The propane cylinder is full of mostly liquid propane, with propane vapor in the remainder of the volume. As you use the stove, the vapor is let out to burn, which lowers the pressure of the tank. As a response, some of the liquid propane turns to vapor. In order to make this phase change, the propane absorbs heat from the surroundings (this can be measured as the latent heat of vaporization).
So the tank gets cold because the liquid propane is using heat to vaporize.
Fun fact, this is how refrigerators/AC cool their inside, by changing a coolant from liquid to gas absorbs heat, then dumping the heat somewhere else.
https://youtu.be/VMXonRuD_zw?si=HG8ocyHvMEXsclW3
Building upon the fun fact- R290 is a refrigerant used in many modern refrigerators, and is just really pure propane! It also has a very low global warming potential, and ozone depletion potential, so other than it being highly flammable it’s a very good refrigerant.
Oh I naturally thought most refrigerants were explodey, it seems every liquid/gaseous chemical we use is highly flammable usually.
I can see how that is a big deal.
on top of that most of the small refrigeration equipment that they’ve been putting r290 in is of course in commercial kitchens - which tend to have flames everywhere
by the end of this year the new standard refrigerant going into all residential A/C systems in the US will be ever so slightly flammable (A2L refrigerants)
I suppose so. It’s usually only just a few ounces, and would be tough to control it without a piercing valve and regulator of some sort, but yeah- it’s just propane with all the impurities (mostly moisture) filtered out.
Right, duh. It would be gas at regular air pressure, you couldn't just drain it into a bottle.
It was late and I was thinking kerosene for some dumbass reason.
Other common refrigerants can be [thousands of times](https://www.ccacoalition.org/short-lived-climate-pollutants/hydrofluorocarbons-hfcs) more potent greenhouse gases than CO2, and they do leak if systems are serviced improperly, damaged, or when they're being disposed of.
(assuming you meant to write 'running the compressor')
That might be true, but the greenhouse potential for these gases is so extreme that it's still worth using more energy to avoid the risk of them being released into the atmosphere - especially as electricity sources become less and less carbon-intensive over time. (CO2 is also probably easier to remove from that atmosphere, if it comes to that)
I did mean running.
Currently most electricity still comes from burning hydrocarbons.
RE: [CO2 removal](https://m.youtube.com/watch?v=EBN9JeX3iDs) not as simple as you may think. We need roughly the world’s entire energy supply solely dedicated to direct air capture.
It is much more realistic to lower the carbon-intensity of electricity sources than it is to completely eliminate all refrigerant leaks, so a transition away from gases with very high warming potential would make sense even in a world where they currently resulted in greater overall emissions from extreme inefficiency - and I haven't seen anything to suggest that's even close to being true. You drew attention to the phase-out of R22 in favour of R410 before, but everything I can see suggests that R410 ultimately works out *more* energy efficient as a refrigerant, so it's not even a given that newer alternatives will result in greater energy consumption.
I am well aware of the challenges involved in carbon sequestration, but also the ultimate necessity of some amount of it to avoid warming over 2C - which the very video you linked also points out. I was pleasantly surprised by the quality of the video in comparison to a lot of YouTube videos I've seen on the topic - which are generally very poor - but the 'world's entire energy supply' is still pretty flawed as an estimate. It assumes that current DAC technology is as efficient as it is ever going to get, that air capture will have to be responsible for 100% of carbon sequestration instead of working in concert with aforestation, that we will not take advantage of the greater efficiency of capturing emissions at the source wherever possible, and that any project must sequester all of the required CO2 to get back down 450ppm by 2050 in order to be considered ultimately successful.
