Sciencemadness Discussion Board - Ionisation to cool gas jet

Ionisation to cool gas jet

D4RR3N - 6-4-2009 at 02:18

Can ionisation of a gas be used to reduce its temperature? Attached is a quick sketch, compressed gas flows over a grid which is attached to a high voltage source. Electrons are ripped from the gas molecules as it flows over the grid before exiting the nozzle. If removing electrons from an atom thus forming an ion reduces the energy state of that atom will this reduced energy state result in a lowered temperature?

not_important - 6-4-2009 at 07:30

If ionising something removed energy from it, wouldn't molecules tend to spontaneously ionise unless there was a large barrier to get over? If an ion was at a lower energy than the neutral compound, why would it ever recombine with an electron?

sakshaug007 - 6-4-2009 at 07:43

Yeah I don't believe this would cool the gas in fact if anything you might create a plasma which as you know exhibits temperatures that rival that produced by the sun. In inductively coupled plasma mass spectrometers, Argon gas is ionized from a nozzle using an RF source which create a plasma of approximately 10000K. This is due to the bombardment of free electrons in the plasma with argon ions as well as argon atoms which then get ionized and causes a self sustaining reaction (as long as argon gas is sourced). So short answer I believe your technique would result in heating the gas (possibly plasma) rather than cooling it.

Hope this is helpful.

Sedit - 6-4-2009 at 08:28

I remember something veagly discribed by tesla that may be worth looking into deaper for you. What he stated had to do with polarization of ionized air molecules causing them to form chains comming from the source of the ionizer. This caused the airs density to (raise/lower?) which cooled the air.

As I said Its been a while since Iv read this but he talks about it more indepth in a paper he wrote about an experimental flying machine and was discussing how the colun omf air below the machine would cool the air from the ions flowing from its surface.

In my personal work with Tesla coils and other forms of HV plasma in air I have noticed many times the air has cool dramaticly but I never thought to attempt a measure of the temperature loss. Your design seems pretty easy to test and is along the lines of something I would design to test a temperature change. One thing you would have to take into consideration with your design is that the air flowing out of the nozzle will cool regardless if the gas has been compressed. As it expanded out of the nozzle it will lose energy and cool. You will need both the feed and the exit to be at the same pressure to get any kind of accurate reading as to whether the temperature chages when the ionization starts.

[Edited on 6-4-2009 by Sedit]

D4RR3N - 6-4-2009 at 08:46

My thought is simply this, if you remove electrons from a gas you are removing energy after all electrons are energy and the result must be a lower energy state.

Conversely if you add electrons to an atom you are adding energy (electrons) so the result must be a higher energy state.

I was thinking therefore that positively ionising a gas may cool it whilst negatively ionising a gas may heat it.

I was thinking of an ioniser rather then a device with surficent electrical energy to generate a plasma.

D4RR3N - 6-4-2009 at 08:53

Quote: Originally posted by Sedit

I remember something veagly discribed by tesla that may be worth looking into deaper for you. What he stated had to do with polarization of ionized air molecules causing them to form chains comming from the source of the ionizer. This caused the airs density to (raise/lower?) which cooled the air.

As I said Its been a while since Iv read this but he talks about it more indepth in a paper he wrote about an experimental flying machine and was discussing how the colun omf air below the machine would cool the air from the ions flowing from its surface.

In my personal work with Tesla coils and other forms of HV plasma in air I have noticed many times the air has cool dramaticly but I never thought to attempt a measure of the temperature loss. Your design seems pretty easy to test and is along the lines of something I would design to test a temperature change. One thing you would have to take into consideration with your design is that the air flowing out of the nozzle will cool regardless if the gas has been compressed. As it expanded out of the nozzle it will lose energy and cool. You will need both the feed and the exit to be at the same pressure to get any kind of accurate reading as to whether the temperature chages when the ionization starts.

[Edited on 6-4-2009 by Sedit]

Sounds very interesting, I would like to read more about this Tesla device. Do you know the name of the paper?

sakshaug007 - 6-4-2009 at 10:22

Quote: Originally posted by D4RR3N

My thought is simply this, if you remove electrons from a gas you are removing energy after all electrons are energy and the result must be a lower energy state.

Conversely if you add electrons to an atom you are adding energy (electrons) so the result must be a higher energy state.

I was thinking therefore that positively ionising a gas may cool it whilst negatively ionising a gas may heat it.

