Experience of Measurements with a Vibrating-Wire Viscometer on Natural Gases

A vibrating-wire viscometer designed for high-precision measurements on gases was applied to determine the viscosity coefficient of natural gases. The experiments were carried out at nominal temperatures of 260, 280, 300, and 320K up to pressures of 20MPa. A suitable experimental procedure had to be developed in order to minimize the influence of the retrograde behavior and the effects of adsorption and desorption that have to be expected in the thermodynamic range under study. As a consequence, the series of measurements could successfully be performed starting from vacuum followed by successive points up to the maximum pressure. The densities were calculated according to the ISO 12213 standard using the AGA-8 detailed characterization equation. The isotherms could adequately be represeInted with power series in density restricted to the fourth power. The reproducibility of the measurements was ±0.2%, whereas the uncertainty is estimated to be ±0.5%.