×
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

volume-pressure question

volume-pressure question

volume-pressure question

(OP)
If I have a tube with gas being pumped through it, and it is experiencing a large temperature drop (ie the gas flowing in the tube is being cooled) does the pressure or the volume of the gas change or both? (from the ideal gas law PV=nRT)

I guesse I am asking if this is a isobaric process or an isochoric process.

 

RE: volume-pressure question

Mielke,

I don't think the volume can change unless your tube changes its shape...

Based on this and your other post, perhaps it would be best if you gave us a really good description of your project. It sounds like you may be in over your head just a bit...

Best to you,

Goober Dave

 

RE: volume-pressure question

mielke,

Based on your description, I would expect both pressure and volume (density) to change as gas flows through the pipe. I am not sure if the process can be easily categorized as isobaric or isochoric.

Check out http://www.pipeflowcalculations.com/airflow/index.htm

 

RE: volume-pressure question

(OP)
DRWeig,

Can the volume of the gas not change axially with respect to the length of the tube?

RE: volume-pressure question

Hi Mielke,

Volume is a fixed amount.  The density (kg/cubic meter) will change as you cool the gas, but the volume of your container pipe will not.

Imagine if your tube has caps on each end.  The volume of what's inside cannot change unless the pipe changes its shape.

Again, please give us details about your project.  This is basic physics we're dicussing here.  If we have details, we can share some experience.

Good on ya,

Goober Dave

RE: volume-pressure question

(OP)
The application is a heat exchanger. We're taking hot compressed gases and cooling them down.

I know compressor industries use heat exchangers. They compress a gas which decreases the volume and increases the pressure, as well as increasing the temperature of the gas (thanks to ideal gas law PV=nRT) after they do this they cool it down with a heat exchanger. If you cool down a gas either the pressure or volume or both go down. It just seems conter-productive if the heat exchanger would lower the pressure by lowering the temperature of the compressed gases and I know that they design heat exchangers for about a 1psi pressure drop (which is just calculated from the friction).

RE: volume-pressure question

DRWeig,

I think mielke means specific volume (units: m^3/kg) which is the inverse of density. So yes, the volume will change.

mielke,

I do not claim familiarity with the subject but I would look at compressible flow in pipes as a starting point. Take a look at these links:

http://www.cheresources.com/compressible_flow.shtml
http://www.potto.org/gasDynamics/gasDynamics.php

From what I understand of your process, the pressure and temperature will decrease. The specific volume may either decrease or increase depending upon flow velocity, rate of heat exchange and the gas properties.

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