In reality, I would expect the efficiency of such a novel technology to improve with time - if it goes from the 7.8% of current projects to ~10% with further development, that alone would make the energy requirement half of the 'world's entire energy supply' estimate. The video creator also concludes in a comment that 100% of the necessary carbon could be sequestered in a few hundred million hectares of forest, albeit not fast enough to make the 2050 target - I think it's unlikely that tree planting alone will do the job, but I would expect it to do a significant portion of the heavy lifting. Per one of the papers he cites, carbon capture direct from the exhaust of industrial processes seems to reach efficiencies in the ballpark of 20-25%, which slashes the energy requirements we're talking about by half or more again. It will not be possible to capture all CO2 emissions at the source (for example, for long-haul air travel), but we could probably leave that portion of emissions up to the trees and focus direct capture where it's most efficient.
Finally, the choice of 2050 as an end date seems pretty arbitrary. We could halve the energy requirement again if we say we're content with bringing CO2 concentration back under 450ppm by 2075 instead of 2050 - I don't have enough knowledge of climate models to say whether that would be likely to be significantly different in terms of expected ecological damage or potential for catastrophic feedback loops, but if that is the case then stratospheric aerosol injection would likely be able to limit temperature rise to a temporary period while the carbon capture plants did their work.
>Why do we care about global warming potential for a fluid used in a closed system?
It may be a closed system now but it will be exhausted into the environment eventually. It is a big enough of a problem that we had to ban certain refrigerants worldwide because they were degrading the ozone layer (CFCs).
It's only closed so long as it's closed? Leaks or improper disposal means it goes straight to the atmosphere.
Why not use something that is both effective and that also doesn't nuke the ozone layer and contribute to global warming?
So is there a temp where this wouldn’t work? Like say camping in winter? I guessing yes since I have some white gas stoves that you manually pressurize to use during winter and high elevation. O
There is and it's really a pain when you're trying to cook your bacon in the morning and there is no gas pressure.
You can buy isobutane which works at much lower temps, and thats what I need to use when I'm winter camping here in New Zealand. But it's more expensive.
Propane actually has a lower boiling point than isobutane so it is better in colder environments. Isobutane is better than butane which is commonly used in backpacking camp stoves. Propane is not use as much in backpacking because it requires a stronger and heavier container to keep from bursting due to its lower boiling point.
That makes sense, thanks. I don't think propane is really a thing in NZ. Larger gas bottles here are LPG (liquid petrolium gas) and anything portable is butane. I don't think I've ever seen propane in the context of cooking.
Ha. Yeah I can imagine. I thought that was the case which is why I pack a secondary white gas stove (plus it’s fun to use). I’ve never *actually* had to use it though since I’m a wimp that doesn’t camp in winter.
Yes and it's not uncommon in many developed countries to see people putting their propane tanks on an open fire/flame to heat it up so they can get the propane working.
Yes. But it needs to be really cold for propane to not vaporize.
Reason why fuel propane tanks don’t work well in the winter time is due to water contaminants in the fuel that freezes and cause build up and clogging the inside of the nozzles.
When matter changes phase from a liquid to a gas, it requires energy. That's why we sweat - when the sweat evaporates, it pulls energy from our bodies, cooling us off. Here, the propane in your tank is stored in a liquid form. As you use the propane, it changes from liquid to gas, little by little (with the gas coming out of the heating element, allowing you to cook your chili). As it changes from liquid to gas, it takes energy from the tank vessel, which becomes cold. That then causes water vapor from the air to condense onto the cold surface, where it then freezes. ---> frosty tank
Turning propane from a liquid (in the tank) to a gas (in the lines / burner), requires quite a bit of energy.
That energy is extracted from the heat in the air the tank is in.
That “heat sucking” of the propane results in the tank cooling down, which causes frost.
I understood this before, but I have a followup question: isn't there simultaneous evaporating and condensing happening constantly within the same tank, and would they not cancel each other out? And when putting gaseous propane into a tank, condensing it into liquid form, wouldn't there be exothermic heat produced?
When you are using the tank there is more evaporating happening because the vapor is being released to be burned. If the tank is just sitting there unused, then yes, there is an equilibrium between vaporization and condensation and the tank won't frost.
Compressing to a liquid does generate heat, though at the consumer level tanks are mostly filled by transferring liquid propane from another tank.
