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.