Combined Dielectric-Constant Gas Thermometry and Expansion Experiments - Virial Coefficients of Argon

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Combined Dielectric-Constant Gas Thermometry and Expansion Experiments – Virial Coefficients of Argon In this thesis, the capabilities arising from a combination of Dielectric-Constant Gas Thermometry (DCGT) with two expansion methods are investigated regarding the determination of real gas properties. For DCGT, pressure and capacitance data is utilized simultaneously to determine the so called DCGT-virial coefficients. They are combinations of density (B(T), C(T),… ) and dielectric virial coefficients (b(T), c(T),…) whereas it is not possible to differ between both contributions. An independent determination of B(T), C(T),… and b(T), c(T),… was enabled by a combination with the Burnett expansion principle and its dielectric equivalent, respectively. An innovative apparatus was developed that allows to perform the complex measurements simultaneously and automated. Novel working equations directly including dead volumes at different temperatures as well as the deformation of the system under pressure were deduced. Based on these equations and Monte-Carlo simulations, uncertainty budgets for all three approaches were derived. The principle was validated by isothermal measurements with argon at temperatures of 254 K, 273 K, 296 K and 303 K for pressures between 1 MPa and 7 MPa. The set of derived virial coefficients was self-consistent and in good agreement with available literature values mostly on the level of the standard uncertainties. Additional measurements with helium were performed to constraint the apparatus constant which lowers the uncertainty for the expansion experiments by a factor of two. The reached relative standard uncertainties are 0.15 % to 0.3 % for the second and 1.5 % to 3 % for the third DCGT-virial coefficient. For B(T), 0.5 % to 0.9 % were achieved while for the two orders of magnitude smaller value of b(T) the relative standard uncertainties are in the order of 15 %.

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Chistian Günz

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Burnett expansion principle Dielectric-Constant Gas Thermometry Monte-Carlo-simulations PTB Thermodynamik expansion experiments real gas properties relative standard uncertainties

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