Pick the Best Compressed Air Inlet for Loop Pipeline

[downeast]

Which compressed air inlet to a ring (loop) pipeline would likely be best in terms of least turbulance and best flow (avoiding dead head)?

Given:
1) The inlet has to be in the corner of the rectangular loop.
2) Air consumption will be constant and evenly distributed throughout the loop.
3) The loop will be level.

Is the design on the left or the right better in the following diagram (or neither)?

 

[Baluncore]

Welcome to PF.
I would use the one on the right.
The air does not flow in a complete loop, it flows half way round the loop in each direction. The balance of the two flows is corrected at the opposite point to the inlet.

 

[downeast]

Hi, and thanks for your input.

Is it at least safe to say with the design on the left, the two opposing air flows might meet slightly closer to the inlet (bottom right of the loop), and with the design on the right, they would likely meet closer to the top left of the loop (opposite corner of the inlet)?

Wherever the opposing flows meet and the intial turbulance that it causes, would it have any real effect on consumption in that area. I assume even if so, it would just be momentary and only on startup.

 

[Baluncore]

I was considering steady state, not a transient at the onset of flow.
The principles to follow are; do not change the direction of fluid flow back on itself. Minimise the distance that the fluid must flow.

With Left, air must flow a maximum of 100% round the loop to avoid counter-flow at the supply connection. Average flow is 50% of the total at a distance of 50% round the loop.

With Right, the two streams separate early, then flow a maximum of 50% around the loop, with 25% flow, at 25% of the loop on each side. That lower flow for a shorter distance means that Right will be the more efficient.

 

[downeast]

Excellent, thank you so much for taking the time to explain. Putting it that way it now makes sense to me.

 

[Benjies]

Are you two discussing a configuration best suited for a compressed air line that will service potential users at adequate pressures along the ring? Just wanting to understand the discussion here. If so, then I'd support Baluncore's statement- if adequate energy is imparted to the flow to enable it to reach all points of the line then his configuration would in theory require less energy due to reduced line losses.

I suppose my confusion and concern though comes from the diagram and discussion seeming to indicate that the line must be a closed-loop (which makes sense for practical purposes). We have pretty awful pressure issues at the top-left of the right-side configuration, as the singularity where the two diverged flows meet would have to resolve itself somehow (either by bursting the pipe or slowly moving the point of flow convergence towards the inlet until flow direction becomes universally one-directional).

My background is largely in open-loop gas flows from propulsion and don't know much about looped flows with gases, so please educate me! Thanks.

 

[Baluncore]

Are you two discussing a configuration best suited for a compressed air line that will service potential users at adequate pressures along the ring?

Yes, but the users are spread evenly around the ring, and flow is continuous in time. I think it is the equivalent to an electrical ring main.

My background is largely in open-loop gas flows from propulsion and don't know much about looped flows with gases, so please educate me!

I am also here to learn.
What is an "open-loop gas flow" ?
Is your "loop" a control feedback loop ?

 

[Benjies]

Thanks for the response and questions. I suppose my "open-loop gas flow" is radically different than what you might be picturing, because the residence time of gases and liquid in engines is incredibly low compared to pipelines that service neighborhoods. Controls aside, an engine just spits out the gases in one direction out of the engine, thus all of the gases/liquids do not enter any closed-loop flows, or feedback flows. The gases enter the engine, and then just fly out of the nozzle, never re-encountering any part of the engine a second time.

Frankly though, two things:

1) My verbiage may be challenged and roping in the word "loop" to begin with may be a misnomer since the gas/liquid flow never sees any part of the engine twice.
2) Rocket engines have so many tertiary flowpaths and are so complex that it wouldn't surprise me if there were in fact a couple of closed-loop flows, where propellant flows through a portion of the engine twice. See the Space Shuttle Main Engine (Imgur). For a simpler example, see Autogenous Pressurization (Wikipedia) for propellant re-entering the storage tank (the closest thing I can think of for a closed-loop flow in an engine, even though the propellant simply enters the tank it began in).