No abstract

The paper re-analyzes the results of earlier, very precise measuremen~s of the viscosity of water at essentially atmospheric pressure. This is done in terms of a new, theoretically-based equation for the operation of a capillary viscometer rather than in terms of semi-empirical equations used by the original authors. The new analysis eliminates possible systematic errors and permits the establishment of reaJistic error bounds for water in its role as a standard reference substance for viscosity. The latter are smaller than those embodied in the most recent International Formulation. Btandarct values of the ratIo of vIscosIty at a temperature T to its value at 20 °0 have been derived from the re-analyzed data because the uncertainity of this ratio is an order Of magnitude smaller than that of the absolute values. The ratios are used to generate absolute values with the aid of the standard NBS datum p.= 1002.0 p'Pa s at 20 0 0. The viscosity ratiOS have been correlated with the ald of two empirical equations. The more accurate equation covers the range OOO::::t:::: 40 °0 with an unce'rtaintyof ± 0.05%.

The paper contains new, representative equations for the viscosity and thermal conductivity of carbon dioxide. The equations are based in part upon a body of experimental data that have been critically assessed for internal consistency and for agreement with theory whenever possible. In the case of the low-density thermal conductivity at high temperatures, all available data are shown to be inconsistent with theoretical expectation and have therefore been abandoned in favor of a theoretical prediction. Similarly, the liquid-phase thermal conductivity has been predicted owing to the small extent and poor quality of the experimental information. In the same phase the inconsistencies between the various literature reports of viscosity measurements cannot be resolved and new measurements are necessary. In the critical region the experimentally observed enhancements of both trans: port properties are well represented by theoretically based equations containing just one adjustable parameter. The complete correlations cover the temperature range 200 K~T < 1500 K for viscosity and 200 K~T~l000 K for thermal conductivity, ~nd pressures up to 100 MPa. The uncertainties associated with the correlation vary according to the thermodynamic state from ± 0.3% for the viscosity of the dilute gas near room temperature to ± 5% for the thermal conductivity in the liquid phase. Tables of the viscosity and thermal conductivity generated by the representative equations are provided to assist with the confirmation of computer implementations of the calculation procedure.

No abstract

When representative equations for the viscosity of carbon dioxide were published in 1990, it was recognized that, owing to inconsistencies among the available experimental liquid viscosity data which could not be resolved, new measurements were necessary. Since then, two new sets of measurements have been performed and it is appropriate to revise the published equations in order to improve their performance in the liquid region. In the previous work, the excess viscosity was represented by two separate equations, one for the gas phase and the other, a provisional one, for the liquid phase. Both equations were joined by a blending function. In the present work, the excess viscosity for the whole thermodynamic surface is represented by one equation. The resulting overall viscosity representation for carbon dioxide covers the temperature range 200 K⩽T⩽1500 K and densities up to 1400 kg m−3. In terms of pressure, the viscosity representation is valid up to 300 MPa for temperatures below 1000 K, whereas for higher temperatures and owing to the limitation of the equation of state used, the upper pressure limit is restricted to 30 MPa. The uncertainties associated with the proposed representation vary from ±0.3% for the viscosity of the dilute gas near room temperature to ±5.0% at the highest pressures. Tables of viscosity generated by the representative equations are included for easy reference and to assist validation of computer coding.