×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Equipment pressure drop extrapolation - Leq method versus K method

Equipment pressure drop extrapolation - Leq method versus K method

Equipment pressure drop extrapolation - Leq method versus K method

(OP)
Hello all,

First let me present myself: i am a french junior process engineer, so please be indulgent with my english.
 
My questions deals with the better way to extrapolate equipment/instruments pressure drop from known conditions.
 
Nomenclature:
hf0 and hf are the known and unknown friction heads of equipment,
q0 and q the known and unknown flowrates,
F0 and F the known and unknown Darcy friction factors.
DP100 the known linear pressure drop in feet
dp100 the new linear pressure drop in feet
 
Reference 1:
The author says that the resistance coefficient K from Crane for fittings and valves is independant of Reynolds number and K=Fturb*(L/D). As a result, using the equivalent length method by summing the straight pipe length and the total equivalent length of fittings with the same friction factor is not rigorous as there is a higher degree of turbulence in the fittings than in the pipe.
However, at the end of the article the author mentions new correlations like the one proposed by Darby that state that the resistance coefficient K varies with the Reynolds number and that is destined to become the new standard.
These two observations seem in disagreement with each other. So, is K a constant as for Crane or a function of the Reynolds number as for Darby?
 
Reference 2:
Perry 1997 6-16 shows that f=(D/4L)*K, and Perry's 1997 6-17 notes that K for fittings and valves is stable at Re from 2000 to 500 and then increases rapidly as Re decreases below 500.
This observation seems to corroborates the fact that K varies with the Reynolds number.
 
Now let´s go to the point (equipment/instruments pressure drop extrapolations):
 
Reference 3:
In this article, it is said that we can safely extrapolate equipment pressure drop from known conditions (for 500<Re<2100 and Re>5000) by: hf=hf0*(q/q0)^2. Obviously this relationsship is based on hf=K*(v^2/2g) with K being a constant.
Is this method valid if K depends on the Reynold number as Darby stated?
 
Reference 4:
In this article, the author uses the equivalent length method: from known hf0 and operating conditions, he calculates a Leq at a selected pipe size D by Leq=100*(hf0/DP100). Then he calculates dp100 with the new operating conditions and determinates hf by hf=dp100*(Leq/100).
If we consider:
DP100=F0*(100/D)*(v0^2/2g)
dp100=F*(100/D)*(v^2/2g)
Then, hf=hf0*(dp100/DP100) <--> hf=hf0*(F/F0)*(q/q0)^2
Do you agree with this method? For me it seems very convenient as we can use it in all flow regime. I would like your point of view as experienced engineers.
 
Thanking you in advance
 
References:
1/ http://www.cheresources.com/eqlength.shtml
2/ Perry's Handbook 1997
3/ Anthony, James, Pumping System Head Estimation, Chemical Engineering, February 2005
4/ Yu, Frank, A simple way to estimate equipment pressure drops, Hydrocarbon Processing, August 2005

 
Kind regards
 

Small people talk about others, average people talk about things, smart people talk about ideas and legends never talk.

RE: Equipment pressure drop extrapolation - Leq method versus K method

(OP)
My question is dealing with equipment/instruments pressure drop not fittings and valves.

However i had a look on thread378-173164: Crane 410 fittings: Crane 410 fittings, and i could not find a conclusion on this long but interesting discussion.

So could anyone definitively and clearly conclude on this topic?
 

"Small people talk about others, average people talk about things, smart people talk about ideas and legends never talk."

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources