Hi Jacques
my concern is the pressure rise, if any, when the higher velocity liquid
in the part full pipe section hits the lower velocity liquid in the
completely full pipe section.
The inflow to the pipe is regulated so that no more than 60l/s (or other
preset amount) can enter the pipe. The pipe is vented.
I absolutely hate valves at the end of gravity lines; people keep closing them. If I substitute an orifice plate, it will only work at one flow rate/pipe condition. I am anticipating set flows over a wide range with 60l/s the upper limit.
With no valve and a fixed inflow into the vertical leg of an "L" shaped pipeline (outflow from the horizontal leg), there will be a transition from part full to completely full pipe somewhere down the vertical leg. I am interested to know if there is a pressure rise at the transition zone, if not, why not, and if so how to calculate the magnitude. To visualise my pipeline, imagine the vertical leg is 150m and the horizontal leg is 2km. The transition zone should be somewhere about 30m up from the corner of the L.
Cheers
Steve
-----Original Message-----
From: Jacques Chaurette [mailto:jchaurette@fluidedesign.com]
Sent: Friday, June 18, 2004 12:25 AM
To: PipingDesign@yahoogroups.com
Cc: Normand Chabot
Subject: Re: [PipingDesign] Part full line - water hammer estimation
Steve, greetings from Montreal. I am afraid that I do not understand your question or the problem. You mention water hammer estimation but you do not state if this is the problem or goal. Can you try a restatement of the problem?
Anyway I am going to ramble on and make a few suggestions. It seems that your system is gravity driven, the fiction head is 30m, that's about right for the flow rate of 60 l/s, I checked. There is way more static head (150 m) than friction head which means and you must have a valve at the discharge pipe end to control the flow rate at 60 l/s as mentioned. If you have a valve partially closed to control the flow this means that the pipe is necessarily full as pressure will build up behind the valve which should alleviate any concerns about having a partially full pipe, unless you have an air pocket but you should be able to get rid if that, are there any high points in the line where this could occur? So far so good.This is as far as I get because I really don't know what the problem is and I'm kinda spinning my gears.
On a similar but unrelated topic I found an article lately that discusses what the conditions are to maintain a full pipe titled "Criteria for filling of liquid filled pipes" not a trivial problem. If the article interest you I can scan it and make it available.
Jacques
Gents + 1
I am looking at a water pipeline 2.8km long, flow rate 60l/s, ID
227mm.
The inlet is atmospheric from a tank. For the first 800m, the line
drops 150m in elevation. For the remaining 2km, the line is near
enough to horizontal, discharging into a pond. The friction loss
under full pipe conditions will be about 30m (dirty). This means that
the water will drop the first 120m (vertical) the line will run part
full, with fairly high velocities. At the -120m point the line will
become full with a fairly sharp head rise due to the sudden velocity
rise forming a sort of hydraulic jump. I can take a rough stab at the
part full velocity (using open channel flow theory) and I know the
full pipe velocity. To get the surge rise, I thought I may be able to
use Joukowsky's formula; delta H = a delta V /g; a is celerity.
However, I think the result will be overly conservative,and would
need to do a fair bit of work before being confident about the result.
This is a fairly common operating condition, but I do not seem to
have a clear estimation procedure for this.
Can anyone point me to a book or other reference?
Cheers
Steve
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