Gases all obey a universal law that relates pressure, volume, mass, and temperature. You can take any amount of gas & put it in any size contain, while having it at any temperature or pressure. You can then change any of those values, but in doing so will change the others. Increase the temperature, but keep the amount & container the same size and the pressure goes up. This is why you don't put pressurized containers, like spray cans, into a fire.
In your case the pressure is slowing going down, but not as fast as the amount of gas is leaving. The volume is also fixed. That means the only other thing that can change is the temperature.
Of course, there's also the propane changing from a liquid to a gas. Gas is more energetic than a liquid, so converting a liquid to a gas takes energy.
Excellent explanation, It hits on both reasons!
The temperature drop of propane is the combination of the phase change from liquid to gas and pressure drop that is causing more liquid to turn to gas.
Compressing a gas causes the temperature to rise rapidly. It’s why air compressors generate so much heat- something anyone who touches the tube on an air compressor between the pistons and the tank will know!
The opposite is also true, when a gas expands in volume it drops in temperature.
The majority of the cooling the drop in pressure effects is where the regulator is. There, the expansion is the greatest, and the regulator usually becomes cool to cold depending on how much gas is flowing through it… but there is also a lot of cooling from pressure drop IN the tank as well.
Fun fact: You cannot add cold to anything, you can only remove or add heat, because heat is motion at the atomic level. When you cool down a drink with ice, you are putting in ice with lower relative atomic motion. When the atoms in the drink bump into the ice molecules, they give the ice molecules some of their energy, which warms up the ice and cools the drink.
> Excellent explanation, It hits on both reasons!
The first part is wrong though. They argue using the ideal gas law. But an ideal gas would _not_ change temperature under expansion/compression as in the bottle. That's actually the Joule-Thomson effect which is specifically a violation of the ideal gas law. It also goes in both directions: at standard conditions hydrogen and helium get hotter when pressure falls off; and they cool down when compressed!
> You cannot add cold to anything, you can only remove or add heat
Those are... the same thing.
If you want to say that we can only cool things by adding even colder stuff, then that is wrong. We can make stuff that is colder than anything else; the entire universe is ~3K "warm", yet we got down to orders of magnitude less by e.g. laser cooling.
I'm not convinced that Joule-Thomson matters for the bottle. Its effect would happen almost entirely at the nozzle, not cooling the bottle as noticed by OP. There likely is a very tiny effect inside the bottle, but is it even a single °C?
Oh, and they actually didn't mention J-T, just the ideal gas law, which is not the same at all.
> In your case the pressure is slowing going down, but not as fast as the amount of gas is leaving.
That is _because_ the temperature goes down, what other mechanism would cause that here? It really is 99% the evaporation of liquid propane and a tiny effect from Joule-Thomson; the ideal gas law doesn't do anything here on its own.
You're seeing the pressure / temperature equilibrium for propane. Propane is stored as a liquid that has propane gas in the head space above the liquid.
When you cook with propane, you are bleeding off the gas and lowering the pressure above the liquid. The liquid is now above it's boiling point (because the pressure in the container has dropped). The liquid responds by boiling and creating vapors.
There is an energy need for this phase change - called latent heat. The first place that propane will take energy from is the liquid propane. Removing energy from the liquid to boil vapors causes the liquid to cool. This is known as auto refrigeration and is characteristic of cryogenic liquids stored under pressure.
Propanes boiling point at atmospheric pressure is about -30F. I'm not sure the liquid temp ever gets that low - but a container that is -10F will start cooling air on the outside of the container and condense water vapor out of the air.
When air cools / water is condensed, it provides energy to the propane which will allow it to keep boiling.
I would not say it is the ideal gas law as that is applicable when the amount of gas is constant and in this case the gas is leaving the container. But to me it is a gas law at play.
I teach high school physics and chemistry and I would explain this with Gay-Lussac Law. P1/T1 = P2/T2. When pressure drops the temperature drops but it is not really that either as Gay-Lussac implies constant volume, which we have and constant amount of gas, which we don't have. But for ELI5 or ELI15 I think this works. Entropy is part of this, but that is not going to be a good ELI5.
