Volume 27, Issue 4, July 1998
Index of content:
Revised Formulation for the Refractive Index of Water and Steam as a Function of Wavelength, Temperature and Density27(1998); http://dx.doi.org/10.1063/1.556029View Description Hide Description
Schiebener et al. published a formulation for the refractive index of water and steam in 1990 [J. Phys. Chem. Ref. Data 19, 677 (1990)]. It covered the ranges 0.2 to 2.5 μm in wavelength, −12 to 500 °C in temperature, and 0 to 1045 in density. The formulation was adopted by the International Association for the Properties of Water and Steam (IAPWS) in 1991. In the present article, the data, after conversion to ITS-90, have been refitted to the same functional form, but based on an improved equation of state for water adopted by IAPWS in 1995. The revised coefficients are reported, and some tabular material is provided. The revised refractive-index formulation was adopted by IAPWS in 1997 and is available as part of a National Institute of Standards and Technology Standard Reference Database. For most conditions, the revised formulation does not differ significantly from the previous one. A substantial improvement has been obtained in supercooled water at ambient pressure, where the previous formulation was defective. Special attention has been paid to the behavior of the refractive index in the near infrared, where strongly oscillating data were reported after the correlation of Schiebener et al. had appeared, leading to subsequent curtailing of the range of validity of the formulation. Newer results do not show these oscillations. They are compared with the revised formulation.
An International Standard Equation of State for the Thermodynamic Properties of HFC-125 (Pentafluoroethane)27(1998); http://dx.doi.org/10.1063/1.556021View Description Hide Description
An 18-coefficient modified Benedict–Webb–Rubin equation of state for HFC-125 (pentafluoroethane) has been developed. Correlations of vapor pressure and saturated liquid density are also presented. This equation of state has been developed using experimental data for the relationship of pressure-volume-temperature of fluid, saturation properties, isochoric heat capacity data, and speed of sound data. The equation of state is valid in the superheated gaseous phase and the compressed liquid phase at pressures up to 68 MPa, densities to and temperatures from the triple point (172.52 K) to 475 K. This equation of state has been selected as an international standard formulation for HFC-125 based on an evaluation of the available equations of state by Annex 18 of the International Energy Agency.
27(1998); http://dx.doi.org/10.1063/1.556022View Description Hide Description
A compilation is presented of published experimental and computational reports (191 references) on the structures, vibrational frequencies, molar enthalpies of formation and standard entropies for 26 gas phase boranes for the temperature range from 0 to 1500 K. The thermochemicalproperties have been collated via standard programs and are listed in a convenient tabular format. Levels of uncertainties in the thermodynamic functions have not been assessed, because of the limited experimental and computational data. The tabulated values were fitted to standard seven-parameter (NASA) polynomials to facilitate the computation of enthalpies of formation,entropies, and heat capacities for modeling purposes. Within the context of intrinsic uncertainties, the equilibrium compositions of the gas phase were calculated, constrained to constant temperature and volume, for several boron–hydrogen (B/H) ratios, at various temperatures and pressures. The (unexpected) results indicate that in none of the reported gas-phase kinetics studies was thermodynamic equilibrium attained, even though the measured concentration profiles appear to extrapolate to steady state product distributions.