Orifice vs Weir 2

[SMIAH]

I'm trying to find out when to use weir equation or orifice equation for an orifice in an horizontal pipe.

Is this relation true?
Orifice equation when submerged i.e H >0.5*D
H = Head above center line of orifice
D = Diameter

And is there "any rule" such as this one for a Riser pipe (vertical drain).

Thanks in advance!

 

[Ryb01]

This thread may be helpful...

http://www.eng-tips.com/viewthread.cfm?qid=240054&page=2

Hope this helps.

Ryb01

 

[Drew08]

When an orifice is submerged on both ends: H = difference in energy heads. Don't forget velocity head if applicable. When the upstream end is submerged, and the outlet is free fall, i.e. super critical, H = energy head above centerline of orifice. Submergence is usually considered to develop at the depth of head water, not energy, of d > 0.2D above the top of the inlet, or 1.2D above the invert. But, more simply, solve for both the weir equation and orifice equation, and take the lesser of the two discharges. A vertical riser pipe is no different. it just so happens the centerline of the pipe is at the same elevation as the invert of the pipe.

 

[SMIAH]

Thanks!
Helpful!


This link too :

http://books.google.ca/books?id=_uZGhInQaugC&printsec=frontcover#PPA147,M1

 

[ropotto]

The discharge for a circular orifice is
1/2
Q = C a (2gh)
Where:
C=Discharge coefficient
a=Submerged area
g=Gravitational constant
h=Effective head

Vertical Orifice

For an orifice opening in a vertical plane, the effective head is given by:
h=H-max(r,TW) (if fully submerged: H>2r)
h=H-max(H/2,TW) (if partially submerged: H<2r)
Where:
H=Head above invert
TW=Tailwater depth above invert
r=Radius