×
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

Saturation steam flow through pipeline

Saturation steam flow through pipeline

Saturation steam flow through pipeline

(OP)
Dear All,
Do I have to suppose that when the saturated steam flows through a pipeline it expands (due to friction losses, in my case about 2 bars) according to the isenthalpic-adiabatic model similar to the saturated steam expansion  through a pressure control valve or an orifice?
 Is the saturated steam becomes superheated along the line?

Thanks in advance, Mike   
 

RE: Saturation steam flow through pipeline

No.

RE: Saturation steam flow through pipeline

(OP)
quark,

Can you please explain why no ?

RE: Saturation steam flow through pipeline

Frictional loss is not isenthalpic (nor adiabatic). Energy is lost from the fluid due to friction and the energy gets dissipated out of the control volume. So, you can't model it as isenthalpic expansion.

As for superheat, since I never thought of this and came across first time, I would give it some thought before responding. So far, I assumed saturated conditions.

RE: Saturation steam flow through pipeline

Mike, what generally happens in a steam line is that it would be designed for relatively low pressure drop (because the user wants the pressure at the other end!) but because it is hot a significant amount of heat can be lost through the pipe wall and insulation. In normal practice steam traps have to be installed along the line to remove the condensate generated from the lost heat.  In this case the steam remains saturated all along the length of the line.

It is conceivable that if the line was very well insulated but had a high pressure drop then the pressure could drop faster along the line than the corresponding saturation pressure due to heat loss.  In this case you could get superheat developing but I would say that this is very much a non-typical situation.

To get to the specific behavior in your application you would have to work out how much heat is transferred through the pipe wall and insulation, and then knowing the heat content of the steam at the downstream end (from this calculation) and the pressure (from the friction pressure drop) you can work out whether you have had some condensation or else generated some superheat.

Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

RE: Saturation steam flow through pipeline

...or check the steam temperature at reduced pressure.

RE: Saturation steam flow through pipeline

(OP)
Gentlemen,Thanks

It is very interesting issue.

I did an estimation of the pressure drop of the saturation steam through the about 1 km pipeline using the WinSim simulator.

Based on the WinSim that used adiabatic model,steam at the pipe outlet is superheated. Is this make sence?

If J-T effect is applicable for this case?

In which case the isenthalpic-adiabatic model can be used?  

RE: Saturation steam flow through pipeline

Of course if you have an adiabatic process and you reduce the pressure of a saturated vapor then it is going to get superheated. But it is not reasonable to assume a 1 km pipeline is adiabatic. If it were, Armstrong and Spirax would have gone out of business long ago.  You have to take the heat losses through the insulation into account if you want an accurate estimate of the exit condition of the steam.

In general, it is not a bad estimate to assume the flow of steam in a header or pipeline is incompressible.  If you are working with high pressure steam and relatively low pressure drops then the steam density is virtually constant over the length of the pipeline.  You can treat it as an adiabatic or even isothermal compressible flow if you want to be a bit more accurate in your calculation of the pressure drop. But you cannot then use that assumption to determine the exact condition of the steam at the exit.  These assumptions are OK for determining the density changes because they are so small, but not OK if you want to determine the exact condition of the exit steam.

As the steam flows down the pipeline it will cool because of heat losses. This increases the density. But the pressure decreases because of friction. This decreases the density. Overall you will find only a small change in density unless you have a very non-typical installation.

Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

RE: Saturation steam flow through pipeline

(OP)
Katmar,

Thanks for your explanation.


I would like to ask you a last question.

Why a steam expansion through the orifice is differ from the saturated steam expansion through the pipeline from the thermodinamic point of view.

Why the 1st process is isenthalpic and 2nd not.  

RE: Saturation steam flow through pipeline

It's simply a question of available heat transfer area.  An orifice or valve will have a small heat loss relative to the pressure drop when compared with a steam pipeline.  The heat loss is small enough that the valve/orifice case can be regarded as isenthalpic.

Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

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