Thermal conductivities of gaseous mixtures containing polar gases. Part 2.—One polar constituent

Abstract

The thermal conductivities of seven sets of binary gaseous mixtures containing one polar constituent (sulphur dioxide or ammonia) have been measured at 50 and 100°C. The mixtures investigated were : SO₂+ Ar, SO₂+ N₂O, SO₂+ CO₂, SO₂+ CH₄, and NH₃+ Ar, NH₃+ N₂O, NH₃+ CH₄. The apparatus was of the two-wire type used previously. The precision of the measurements is about 1 %. The thermal conductivities of mixtures containing ammonia show positive departures from the molar average; when SO₂ is the polar constituent the thermal conductivities of the mixture either show negative departures from the molar average (+CH₄ and +Ar) or else vary almost linearly with composition (+N₂O and +CO₂). The results are analyzed in terms of the Hirschfelder-Eucken approximation to rigorous theory which underestimates the experimental observations by 3.5 % on average. Modifications to the Hirschfelder-Eucken theory based on a re-apportionment of the contributions to translational and internal energy transport are also examined, and are shown to improve agreement with experiment. Calculations for systems containing argon show some slight anomalies, which are discussed. A simple modification which uses a theoretical value for f_int rather than for f_trans, decreases the average discrepancy between the observed and calculated thermal conductivities to 0.5 %, which is within the experimental uncertainty of the measured values.