THERMOPHYSICAL PROPERTIES OF NATURAL GASES FOR ONLINE METERING

The evaluation of the background transport properties of natural gas m ulticomponent mixtures over a moderate temperature and pressure range around ambient is considered in the context of the development of cert ifiable sensors for the measurement of mass and energy fluxes. The bes t available, theoretically based procedures to predict the properties are compared with experimental information to test the internal consis tency, accuracy, and range of validity of the prediction. This is of p rimary concern to the demonstration of the viability of such sensors. It is shown that for low to moderate pressures, it is possible to achi eve an internal consistency of the order of a Few parts in a thousand and an accuracy of better than +/- 1%. At very high pressures the pred ictive scheme is also satisfactory, with errors of the order of a few percent. However, the procedure employed here systematically underesti mates the thermal conductivity of the gas mixtures studied for interme diate pressures owing to the neglect of the critical enhancement even for temperatures quite far removed from the critical. The range of con ditions for which the critical enhancement of the thermal conductivity is significant in mixtures is explored with data for binary mixtures of methane and ethane.