I was thinking of an ioniser rather then a device with surficent electrical energy to generate a plasma.

Sorry but this is not true, because if so, all matter would seek the lowest energy state which would simply be the nucleus of an atom in this case. Everything would disintegrate into a sea of particles (protons and neutrons)! You forgot about the potential energy stored in chemical bonds that prevents this from happening as well as the electromagnetic force that exists between protons and orbiting electrons. If an atom/molecule has less electrons than protons it is positively charged and wants to acquire electrons in order to be stable, conversely if it has more electrons that protons its negatively charged and will want to give up electrons to be stable.

Also, remember that it always takes energy in some form or another to ionize a species.

[Edited on 6-4-2009 by sakshaug007]

Sedit - 6-4-2009 at 10:53

@D4RR
Ill see if I can Find the text its in PDF format somewhere here on my computer but its been like 10 years since Iv accessed it so it may take some time to find what I did with it when moving from one computer to another. A quick web seach turned up first link the same think but it was nothing more then a quote from the PDF that I have. Try searching Google and if you turn up nothing Ill start digging thru my Zip files to see if I can find it.

D4RR3N - 6-4-2009 at 13:31

Quote: Originally posted by Sedit

@D4RR
Ill see if I can Find the text its in PDF format somewhere here on my computer but its been like 10 years since Iv accessed it so it may take some time to find what I did with it when moving from one computer to another. A quick web seach turned up first link the same think but it was nothing more then a quote from the PDF that I have. Try searching Google and if you turn up nothing Ill start digging thru my Zip files to see if I can find it.

I searched and read all I could on Teslas flying machine and I did not find anything quoting him saying ionisation can minipulate air density or temprature. This address contains all known quotes tesla made with regards to how his flying machine functions.

http://www.frank.germano.com/flying_machine.htm

His device obviously used gyroscopic stabilisation so I'm guessing the heart of his machine was his Tesla turbine somehow adapted to produce a jet engine, he talks about powerful jets of air that can be directed in any direction. He also says his device can move in any direction.
My thoughts ate a circular craft with a central downward jet providing lift and a movable jet providing change in direction.

D4RR3N - 6-4-2009 at 13:36

Quote: Originally posted by sakshaug007

Quote: Originally posted by D4RR3N

If all matter were to seek the lowest possible energy level then everything would be frozen would it not?

Rather matter seeks equilibrium with its environment. If it is at a lower energy state it will seek to increase its energy state and if its at a higher energy state it will seek to reduce its energy state.

not_important - 6-4-2009 at 16:55

Quote:

If all matter were to seek the lowest possible energy level then everything would be frozen would it not?

But the energy has to go somewhere, and it can't go "uphill", from a cooler to a hotter area. Plus there is impedance to its leaving, it can only leave an area at a certain rate.

The lowest possible energy level is that which is in equilibrium with its environment; below that is not lower in energy in terms of the system, just the object taken on its own and you can't really consider objects in isolation except in though experiments.

The Earth isn't frozen solid because the Sun continuous to supply it with energy. The Sun stays hot because of the nuclear reactions in its interior; it will stay so for as long as those reactions are able to happen, and there is a measure of rate self-regulation in the Sun.

Quote:

Electrons are not energy, save in the E=MC2 sense. Ionised gas is in a higher energy state than the unionised gas, when an electron rejoins an ionised atom or molecule it emits energy, often in the visible or UV range for outer electrons.

Quote:

ground state:

The condition of an atom, ion, or molecule, when all of its electrons are in their lowest possible energy levels, i.e., not excited. When an atom is in its ground state, its electrons fill the lowest energy orbitals completely before they begin to occupy higher energy orbitals.

Sedit - 6-4-2009 at 18:03

Quote: Originally posted by D4RR3N

Quote: Originally posted by Sedit

His design consisted of an array of capacitors on the bottom of the craft that where in two phases so when half where discharging the other half was charging. No one knows if he could have constructed such a craft but his thoughts where that he would be able to use the craft to repel against the magnetic field of the earth.
Ill take a look and see if I can find the papers on it for you. Remeber its only a theoretical design of his but he wasnt a moron either.

chief - 7-4-2009 at 05:34

Ionization <--> recombination is a balance system; ionization requires addition of energy, and recombination sets it free.

