Naked Science Forum
General Science => General Science => Topic started by: neilep on 12/12/2007 20:11:25
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Dearest Peeps Who Know So Much,
See this spray ?
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Nice eh ?...amazing how I managed to spray and photograph it at the same time !!...all of this using a Kodak Brownie 44a !!
......brrrrrr !! *sheepy shivers*.....I got caught in the spray and it's so cold !!!.....why's that then ?
Thank ewe
Neil
xxxxx
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Aerosol cans vary with the droplet size and the propellant. small droplets have a smaller surface size when sprayed so that the propellant evaporates faster thus feels warmer then larger drops which contain more propellant and have to take longer to evaporate which feels cooler to the skin.Liquid evaporating has a cooling down effect.Kinda like sweating. when you sweat and slow down and allow the sweat to evaporate it cools your body off!
So if you want like a body spray to feel warmer on your skin you must make sure it breaks up into smaller particles coming out of the can in order for the propellant to evaporate quicker. a finer mist smaller spray openings.
If you want it cooler use a larger spray nozzle which leaves the droplets exiting the can Larger when they come out to produce more evaporation at a slower rate.
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What is your spray.. I think also it would depend on what you were spraying also.
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Air conditioners work on this principle. Pressure and temperature have a direct relationship- As P increases so does T and vice-versa (we'll leave volume out the equation for the time being). That spray that you so brilliantly captured being released from the aerosol (pressurized) can is moving from a high pressure zone to a low pressure zone, resulting in a corresponding drop in temperature.
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Also, remember that as you spray, you are decompressing the remaining fluid in the cannister, which causes the remaining fluid to cool (Gay-Lussac's law, or some such).
Sorry, Bass got there first (by 1 minute 37 seconds).