2 replies to this topic

[serlan]

Hi,

 

I would like some help calculating a siphon pipeline from a lake, over a dam crest and finaly to a pit.

 

I have the water elevation in the lake at 133,6m (will never change)

I have the dam crest elevation at 138m

and the exit of the siphon pipe at 129m (to atmosphere, not submerged)

 

I tried to calculate the max vacuum pressure in the peak of the dam crest but I am having trouble.

 

Anticipated flow is 189 l/s for a 287 mm pipe. total headloss is 4,6m (friction + minors). total pipe length is 164m.

 

I tried to apply Bernouilli's equation to resolve pressure at dam crest elevation which should be pretty simple I think, but for some reason I seem lost with units and I am still unsure if my result is absolute pressure or vacuum pressure...

 

Any help would be appreciated.

 

Thank you all.

[samayaraj]

Hi,

 

Can you submit the calculation for review?

 

The pressure at the crest = static head of pipe coming down (pipe at crest level to lower level) - static head (from water level pipe at crest level) - pressure drop due to friction - velocity head

 

In the above, yo have convert the 'head' to pressure while solving.

 

You can solve by taking pressure in absolute. Lets the pressure drop be 0.4 bar, static head from water level to pipe crest level be 0.3 bar and static head from pipe at crest level to lower level is 0.9 bar. Neglecting velocity head (since its very small), pressure at the crest = 0.9 - 0.4 - 0.3 = 0.2 bar (a)

Edited by samayaraj, 06 May 2016 - 02:03 PM.

[breizh]

Hi ,

 

Consider the resource attached to support your work :

 

http://www.fao.org/d...44e09.htm#3.7.1

 

Good luck

 

Breizh

Edited by breizh, 06 May 2016 - 10:49 PM.