AN INTERNATIONAL STANDARD EQUATION OF STATE FOR DIFLUOROMETHANE (R-32) FOR TEMPERATURES FROM THE TRIPLE POINT AT 136.34 K TO 435 K AND PRESSURES UP TO 70 MPA

A fundamental equation of state for the Helmholtz free energy of R-32 (difluoromethane) is presented which is valid from the triple point at 136.34 K to 435 K and pressures up to 70 MPa. It is based on accurate measurements of pressure-density-temperature (p,rho,T), speed of soun d, heat capacity, and vapor pressure currently available. New values f or the isobaric heat capacity c(p) degrees of the ideal gas calculated from spectroscopic data taking into account also first order anharmon icity corrections are presented. The Helmholtz free energy equation of state has 19 coefficients and represents all selected experimental da ta within their estimated accuracy with the exception for heat capacit ies and speed of sound in the region close to the critical point. Typi cal uncertainties are +/-0.05% for density, +/-0.02% for the vapor pre ssure and +/-0.5%-1% for the heat capacity. This equation of state has been compared to equations developed by other research groups by Anne x 18 of the International Energy Agency and has been selected as an in ternational standard formulation for the thermodynamic properties of R -32 by this group. (C) 1997 American Institute of Physics and American Chemical Society. [S0047-2689(97)00306-1].