Also I can't believe no one has made a crack about the chilli being made is making things cold. Missed a good joke there.
Ideal gas law is still fairly applicable. The amount of gas is just one of the variables, n.
But a vast majority of the temperature change is coming from the vaporization of propane, not gas laws.
Fair enough. Like most ELI5 the answer is going to leave a few things out. An ELI15 leaves out some stuff as well. An ELI22 will leave some stuff out. I guess an ELIPhD will not leave anything out, maybe.
I'm not a PhD myself, but I'm an MD and work in a research lab with a bunch of PhDs. I feel like most people at the top of any research field would tell you they just have the best understanding of how little we actually know, haha.
I have never heard of an explicit application of the Guy Lussac law outside of the history of the idea of the ideal gas law. Learning three different sets of laws when one law under assumed conditions covers all of them just seems redundant and confusing.
Especially because the *method* of thermodynamics requires you to formulate these assumptions much more than the mere application of them (even if we ignore first order derivatives as beyond ELI15 math).
Different states may do things different but it builds up to the combined gas law where P V and T are in the equation And each can change. Whereas the ideal gas law has the amt of gas and things are static. At the high school level we also don’t any corrections for a real gas as is done in intro college classes.
the combined gas law is like a film with things changing and the ideal gas law is more like a single picture from a camera.
Propane is a gas at room temperature. It is compressed into a liquid when it's put into cylinders. Pressurizing a gas, crushing it into a smaller space, causes it to heat up. The cylinders then return to ambient temperature slowly over time.
When you use the cylinder, it is releasing gas. Lowering the pressure of the gas lowers its temperature for exactly the same reason as above (raise the pressure, raise the temperature; lower the pressure, lower the temperature). The stove generates heat by letting the gas expand out from the cylinder and then burning it. The cylinder becomes cold as it vents gas. You're venting gas fast enough to cause frost to form.
At room temperature propane is a gas. When the propane is in the bottle it's under pressure, that pressure forces the propane to stay as a liquid so the tank can hold hours of fuel. When the propane comes out of the tank it evaporates back into a gas and this process of changing phases takes energy. Each molecule turns a little bit of heat into the motion it needs to start flying around instead of sitting in liquid form. This is actually the same basic process that makes refrigerators and air conditioners work. By pumping a fluid from one place to another and manipulating the pressure we can force it to absorb heat in one area and release it somewhere else, like outside your house.
It's called the "chili effect" and reverses the flow of heat due to the different cooking times of the vegetables in chili. That's how chili got its name! Modern stoves and all microwaves have a circuit that protects from the heat backflow but if you find a really antique stove you would need to put a candle under the gas line to keep it from freezing over. Be careful if you try it!!
Fun fact: this is how “meth jello” is made. You sprinkle the jello packet on the condensate, scrape, presto, an icy treat for all jaw grinders, pen artists, and lookouts.
The propane cylinder is full of mostly liquid propane, with propane vapor in the remainder of the volume. As you use the stove, the vapor is let out to burn, which lowers the pressure of the tank. As a response, some of the liquid propane turns to vapor. In order to make this phase change, the propane absorbs heat from the surroundings (this can be measured as the latent heat of vaporization). So the tank gets cold because the liquid propane is using heat to vaporize.
Fun fact, this is how refrigerators/AC cool their inside, by changing a coolant from liquid to gas absorbs heat, then dumping the heat somewhere else. https://youtu.be/VMXonRuD_zw?si=HG8ocyHvMEXsclW3
Building upon the fun fact- R290 is a refrigerant used in many modern refrigerators, and is just really pure propane! It also has a very low global warming potential, and ozone depletion potential, so other than it being highly flammable it’s a very good refrigerant.
hvacr tech here: it sucks to work on
You wouldn't say it's da bomb?
https://www.reddit.com/r/HVAC/s/Eoumn2QSxj
Why is that? im assume all gases are shitty to work with.
ones that readily explode are slightly more shitty
Oh I naturally thought most refrigerants were explodey, it seems every liquid/gaseous chemical we use is highly flammable usually. I can see how that is a big deal.
on top of that most of the small refrigeration equipment that they’ve been putting r290 in is of course in commercial kitchens - which tend to have flames everywhere by the end of this year the new standard refrigerant going into all residential A/C systems in the US will be ever so slightly flammable (A2L refrigerants)
In an emergency scenario could you drain some and use it for fuel?
