Abstract
When injecting gas into a vacuum system, quite often the gas is distributed through a gas injection manifold. However, designs normally rely upon practical experience. By considering the manifold arrangement as a network of flow restrictions it is possible to optimize the distribution of gas throughout the manifold. The methodology for determining the flow distribution through the two simplest topologies of gas manifold, single- and double-opening manifolds from a single-gas injection point, is derived in this article. It is shown that the double-opening manifold topology tends to provide more uniform flow distribution than the single-opening manifold topology for similar conductance ratios. The results of this work include a summation formula for the single-opening manifold. In addition, guidelines for one type of tailored flow manifold are given. Finally, three basic design rules are presented: (1) use as few holes in the manifold as possible, (2) use a double opening manifold when possible, and (3) specify tube dimensions such that the tube/spray hole conductance ratio is maximized.

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