×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*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.

Throttling of saturated steam

Throttling of saturated steam

(OP)
Dear all,

I would like know the logical reasoning for temperature reduction during throttling process of saturated and superheated steam eventhough its enthalpy, meaning total energy of the system is constant? What is the science behind it. Thank you.

RE: Throttling of saturated steam

H = U + PV.

In real gases, PV changes.

If PV increases, with H constant, then U must decrease as a result of the fluid doing work on its surroundings. This produces a decrease in temperature.

This, and more, should be in your College Thermo textbook(s).

Good Luck,
Latexman

RE: Throttling of saturated steam

(OP)
Thanks for your reply sir, you mean to say, the reduction of pressure to be seen as expansion of gas, that work done causes lesser internal energy. Right sir?.

Most of the throttling videos on YouTube, showing workdone as zero, have no idea why it is done so, causing much more confusion to it.

RE: Throttling of saturated steam

Joules Law states that for real gases temperature is dependent on pressure even though no work is done and enthalpy remains constant (internal energy also remains constant and so does PV term although in state 2 pressure is lower and volume is larger) in a throttling process such as across a pinched valve. See thermodynamics books of fundamentals. This change in temperature with pressure at constant enthalpy is more noticeable at higher pressures.

RE: Throttling of saturated steam

Quote (Gvcr)

Thanks for your reply sir, you mean to say, the reduction of pressure to be seen as expansion of gas, that work done causes lesser internal energy. Right sir?.

Most of the throttling videos on YouTube, showing work done as zero, have no idea why it is done so, causing much more confusion to it.

Right. A real gas usually does positive internal work during a throttling expansion, and its temperature decreases. No external work is done.

I didn't see the videos, so cannot comment. Have you looked at Wikipedia?

Not a criticism; just advice. Your choice of words is a bit sloppy, and I think it would help you if you were more exact/precise. I.e. be true to the exact definitions of the thermodynamic terms, and I think you will get through your confusion faster and easier. Enthalpy is total internal energy plus pressure times volume. H = U + PV. PV is referred to as pressure energy. "Total energy of the system" is somewhat right, but it lacks precision, and, therefore, limits the conversation and the understanding. Again, this is advice; not criticism.

Good Luck,
Latexman

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.

Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!