Latent heat at the molecular level: How does it work

[sigurdur]

Sept 20, 2017 0:20:21 GMT duwayne said:

It's a good idea to set up a new thread on this subject since it is much broader than Hurricane 2017. I've posted below my "layman's definition of latent heat from that thread. Note that it doesn't speak to how the latent heat process works at the molecular level.

"A water molecule has an almost magical ability to grab an extensive amount heat from its surroundings as it is turning from a liquid into vapor and hide that heat so you don’t see any outward signs that it is present. The water vapor molecule can then “float” up into the atmosphere and condense into water droplets and in so doing it will release its hidden load of heat which results in warming of the surrounding air. That “hidden” heat is called latent heat while it is hidden but it is heat that you can feel both before and after it is latent heat."

This definition as written does allow for some energy to be lost as photons but the intent is that essentially all of the latent heat ends up as sensible heat.

Something to be added to the discussion... One of my degrees is in Chemical Engineering and I have experience in chemical plant design. Every petrochemical process that I know of makes extensive use of distillation which involves vaporizing and condensing large quantities of chemicals and water on a continuous basis. Fuel is a major expense. Heat balances are used extensively to watch and measure where every BTU goes. It's clear from measurements that upon condensation the latent heat is recovered as sensible heat although it is possible due to small errors in measurement that very small (1% ?)radiation losses could go undetected.

One question I would be interested in having answered is how does the energy of one IR photon compare with the energy in the latent heat of 1 molecule of water.

The energy of 1 IR photon is much less than the latent heat of a water molecule.

[duwayne]

Sept 20, 2017 11:32:09 GMT sigurdur said:

Sept 20, 2017 0:20:21 GMT duwayne said:

It's a good idea to set up a new thread on this subject since it is much broader than Hurricane 2017. I've posted below my "layman's definition of latent heat from that thread. Note that it doesn't speak to how the latent heat process works at the molecular level.

"A water molecule has an almost magical ability to grab an extensive amount heat from its surroundings as it is turning from a liquid into vapor and hide that heat so you don’t see any outward signs that it is present. The water vapor molecule can then “float” up into the atmosphere and condense into water droplets and in so doing it will release its hidden load of heat which results in warming of the surrounding air. That “hidden” heat is called latent heat while it is hidden but it is heat that you can feel both before and after it is latent heat."

This definition as written does allow for some energy to be lost as photons but the intent is that essentially all of the latent heat ends up as sensible heat.

Something to be added to the discussion... One of my degrees is in Chemical Engineering and I have experience in chemical plant design. Every petrochemical process that I know of makes extensive use of distillation which involves vaporizing and condensing large quantities of chemicals and water on a continuous basis. Fuel is a major expense. Heat balances are used extensively to watch and measure where every BTU goes. It's clear from measurements that upon condensation the latent heat is recovered as sensible heat although it is possible due to small errors in measurement that very small (1% ?)radiation losses could go undetected.

One question I would be interested in having answered is how does the energy of one IR photon compare with the energy in the latent heat of 1 molecule of water.

The energy of 1 IR photon is much less than the latent heat of a water molecule.

Thanks Sig,you're amazing.

Observationally, latent heat ends up as sensible heat in the surrounding molecules on condensation. But this doesn't rule out the possibility of a photon being released. Since it's energy is so small compared to the latent heat it could go unnoticed in the overall heat balance but on a gross basis where there are huge quantities of latent heat it could be detectable.


I could buy into a molecular physics explanation of evaporation and condensation which involves the absorption and emission of a photon.

[acidohm]

Sept 20, 2017 15:38:05 GMT duwayne said:

Sept 20, 2017 11:32:09 GMT sigurdur said:

The energy of 1 IR photon is much less than the latent heat of a water molecule.

Thanks Sig,you're amazing.

Observationally, latent heat ends up as sensible heat in the surrounding molecules on condensation. But this doesn't rule out the possibility of a photon being released. Since it's energy is so small compared to the latent heat it could go unnoticed in the overall heat balance but on a gross basis where there are huge quantities of latent heat it could be detectable.,


I could buy into a molecular physics explanation of evaporation and condensation which involves the absorption and emission of a photon.