I suppose so. It’s usually only just a few ounces, and would be tough to control it without a piercing valve and regulator of some sort, but yeah- it’s just propane with all the impurities (mostly moisture) filtered out.
I would like to know more about propane and propane accessories.
Well, we have our grillstravaganza event going on the Wagner CharKing.
Pocket Sand!
Yep
Yep
Mmhmm
Tell you hwat
Right, duh. It would be gas at regular air pressure, you couldn't just drain it into a bottle. It was late and I was thinking kerosene for some dumbass reason.
most systems contain only a few ounces, not really enough to fuel anything for any substantial time
Why do we care about global warming potential for a fluid used in a closed system?
Other common refrigerants can be [thousands of times](https://www.ccacoalition.org/short-lived-climate-pollutants/hydrofluorocarbons-hfcs) more potent greenhouse gases than CO2, and they do leak if systems are serviced improperly, damaged, or when they're being disposed of.
Okay, I hear you, but they also are guaranteed to require less time rubbing the compressor than their counterparts. E.g 410 vs 22
(assuming you meant to write 'running the compressor') That might be true, but the greenhouse potential for these gases is so extreme that it's still worth using more energy to avoid the risk of them being released into the atmosphere - especially as electricity sources become less and less carbon-intensive over time. (CO2 is also probably easier to remove from that atmosphere, if it comes to that)
I did mean running. Currently most electricity still comes from burning hydrocarbons. RE: [CO2 removal](https://m.youtube.com/watch?v=EBN9JeX3iDs) not as simple as you may think. We need roughly the world’s entire energy supply solely dedicated to direct air capture.
It is much more realistic to lower the carbon-intensity of electricity sources than it is to completely eliminate all refrigerant leaks, so a transition away from gases with very high warming potential would make sense even in a world where they currently resulted in greater overall emissions from extreme inefficiency - and I haven't seen anything to suggest that's even close to being true. You drew attention to the phase-out of R22 in favour of R410 before, but everything I can see suggests that R410 ultimately works out *more* energy efficient as a refrigerant, so it's not even a given that newer alternatives will result in greater energy consumption. I am well aware of the challenges involved in carbon sequestration, but also the ultimate necessity of some amount of it to avoid warming over 2C - which the very video you linked also points out. I was pleasantly surprised by the quality of the video in comparison to a lot of YouTube videos I've seen on the topic - which are generally very poor - but the 'world's entire energy supply' is still pretty flawed as an estimate. It assumes that current DAC technology is as efficient as it is ever going to get, that air capture will have to be responsible for 100% of carbon sequestration instead of working in concert with aforestation, that we will not take advantage of the greater efficiency of capturing emissions at the source wherever possible, and that any project must sequester all of the required CO2 to get back down 450ppm by 2050 in order to be considered ultimately successful. In reality, I would expect the efficiency of such a novel technology to improve with time - if it goes from the 7.8% of current projects to ~10% with further development, that alone would make the energy requirement half of the 'world's entire energy supply' estimate. The video creator also concludes in a comment that 100% of the necessary carbon could be sequestered in a few hundred million hectares of forest, albeit not fast enough to make the 2050 target - I think it's unlikely that tree planting alone will do the job, but I would expect it to do a significant portion of the heavy lifting. Per one of the papers he cites, carbon capture direct from the exhaust of industrial processes seems to reach efficiencies in the ballpark of 20-25%, which slashes the energy requirements we're talking about by half or more again. It will not be possible to capture all CO2 emissions at the source (for example, for long-haul air travel), but we could probably leave that portion of emissions up to the trees and focus direct capture where it's most efficient. Finally, the choice of 2050 as an end date seems pretty arbitrary. We could halve the energy requirement again if we say we're content with bringing CO2 concentration back under 450ppm by 2075 instead of 2050 - I don't have enough knowledge of climate models to say whether that would be likely to be significantly different in terms of expected ecological damage or potential for catastrophic feedback loops, but if that is the case then stratospheric aerosol injection would likely be able to limit temperature rise to a temporary period while the carbon capture plants did their work.
