colebrooks equation 8

[freefallingbody]

Guys,

This is peanuts for you folks here. Won't take much of your valuable time.

Calculating pressure drops in pipeline, as I understand, needs first, an estimation of friction factor. I have referred to some books, and almost all of them gave me the following.


1/sqrt(f) = -2 x log10 [(e/ 3.7D)+ (2.51/Re sqrt(f))]

I learned that this was formulated in 1945. My question is, Is there any other type of colebrook equation, which is more recent or more accurate. Is the above one the current one?

(Is this really a stupid question, like asking if there is a better versin of ohms law or newtons third law of motion?)

thanks in advance

dinesh

 

[siretb]

There is:
1/sqrt(f) = -2 log10 [(e/ 3.7D)+ (2.51/(Re sqrt(f)))]
(the one you quote)

1/sqrt(f) = 1.74 -2 log10 [(2 e/D)+ (18.7/(Re sqrt(f)))]

1/sqrt(f)= 1.14+2log10(D/e)-2log10[1+(9.3/(Re e/D sqrt(f))]

http://www.cheresources.com

give the three above and compares

 

[hacksaw]

more accurate?

these are empirical equations based on specific piping and flow testing, usually in water.

 

[quark]

There are many approximations to colebrook's equation which are explicit functions of 'f'.

If you want an excel spreadsheet solver for colebrook equation go to,

http://me.queensu.ca/courses/mech441/spr/moody.xls

Also check this interesting page,

http://me.queensu.ca/courses/mech451/losses.htm

Regards,


I wish us all A Happy and Prosperous New Year

 

[Guidoo]

The exact links to the articles Siretb is refering to are:

http://www.cheresources.com/colebrook1.shtml

http://www.cheresources.com/colebrook2.shtml

http://www.cheresources.com/colebrook3.shtml

 

[Montemayor]

siretb /quark / Guidoo:

You guys should be recognized for the direct, succinct, and valuable contribution to FreeFall's request. This series of articles goes to the grain of dealing with an out-dated, implicit equation and offers practical, up-dated explicit solutions that can be directly employed by engineers in their own programs or spreadsheets for quick and accurate fluid flow solutions. You guys have not only helped FreeFall, but you've assisted countless others who will read this thread. Kudos to you all.

Art Montemayor
Spring, TX

 

[rbcoulter]

I think the actual answer to the question is that the Colebrook equation is still the best equation and that nothing has come along to replace it yet. There are explicit equations that are approximations (even to a high degree) of the Colebrook equation, but the Colebrook equation is still the "gold" standard.

 

[freefallingbody]

Guys,

Thank you so much for ur clarifications. It really helped me.

Wishing you all a great 2005 ahead.

Dinesh

 

[vzeos]

There actually has been quite a bit of work going on in the pipeline industry regarding the transmission factor equations. Most notable is the GERG equation, which improves the Colebrook-White combined law model by correctly incorporating an efficiency factor and by providing an “n” parameter which controls the rate of transition. The rate of transition was identified as early as 1956 by the natural gas industry as being the main problem with the Colebrook-White equation.

Dr. Zaragola’s experiments with the Princeton University super pipe have redefined Prandlt’s smooth pipe law. The partially turbulent flow portion of the GERG equation conforms to the Zaragola equation.

For more info, see the papers below:

http://www.psig.org/Papers/archive.asp?year=2002&submit=Retrieve+Papers

Paper 0202 - Taking the Rough With The Smooth – A New Look At Transmission-Factor Formulae

http://www.psig.org/Papers/archive.asp?year=2001&submit=Retrieve+Papers

Paper 0112 - A Tutorial on Pipe Flow Equations

 

[quark]

Nice link.

Regards,