It would certainly explain ir images of hurricanes??

[acidohm]

Can anyone describe evaporation at atmospheric temperatures??

I.e. from an ocean, it's vapourisation below boiling point?

[nautonnier]

Sept 20, 2017 15:49:24 GMT acidohm said:

Can anyone describe evaporation at atmospheric temperatures??

I.e. from an ocean, it's vapourisation below boiling point?

It follows Raoult's law.

See Vapor Pressure and Raoult's Law brilliant.org/wiki/vapor-pressure-and-raoults-law/

"The molecules at the surface of a liquid are weakly bonded compared to the molecules beneath the surface. For this reason, the molecules at the surface easily vaporize at temperatures lower than the boiling point. This process is called evaporation.

All liquids undergo evaporation, but not forever. They evaporate until the partial pressure of their gas form reaches a certain level, which is known as vapor pressure. Vapor pressure is defined as the partial pressure of a vapor in dynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system."

There is lots more on that web page....

[acidohm]

I like vapour pressure, roaults law loses me completely....

Deals with solutions??

I did chemistry at A level....awful experience 😝

[sigurdur]

I am not amazing, just an old farmer with a love of chemistry and physics.

Long time continual use of both helps too.

Now, spill the beans!!! Duwayne! I want to see if my feeble old mind can grasp molecular level.

[nautonnier]

This looks interesting as a PhD dissertation it must be 'new research' one would have thought that latent heat would have been fully researched by now - but it appears that after K-12 level descriptions all that is done is measure it not describe how it works.

"The radiative relaxation mechanism of water between its different phases is
studied to understand an uncommon radiation phenomenon observed in the first-order
phase-transition process of water. This kind of radiation is often referred to as phasetransition
radiation, whose nature is different from the Planckian radiation because its
strength can be even stronger than blackbody radiation at the same temperature."

www.ideals.illinois.edu/bitstream/handle/2142/29706/Wang_Kuo-Ting.pdf?sequence=1

[Ratty]

Sept 21, 2017 10:27:10 GMT nautonnier said:

This looks interesting as a PhD dissertation it must be 'new research' one would have thought that latent heat would have been fully researched by now - but it appears that after K-12 level descriptions all that is done is measure it not describe how it works.

"The radiative relaxation mechanism of water between its different phases is
studied to understand an uncommon radiation phenomenon observed in the first-order
phase-transition process of water. This kind of radiation is often referred to as phasetransition
radiation, whose nature is different from the Planckian radiation because its
strength can be even stronger than blackbody radiation at the same temperature."

www.ideals.illinois.edu/bitstream/handle/2142/29706/Wang_Kuo-Ting.pdf?sequence=1

I think they probably used an early version of your infrared sensor, Acid.

[fred]

When I was at college I was told that the water molecule was not just H2O but (H2O)n. This means that the bonds are not a simple 3 molecular bond but much tighter as more molecules are involved. This allows the gaseous state to become liquid and stay liquid. The simple H2O molecule would disappear into space very quickly if not joined to lots of other molecules.

As I was learning about pharmacology it really wasn't necessary to know if this was in fact true, I only have the vague memory of his statement. Maybe somebody on here could confirm or refute this fact.

[icefisher]

Sept 21, 2017 10:27:10 GMT nautonnier said:

This looks interesting as a PhD dissertation it must be 'new research' one would have thought that latent heat would have been fully researched by now - but it appears that after K-12 level descriptions all that is done is measure it not describe how it works.

"The radiative relaxation mechanism of water between its different phases is
studied to understand an uncommon radiation phenomenon observed in the first-order
phase-transition process of water. This kind of radiation is often referred to as phasetransition
radiation, whose nature is different from the Planckian radiation because its
strength can be even stronger than blackbody radiation at the same temperature."

www.ideals.illinois.edu/bitstream/handle/2142/29706/Wang_Kuo-Ting.pdf?sequence=1

Aha! Finnbane!

