Why do tanks get hot when you fill them from higher pressure tanks?

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final thought on gas leaving a tank. if you watch this video you will see gas truly expanding. Notice the white contrale.... that is moisture in the air surrounding the tank being rapidly cooled by expansion. Since there is no recieving tank, the air outside the tank and the tank itself are both rapidly expanding/cooling, although the it is a little hard to see condensation collecting on the tank....

[video=youtube;hu62940nMmc]http://www.youtube.com/watch?v=hu62940nMmc&feature=related[/video]
 
final thought on gas leaving a tank. if you watch this video you will see gas truly expanding. Notice the white contrale.... that is moisture in the air surrounding the tank being rapidly cooled by expansion. Since there is no recieving tank, the air outside the tank and the tank itself are both rapidly expanding/cooling, although the it is a little hard to see condensation collecting on the tank....

Yeah, but suppose you tried a similar experiment using a vacuum instead?

[video=youtube;DB-GZR0lRos]http://www.youtube.com/watch?v=DB-GZR0lRos[/video]

[video=youtube;uXCdDpw8XFE]http://www.youtube.com/watch?v=uXCdDpw8XFE[/video]
 
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Yeah, but suppose you tried a similar experiment using a vacuum instead?
QUOTE]

Not enough pot in North America to make that one funny (1st one). Of course if the hammer or axe bounced back into his crotch it might....


Video 2? the expansion of the vacuum is still exothermic....
 
Okay, let me see if I have a handle on this thread so far...

OP: I have a few questions
Others: answers answers answers

OP: But that's not what I think. I see it this way....

Others: answers answers explanation answers answers explanation

OP: That may be true, but I still think...

Others: answers answers explanation answers answers answers answers explanation answers answers

OP: Well, if that is true, then why....

Others (more others now): answers answers explanation answers answers DIAGRAM answers answers explanation answers answers

OP: I don't get it. It still seems like it should be...

New Others (the first others got tired of beating heads against walls): answers answers explanation answers answers QUOTES of historically brilliant scientists

OP: But I still think...

Others (those who haven't unsubscribed from thread): CUSSING answers answers explanation answers answers explanation ILLUSTRATION answers answers explanation answers

OP: I still don't get it.

Others (numbers falling off now): MORE CUSSING answers answers explanation explanation ILLUSTRATION answers answers explanation answers OFFER TO PROVIDE CHEAP SEX TO STOP DISCUSSION


Does that about sum it up?
 
Okay, let me see if I have a handle on this thread so far...

OP: I have a few questions
Others: answers answers answers

OP: But that's not what I think. I see it this way....

Others: answers answers explanation answers answers explanation

OP: That may be true, but I still think...

Others: answers answers explanation answers answers answers answers explanation answers answers

OP: Well, if that is true, then why....

Others (more others now): answers answers explanation answers answers DIAGRAM answers answers explanation answers answers

OP: I don't get it. It still seems like it should be...

New Others (the first others got tired of beating heads against walls): answers answers explanation answers answers QUOTES of historically brilliant scientists

OP: But I still think...

Others (those who haven't unsubscribed from thread): CUSSING answers answers explanation answers answers explanation ILLUSTRATION answers answers explanation answers

OP: I still don't get it.

Others (numbers falling off now): MORE CUSSING answers answers explanation explanation ILLUSTRATION answers answers explanation answers OFFER TO PROVIDE CHEAP SEX TO STOP DISCUSSION


Does that about sum it up?

One more trout in the pool. But it may not be rising.
 
Does that about sum it up?

I'd say it's more -
1) I have questions
2) Answers, some good, some very bad, none complete
3) Research leads to more complete answers.
4) More complete answers presented to see whether others agree.
5) Most others don't agree.
6) Careful explanation of why answers seem to be more complete, with set of simple questions leading to those answers and supporting references showing why those answers seem correct.
7) Refusal by most others to answer set of four simple questions. Those who do answer have answers that agree with OP's answers. Those answers lead to the answer to the original question.
8) No one able to answer original question using accepted math/physics/gas laws to explain heating when transfilling.