After all ionization of a gas leads to a plasma; plasma is a higher state of aggregation, bound to higher temperatures ; to decrease temperature therefore a lower state has to be searched, eg. the liquid one.

watson.fawkes - 7-4-2009 at 07:15

First things first. In chemistry terms, the reaction is Neutral + Energy --> Ion + Ion. Thus it's an endothermic reaction and the ion products contain more energy than the neutral reagent.

On the other hand, there might be something to the observed cooling near HV equipment. It's certain that ions of a given gas species have a different Joule-Thomson coefficient than the non-ionized gas. The difference is that an ionized gas has appreciable potential energy in the electrostatic repulsion of the ions with each other. What I don't know offhand is whether the effect is large enough to be readily observable.

D4RR3N - 7-4-2009 at 12:01

I do believe that the application of high voltage can be used to cool air, just trying to figure out how it works.

Lets look at it from another angle. When a gas expands it cools, as a gas expands its density decreases also.

If you ionise air then the air molecules all being of the same charge must mutually repel each other. This mutual repulsion must cause the charged air cloud to expand. The expansion must result in a density decrease.

sakshaug007 - 7-4-2009 at 12:34

Quote: Originally posted by D4RR3N

I do believe that the application of high voltage can be used to cool air, just trying to figure out how it works.

Lets look at it from another angle. When a gas expands it cools, as a gas expands its density decreases also.

If you ionise air then the air molecules all being of the same charge must mutually repel each other. This mutual repulsion must cause the charged air cloud to expand. The expansion must result in a density decrease.

I could be wrong but I'm not so sure the ideal gas law (PV=nRT) would apply with ionized gases, being that they are not an ideal gas. This repelling expansion of like charged ions might occur but perhaps for only a fraction of a second before they recombine with the free electrons being generated and release energy in the form of heat and light.

Just a thought.

D4RR3N - 7-4-2009 at 14:35

Ions last in the environment allot longer then a few seconds otherwise electric air ionisers would be useless.

Sedit - 7-4-2009 at 15:04

They work on the principle of combining with positive charged particals in the air rendering them neutral where they fall to the ground.

sakshaug007 - 7-4-2009 at 15:51

I believe the way those so called "air ionizers" work i.e. Sharper Image Ionicbreeze. Simply use electricity to charge plates (capacitor) which attracts statically charged dust particles, basically what Sedit described. This is different than gas ionization, i.e. plasma, as your device describes. Statically charged dust particles will likely remain charged longer than a gas ion in the same environment if for no other reason than there is more charge to neutralize on the dust than on the gas ion.

[Edited on 7-4-2009 by sakshaug007]

D4RR3N - 7-4-2009 at 16:18

Ionised gas is not a plasma necessarily. If you get a high voltage supply say 100kv
and attach a needle to the output you can charge up objects across the other side of the room just by pointing the needle at them. It proves that ione can easily travel several meters.

The home ionisers you purchase are only say 3kv max

sakshaug007 - 7-4-2009 at 20:18

D4RR2N,

I understand the concept you put forth, that by ionizing the gas it would create positive ions of like charge that would want to rapidly expand away from one another thereby causing a cooling effect. According to the Joule-Thomson effect, however, in order for the cooling effect to take place upon expansion of the gas there has to be a van der waals attraction between molecules as stated by the following quote from the wiki article, of all places

"As a gas expands, the average distance between molecules grows. Because of intermolecular attractive forces (see Van der Waals force), expansion causes an increase in the potential energy of the gas. If no external work is extracted in the process and no heat is transferred, the total energy of the gas remains the same because of the conservation of energy. The increase in potential energy thus implies a decrease in kinetic energy and therefore in temperature."

Since the gas you're speaking of creating (positively charged ions) would have no significant van der waals forces acting on the ions due to the much stronger coulombic repulsion taking place and therefore:

"A second mechanism has the opposite effect. During gas molecule collisions, kinetic energy is temporarily converted into potential energy. As the average intermolecular distance increases, there is a drop in the number of collisions per time unit, which causes a decrease in average potential energy. Again, total energy is conserved, so this leads to an increase in kinetic energy (temperature). Below the Joule–Thomson inversion temperature, the former effect (work done internally against intermolecular attractive forces) dominates, and free expansion causes a decrease in temperature. Above the inversion temperature, gas molecules move faster and so collide more often, and the latter effect (reduced collisions causing a decrease in the average potential energy) dominates: Joule–Thomson expansion causes a temperature increase."

All positively charged molecules would want to move away from one another thereby increasing kinetic energy and thus temperature.

