Perforated Pipe Pressure Drop
Ben Walker
Has anybody got anything on pressure drop/flow distribution for
perforated pipe flow distributors. I looked in Perry's and they only had
a brief blurb and a formula for pressure drop that doesn't work with any
length/diameter. Any help would be appreciated. Thanks.
Ben
CKruger
Dear Ben
From you email address I see you are from Amoco, and even though I
have never worked for them, I can bet my right arm that there will be
someone in Amoco (actually more than one) that knows more than me
about distributors. But anyway, here goes.
It depends on what the distributor is for, for example:
1) Equal distribution between all holes. In this case the pressure
drop across the holes must be high enough compared to the pressure
drop through the pipe (I think a guy called Simpson wrote an article
on this quite some time ago, and he is also quoted in Perry). An easy
guideline that I have seen is to make the hole velocity twice the pipe
velocity, with some upper limit on hole velocity (say 10 ft/s,
although some companies will limit it to 4-5 ft/s in some cases) to
prevent excessive turbulence/disturbances. The pressure drop thru the
hole can be calculated with the normal orifice equations, which are
normally simplified for this application and exclude any pressure
recovery term. A special case is maybe very long distributors such as
for irrigation. I would tend to do a detail pressure drop analyses
over the entire pipe for such cases.
2) Proper entry into vessel. The idea here is to put the liquid/vapor
into a vessel with minimum turbulance to improve phase separation,
etc. Here an easy guideline is to make the total hole or slot area
twice the pipe area.
3) Proper contact. Sometimes you want to limit the drop size to
enhance interphase transport/extraction. I don't know what the maximum
is, but I have often seen sizes in the range of 10 mm (0.5 in ID) and
smaller.
Hope it helps
Christiaan
Ben Walker
Chris, (If I may call you that)
Thanks for the tips. Actually I am looking not only for a way to design
a distributor, but also a way of predicting the mal-distribution in an
existing distributor. The Perry's article put forth a method, but it
doesn't work for the dimensions I've got (I'd like to know why?) A Paul
Shain clued me in to an article by Greskovich and O'Bara that I'm trying
to get a hold of. Also I've got our library people trying to find some
information. The Amoco Intranet has a newsgroup for process engineers
that it seems only me and a guy in Indonesia look at, so I have gone out
here for help, and thanks to helpful people like you, I am getting it.
Thanks for your comments again!
Ben
Ben Walker
Ben Walker
Andrew W. Sloley
Pressure drop and flow distribution in a perforated pipe is relatively
complex. The upstream piping can have a significant impact on the flow
distribution out of each hole. For a starting point, use an orifice
equation for flow out of each hole. Approximating this as a sharp edge
orifice should give a reasonable flow distribution. Don't forget to add in
the affect of recovered head from fluid velocity droping as you flow
through a pipe distributor. This will work reasonably well for a straight
pipe of reasonable length (L<100 D).
For piping networks a first step would be to use dividing flow equations
for manifolds from a reference such as 'Piping Handbook' by Crocker and
King to determine flow through each pipe element then us the sharp edge
orifice to determine flow through each hole.
The best way of all is to build the distributor with the correct upstream
piping, connect it to a water line, and measure flow out of each hole.
Ben Walker <zbj...@amoco.com> wrote in article
<5mufh8$6...@tabloid.amoco.com>...
Lynn McGuire
>>> perforated pipe flow distributors. I looked in Perry's and they only had
>>> a brief blurb and a formula for pressure drop that doesn't work with any
>>> length/diameter. Any help would be appreciated. Thanks.
>>
>>> Ben
>
Is the pipe capped?
I would guess that each hole can be treated as an orifice?
Lynn