water running over a border

[milena02]

Maybe a wrong forum to post it.
If so please redirect me.
A swimming pool will have all around it a leveled border.
Width 4.4 meter , length 13 meter
The pump can deliver 35 m3/hour.
The water will overflow all around the border.
Now the one million dollar question.
HOW MUCH WILL THE WATER RISE FROM THE BORDER??

 

[prex]

I'm not expert in weirs, but the relationship for Q in point 1) of the 2nd reference given by cvg seems to be completely out concerning dimensions. However that relationship reduces to Q=bh^3/2/3 for the simple case under examination.
Another reference gives me the following equation:
q=Kh^3/2
where K is a dimensional constant depending only on fluid density (and the gravitational constant) and q is q=Q/b (b=width of weir or pool perimeter in the present case). So the formula above is confirmed.
In conclusion, if the goal is to keep the same crest height in the model as in the actual pool, then simply Q/b must be kept constant.

prex

http://www.xcalcs.com

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[milena02]

Hi all, thanks again for your post.
I have to ask you , please understand my point of view.

1._ It is not a open channel weir.
In a open channel, weir it is only one side , 2 sides are the channel border , and the 4th is the water upward the channel, so the the water is constrain in 3 sides.

2._ The pool area is the same as a BIG HUGE pipe end standing vertical, so its border is horizontal, and water overflow all over the border, there is no constrain.
Some where I see the way to size flow by the height the water rise in a open vertical end pipe.

3._ guess it is a circle pipe , it will have the hydraulic radius as Hr = pi*r*r/2*pi*r or Hr= r/2

, for a 1.0 meter diameter Hr = 0.25 m , and perimeter = 3.14 m , and area 0.785 m2, for a flow of 35 m3/h the speed is 0.012 ms
4._ Now for a rectangle with the same wet perimeter as the pipe, but with a 1.5 m side by 0.07 m have the same perimeter 3.14 m but the area is 0.105 m2 so the Hr = 0.0334 m . and for the same flow 35m3/h the speed is 138.88m/s, it is only a sample calculation, maybe it can not be a real case , as speed is 500 km/hr.
5.- So it can not behave the same way for a given flow,
it is evident that in the rectangular shape the water will rise upper than in the round pipe.

 

[prex]

You've already been warned above by someone else: you are on the wrong path. The pool has nothing to do with a BIG HUGE pipe.

prex

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes and launchers for fun rides

http://www.levitans.com

: Air bearing pads

 

[milena02]

Hi Prex , if not so , can you tell me , not talking about a pool.

What is a circular vertical thank ,15 m diameter , when it is fill by the botton end.
The same used at oil industrie to hold fluids.

Is or is not a pipe?

Will fluid overflow by its border or not, when the fluid reach the border.

 

[prex]

You can call it as you like, and OK, you can view it as a pipe, if this suits you.
The point is that this is not the correct model to calculate the height of the crest going beyond the border, as the velocity in your BIG HUGE pipe is negligible with respect to the velocity of the overflowing water and has no influence on crest height.

prex

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes and launchers for fun rides

http://www.levitans.com

: Air bearing pads

 

[milena02]

I agree with you, thing are going clear, now.
Thanks