Abstract
An apparatus for the measurement of gaseous diffusion coefficients D by the Stefan method was developed and the diffusion coefficient of diethyl ether vapor into dry air was measured at 303.15 K (30 °C)and at atmospheric pressure, using a Pyrex evaporation tube (inner diameter 4×10-3 m). The diffusion path lengths L (≃ 80, 120, 160×10-3 m) and the air flow rates Q (0.8-83×10-6 m3s-1 (50-5000 cm3min-1)) were systematically changed. A loose polyester cotton plug was inserted into the horizontal tubing (inner diameter 8×10-3 m) just upstream of the mouth of the evaporation tube to straighten air flow and the results were compared with those obtained without the cotton plug. The use of the cotton plug reduced scatter in the experimental data and the air flow rate Q suitable to the measurement increased significantly from 3-16×10-6 m3s-1 (200-1000 cm3min-1) to 10-33×10-6 m3s-1 (600-2000 cm3min-1). At L ≃ 80×10-3 m, the measurement could be done reasonably only with the cotton plug. The present experimental value (D = 0.093×10-4 m2s-1) agrees well with the extrapolation of our experimental data obtained by the Taylor dispersion method to lower temperature.
