Sleep has been really tough on me, I guess. But more or less, I've gotten used to it. I no longer need to panic when I still have a million things to do, and it's ten or eleven P.M. And my parents, my loving parents, do tend to understand. They don't really bother me anymore, understanding that Iolani is really unforgiving as far as homework goes. And me, sinister ol' me, still spends substantial amounts of time while 'doing homework' talking to friends and not being productive. Food for next year's New Year's Resolutions, I guess.
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Today is Sunday, and I decided to crack open my desktop PC (literally) to clean the inside. I went to Walmart and bought a can of compressed air to remove damage-causing dusts and lints in inaccessible areas. The last time I did this was years ago, so the dust buildup was tremendous. I had to use the entire can! With 20% more! (thanks, Walmart)
Towards the end of the can's life, I noticed that it got extremely cold to the touch. I thought about it, and initially assumed that it was an application of the Ideal Gas Law. Since pressing the valve and releasing air reduced overall pressure in the can of compressed air, temperature should consequently decrease, because pressure and temperature are proportional:
PV = nRT (can)
R and n remain constant. Hence, PV = T; Pressure and Volume are directly proportional to Temperature.
Fair enough. But then, I read the fine print on my CleanSafe can, which indicated that less than 5% of the product was actually gas; the name "compressed air" is misleading in that most of the product (the other 95%) is actually stored as a liquid at an extremely low temperature. What we need is an equation that applies to both gases and liquids.
Upon doing some further research, the answer appears to be the Joule-Thomson effect, something we haven't learned yet. But here's the Wikipedia definition:
"In thermodynamics, the Joule–Thomson effect or Joule–Kelvin effect or Kelvin–Joule effect describes the temperature change of a gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment.[1][2][3] This procedure is called a throttling process or Joule–Thomson process.[4] At room temperature, all gases except hydrogen, helium and neon cool upon expansion by the Joule–Thomson process.[5][6]"
I'm not going to publish this as some sort of discovery, because I don't expect to be right on the money. In fact, I may be completely off the mark. But here's my interpretation of it (in English!)
Fluid exits the valves and is accelerated. Since energy is conserved, the additional KE must come from somewhere. "Somewhere" is the internal energy of the gas. Internal energy is directly related to temperature, as we've learned in class.
Hence, the accelerated gas will have a lower internal energy than the canister gas and will therefore have a lower temperature. That's why upon usage of the can, compressed air eventually feels extremely cold.
I feel like a SCIENTIST! (Someone tell me, please, if I'm completely wrong, so I can change this blog)
plus, I look kind of creepy. especially if you enlarge the photo :[
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