8 replies to this topic

Hello everyone,
I have just some doubts about the pressure drop in pipeflow. Does the pressure drop depends on the tube diameter? Given a fixed diameter and a fixed total length, would it be more advantageous usign more tubes in parallel rather than an unique tube?

Thanks in advance

Hi
fixed diameter is more important because it appears for evaluating h(f) at bernoly equation and calculating reynolds number (specailly when we have laminar flow ) .
good luck

[latexman]

An_drea,

Have you ever said “if I only knew then, what I know now”? If you are like most people, the answer is YES!

Well, I wish I had had Crane’s Technical Paper 410 when I went through University. Without a doubt, it is one of the best references a CHE can own. I have used one for about 27 years. It is thorough, yet written concisely, and it is full of formulas, conversion factors, steam tables, and physical properties. I wish fluid flow courses gave a copy to each student.

If you can afford it, I HIGHLY recommend you buy a copy. Order it at:

http://www.tp410.com/

If you cannot afford it, I recommend you get a part-time job until you can; it’s that good!

Now, to answer your questions:

“Does the pressure drop depends on the tube diameter?”

Pressure drop depends heavily on the internal diameter of the pipe. In laminar flow (Re < 2000), Poiseuille’s law says pressure drop is inversely related to the diameter to the 4th power as follows:

dP is proportional to 1/d^4

In turbulent flow (Re > 4000), pressure drop is inversely related to the diameter to the 5th power as follows:

dP is proportional to 1/d^5

“Given a fixed diameter and a fixed total length, would it be more advantageous using more tubes in parallel rather than one unique tube?”

You may have to explain your question in more detail, but in a new piping design, it is usually more economical to have one pipe of the required diameter, or larger. Since pipe only comes in certain sizes, one usually selects the available size that will work. However, if one already owns a lot of pipe of a certain diameter and length, it may make economic sense to use it and run parallel pipes to handle the required flow. If you are adding capacity to an existing unit, it is usually more economical to add a pipe in parallel to the existing pipe versus tearing out the small line and putting in a larger line. Of course, there could be some good reasons to do the latter, like the old line is corroded, the pipe rack is full, etc. As usual, it depends on your specific case.

[Art Montemayor]

an_drea:

What you have received has to be one of the most accurate, articulate, and well-written responses to a specific engineering query. It is unfortunate that we don't enjoy such well thought-out and excellent responses like latexman's - with the exception of some of Milt Beychok's classics and a few others. I sincerely hope a lot of young ChE students are reading this thread and printing out and pasting Latexman's response in their fluid flow notes and text books because the advice and recommendations are priceless when you are just a student and you don't have the specific information given you as Latexman has doled out. Believe everything he has given you and use it to dominate and thoroughly take on the subject of Fluid Mechanics. You will never regret the time and effort you spend on it now and you will certainly use it when you get into the profession and have to deal with it.

Latexman:

Thank you for a quality writeup and valuable short seminar on fluid mechanics. All of us stand to profit from your accurate and experienced recommendations and comments. I believe a lot of fortunate students who read this thread will profit from this valuable experience if they take what is offered seriously and with enthusiasm.

I hope your visits to our Forums continue and are more frequent.

Art Montemayor

With a little bit of delay....thanks.
I read your replies soon after you wrote but I couldnt reply due to technical reasons. Anyway I got the paper and treasured your suggestions through my studies and now through my first job experiences. Thanks a lot...now I am again on-board

[latexman]

an_drea,

A little bit of delay? Oh well, better late, than never!

I can't come down too hard on you. My 10 year old daughter is an Andrea. She is late from time to time. And, sometimes solving technical issues can be quite demanding!

[Qalander (Chem)]

an_drea,

A little bit of delay? Oh well, better late, than never!

I can't come down too hard on you. My 10 year old daughter is an Andrea. She is late from time to time. And, sometimes solving technical issues can be quite demanding!

Dear Latexman, Merely Splendid/Accurate!
I request you to keep it up with the help of Almighty indeed.
Best regards
Qalander

an_drea,

A little bit of delay? Oh well, better late, than never!

Exactly. I could sign up again with a different name but I value a lot gratitude.

[pjadams]

Pressure drop depends heavily on the internal diameter of the pipe. In laminar flow (Re < 2000), Poiseuille’s law says pressure drop is inversely related to the diameter to the 4th power as follows:

dP is proportional to 1/d^4

In turbulent flow (Re > 4000), pressure drop is inversely related to the diameter to the 5th power as follows:

dP is proportional to 1/d^5

Thank you. But what is the formula? I found one expression:

 Untitled.jpg   23.97KB   27 downloads

I wonder if this is what you talked about.

PJ