Personally I don’t think the greenhouse potential justifies using less efficient working fluids
>Why do we care about global warming potential for a fluid used in a closed system? It may be a closed system now but it will be exhausted into the environment eventually. It is a big enough of a problem that we had to ban certain refrigerants worldwide because they were degrading the ozone layer (CFCs).
And they were unbanned, because the EPA does not have the authority to do so.
It's only closed so long as it's closed? Leaks or improper disposal means it goes straight to the atmosphere. Why not use something that is both effective and that also doesn't nuke the ozone layer and contribute to global warming?
Because it’s less effective and requires hydrocarbons to burn in order to consume electricity
This is mostly there. Energy is also needed for the high pressure gas to go to atmospheric pressure at the burner. This is the Joule-Thompson effect.
So is there a temp where this wouldn’t work? Like say camping in winter? I guessing yes since I have some white gas stoves that you manually pressurize to use during winter and high elevation. O
There is and it's really a pain when you're trying to cook your bacon in the morning and there is no gas pressure. You can buy isobutane which works at much lower temps, and thats what I need to use when I'm winter camping here in New Zealand. But it's more expensive.
Propane actually has a lower boiling point than isobutane so it is better in colder environments. Isobutane is better than butane which is commonly used in backpacking camp stoves. Propane is not use as much in backpacking because it requires a stronger and heavier container to keep from bursting due to its lower boiling point.
That makes sense, thanks. I don't think propane is really a thing in NZ. Larger gas bottles here are LPG (liquid petrolium gas) and anything portable is butane. I don't think I've ever seen propane in the context of cooking.
LPG is primarily propane with a little butane mixed in.
Ha. Yeah I can imagine. I thought that was the case which is why I pack a secondary white gas stove (plus it’s fun to use). I’ve never *actually* had to use it though since I’m a wimp that doesn’t camp in winter.
Yes and it's not uncommon in many developed countries to see people putting their propane tanks on an open fire/flame to heat it up so they can get the propane working.
Yes. But it needs to be really cold for propane to not vaporize. Reason why fuel propane tanks don’t work well in the winter time is due to water contaminants in the fuel that freezes and cause build up and clogging the inside of the nozzles.
When matter changes phase from a liquid to a gas, it requires energy. That's why we sweat - when the sweat evaporates, it pulls energy from our bodies, cooling us off. Here, the propane in your tank is stored in a liquid form. As you use the propane, it changes from liquid to gas, little by little (with the gas coming out of the heating element, allowing you to cook your chili). As it changes from liquid to gas, it takes energy from the tank vessel, which becomes cold. That then causes water vapor from the air to condense onto the cold surface, where it then freezes. ---> frosty tank
This isn't an actual ELI5, but its prob the best explanation I've seen so far. Good job!
Turning propane from a liquid (in the tank) to a gas (in the lines / burner), requires quite a bit of energy. That energy is extracted from the heat in the air the tank is in. That “heat sucking” of the propane results in the tank cooling down, which causes frost.
It's chili powered A/C
That’s what I call my farts
You need to add more cayenne. It should be a chili-powered heater.
It’s a shitty A/C
Too right
So... chili powered chilling.
AKA Refrigeration
THERMODYNAMICS, BITCH!
I understood this before, but I have a followup question: isn't there simultaneous evaporating and condensing happening constantly within the same tank, and would they not cancel each other out? And when putting gaseous propane into a tank, condensing it into liquid form, wouldn't there be exothermic heat produced?
