×
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

Raleigh Flow!

Raleigh Flow!

Raleigh Flow!

(OP)
Hi,
I am attempting to complete a pneumatic circuit with a known requirements for flow to approximate pressure loss in the circuit and therefor the operating head for the pump in the circuit.  I am neglecting friciton in the tubing simplifying it a little.  The circuit contains heated and cooled portions as well as one point where the flow is volumetrically split to be reunited at the same pressure near the end of the loop.

My question is two parted.

1) Regarding splitting the flow, I am using an area ratio to split the flow and will emperically match the pressures when they join together later in the circuit.  Due to manufacturability of the holes I am scaling the area of the exiting ducts to double that of the entrance duct.  Is this better for head loss in the split or will keeping a 1:1 ratio for the split ducts and the entrance duct minimize head loss.  I believe 1:1 would minimize the pressure drop because there would be less heat generated and dissipated in the non-ideal non-isentropic expansion in an area change.

More importantly.

2)  I have run into this analysis block at any of the heating or cooling portions of a constant area "no friction" duct.  I only have all the starting conditions and the change in temperature.  I believe I need to have TWO flow characteristics at the exit to be able to calculate the rest of the flow characteristics (ie. density, velocity, entropy, enthalpy, Mach #, T stag, pressure, temperature).  
Is there a way around this?!

Many thanks and godspeed. :)  
Your help is appreciated.

RE: Raleigh Flow!


I'm not familiar with the problem in hand but may be this definition taken from a book may be of help:

Quote:

Rayleigh flow is an idealized type of gas flow in which heat transfer may occur, satisfying the assumptions that the flow takes place in constant-area cross section and is frictionless and steady, that the gas is perfect and has constant specific heat, that the composition of the gas doesn't change, and there are no devices in the system which deliver or receive mechanical work.

Highlights are mine.
 

RE: Raleigh Flow!

(OP)
Thanks friend, but I'm beyond the defenition in the book.  

It's well worded and highlighted!

RE: Raleigh Flow!

(OP)
Not beyond the spelling though, in any measure, it seems.

RE: Raleigh Flow!


Do you mean Rayleigh, not Raleigh (wrong!) as in the heading ?

RE: Raleigh Flow!

(OP)
Yep! Rayleigh.

So I think I'm going to work with convection and conduction equations to find the dQ for use in flow calculations.

Any comments or questions?

RE: Raleigh Flow!

(OP)
Hey 25362,
I was looking over the definition that I am "beyond."  What is your interpretation of the reference that the composition of the gas doesn't change.  This is due to the Cv staying constant.

RE: Raleigh Flow!


Just a thought. In the case of splitting the flow of a gas mixture, segregation due to factors such as density or viscosity wouldn't take place.

RE: Raleigh Flow!

(OP)
Yes, ok, that makes sense.  The composition would stay at the same composition regardless of the various gas properties in the mixture.

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