calculating head height

[dpiekkola]

I need to determine the height of the fluid that will form above my drain pipe. I have a flow of 1600 gpm flowing into a tank through a 12 in diameter pipe. The tank has a 14 in diameter drain pipe in the bottom that is gravity feeding into another vessel. Length of 14 in drain pipe is 4 feet. Both the box and the other vessel are at atmosphere. I am trying to determine what the height fluid will be in the initial tank to prevent overflow. thx.

 

[Killstadogg]

I think what you should do here is find your head loss for flow through your 14" pipe @1600 gpm (include entrance and exit losses and whatever other minor losses there may be). That amount of head loss will be roughly what hight of fluid you need to push your required flow through the drain. Add a ~100% factor to that and call it good.

 

[DLite30]

That much flow through a 14" is about 3.32 fps. That's no where near enough volume to get a solid stream through it. As long as your tanks are ventilated well enough, then you should see no fluid build up in the top tank.

 

[Killstadogg]

According to DLite30, you can just pour the water onto a flat plate and it will drain into your final tank. Couldn't imagine that working too well. The same thing is going on with the drain in your bathroom sink, but you still have a basin to collect water in.

Yes there will be all kinds of vortices and the flow will not be fully wetted flow, but that indicates that you would get LESS flow through the pipe than assuming fully wetted flow without all these weird fluid effects. The last thing you want to do is design this and have water spilling over the edge - you'll look like a dumbass. I calculated the head required to push that much water through the 14" pipe and it's roughly 4". So double that number as a guesstimate of how the vortices, unknowns, etc. will affect your flow and you get 8". That's not all that high; so you'll want to now look at your fluid stream into the draining tank. Does this fluid come in a way that will cause a lot of sloshing? If so then you need to consider that. If not than 8" to 12" is probably fine.

 

[racookpe1978]

And don't forget to smoothly Slope the bottom of the upper and lower tanks towards their drain pipes. That difference in height will help your flow out.