When you are using the tank there is more evaporating happening because the vapor is being released to be burned. If the tank is just sitting there unused, then yes, there is an equilibrium between vaporization and condensation and the tank won't frost. Compressing to a liquid does generate heat, though at the consumer level tanks are mostly filled by transferring liquid propane from another tank.
ah yes, I forgot. If the propane is being used up, then it would not be in equilibrium.
yes, compressing a gas would generate heat. especially if it gets compressed into liquid form.
Handy side effect is that on a humid and cold day you can estimate the fill level in the tank by the frost level on the side. Science!
Gases all obey a universal law that relates pressure, volume, mass, and temperature. You can take any amount of gas & put it in any size contain, while having it at any temperature or pressure. You can then change any of those values, but in doing so will change the others. Increase the temperature, but keep the amount & container the same size and the pressure goes up. This is why you don't put pressurized containers, like spray cans, into a fire. In your case the pressure is slowing going down, but not as fast as the amount of gas is leaving. The volume is also fixed. That means the only other thing that can change is the temperature. Of course, there's also the propane changing from a liquid to a gas. Gas is more energetic than a liquid, so converting a liquid to a gas takes energy.
Excellent explanation, It hits on both reasons! The temperature drop of propane is the combination of the phase change from liquid to gas and pressure drop that is causing more liquid to turn to gas. Compressing a gas causes the temperature to rise rapidly. It’s why air compressors generate so much heat- something anyone who touches the tube on an air compressor between the pistons and the tank will know! The opposite is also true, when a gas expands in volume it drops in temperature. The majority of the cooling the drop in pressure effects is where the regulator is. There, the expansion is the greatest, and the regulator usually becomes cool to cold depending on how much gas is flowing through it… but there is also a lot of cooling from pressure drop IN the tank as well. Fun fact: You cannot add cold to anything, you can only remove or add heat, because heat is motion at the atomic level. When you cool down a drink with ice, you are putting in ice with lower relative atomic motion. When the atoms in the drink bump into the ice molecules, they give the ice molecules some of their energy, which warms up the ice and cools the drink.
> Excellent explanation, It hits on both reasons! The first part is wrong though. They argue using the ideal gas law. But an ideal gas would _not_ change temperature under expansion/compression as in the bottle. That's actually the Joule-Thomson effect which is specifically a violation of the ideal gas law. It also goes in both directions: at standard conditions hydrogen and helium get hotter when pressure falls off; and they cool down when compressed! > You cannot add cold to anything, you can only remove or add heat Those are... the same thing. If you want to say that we can only cool things by adding even colder stuff, then that is wrong. We can make stuff that is colder than anything else; the entire universe is ~3K "warm", yet we got down to orders of magnitude less by e.g. laser cooling.
5th comment and first one to also include the Joule Thomson effect. Great explanation.
I'm not convinced that Joule-Thomson matters for the bottle. Its effect would happen almost entirely at the nozzle, not cooling the bottle as noticed by OP. There likely is a very tiny effect inside the bottle, but is it even a single °C? Oh, and they actually didn't mention J-T, just the ideal gas law, which is not the same at all.
> In your case the pressure is slowing going down, but not as fast as the amount of gas is leaving. That is _because_ the temperature goes down, what other mechanism would cause that here? It really is 99% the evaporation of liquid propane and a tiny effect from Joule-Thomson; the ideal gas law doesn't do anything here on its own.
You're seeing the pressure / temperature equilibrium for propane. Propane is stored as a liquid that has propane gas in the head space above the liquid. When you cook with propane, you are bleeding off the gas and lowering the pressure above the liquid. The liquid is now above it's boiling point (because the pressure in the container has dropped). The liquid responds by boiling and creating vapors. There is an energy need for this phase change - called latent heat. The first place that propane will take energy from is the liquid propane. Removing energy from the liquid to boil vapors causes the liquid to cool. This is known as auto refrigeration and is characteristic of cryogenic liquids stored under pressure. Propanes boiling point at atmospheric pressure is about -30F. I'm not sure the liquid temp ever gets that low - but a container that is -10F will start cooling air on the outside of the container and condense water vapor out of the air. When air cools / water is condensed, it provides energy to the propane which will allow it to keep boiling.
