26 Oct 15
Originally posted by sonhouseYes. But I think several of the other theories would show similar correlations.
If you had a bottle of butane that was totally full, wouldn't that show pretty much zero temperature decrease, if the effect was due to evaporation? If it was totally full, there would be no volume in which to evaporate and if there were, it would be a very small percentage of the total volume so that should be a test of the evaporation theory.
Conversel ...[text shortened]... n a bottle say only 1/\4 full should have a lower temperature when shaken than one say 3/4 full.
26 Oct 15
Originally posted by sonhouseYes, that's correct. I kept having to take that into account in my calculations. Most of my calculations assume the can is half full and the amount of material lost from the fluid is small.
If you had a bottle of butane that was totally full, wouldn't that show pretty much zero temperature decrease, if the effect was due to evaporation? If it was totally full, there would be no volume in which to evaporate and if there were, it would be a very small percentage of the total volume so that should be a test of the evaporation theory.
Conversel ...[text shortened]... n a bottle say only 1/\4 full should have a lower temperature when shaken than one say 3/4 full.
31 Oct 15
I have an empirical result to report. I started with a 250 ml glass bottle of white gasoline, half full. I measured the temp of the gasoline at 16.2 C. I then shook the bottle vigorously 20 times up and down by gripping the screwed-down top, without touching the glass sides (which would have introduced body heat into the container), and measured the contents again: 15.7 C.
31 Oct 15
1 edit
Originally posted by moonbusSimilar to my result. Try it again with a full bottle. White gas evaporates quickly. I predict a full glass will not result in a change in temperature.
I have an empirical result to report. I started with a 250 ml glass bottle of white gasoline, half full. I measured the temp of the gasoline at 16.2 C. I then shook the bottle vigorously 20 times up and down by gripping the screwed-down top, without touching the glass sides (which would have introduced body heat into the container), and measured the contents again: 15.7 C.
I hope you don't smoke🙂
31 Oct 15
Originally posted by moonbusAre you able to repeat the experiment with water?
I have an empirical result to report. I started with a 250 ml glass bottle of white gasoline, half full. I measured the temp of the gasoline at 16.2 C. I then shook the bottle vigorously 20 times up and down by gripping the screwed-down top, without touching the glass sides (which would have introduced body heat into the container), and measured the contents again: 15.7 C.
02 Nov 15
Originally posted by twhiteheadNo, the effect with water will be microscopic, it's not volatile enough. Lighter gas is going to give the largest effect. At standard temperature and pressure butane is a gas, it is only liquid in the can because the pressure in there is 170 kPa, it is relatively easy to get it to evaporate. I've got no way of measuring it but I'm pretty sure the temperature drop is more than the drops moonbus and sonhouse measured. You'd expect the temperature drop to be lower with gasoline as it's got twice the relative molecular mass (at least octane does) and is liquid at normal pressures. So it depends on what sonhouse did the measurement on.
Are you able to repeat the experiment with water?
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02 Nov 15
Originally posted by twhiteheadIt can't be both?
I am still of the opinion that the effect is entirely due to heat of evaporation.
Thermal conduction is a powerful effect in our perception of temperature.
When we touch an insulator the surface rapidly warms as well as the thermal conduction
rate being lower. [because of]
When we touch a conductor the surface draws our heat away and it 'feels' much cooler because
of that.
When you shake the can you are increasing the thermal conduction abilities of the can either
by bringing the conducting liquids in contact with the surface you are holding, or by increasing
internal circulation and thus heat convection, or both.
This SHOULD make the can 'feel' colder.
The fact that the can is apparently ALSO getting cooler doesn't mean that the above effects are not
happening. It also does not tell us which if either effect is dominant.
To tell which is dominant we would have to get data on what [if any] increase the shaking produces
in thermal conduction rates [theoretically or experimentally] as well as how responsive our sense
of temperature is to changes in thermal conduction rates as well as determining our sense of temperature
against an actual change in temperature with constant thermal conduction rates. [in the desired temperature
range at which we are conducting these experiments].