[icefisher]

Sept 20, 2017 0:20:21 GMT duwayne said:

Something to be added to the discussion... One of my degrees is in Chemical Engineering and I have experience in chemical plant design. Every petrochemical process that I know of makes extensive use of distillation which involves vaporizing and condensing large quantities of chemicals and water on a continuous basis. Fuel is a major expense. Heat balances are used extensively to watch and measure where every BTU goes. It's clear from measurements that upon condensation the latent heat is recovered as sensible heat although it is possible due to small errors in measurement that very small (1% ?)radiation losses could go undetected.

Seems to me that all distillation processes being measured are contained in IR opaque vessels, thus all radiation would be recovered as sensible heat from being captured by the inside surfaces of the vessel as they are in a typical room where Planck radiation need not be singled out from conductive and convective heat transfer as is thought necessary by climate science.

However, with extensive experience in designing living spaces radiation plays a huge comfort role within those spaces. Thus you can have a room that is 80F in a climate that is 0F and if you don't have insulation in the walls to keep at least the inside surfaces of those walls well above the half way point (40F) between the inside temperature and the outside temperature its going to be somewhat uncomfortable unless you wear a sweater or some other heavy clothing.

The question regarding weather phenomena releasing photons through the IR window, which is far larger at the top of the troposphere than at the surface is an entirely different experiment than measuring the heat retained by a distiller.

[duwayne]

Sept 20, 2017 15:47:51 GMT acidohm said:

Sept 20, 2017 15:38:05 GMT duwayne said:

Thanks Sig,you're amazing.

Observationally, latent heat ends up as sensible heat in the surrounding molecules on condensation. But this doesn't rule out the possibility of a photon being released. Since it's energy is so small compared to the latent heat it could go unnoticed in the overall heat balance but on a gross basis where there are huge quantities of latent heat it could be detectable.,


I could buy into a molecular physics explanation of evaporation and condensation which involves the absorption and emission of a photon.

It would certainly explain ir images of hurricanes??

Acidohm, my understanding from Nautonnier's post on the other thread is that the "images of hurricanes" are showing temperatures at the top of the the clouds and therefore the cloud heights. They do not indicate the amount of IR.

[duwayne]

Sept 21, 2017 16:08:59 GMT icefisher said:

Sept 20, 2017 0:20:21 GMT duwayne said:

Something to be added to the discussion... One of my degrees is in Chemical Engineering and I have experience in chemical plant design. Every petrochemical process that I know of makes extensive use of distillation which involves vaporizing and condensing large quantities of chemicals and water on a continuous basis. Fuel is a major expense. Heat balances are used extensively to watch and measure where every BTU goes. It's clear from measurements that upon condensation the latent heat is recovered as sensible heat although it is possible due to small errors in measurement that very small (1% ?)radiation losses could go undetected.

Seems to me that all distillation processes being measured are contained in IR opaque vessels, thus all radiation would be recovered as sensible heat from being captured by the inside surfaces of the vessel as they are in a typical room where Planck radiation need not be singled out from conductive and convective heat transfer as is thought necessary by climate science.

However, with extensive experience in designing living spaces radiation plays a huge comfort role within those spaces. Thus you can have a room that is 80F in a climate that is 0F and if you don't have insulation in the walls to keep at least the inside surfaces of those walls well above the half way point (40F) between the inside temperature and the outside temperature its going to be somewhat uncomfortable unless you wear a sweater or some other heavy clothing.

The question regarding weather phenomena releasing photons through the IR window, which is far larger at the top of the troposphere than at the surface is an entirely different experiment than measuring the heat retained by a distiller.

Fair enough. So that wasn't a very good argument on my part since all the vessels in chemical plants are opaque as you say. But there are lots of other arguments.

[acidohm]

Sept 21, 2017 19:52:36 GMT duwayne said:

Sept 20, 2017 15:47:51 GMT acidohm said:

It would certainly explain ir images of hurricanes??

Acidohm, my understanding from Nautonnier's post on the other thread is that the "images of hurricanes" are showing temperatures at the top of the the clouds and therefore the cloud heights. They do not indicate the amount of IR.

Fair enough Dwayne, I clearly missed the point at some stage!