OP departs. Ultimately either someone will find an error in OP's posts and answer the original question, or others will continue believing in imaginary compression heating.

These things are clear:
1) There is no volume of gas in the original high pressure tank - no single cc parcel of gas that does anything other than expand - whether it stays in the original tank or leaves the original tank. All the gas goes from an initial compressed state to a final more expanded state.
2) Physics and gas laws say that gas that expands always remains at constant temperature if no energy is added or removed = "free expansion".
3) The gas that remains in the donor tank gets colder, so energy must have been removed from the gas in that tank.
4) Gas that leaves the donor tank gets hotter, so energy must have been added to the gas going to the destination tank.
5) The sum of energy removed from donor tank and energy added to receiving tank is zero since no energy was added or removed to to/from the original system of gas.

The answers are there if anyone wants to look for them.
 
1) There is no volume of gas in the original high pressure tank - no single cc parcel of gas that does anything other than expand - whether it stays in the original tank or leaves the original tank. All the gas goes from an initial compressed state to a final more expanded state.

You continue to confuse "movement" with "expansion." Some of the molecules of gas in the donor tank moved to the receiving tank, due to a pressure gradient. Not the same as expansion. That movement COULD occur along with expansion of gas, if we emptied the donor tank into a giant balloon.

Since you mentioned cc's of gas expanding, please explain how/where there is expansion of any gas in the system when the system starts with 20 liters (2x10) and ends with 20 liters (2x10).

Think about pressure gradient as a diffusion gradient since, in effect, they are very similar. Over time (albeit a short period of time) some of the the gas molecules in the donor tank are moving from an area of high concentration to an area of low concentration (the receiving tank). However, there has been no "increase in volume" because the volume of gas in the system has not increased. Not even temporarily.

Diffusion.png


---------- Post added March 6th, 2013 at 01:23 PM ----------

The answers are there if anyone wants to look for them.

thetruthisoutthere.jpg
 
Adiabatic Expansion Cooling of Gases

See equation 10 and the explanation:

The thermodynamic expressions used to derive the heat capacity ratio apply only to the part of the gas that remains in the carboy after the stopper is replaced since molar volumes and molar heat capacities were used. Physically, the reversibility of the expansion can be justifed as follows: One can imagine an invisible surface separating the gas that remains within the carboy and the gas that escapes when the stopper is removed. The gas below this surface expands in an approximately reversible way against the surface. Work is done as the upper gas is pushed out. The change is approximately adiabatic only because it is rapid copared to heat flow but slow on the scale of the mechanical work. No appreciable amount of heat is transferred between the reservoir and the gas in the carboy during the short period of the expansion, but after the stopper is replaced, the temperature is seen to increase as thermal equilibrium is reestablished for the gas remaining in the vessel.

Cv ln( Tf - Ti ) = -R ln (Vf - Vi)

You can find the volume of the donor cylinder which will actually be Vf. As the text suggests for Vi you partition the cylinder so that the gas that remains in the cylinder occupies a fraction of the volume initially. You now know Vf and Vi. Plug in Ti at room temperature and the gas constant and the Cv of the gas and you can solve for the final temperature which will decrease.

The free expansion case considers perfect gases where the system as a whole is perfectly insulated, but the chambers become thermally connected, so the heating on one side will cancel the cooling on the other side. This is not the case in filling tanks since the tanks get hot and we observe the heat transfer to the surroundings from both tanks, and the fill whip poorly transfers heat between the vessels. You have a reversible adiabatic isentropic process going on when you let the gas flow, but then the heat or cold you feel on the tanks is work being done to/from the surrounding environment which is not a reversible or isentropic process.

You can most likely use the work done by both cylinders on the surrounding environment to solve for what the initial volume should be in the compression case of filling the receiving cylinder. I suspect you have to take the amount of gas which is transferred and consider it to occupy a volume at the same initial pressure and temperature of the receiving cylinder and then compress that volume to the size of the cylinder.
 
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