Air Velocity Calculation in Pipes

piping_engineer, eh?

For your application, the Colebrook equation would probably be better.

A rose by any other name.

You sir are a master of subtlety. Thumbs up.

Piping Engineer,

You cannot use Bernoulli equation for that problem. You have to use the complete energy equation and use the Darcy-Weisbach equation to represent the head loss in the energy equation. The equation you quoted for velocity may be correct but you have to check all the assumptions made to arrive at the factor 25000 in the equation and make sure they apply to your case. Those assumptions include:

i) The flow is turbulent.

ii) Value of friction factor (which depends on pipe material & diameter only, for high Reynolds number flow)

iii) Air density

You're right in telling him that he can't use Bernoulli here because it's compressible flow. However, using Darcy-Weisbach for friction won't make much of a difference though. He doesn't want to try to solve the energy equation using compressible flow by hand.

Check Crane Technical Paper 410. You can probably find a good way to calculate it in there.

I would be willing to bet though that dropping the pressure from 100 bar to 10 bar gives you sonic flow. If you have no expansions in the line, I'm guessing your velocity is Mach 1.

As Tornado Posted in 1 Colebrook Equation is the one to use it factors in Darcey friction loss.

Well I hope you guys have more experience working with this than I do because just looking at this from old college knowledge, I would think that air friction is relatively negligible. You can find this velocity using Gas Dynamics and not Colebrook equation for friction factor.

Static pressure is 100 and back pressure is 10. So P/Pt is 0.1. If I remember right the ratio you need for sonic flow is roughly 0.5. Therefore, this should be sonic flow (at least) coming out of the reducing valve. When you expand to the larger diameter pipe, it could reach supersonic. I would use Mach tables and Gas Dynamics first but like I said, I've never worked with this before. Just a guess

Also, doesn't Darcy-Weisbach also assume incompressible flow?

This tool is designed for that purpose: http://www.vpinstruments.com/tools/calculator/flow_velocity.php

The flow rate "Q" depends on the Area "A" and velocity "V".ie, Q=AXvArea in meter squareV- meter /hourQ= cubic meter per hour.so rearranging the equation we will get the velocity of fluids in pipesNB. Area of pipe is 3.14x inner dia square/4

What is the problem?

Is this home work?

Yes it is Year one home work at Cal- Poly

Hmm....I used to do my home work at the cafeteria with books, friends, and gallons of coffee..."Internet"? What dark magic is this?

Yes I remember late nights on State Street in the apartment over the Ace Hardware, single light burning, coffee percolating (took my moms percolator when I left) and the cup of soups, lots of cup of soups, beef, chicken and the ever not so favorite shrimp.

But it was cheep by the case and came previously assorted.

Now we have 4 kids, recently we have had to go through detox with our daughter while keeping a stiff upper lip for our grand daughter and also keeping our 18 year old on the straight and narrow (which is easy since he has seen his sisters life rot due to prescribed and non prescribed drugs). At times the cup of noodles seems comforting, though the pressures were great and the stress was there to succeed, it was just me.

But I will say My kids have given me more sunshine in the past 32 years of their lives than Rain, and no matter the problems they are mine to love.

Sorry that got kinda sappy, but happy holidays and happy new year.

NO GO DO YOUR OWN HOMEWORK LIKE WE ALL HAD TO DO!