New FAQ
New FAQ
(OP)
Site management asked me to highlight FAQ378-1864: What does the flow profile look like for a Pipeline Blowdown? in this forum. Take a look at it if you are interested in the topic and give me some feedback either in this thread or in the e-mail feature.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist





RE: New FAQ
RE: New FAQ
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: New FAQ
Obviously, the example is a case where the surrounding pressure at the 1.5" hole is sub-atmospheric. I'm not that familiar with pipe blow downs, but isn't blowing down to atmosphere the norm? This may puzzle some folks.
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: New FAQ
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: New FAQ
There is a bit of theoretical difficulty in converting an irregular hole, or crack, to a regular circular hole. There should be some kind of a Cd coefficient, or did you include Cd for an irregular hole and its equivalent in "irregular" dimensions, converted to an equivalent circular hole, or is that ignored. As you know, even a round hole has a Cd coefficient that depends on the edge type as well. What edge shape did you use?
RE: New FAQ
Surely what is being given is the basic shape of the graph. The actual number will vary with atmospheric pressure, temperature etc so perhaps just remove the numbers and put in a marker like critical pressure, 90% of Pcrit and atmospheric pressure at the end and be done with it.
Usually on a blowdown the big issue is temperature, either local at the hole (minus xxx) or the gas temperature along the line, especially as the pressure gets low and hence expansion rate is highest.
usually the question is "how long will it take" or "how fast can I blow it down".
It's a good start, but maybe just a bit too precise when only an example can be given. volume to be blown down clearly affects time and temperature fall.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: New FAQ
That is a great point. I've changed the graphic to get rid of the numbers and added the equations (without adding nomenclature, or explaining exactly how often you need to iterate, or the importance of recalculating friction factor at every time step--I knew there was a reason that I didn't include the equations to start with). That gets rid of a lot of the irrelevancies.
I've done this calc for a lot of blowdowns, and the end of choked flow is really easy to see in the field, and the elapsed time is not dependent on local ambient temperature. The temperature I use (for buried pipelines) is a ground temp of 65F and the gas at ground temp. I've seen the drop out of choked flow within seconds of when I predicted on blowdowns that took hours.
Now predicting the duration of the transonic region is a different kettle of fish, and I've never been close to predicting that one, consequently I've never come close to predicting the time to zero.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: New FAQ
However, on my laptop tonight the graphic is about 2X the size of my screen. Is anyone else seeing that? If weather permits, w ill look tomorrow on my big flat screen at work.
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: New FAQ
RE: New FAQ
RE: New FAQ
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: New FAQ
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: New FAQ
RE: New FAQ
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: New FAQ
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: New FAQ
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
RE: New FAQ
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: New FAQ
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: New FAQ
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: New FAQ
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.
RE: New FAQ
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist