6 replies to this topic

[Dilbar]

Hi every body.
I am given an assignment "Design of Siphons" my data is
Dicharge = 15 cusecs
Manning's = 0.011
U/s water level= 1441.66 ft
D/s water level= 1440.00 ft
Length of Siphon = 330 ft
the siphon is passing under a dry drain almost no flow.....

please any one can help me in calculation an optimum diameter for the given discharge.

[breizh]

http://www.fao.org/d...44e09.htm#3.7.1
Dilbar,
Consider this resource to support your query .
Hope this helps
Breizh

[Dilbar]

thanks breizh i read that link its nice but its for simple siphons and mine is inverted siphon is it ok to to use these formulas for inverted siphons as well??

[katmar]

An inverted siphon is not a siphon at all. None of the principles of siphon design are involved here. An inverted siphon is more accurately called a trap. All you need to know is the length of the pipe, make some allowance for the fittings, and calculate the flow rate from the available static head (pressure drop) based on the assumption that the pipe runs full - which it will because the final section runs upwards.

It is unusual for a chemical engineer to use Mannings, but I suppose with the high volumetric flow you are using you are more likely involved with large waterworks. Using the Darcy-Weisbach formula I estimate your pipe diameter is going to be between 2.7 and 3.0 meters diameter. Hopefully this is just a theoretical exercise and you are not going to actually build it. If you are going to build it, get some professional advice. Using a couple of the online Mannings calculators I seem to get nonsense answers. You need to get advice from someone who has worked at this scale before, and that will most likely require a civil engineer rather than a chemical engineer. Your Manning roughness of 0.011 also seems very low for a (concrete?) pipe this size.

[Art Montemayor]

Dilbar:

LMNO Engineering discusses this and offers calculation solutions on their webpage: http://www.lmnoeng.c...ertedSiphon.htm

If you are a student and doing this as homework, the LMNO source might work for you. However, if you are debating a real construction of this nominal 3-meter diameter inverted syphon, I would heed Katmar's valued advice.

[Dilbar]

Katmar and Art Montemayor thank you so much for giving such precious advice and other thing this is a practical design and is going to be implemented soon its design get completed and Katmar the Manning's 0.011 is for newly steel pipe, we are not using concrete pipe. i have done some calculations using manning's equation and will be sharing with you as well to get your expert opinion.

[katmar]

Dilbar, that will be great if you can come back with the Mannings equation results. I have little experience with Manning and comparing methods this way enables us all to learn (which is why we are here ). Take care to include the entrance and exit effects in this project. In pumped systems with liquids they can often be ignored because they are relatively small, but because your driving force is so small you will find these losses are proportionally bigger. I look forward to seeing your calculations.