Sedit - 7-4-2009 at 20:34

The way I see it this is so easy to test why is there even a discussion on it. Two thermometers, a tube with a coil inside to one terminal and a coil outside to another, and an HV source. Feed air in and measure the temperature before and after it is ionized and it will give you your definitive answer. I could have a set up such as this done in a matter of hours. Experimentation is King.

sakshaug007 - 7-4-2009 at 21:15

Quote: Originally posted by Sedit

The way I see it this is so easy to test why is there even a discussion on it. Two thermometers, a tube with a coil inside to one terminal and a coil outside to another, and an HV source. Feed air in and measure the temperature before and after it is ionized and it will give you your definitive answer. I could have a set up such as this done in a matter of hours. Experimentation is King.

I agree sedit, I am curious to see what the experiment would reveal. I'm not trying to instigate an argument, in fact I think its fun discussing it. I'm simply stating the science I'm familiar with as anyone would be expected to. It's all good!

"If everyone knew everything what would be the point?"
-Anonymous

PHILOU Zrealone - 8-4-2009 at 02:31

It looks a bit like magnetohydrodynamic (MHD)...the presence of ions/ionisation is suited...
In MHD usually one heats the media to a plasma and make use of easily ionisable salts

The intital drawing in initial post will give some troubles because the gas comes from a closed vessel!
-If it is liquefied gas...it will boil and reduce its temperature by itself when the gas expand into the universe, this might give some toubles to notice the temperature difference if any occurs, and the system will not last long unless the vessel is warmed...
-If it is gaseous, assuming the process works, there will be a depressurisation that will be very fast compensed by income of external atmospheric pressure via the oposite opening...
--> the system must be an two opened one with a perfecly cylindrical reactor.

Something that must also be considered is the self heating of the coil that might give heat to the gas in the reactor...so reactor must be insulated from the coil

There are a lot of experiments in electricity that provides tips for the design:
-the power of needles: if a open wire ends with a sharp end (like a needle) and is submitted to a high voltage one can observe a polarised wind...this is used in the famous "caroussel experiment" where a free moving conducting 4 arm cross (perpendicular to each other) made out of wires ended with perpendicular needles a bit like the nazi's cross...the center of the cross display a notch that allows to put the cross in equilibrium on a needle (perpendicular to the cross plane). If a high voltage is submitted to the system, the cross starts to turn arround the supporting needle...the turning speed depends on the voltage
-the famous flying triangle structure called "LIFTER" is also based on a very high voltage on a conducting cylinder; by reaction a tiny wire parallel to the cylinder and not touching it charge to the opposite charge...the wire and the cylinder repel themselves air comming arround the big cylinder surface charge and flows in the direction of the wire creating a polarised wind...Note again the need for an asymetry!
By assosiation of serveral triangle structures one can actually build very large objects...each triangle can lift a few grams but it cost very high voltage to do so...increasing the amount of triangle structures will allow to lift more weight...triangles are used to consolidate the structure.
Conductors are hold in place by resistant insulated and light structures like plastic straws or balsa woden stocks.

[Edited on 8-4-2009 by PHILOU Zrealone]

chief - 8-4-2009 at 02:59

From the atomic physics scale it's just simple: To take off electrons from a atom (i.e. "ionizing it"), a characteristic amount of eV ("electronVolts") has to be put into the system. eV can easily be converted into Joule: 1 ev == 1.60217653(14)×10−19 joules, so if some table says the second ionization energy of nitrogen == 29.601 eV that means: For charging 1 N-atom to 2+ those 29 eV are needed ; convert this into kJ/mol, quite much !

This energy is put into the system by the electric current, with less than 100 % efficiency. So there will be expected heating, not cooling.
The impression of cooling might come from the electric wind from some corona discharge, that should cool like any other wind by evaporating the moisture of the skin etc. .

Of course: If it were possible to superheat gas, while preventing the ionization by some trick, and then to sudenly allow ionization, then this ionization would take heat out of the gas, thereby cooling it. That would maybe function by some quite ingenious experimantation setup in the temperature range of 1000s of Celsius.

[Edited on 8-4-2009 by chief]

watson.fawkes - 8-4-2009 at 07:09

Quote: Originally posted by sakshaug007

All positively charged molecules would want to move away from one another thereby increasing kinetic energy and thus temperature.

I hadn't even considered that the J-T coefficient would change sign, but that seems eminently possible given this explanation.