Subatmospheric vapor pressures evaluated from internal-energy measurements
- National Inst. of Standards and Technology, Boulder, CO (United States)
Vapor pressures were calculated from measured internal-energy changes in the vapor + liquid two-phase region, {Delta}U{sup (2)}. The method employed a thermodynamic relationship between the derivative quantity ({partial_derivative}U{sup (2)}/{partial_derivative}V){sub T} and the vapor pressure (p{sub {sigma}}) and its temperature derivative ({partial_derivative}p/{partial_derivative}T){sub {sigma}}. This method was applied at temperatures between the triple point and the normal boiling point of three substances: 1,1,1,2-tetrafluoroethane (R134a), pentafluoroethane (R125), and difluoromethane (R32). Agreement with experimentally measured vapor pressures near the normal boiling point (101.325 kPa) was within the experimental uncertainty of approximately {+-}0.04 kPa ({+-}0.04%). The method was applied to R134a to test the thermodynamic consistency of a published p-p-T equation of state with an equation for p{sub {sigma}} for this substance. It was also applied to evaluate published p{sub {sigma}} data which are in disagreement by more than their claimed uncertainty.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 669893
- Journal Information:
- International Journal of Thermophysics, Vol. 18, Issue 1; Other Information: PBD: Jan 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
Molar heat capacity at constant volume of difluoromethane (R32) and pentafluoroethane (R125) from the triple-point temperature to 345 K at pressures to 35 MPa
Measurements of the vapor pressures of difluoromethane, 1-chloro-1,2,2,2-tetrafluoroethane, and pentafluoroethane