Diffusion of helium, carbon monoxide and sulfur hexafluoride in gas mixtures similar to alveolar gas

Abstract

Diffusion of He, CO and SF 6 (test gases, fractional concentration below 10%) was examined in gas mixtures similar to alveolar gas (14% O% 2, 6% CO 2 and 80% N 2 or other inert gas; ambient pressure; 37 C; dry or saturated with water vapor) using the same subdivided tube technique as previously applied to study of binary gas diffusion (Worth et al., 1978). The following main results were obtained. 1. 1. Significant departures from binary diffusion characteristics were not observed. Therefore, values for effective diffusion coefficient, D', in cm 2-sec, could be established for diffusion of the test gases in non-binary, multicomponent, mixtures. 2. 2. Values of D' in multicomponent mixtures were found to be in good agreement with values predicted on the basis of reciprocal binary diffusion coefficient values weighted according to fractional concentrations. 3. 3. The diffusion of a test gas was not influenced by the simultaneous diffusion of another test gas when the concentration of both test gases was low (varying from 0 to 1% during the process of diffusion). With higher test gas concentrations (varying from 0 to 10%), however, apparent interactions were observed, which could be qualitatively explained as due to changed diffusion medium. 4. 4. In the multicomponent gas mixtures studied, water vapor was found to decrease D' (compared to dry conditions) in mixtures mainly composed of light gases (He, H 2) and to slightly increase D' in mixtures containing heavy gases (SF 6). In the case of gas mixtures resembling normal alveolar gas i.e. with N 2), water vapor had no significant effect on D' of the test gases used.