×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Water flow in GPM and velocity question

Water flow in GPM and velocity question

Water flow in GPM and velocity question

(OP)
If I have a 35' diameter pipe at 326 PSI, how much water (seawater) would flow through this pipe in GPM? And at what velocity would this be flowing at? thanks for the help!

RE: Water flow in GPM and velocity question

There are really too many unknowns here to accurately answer your question.  Some of the questions to be answered are:

1. What kind of pipe is this?
2. What is the slope of the pipe?
3. What is the static head?
4. What is the length of the pipe?
5. What is the tailwater elevation?
6. What are the head losses in the system?

It sounds to me like you are dealing with a penstock situation in a hydraulic power plant.

Mike McCann
MMC Engineering

RE: Water flow in GPM and velocity question

For flowrate you need to fill in some more unknowns.

length?
elevation of inlet and outlet?
inlet pressure or head?
outet pressure or head?
pipe material?
 

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

RE: Water flow in GPM and velocity question

I thought it was an ocean power thing.

The flow and velocity changes according to the conditions at the outlet of the stream.  With the same inlet head as you have on the outlet, as shown in your diagram, you get zero flow, zero velocity.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

RE: Water flow in GPM and velocity question

Um.  I don't think the turbines are 35' diameter, are they?  The cross-section area thru the turbine spools will determine (along with the inlet gates, blade angles, etc.) the flow of water, which is presumably coming from a 700' elevation dam, and is fresh not salt water.  The 35' outlet pipe is what you are worried about?  That won't run full, I think.

RE: Water flow in GPM and velocity question

(OP)
the facility would be in the ocean, so it is sea water. I also want to install pumps that would pump the water out. the actual diameter of the turbine shaft we'll call 10' in diameter. so assuming the angle of the blades is at a 45 degree angle, and there is no problem with getting the water out of the facility causing no slow up there, what roughly could I expect the flow rate to be in GPM? thanks again for the help

RE: Water flow in GPM and velocity question

If this is a penstock, the penstock probably bifurcates into two smaller penstocks and then these are then transformed, as is the force and direction of the flow, into the scrollcase, which gradually decreases in diameter as the force of the water turns the turbine, exiting into the tailwater.

There are a lot of things going on here, and one is the limiting factor of the whole picture, which will determine the ultimate flow through the system and your penstock.

Mike McCann
MMC Engineering

RE: Water flow in GPM and velocity question

You can't assume blade angle until you know your optimum flow velocity, or the blade angle you assume will set your optimum velocity.  You're not thinking about variable pitch blades?

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

RE: Water flow in GPM and velocity question

seems like you are trying to re-invent the wheel, my advice would be to contact any of the major turbine manufactures and get the design and advice from the experts.

RE: Water flow in GPM and velocity question

(OP)
Yes, trying to talk to a turbine manufacturer was the first thing I tried to do.  But after talking with two engineers in that field and a couple physicists associated with them, they all but outright refused to tell me. I pretty much got the feeling that unless I have tons of money, am a big corporation, or personally know the president of these companies, I am not going to be told anything.  Which is why I was directed here.  I'm not looking for an exact figure. I just need a rough idea on flow so I can continue with some of my other calculations. You guys asked for arbitrary numbers so I gave them to ya. If it's easier to figure it out without the turbines in there, just ignore them. again I just need a ballpark figure. Not the exact actually built in the field spot on amount. I am attaching an above view looking down on the facility to give you a better idea on where the water goes after leaving the initial tube I need the numbers on. This is just a rough layout as of now, and will probably not be the exact layout later.  Now to explain the picture. The 2 items to the left in magenta are gates which will direct the water to either the upper or lower pumps which you see to the right side are also in magenta. I need the flow figure so I can determine the actual number of pumps that I will need.  Again thanks for any help on getting the rough GPM and velocity specs.

RE: Water flow in GPM and velocity question

This is reading like a student asking questions/help about a hypothetical design.   

RE: Water flow in GPM and velocity question



1. The maximum flow through the pipes are one thing, but as already explained by others, and common when all the factors you have mentioned are known, is the turbine manufacturor to give 'the maximum throughflow' of the turbine. This is just as usual as a pump manufactorer to give a pump capacity.

2. All turbine manufacturors will stall at your seawater question, although the material technology is well known in ship pump technology, offshore applications and seawater cooling. Also even worldwide for seawater turbine newer/existing or developing projects, although for lower pressures (Norway and other nations).

You could try to ask a turbine manufacturor for a budget approximation, unbinding price and ubinding performance (throughflow) based on freshwater to get an approximation. Try European or others than US if you haven't done that already. If positive answer try to get accuracy limits (plus minus xx%). You will even then have the question if this can be transferred to seawater without corrosion and cavitation problems. Exotic materials needed!

3. Based on the turbine designed maximum througlet you can check the velocity in the pipe and calculate the loss in pipe, an approximation based on pipelength, layout, restriction, component and roughness. However: the limitation is what the turbine can withstand and produce, not the maximum flow through the pipeline, which is high! As an example for freshwater turbine inlet ball valves can run as high as 17m/s, but more common are perhaps 6-8m/s?

See my point? You have to find that turbine/generator supplier to hold your hand!

RE: Water flow in GPM and velocity question

A conservative number for flow is 6 feet/sec and a not so conservative number is 10.  Pick your poison in somewhere in between.

rmw

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources