calculation with over flow

[Cristian Cox]

Hello, please I need some help.
In the picture below you can see a water tank that has an over flow.
this overflow comes from the bottom of the tank and as you can see it goes all the way up through pipe "a".
so the internal water line matches with the pipe "a" line and the overflow goes to waste through pipe b

I have been using Darcy Wasibach equation but I am not sure if I can use since it might be that pipe b is not 100% full of water.


I have a network of 150 tanks delivering by overflow to a 4 tanks system a the very far right.

what equation I should use? in this case? Darcy or Manning (open flow channel)?

I would apreciate your help

best regards

Cristian

 

[JStephen]

My suggestion:
1) Check flow rate assuming you just removed that tee where it says "Open" and just let the water discharge into the atmosphere. That would be one limiting flow rate.
2) Check flow rate assuming pipe B is full with flow on through the whole system. That would be a second limiting flow rate.
Using Bernoulli-equation variations, you're primarily concerned with energy at the beginning and end of the pipeline. It is possible that this analysis will overlook "impossible" conditions in the intermediate locations. Specifically, the flow rate calculated by #2 may also calculate out with a negative gauge pressure at that elevated tee, which violates the "open" condition. If so, then the flow from #1 should limit.
It's also possible that actual flow through the system might give some sort of pulsed flow and periodically be splooshing water out that open end, so it'd be helpful to have examples of similar geometry that are known to work okay.

 

[LittleInch]

I'm kind of with J Stephen here, but that network of tanks is quite something.

What are your assumptions with respect to the number of tanks overflowing at once?

I think your max flow is going to be when pipe b is full up to the open tee, otherwise it will just spill out.

Then calculate that based on a full pipe from the furthest tank to the drain tanks with that maximum head. Now this is where you need to look at max inflow and also do other tanks overflow at the same time?

If the capacity of the overflow in this situation is higher than the max inflow then you're ok and any other situation will be lower flow.

If it isn't you might end up with water spilling out of the open end. Is that a problem?

An overflow should always be a fault in the system and not a normal or regular occurrence.

To start with the flow will be open channel / vertical pipe flow which as the flow increases will transition to full pipe flow. This will likely involve some slug type flow, lots of air being dragged through the pipes and until full pipe flow is fully developed, may result in transient pressures higher than the steady state full pipe flow. So I would extend the pipe in the vent up a bit to allow for some slugging type behaviour without splashing over the top.

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