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|Author(s):||Michael R. Moldover; Mark O. McLinden;|
|Title:||Using Ab Initio "Data" to Accurately Determine the Fourth Density Virial Coefficient of Helium|
|Published:||June 25, 2010|
|Abstract:||We combine accurate ab initio calculations of the second and third density virial coefficients, B(T) and C(T), of 4He with measurements of its pressure-density-temperature behavior to determine the fourth density viral coefficient D(T). The measurements were made with a two-sinker, magnetic-suspension densimeter at pressures up to 38 MPa. The measurements on isotherms from 223 K to 323 K were previously published; new measurements from 323 K to 500 K are presented here. On each isotherm, a regression of the virial expansion was constrained to the ab initio values of B(T) and C(T); the regression determined D(T) as well as two apparatus-dependent parameters that compensated for systematic errors in the measurements. The relative uncertainty of D(T) ranged from 2.9 % at 223 K to 10.7 % at 400 K to 26.4 % at 500 K with a coverage factor of k = 2. This uncertainty is 1/6th of the uncertainty obtained without the ab initio values of B(T) and C(T). The apparatus-dependent parameters can be used to calibrate the densimeter, and this will reduce the uncertainty of future measu|
|Citation:||Journal of Chemical Thermodynamics|
|Pages:||pp. 1193 - 1203|
|Keywords:||helium, virial coefficients, two-sinker densimeter, calibration, equation of state, reference data, gas metrology, fourth virial coefficient|
|Research Areas:||Metrology, Chemical Engineering & Processing, Physical Properties, Thermophysics|