Rarefied flow through sudden enlargements

Results of an experimental study on rarefied gas flow through circular tube with sudden increase in its cross-sectional area are presented. The Knudsen numbers considered are from 0.0026 to 1.75, which encompass the flow regimes from near continuum to significantly rarefied. Upstream pressures of 0.003 to 2.00 torr were considered. For every upstream pressure value the pressure ratios across the passage covered were from 2 to 100. On the geometrical side the length to diameter ratio of the model was varied from 1 to 10 for each of the three models tested, which had the diameter ratios of 1.84, 2.21, and 3.32. The experimental results show that the flow and geometrical parameters considered influence the discharge through sudden enlargement very strongly in the transition regime of rarefied flows. Results presented highlight the effect of the relief due to the sudden area change on discharge at different levels of upstream pressures. Also, it is evident from the results that the relief is almost independent of the pressure ratio across the passage. © 1995.