everyday thermodynamics question

Ben M

Ben M

Ben M

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Why do aerosol cans always feel cold?

Is it because:
pv=nrt

They are pressurised, so they "try" and take in heat to balance out, them taking in heat makes them feel cold?

or am I missing it completely?
 
a couple of reasons.

firstly:
the liquid gas propellant inside the cans was liquidised by chilling it. thus, it will try to absorb heat to become a gas, because this is its natural state.

Secondly:
while the can may be the same temperature as the table its sat upon, the metal that the can is made of will conduct heat much faster than something that is more insulated, making it "feel" colder even when it isn't.
 
What? Aerosol cans feel cold because they're made of metal, which is a good heat conductor. If you touch a good heat conductor that is colder than your hand, it quickly removes heat from your hand making it feel cold.

Unless you mean when they're being sprayed?
 
Aod said:
a couple of reasons.

firstly:
the liquid gas propellant inside the cans was liquidised by chilling it. thus, it will try to absorb heat to become a gas, because this is its natural state.

Secondly:
while the can may be the same temperature as the table its sat upon, the metal that the can is made of will conduct heat much faster than something that is more insulated, making it "feel" colder even when it isn't.
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I'd thought about the latter, but decided it wasn't due to that because it feels different to just a piece of metal would.

With the first point, if it did become a gas, would the pressure not increase the longer it was left?
 
It will be room temperature and the pressure inside will adjust itself to suit because of the constant. It feels cold because it's a lower temperature than your hand (room temperature I'm guessing) and you're feeling it absorb the heat out your hand.
 
Jonny69 said:
It will be room temperature and the pressure inside will adjust itself to suit because of the constant. It feels cold because it's a lower temperature than your hand (room temperature I'm guessing) and you're feeling it absorb the heat out your hand.
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time to hold a can for the next 20 mins and see if it warms up :p
 
Ben M said:
time to hold a can for the next 20 mins and see if it warms up :p
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Don't hold it put it in your arm pit, for 10-20 mins then instead of touching it with your fingers/ hand put it on your cheek or elbow.

Your hands are terrible heat sensors and are terrible for heating things.
 
held it for about a minute then put it on my face and discovered that you were right. i was hoping there was something more interesting to it that this :p oh well, thanks guys and gals.
 
Ben M said:
held it for about a minute then put it on my face and discovered that you were right. i was hoping there was something more interesting to it that this :p oh well, thanks guys and gals.
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If it just constantly took in heat turning more and more of the fluid to gas it would explode ;)
 
manoz said:
Air cans get the coldest(ime), can't hold them for more then 30 seconds or so of continuous use
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I think the ones with the highest latent heat of evaporation will get the coldest, assuming it's liquid propellant and not compressed gas. Ah the geek in me comes crawling out with his hands in the air ;D

Running my pulsejet on propane makes the bottle freeze. The pressure drops off to the point that it won't run until the temperature is back up.
 
Jonny69 said:
I think the ones with the highest latent heat of evaporation will get the coldest, assuming it's liquid propellant and not compressed gas. Ah the geek in me comes crawling out with his hands in the air ;D

Running my pulsejet on propane makes the bottle freeze. The pressure drops off to the point that it won't run until the temperature is back up.
Click to expand...

Yeah when you shake it, it sounds liquidy!
 
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