3 replies to this topic

[Syed saqib ahmed]

We have an nitrogen methane stream having methane 99+ mol% at temp -148.7•c and 28.5bar we install jt valve to reduce pressure upto 7.7bar but as we did this temp increase to -148.1•c.
But from my knowlegde in jt valve with pressure temp also reduce.what was the reason behind this behaviour?
Stream is liquid phase.

[MrShorty]

How much "reason" do you need? My answer (without knowing all of the thermodynamic and molecular reasons for it) is that you have fallen into the trap of believing that, just because something is true for many common gases, it must be true for all fluids under all conditions. Yes it is common for many gases to decrease in temperature when expanded adiabatically. It should not take very much research to find examples of gases that will increase in temperature during Joule-Thomson expansion. And, based on a project I did a few years ago, I learned that many liquids will also increase temperature when expanded adiabatically.

 

From there, I think the English Wikipedia page seems to describe this phenomenon well in more detail. https://en.wikipedia...–Thomson_effect

[Art Montemayor]

Syed saqib ahmed:

 

As usual, Shorty gives an excellent response to your query.

Because this is the Student Forum, we strive to guide and advice students on their studies - rather than their experiences.  For that reason, I would only add for your benefit - as well as for all other students reading this - the following tips, experience, and advice:

• Return to your basic Thermodynamic studies - whether they be Physical Chemistry, Chemical Engineering Thermo, or other Thermo course you might have or have had and re-read and study again what is discussed in the Thermo theory: Messrs. Joule and Thomson did their studies and work on GASES and not liquids.  The basic Joule-Thomson theory is based on the free, adiabatic expansion of gases and the results generated were on gases.  You are seeking to link the J-T effect with the free expansion of liquids.  That doesn’t work.  It involves another field of study - perhaps linked to J-T, but not the J-T effect.
• The free, adiabatic expansion of liquids is the basic and primary effect employed in almost all common refrigeration cycles.  This is what drives such refrigeration processes such as ammonia, ethane, propane, ethylene, air, CO₂, and all other common refrigerants.  This process may play an important role in your future engineering career and that is why it is important to know the basics and the differences.
• As Shorty explains, not all gases (including some liquids) cool when expanded freely and adiabatically.  Some well known exceptions are Hydrogen, Helium, and Neon.  Hydrogen gas, especially, heats up and this has been an important experience for me when out in the industrial field.  It is now well known that persons should not get close to high pressure hydrogen piping connections or fittings when out in the field during the daytime.  Any high pressure hydrogen gas leaks will heat up and because of the generated higher temperature and the friction caused, can ignite and cause a bright, almost invisible flame that is not visible in daylight.  I have seen this happen - but only at night time, when the bright, luminous flame appears.  This flame could be a serious hazard during the daytime for anyone passing by.  This, for me, proved the results of Joule and Thomson.
• In studying your Thermo, note that even gaseous Helium can be liquefied using the J-T effect.  However, it must be below its inversion temperature prior to the free expansion.

[Syed saqib ahmed]

Thankyou sir for your great advice.i am really thankful to you.