Tc. Dayton et al., Determination of densities and heat capacities from speed of sound measurements for 1,1,1,2-tetrafluoroethane, J CHEM THER, 31(7), 1999, pp. 847-868
The speed of sound u is both formally independent of the amount of substanc
e and can be measured easily with high precision (typically Delta u/u < 1.1
0(-5)). Measurement of this quantity offers a favorable route for obtaining
density rho, molar isochoric heat capacity C-V,(m), and molar isobaric hea
t capacity C-p,C-m values. This transformation from u to other thermodynami
c properties, involves the solution of a second-order differential equation
on either isobars, or isochores. In this paper, we compare both equation s
ets for 1,1,1,2-tetrafluoroethane (HFC-134a) which is a slightly polar flui
d. In the absence of reliable experimental speed of sound data over the who
le fluid surface, an accurate Helmholtz function equation of state for HFC-
134a was used to simulate property data for this study. These data were gen
erated at reduced temperatures T-r = T/T-c between T-r = 0.75 and T-r = 1.2
5 and at reduced pressures p(r) = p/pc up to pr = 6. The isochoric equation
set was found to be more stable. For data and initial conditions without e
rrors, the fractional uncertainties in rho and C-V,C-m were 0.002 and 0.02,
respectively. Sensitivity studies were conducted on the isochoric equation
set to document effects of interpolation step size, accuracy of initial co
nditions, and presence of random errors in the data. When all sources of er
ror are included, the uncertainties in density and isochoric heat capacity
were no worse than any of the individual sensitivity studies. (C) 1999 Acad
emic Press.