It also might be a factor in the temperature change if the can in the experiment had not fully equalised with its
surroundings then increased thermal conduction between a cold interior and a warmer can surface could cool
the surface without the internal liquids having dropped in temperature.
This is not an easy experiment to wrap up. [the fun ones never are 🙂 ].
That said I still am of the opinion that our sense of hot and cold is dominated by conduction rates over actual
temperature and that such effects could well still dominate even in the presence of an actual temperature change.
I do however acknowledge that I was not expecting such a noticeable actual temperature change and stand corrected
on that front.
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02 Nov 15
Originally posted by DeepThoughtAn experiment with water might help determine how big of an effect thermal conduction
No, the effect with water will be microscopic, it's not volatile enough. Lighter gas is going to give the largest effect. At standard temperature and pressure butane is a gas, it is only liquid in the can because the pressure in there is 170 kPa, it is relatively easy to get it to evaporate. I've got no way of measuring it but I'm pretty sure the temp ...[text shortened]... does) and is liquid at normal pressures. So it depends on what sonhouse did the measurement on.
plays if it does not have a corresponding actual temperature drop when shaken.??
02 Nov 15
Originally posted by googlefudgeIt can, I just don't think it is. In my experiments I found no difference between shaking the can and then touching it and holding it while shaking. If you are correct the latter should feel colder. Of course sense of touch is not all that accurate.
It can't be both?
As I have said before and as you have pointed out testing with different liquids would help identify which is playing the greater role. In addition to water, cooking oil would also be worth trying as that evaporates even less than water and also sticks to the sides longer.
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02 Nov 15
Originally posted by twhiteheadThe other wrinkle I should point out is the power of the brain to deceive you.
It can, I just don't think it is. In my experiments I found no difference between shaking the can and then touching it and holding it while shaking. If you are correct the latter should feel colder. Of course sense of touch is not all that accurate.
As I have said before and as you have pointed out testing with different liquids would help identify whi ...[text shortened]... lso be worth trying as that evaporates even less than water and also sticks to the sides longer.
It's entirely possible that you are expecting certain results and thus that's what
you perceive as happening. Because I get the exact opposite result to you when
I experiment with my can.
A problem I can't see getting around without using double blind test subjects who
don't know what results they are expecting before hand.
02 Nov 15
Originally posted by googlefudgeWhich is why we insisted on using thermometers which demonstrated that there is a very real temperature drop. Although this doesn't rule out the conduction theory as contributing to the experience it does demonstrate that the cooling is not all perception and self deception.
The other wrinkle I should point out is the power of the brain to deceive you..
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02 Nov 15
Originally posted by twhiteheadYes, but the original question is why it FELT colder.
Which is why we insisted on using thermometers which demonstrated that there is a very real temperature drop. Although this doesn't rule out the conduction theory as contributing to the experience it does demonstrate that the cooling is not all perception and self deception.
Identifying that there is an actual temperature change is of course relevant.
But not sufficient to determine why the temp changes or whether that change is
the dominant factor in why it felt colder.
If rate of conduction dominates actual temperature by a factor of 10 [for example] then
the small measured temperature drop could easily be dominated by a change in conduction.
Also, IF the can is not at the same internal temperature as the room, an increase in internal
thermal conduction/heat absorption could cause a surface temperature decrease.
10 Nov 15
Originally posted by moonbusFurther experimental result: nearly-full 250 ml glass of white gas, shaken vigorously etc. Measured drop in temp: 0.1 degree C.
I have an empirical result to report. I started with a 250 ml glass bottle of white gasoline, half full. I measured the temp of the gasoline at 16.2 C. I then shook the bottle vigorously 20 times up and down by gripping the screwed-down top, without touching the glass sides (which would have introduced body heat into the container), and measured the contents again: 15.7 C.