Entrapped air in horizontal pipe 1

[orlandobill]

Does anyone have experience with this? Here's my situation:

Vertical pump sends 15500 gpm of water into an empty 30" diameter 120' long horizontal pipe that turns down 10' vertically, turns and runs another 60' horizontally and then turns up another 20' vertically. The 60' long "trap" holds water every night when the pump is turned off, but the 120' long horizontal pipe drains completely.

Is the pump flow (~7 ft/sec) enought to push all of the air out of the horizontal pipe? Is there any information out there that might help? Should I see huge slugs of air coming out of the discharge? I have flow issues and I'm thinking that a huge air bubble in the horizontal line is restricting the flow. Thanks for any information.

 

[Gator]

Have you guys been trolled before? A sophisticated troll can be hard to detect.

http://www.urban75.com/Mag/troll.html

Having spent more than my fair share of time on usenet years ago I like to think I know one when I see one, but based on katmar's observations now I'm wondering.

Some trolls are harmless in the sense that they get members talking about an issue amongst themselves. If 'orlandobill' is in fact a troll and has carried it this long, he must be a master baiter.

 

[orlandobill]

Whoa! I have no idea what a troll is, but I think I can guess. If you notice, I never asked for advice on my flow issues. That conversation was started by others and I only responded to questions that were asked of me. In fact, at one point (22 Feb 07 13:34) I tried to get everyone back on track, but not everyone listened.

I originally was looking for information on entrapped air in a horizontal pipe. I intentionally neglected the additional information about my system since it had no bearing on the issue of trapping air in a single pipe.

In lieu of the accusation in Gator's latest post, this will be my post in this thread. I appreciate everyone's input on the entrapped air question, I think I have a direction to head.

 

[katmar]

orlandobill, unfortunately it is not possible to decouple the trapped air question from the flow issues. That is why everyone (or at least Artisi and I) have been asking you what the flowrate and pressure drop are. If you have a low flowrate (Froude number < 0.31) the air will remain in the pipe. If the Froude number is > 1.0 the air will be rapidly flushed out. In between these limits you will have "gradual" removal of the air - I don't know if anyone would try to estimate how long it will take to completely remove the air.

Having now seen your pump curve it is clear that even with little or no static head recovery in the 10' vertical section you should still have enough head to pump about 13000 gpm. Even more so if you are running two pumps.

If you are able to observe the discharge to confirm that the air is being flushed out, and you can get a pressure gauge at the start of the 120' section you will be in a much better position to home in on the problem area.

Also, if the pumps do pump according to spec straight after a rebuild and then gradually deteriorate it is more likely to be a problem with the pump than the entrapment of air. I would imagine that an air problem would manifest itself from day 1.

I hope you will not make this your last post. I agree that you have a direction to head and I would be very interested to know the answer once you find it. I spend time at Eng-Tips to learn, not to teach. You should not take too much notice of Gator's question or my venting - technical geeks just want to get their teeth into nice juicy problems and we get frustrated when we are held back.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Artisi]

Good luck - but certainly come back if you still have a problem.