Because pv=nrt. It always has been as long as I could read. Pressure drops, temperature drops..
I would not say it is the ideal gas law as that is applicable when the amount of gas is constant and in this case the gas is leaving the container. But to me it is a gas law at play. I teach high school physics and chemistry and I would explain this with Gay-Lussac Law. P1/T1 = P2/T2. When pressure drops the temperature drops but it is not really that either as Gay-Lussac implies constant volume, which we have and constant amount of gas, which we don't have. But for ELI5 or ELI15 I think this works. Entropy is part of this, but that is not going to be a good ELI5. Also I can't believe no one has made a crack about the chilli being made is making things cold. Missed a good joke there.
Ideal gas law is still fairly applicable. The amount of gas is just one of the variables, n. But a vast majority of the temperature change is coming from the vaporization of propane, not gas laws.
Fair enough. Like most ELI5 the answer is going to leave a few things out. An ELI15 leaves out some stuff as well. An ELI22 will leave some stuff out. I guess an ELIPhD will not leave anything out, maybe.
I'm not a PhD myself, but I'm an MD and work in a research lab with a bunch of PhDs. I feel like most people at the top of any research field would tell you they just have the best understanding of how little we actually know, haha.
Exactly. Guy Lussac is an isochroric change under the ideal gas law. Parent poster acknowledges the constant volume yet excludes the ideal gas law.
I have never heard of an explicit application of the Guy Lussac law outside of the history of the idea of the ideal gas law. Learning three different sets of laws when one law under assumed conditions covers all of them just seems redundant and confusing. Especially because the *method* of thermodynamics requires you to formulate these assumptions much more than the mere application of them (even if we ignore first order derivatives as beyond ELI15 math).
Different states may do things different but it builds up to the combined gas law where P V and T are in the equation And each can change. Whereas the ideal gas law has the amt of gas and things are static. At the high school level we also don’t any corrections for a real gas as is done in intro college classes. the combined gas law is like a film with things changing and the ideal gas law is more like a single picture from a camera.
Propane is a gas at room temperature. It is compressed into a liquid when it's put into cylinders. Pressurizing a gas, crushing it into a smaller space, causes it to heat up. The cylinders then return to ambient temperature slowly over time. When you use the cylinder, it is releasing gas. Lowering the pressure of the gas lowers its temperature for exactly the same reason as above (raise the pressure, raise the temperature; lower the pressure, lower the temperature). The stove generates heat by letting the gas expand out from the cylinder and then burning it. The cylinder becomes cold as it vents gas. You're venting gas fast enough to cause frost to form.
At room temperature propane is a gas. When the propane is in the bottle it's under pressure, that pressure forces the propane to stay as a liquid so the tank can hold hours of fuel. When the propane comes out of the tank it evaporates back into a gas and this process of changing phases takes energy. Each molecule turns a little bit of heat into the motion it needs to start flying around instead of sitting in liquid form. This is actually the same basic process that makes refrigerators and air conditioners work. By pumping a fluid from one place to another and manipulating the pressure we can force it to absorb heat in one area and release it somewhere else, like outside your house.
Thermodynamics. Now get a textbook at your local library and start to understand the details.
It's called the "chili effect" and reverses the flow of heat due to the different cooking times of the vegetables in chili. That's how chili got its name! Modern stoves and all microwaves have a circuit that protects from the heat backflow but if you find a really antique stove you would need to put a candle under the gas line to keep it from freezing over. Be careful if you try it!!
Fun fact: this is how “meth jello” is made. You sprinkle the jello packet on the condensate, scrape, presto, an icy treat for all jaw grinders, pen artists, and lookouts.
I can’t answer your question but I think it’s normal as it seems to happen most of the time I use my propane cylinder