×
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

Flow Conditioning In Tube
2

Flow Conditioning In Tube

Flow Conditioning In Tube

(OP)
We are trying to measure the air velocity and pressure in aircraft air conditioning hoses. We have been using "laminar flow tubes", basically just long straight tubes about 15 times the diameter of the hose. Now we are flowing more air, which means we have increased our hose sizes. The laminar flow tubes are now too long to fit in our space. What simple techniques can we use to "straighten" the air in our laminar flow tubes so that the tubes do not need to be so long?

RE: Flow Conditioning In Tube

Honeycomb material, such as Alcore.

Reidh

RE: Flow Conditioning In Tube

are you using "laminar flow" ducts to increase the flow volume (presumably given a certain pump) ?

maybe your pump (compressor, whatever) isn't big enough to provide the required demand and overcome the losses ?

RE: Flow Conditioning In Tube

(OP)
1. Where can we get small quantities of honeycomb?

2. The laminar flow tube is used to measure the static and total pressures of the airflow in a ventilation hose. The flow tube is installed for test purposes only.We connect a vaccum fan to the laminar flow tube and draw air through a large cabinet. We are interested in measuring the pressure drop across the cabinet.

RE: Flow Conditioning In Tube

I'm assuming that the issue is that your measurements are more accurate if the flow in the "laminar" tube is fully developed.  Depending on the Reynolds number, the flow in the tube may not be laminar at all.  A short length of some kind of flow straightener could help the flow to reach its fully developed laminar or turbulent state more quickly.  If the flow coming out of the cabinet is fairly clean, this may not even be necessary.  I don't know that any kind of flow conditioning can take the place of allowing the flow to fully develop.  If flow conditioning is appropriate, a bundle of small-diameter straws, about 10 times longer than their own inside diameter, should work.  Whether you condition the flow or not, 15 diameters may not be enough for the flow to fully develop.  Look in your Fluid Dynamics book, it should tell you how many diameters of length are required for the flow to fully develop, as a function of Reynolds number.

Good luck

RE: Flow Conditioning In Tube

Your best bet may be to ask some of the large distributors of it for some samples.

Reidh

RE: Flow Conditioning In Tube

Mythbusters used full drinking-straw boxes with the ends cut off to straighten airflow in a recent show.
If the flow through the tube isn't enough to blow the straws out of the boxes and it's not for a permanent test stand that  idea might be worth a look, at least from a cost point of view!

RE: Flow Conditioning In Tube

Making hex is easy.

Crease the paper into strips, using appropriate fold directions.

flatten them back out. Apply glue to one strip in three. Stick another piece of the paper to it. Repeat.

Cheers

Greg Locock

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Flow Conditioning In Tube

if you use long straws to straighten the flow, you will get a large pressure drop across them and you may have a tough time getting the velocity you need downstream of the straws.

i did exactly that years ago, making a small wind tunnel in the basement .....  flow was VERY straight and VERY slow.

also.... tie them down ..... do you know what 2000 straws look like scattered across the room? (i do !)

regards

magicme

------------------------------------
"not all that glitters is gold"

RE: Flow Conditioning In Tube

(OP)
I was recently told that using the foam from off road racing aircleaners was the best way to get the desired result. I will try this in the next few weeks and compare it to the straw method.

RE: Flow Conditioning In Tube

Why not set up the airplane ducts in a lab in the physical layout they exist in the airplane with your measuring sensors; attach some "long straight" tubes with sensors to provide "truth" data and just obtain a calibration of the "as installed" ducting/sensor config. Since this is likely a steady state scenario, could even use the same sensors keeping costs down and improve relative accuracy of the data.

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