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The Second Interaction (Cross) Virial Coefficient for Moist Air
Richard W Hyland1, Arnold Wexler1
1Institute for Basic Standards, National Bureau of Standards, Washington, D.C. 20234.
Summary
Calculations of the second virial coefficient for water vapor and air were performed using National Bureau of Standards (NBS) data. Results were compared with other experimental and theoretical values, providing an empirical equation for interpolation.
Area of Science:
- Thermodynamics
- Physical Chemistry
- Atmospheric Science
Background:
- The second virial coefficient (B) is crucial for understanding gas behavior and intermolecular forces.
- Accurate B values are essential for thermodynamic models and atmospheric predictions.
- Existing data for water vapor and air B coefficients have varying uncertainties.
Purpose of the Study:
- To calculate the second virial coefficient (B) for water vapor and air.
- To compare calculated B values with existing experimental and theoretical data.
- To develop an empirical equation for B coefficient interpolation and extrapolation.
Main Methods:
- Utilized enhancement data obtained at the National Bureau of Standards (NBS) at 30, 40, and 50 °C.
- Performed calculations for the second virial coefficient (B).
- Compared results with data from Politzer and Strebel, Webster, Goff et al., Mason and Monchick, and Chaddock.
Main Results:
- Presented calculated second virial coefficients (B) for water vapor and air.
- Provided an empirical equation for interpolation and extrapolation of B values.
- Quantified uncertainties: random uncertainty ranged from 0.7% to 1.4%, and systematic uncertainty ranged from 4% to 6%.
Conclusions:
- The study provides reliable B coefficient values for water vapor and air based on NBS data.
- The developed empirical equation facilitates B coefficient estimation across a temperature range.
- The quantified uncertainties aid in assessing the precision of the calculated B values.
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