Mutiple Reservoir Systems

[ktulu]

I am working on a mutiple reservoir problem where the flow rate is not given. In the CERM, using Case #1, they state that a flow rate can be assumed so the pressure at a point can be determined. Then you validate the assumption, making changes if the numbers do not work out cleanly.

I know this is a more involved problem than would be seen on the test due to mutiple iterations that could be used, but my question is: What is a typical "best guess" for an initial assumption? They say you can use pipe velocity as a guide.

So, say I have a 3" schedule 40 steel pipe. Would 4.30 ft/sec be a reasonable assumption for flow rate? That would give me 45 gpm, which I would convert to cfs to solve the problem.

TIA.

ktulu

 

[sehad]

I am working on a mutiple reservoir problem where the flow rate is not given. In the CERM, using Case #1, they state that a flow rate can be assumed so the pressure at a point can be determined. Then you validate the assumption, making changes if the numbers do not work out cleanly.
I know this is a more involved problem than would be seen on the test due to mutiple iterations that could be used, but my question is: What is a typical "best guess" for an initial assumption? They say you can use pipe velocity as a guide.

So, say I have a 3" schedule 40 steel pipe. Would 4.30 ft/sec be a reasonable assumption for flow rate? That would give me 45 gpm, which I would convert to cfs to solve the problem.

TIA.

ktulu

For some reason 5 ft/s is standing out as a good velocity. I'm thinking that is the number that I used. I only did these problems in practice and it's been a while ago. I'll check my notes when I get back home and see.

 

[IlPadrino]

I've got a table called "Applied Process Design for Chemical and Petrochemical Plants, Table 2-1, Suggested Fluid Velocities in Pipe and Tubing" (from... wait for it... TESTMASTERS!) that lists suggested trial velocities. For water service (steel) it gives 3-8 (avg 6) fps. So that's probably a good place to start. As you already wrote, it is easy to convert velocity to flow rate.

With any iterative process, you'll do fine so long as you are orders of magnitude right on your first estimate. However, consider this: there are only four answers given... why not plug-and-chug backwards?