| Rarefied gas flow under pressure, concentration, and temperature gradients is of interest in studies of film or crystal growth by PVT/CVD. Two bulbs connected by a capillary (or a bundle of capillaries) are used to investigate the pressure difference phenomena arising from these gradients and to have a better understanding of the interaction between gas molecule and a surface in the PVT/CVD process. Capillary flow of gas mixtures is also of importance in description of the gas behavior in porous media, such as membranes and zeolites, growth of crystals of novel materials in microgravity environments, and in separation of gases.; The mutual diffusion of two pure gases at a constant temperature were measured in a glass two-bulb apparatus with a single capillary and in a stainless steel apparatus with a bundle of seven capillaries under a concentration gradient. Comparison of experimental and theoretical data in the slip flow regime, where the diffusion slip is a dominating effect shows the accuracy of the theoretical expressions for the diffusion slip coefficient. Experimental data of He:Ar, He:N{dollar}sb2{dollar}, and N{dollar}sb2{dollar}:Ar mixtures were used to calculate the tangential momentum accommodation coefficients, {dollar}alphasb{lcub}rm itau{rcub}{dollar}, of individual component of the gas mixture and were found to be equal to 0.9, 1.0, 1.0 for He, N{dollar}sb2{dollar}, and Ar, respectively.; The thermal transpiration effect arising from a temperature gradient was examined in the stainless steel apparatus for simple gases. A recent theory on the solution of the Boltzmann equation for a rigid sphere model was used to compare the experimental data over a wide range of Knudsen numbers. The results showed that the theory was in a quantitative agreement with the experimental data for Ar, CO{dollar}sb2{dollar} and He. The tangential momentum accommodation coefficients for He, Ar, and CO{dollar}sb2{dollar} were found to be 1.00, 1.00, and 0.95 respectively.; The thermal transpiration effect was studied in the same stainless steel apparatus for mixtures of He:Ar, He:CO{dollar}sb2{dollar}, and Ar:CO{dollar}sb2{dollar}, at different compositions. The measurements performed in the slip flow regime confirm the accuracy of the theoretical expressions for the slip coefficients. The accommodation coefficients for He, Ar, and CO{dollar}sb2{dollar} are found to be 0.75, 0.75, 0.80 respectively.; The experimental data provide confirmation that the new theoretical slip expressions. They also provide valuable information of the accommodation coefficients for flows caused by the pressure, concentration, and temperature gradients. |
