuracy test methods for density, speed of sound, and specific heat determinations to enable compressor and turbomachinery designs for a wide range of operating conditions, including the high pressure, supercritical regime. Based on these measured properties, accurate enthalpy and entropy can be determined using SwRI calculated derivations.

The Institute performs high-pressure gas property testing using specialized anti-corrosion, high pressure, SwRI-designed test fixtures to meet the low uncertainty requirements of gas property testing campaigns. All test instrumentation is maintained and calibrated over the expected range of conditions prior to the test. The test fixtures and SwRI test facilities are capable of handing hydrocarbon, high CO2 and high H2S (acid gas) mixtures. On site SwRI testing can also provide gas species analysis at particular temperature and pressure points to verify the two-phase region and liquid/gas content determination.

Current Capabilities

  • Density (compressibility factor), speed of sound, dew point, and specific heat at constant volume (Cv)
  • Stable gas mixtures including CO2, hydrocarbons, combustibles, non-combustibles, and acid gas blends
  • 0-11,000 psi pressure range
  • Ambient to 450°F temperature range
  • Gas sampling and species determination near critical point (gas chromatography)
  • Determination of liquid formation

For more information about acoustically induced vibration analysis and testing capabilities at SwRI or how you can contract with SwRI, please contact Brandon Ridens, at or call (210) 522-3459.

Benefiting government, industry and the public through innovative science and technology
Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.