Random and systematic errors in thermophysical property measurements

Abstract

Two new model consistency tests are developed for checking assumed temperature models in the reduction of sonic velocity and J-T data to B(T). Excellent values of B(T) are then obtained from either type

New method for conversion of gas sonic velocities to density second virial coefficients

“…With Eq. 12, we used R = 83.144 cm3 -bar/mol-K and T, = 425.2 K for n-butane (both in error in Eubank et al, 1994) plus P, = 38.0 bar, b = 80.601 cm3/mol, and a = 2.9014 X 10' cm -barJK/mol* plus the heat capacity equation in Smith et al (1996) ( u/RT'. '), (16)…”

“…Real sonic data contain systematic and random errors as studied in detail by Eubank et al (1994). In one of their tests, random errors were added to a Redlich-Kwong (RK) gas at W 2 levels of 5 ppm and 50 ppm.…”

“…Any closed-form equation of state (EoS) in the form P = P(T, p ) can be used to generate B ( T ) and any of its derivatives with respect to T or t . With a separate equation to generate y ( T ) , it can also provide values of P,(T) as demonstrated by Eubank et al (1994) for the Redlich-Kwong EoS with its parameters derived from the well-known critical constraints and the critical constants for n-butane. We again find P,(T) and then find expressions for its temperature derivatives in Eq.…”

“…However, accurate measurement of B(T) with conventional P-V-T apparatus is expensive, tedious, and difficult, especially for polar gases that show strong molecular adsorption to the container walls. Nonpolar gases also show adsorption for subcritical temperatures where the vapor pressure limits the range of measurements and errors of f 0.03% in the density propagate to f 3% in B ( T ) (Eubank et al, 1994).…”

“…January 2001 propagation factors of 500 (Eubank et al, 1994) so that errors of +20 ppm in sound speeds become _+ 1% in B(T).…”