Gaseous Diffusion Coefficients of FC14, HFC23 and FC116 into Air, Nitrogen and Oxygen

Abstract

The gaseous diffusion coefficients of FC14 (tetrafluoromethane, CF₄), HFC23 (trifluoromethane, CHF₃) and FC116 (hexafluoroethane, C₂F₆) into dry air, nitrogen and oxygen have been measured at temperatures 303, 333, 363, 393, 423 and 453 K and at atmospheric pressure by the use of the Taylor dispersion method. The diffusion coefficents of these gases into oxygen only could be measured correctly in the entire temperature range and the measurements for air and nitrogen in the temperature range 393-453 K, having abnormally small temperature coefficients, were judged to be too small. At temperatures up to 363 K where all the measurements are considered to be correct, the diffusion coefficients do not vary in practice on substituting pure nitrogen or oxygen for dry air. The present results with reasonable temperature coefficients can be reproduced well by the functional form D = AT^B, where D (cm²s^-1) is the diffusion coefficient at 101.325kPa (1 atm) and T(K) is the absolute temperature. The constants A and B are as follows: FC14-(air, nitrogen, oxygen), A = 1.21×10^-5, B = 1.63; HFC23-(air, nitrogen, oxygen), A = 1.74×10^-5, B = 1.58; FC116-(air, nitrogen,oxygen), A = 4.61×10^-6, B = 1.75.