Molecular Diffusion Studies in Gases at High Temperature. I. The ``Point Source'' Technique

Abstract

Experimental apparatus and technique for a new method of measuring the diffusion coefficients of gases are described and critically discussed. The method makes use of the steady injection of a trace gas from a fine, hypodermic tube (essentially a ``point source'') into a slow, uniform, laminar stream of a second (carrier) gas. Measurements of the trace gas concentration downstream of the source by means of precise gas sampling permit the binary diffusion coefficient to be determined. By heating the carrier gas the measurements may be extended to fairly high temperatures. Another advantage offered by the method is that the trace gas concentrations involved are essentially zero, so that uncertainties regarding the concentration dependence of the diffusion coefficient are avoided. Results of about ±1% precision over the temperature range 300–1150°K are presented for the systems He–N₂ and CO₂–N₂.