IAPWS95: Properties of Water from IAPWS-95


Calculate thermodynamic properties of water following the IAPWS-95 formulation.


  IAPWS95(property, T = 298.15, rho = 1000)
  IAPWS95.idealgas(p, delta, tau)
  IAPWS95.residual(p, delta, tau)



character, name(s) of property(s) to calculate


numeric, temperature (K)


numeric, density (kg m^-3)


character, name of property (Helmholtz free energy or its derivatives)


numeric, density divided by critical density


numeric, critical temperature divided by temperature


IAPWS95 provides an implementation of the IAPWS-95 formulation for properties (including pressure) calculated as a function of temperature and density.

The IAPWS95 function returns values of thermodynamic properties in specific units (per gram). The IAPWS-95 formulation follows the triple point convention used in engineering (values of internal energy and entropy are taken to be zero at the triple point).

IAPWS95.idealgas and IAPWS95.residual are supporting functions to IAPWS95 for calculating the ideal-gas and residual parts in the IAPWS-95 formulation. The value of p can be one of phi, phi.delta, phi.delta.delta, phi.tau, phi.tau.tau, or phi.delta.tau, to calculate the specific dimensionless Helmholtz free energy (phi) or one of its respective derivatives.

For IAPWS95 the upper temperature limit of validity is 1000 °C, but extrapolation to much higher temperatures is possible (Wagner and Pruss, 2002). Valid pressures are from the greater of zero bar or the melting pressure at temperature to 10000 bar (with the provision for extrapolation to more extreme conditions). The present functions do not check these limits and will attempt calculations for any range of input parameters, but may return NA for properties that fail to be calculated at given temperatures and pressures and/or produce warnings or even errors when problems are encountered.


A data frame the number of rows of which corresponds to the number of input temperature, pressure and/or density values.


Wagner, W. and Pruss, A. (2002) The IAPWS formulation 1995 for the thermodynamic properties of ordinary water substance for general and scientific use. J. Phys. Chem. Ref. Data 31, 387–535. http://dx.doi.org/10.1063/1.1461829

See Also

util.water for properties along the saturation curve (WP02.auxiliary) and calculation of density from pressure and temperature (rho.IAPWS92). water.IAPWS95 is a wrapper around IAPWS95 and the utility functions, which converts the specific units to molar quantities, and is used in higher-level functions (water).


## calculate pressure for given temperature, density
P <- as.numeric(IAPWS95("P", T=500, rho=838.0235))

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