Experimental study of gas flow through a multi-opening orifice

Gas flow through an orifice can be determined with high accuracy based only on the geometrical dimensions of the orifice and the upstream and downstream pressures when the flow is purely molecular. An orifice with a number of smaller openings in parallel can be used to maintain the molecular flow at higher pressure and high total conductance of the orifice. The question of how close such openings can be without influencing each other is important for practical design. This problem was studied experimentally. Changes in the total conductance versus pressure were followed for a set of multi-opening orifices with regularly arranged differently spaced circular openings. The experimental results show that no influence on the flow through a single opening can be observed at sufficiently distant opening, over the entire pressure range. At centre-to-centre distances shorter than approximately three times the diameter of the opening, notable differences in the total conductance can be seen in the pressure range where the transition from the molecular to transitional flow regime occurs.

► Problem of minimum mutual distances of openings is solved experimentally.
► Critical distance of circular openings is about three times the diameter.
► Question is important at designs of multi-opening orifices.