×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

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!

*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

Liquid Vapour Equilibrium in Liquid Cylinder

Liquid Vapour Equilibrium in Liquid Cylinder

Liquid Vapour Equilibrium in Liquid Cylinder

(OP)
Hi All,

There is something lingering in my head lately regarding the liquid vapour equilibrium.
To be honest, I am not too sure if the problem that I am going to ask here is about this topic.

There is a pressurized cryogenic liquid at 6 barg under operating in a Low Pressured Cylinder (LPC). When the tank pressure goes down to 5 barg, the cryogenic liquid will be passing the Pressure Building Coil (PBC) (actually it is a vaporizer) and transferring back to the tank as a gas to pressurize the tank. Basically, I believed the theory behind is to increase the number of molecules of the gas (under the same volume) as well as the tank pressure. The pressure regulator regulate and stop when the tank pressure reach at 7 barg.

Then this question comes to my mind that if the tank pressure is at 7 barg, does it mean only the gas at 7 barg or the system is going to reach liquid vapour equlibrium and achieved 7 barg eventually? If not, how does the cryogenic liquid achieve at 7 barg?

Hope I explain my question well and looking forward to your reply!
Many thanks in advance!

RE: Liquid Vapour Equilibrium in Liquid Cylinder

In cryogenic tanks saturated conditions (equilibrium) is practically only achieved at the liquid vapor interface. In reality there is thermal stratification in the liquid giving some degree of subcooled product at the bottom of the tank.

If you do a volume balance on the cryogenic tank you will understand that the PBC is able to maintain a certain pressure during product withdrawal as the effectiveness is governed by the ratio of liquid/vapor densities (a function of pressure)

Also, just as an FYI most modern cryogenic storage systems have an economizer circuit as well.

----------------------------------
Not making a decision is a decision in itself

RE: Liquid Vapour Equilibrium in Liquid Cylinder

The surface of the liquid will always be at close to equilibrium with the vapor. When the vaporizer increases the pressure in the tank by absorbing heat and boiling some liquid, the temperature of the vapor also increases. Some of the vapor will condense on the fluid surface and raise the temperature slightly so that its vapor pressure is 7 bar. The liquid below the surface will heat only very slowly because warm liquid is less dense than cold liquid, inhibiting mixing.

The same thing would happen if you used steam to pressurize an insulated tank of cold water. This means that presurization can occur almost instantaneously, and you do not need to heat the whole tank of liquid to do so.

RE: Liquid Vapour Equilibrium in Liquid Cylinder

(OP)
Hi csk62 and Compositepro,

Meaning eventually the liquid will be at same pressure and temperature with the vapour since it achieved equilibrium (even if it at the surface of the liquid, but I believed it will turn out to be the whole liquid slowly).


Thank you!

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! Already a Member? Login


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
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’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:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close