Hello,

I was hoping I could get some feedback on the design of an overflow box. In particular, I want to make sure that I'm sizing the pipe correctly. I have attached a diagram with the relevant dimensions.

In short, there is a water flow of Q=36 m[sup]3[/sup]/h incoming over a weir and I must size the pipe so that the water doesn't accumulate in the box. Additionally, splashing outside the box should be kept to a minimum. The bottom end of the pipe is expected to connect to a much larger pipe that isn't expected to fill up.

After reading threads on this and other forums, the correct approach seems to be the one described in "Designing Piping for Gravity Flow" by P.D. Hills. In particular, the case I'm looking for would be "Self-Venting Flow in vertical Pipes".

Based on this, using a pipe with an inner diameter D=180 mm would result J[sub]L[/sub]*=0.296 which satisfies J[sub]L[/sub]*<0.3 (Equation 6). With this, would it be correct to assume that all incoming liquid will be drained properly, without surging? Does the length of the pipe (H2 in the diagram) matter at all for this scenario?

Another approach to this problem would be to apply the Bernoulli equation covering the height of the box plus the height of the pipe (H1+H2). This would of course include the losses due to friction and the box to pipe transition. If we assume that the bottom of the vertical pipe is exposed to atmospheric pressure (Since the much larger pipe it connects to is never full) then a pipe diameter can be calculated so that the water exits the box at the same rate that it enters it. Would it then be correct to assume that any pipe larger than that would ensure that the box doesn't fill up to H1?

I would greatly appreciate any insight you may have on how to approach this case. It's been a while since I last did fluid mechanics in college and one thing they really drilled into us is to be careful with the assumptions we make.

Also forgive me if the phrasing is awkward. I'm not a native English speaker.

I was hoping I could get some feedback on the design of an overflow box. In particular, I want to make sure that I'm sizing the pipe correctly. I have attached a diagram with the relevant dimensions.

In short, there is a water flow of Q=36 m[sup]3[/sup]/h incoming over a weir and I must size the pipe so that the water doesn't accumulate in the box. Additionally, splashing outside the box should be kept to a minimum. The bottom end of the pipe is expected to connect to a much larger pipe that isn't expected to fill up.

After reading threads on this and other forums, the correct approach seems to be the one described in "Designing Piping for Gravity Flow" by P.D. Hills. In particular, the case I'm looking for would be "Self-Venting Flow in vertical Pipes".

Based on this, using a pipe with an inner diameter D=180 mm would result J[sub]L[/sub]*=0.296 which satisfies J[sub]L[/sub]*<0.3 (Equation 6). With this, would it be correct to assume that all incoming liquid will be drained properly, without surging? Does the length of the pipe (H2 in the diagram) matter at all for this scenario?

Another approach to this problem would be to apply the Bernoulli equation covering the height of the box plus the height of the pipe (H1+H2). This would of course include the losses due to friction and the box to pipe transition. If we assume that the bottom of the vertical pipe is exposed to atmospheric pressure (Since the much larger pipe it connects to is never full) then a pipe diameter can be calculated so that the water exits the box at the same rate that it enters it. Would it then be correct to assume that any pipe larger than that would ensure that the box doesn't fill up to H1?

I would greatly appreciate any insight you may have on how to approach this case. It's been a while since I last did fluid mechanics in college and one thing they really drilled into us is to be careful with the assumptions we make.

Also forgive me if the phrasing is awkward. I'm not a native English speaker.