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I guess I'll have to be happy with soda at 16 degrees-C. That's only an 8 degree drop from room temperature in my office, and it can do that in maybe an hour.
355 ml of soda, 1486 watts per 1 degree-C.
About 6 minutes a degree.
6 * 8 = 48 minutes
... assuming no can and perfect use of the energy for cooling.
So call it an hour for definately colder than room temperature soda.
Crossfire: "Thank you! That explains it very nicely, and in a language that someone other than a physicist can understand..."
Denial is not falsification. You can't avoid a fact just because you don't like it.
"Data" is not the plural of "anecdote"
Heat pumps are more than 100% efficient though--that is, they can move more heat energy than what is required to make it run. According to this (and it seems to jive with what I learned last semester) and some general assumptions (this apparatus is a refridgerator running on a Carnot cycle, room temp 300 K, cool temp 275 K) then efficiency could be as high as 1100% when the temperatures have stabilized! Of course, when the can and the outside are at the same temperature, even Carnot efficiency is still at 100%--but even if you assume that the average efficiency is 300%, then I figure (with fuzzy math, I'm lazy now) it would only take like half an hour to cool the can.
jesusabdullah wrote:Heat pumps are more than 100% efficient though--that is, they can move more heat energy than what is required to make it run. According to this (and it seems to jive with what I learned last semester) and some general assumptions (this apparatus is a refridgerator running on a Carnot cycle, room temp 300 K, cool temp 275 K) then efficiency could be as high as 1100% when the temperatures have stabilized! Of course, when the can and the outside are at the same temperature, even Carnot efficiency is still at 100%--but even if you assume that the average efficiency is 300%, then I figure (with fuzzy math, I'm lazy now) it would only take like half an hour to cool the can.
Aye, that would be true, but mini fridges rely on thermoelectric cooling rather than a compression cycle system like large refridgerators. This gives a mini fridge pretty poor efficiency.
jesusabdullah wrote:Heat pumps are more than 100% efficient though--that is, they can move more heat energy than what is required to make it run. According to this (and it seems to jive with what I learned last semester) and some general assumptions (this apparatus is a refridgerator running on a Carnot cycle, room temp 300 K, cool temp 275 K) then efficiency could be as high as 1100% when the temperatures have stabilized! Of course, when the can and the outside are at the same temperature, even Carnot efficiency is still at 100%--but even if you assume that the average efficiency is 300%, then I figure (with fuzzy math, I'm lazy now) it would only take like half an hour to cool the can.
Aye, that would be true, but mini fridges rely on thermoelectric cooling rather than a compression cycle system like large refridgerators. This gives a mini fridge pretty poor efficiency.
True. I wasn't sure what kind of cooling system the microfridge had, and this was the only way I could think of to cool the can that quickly on so few watts. Plus, having a miniature heat pump system like that would be pretty awesome.
rkolter wrote:Well, clearly the solution is that I have to perform an experiment.
Now I need a thermometer. I wonder if the electronic ones you can get for fevers can test cold temperatures too? They're cheap and quick.
Just don't get your new toy broken.
No no no! Definately not.
I'm thinking of just putting fresh cans of soda in it, and then pulling them out and taking their temperature after different time intervals. That reminds me I have to try our fever thermometer in a can of soda tonight.
Crossfire: "Thank you! That explains it very nicely, and in a language that someone other than a physicist can understand..."
Denial is not falsification. You can't avoid a fact just because you don't like it.
"Data" is not the plural of "anecdote"
Well, the thing looks good, and the cold plate gets very cold, but the bottom lip of the can is very thin, so the can is not really cooling down much. In fact, at all. It's actually warmed up slightly.
Hm. Pending further evaluation.
Crossfire: "Thank you! That explains it very nicely, and in a language that someone other than a physicist can understand..."
Denial is not falsification. You can't avoid a fact just because you don't like it.
"Data" is not the plural of "anecdote"
-D. M. Jeftinija Pharm.D., Ph.D. -- Yes, I've got two doctorates and I'm arrogant about it, what have *you* done with *your* life?
"People who don't care about anything will never understand the people who do." "yeah.. but we won't care."
"Legostar's on the first page of the guide. His opinion is worth more than both of yours."--Yeahduff
I have some ideas for modding my USB refrigerator. The simplest one is to add a few washers to the bottom - on top of the cooling plate. I'm looking to see if it'll cool those washers. If it does, it'll provide additional surface contact.
Next, I'll be looking at molding a convex metal lump that fits the bottom of soda cans. Good thing I work at a manufacturing plant.
I'm also considering blown insulation around the fridge - I notice that the fridge surface is kind of cool, and I'd prefer it not be.
So much fun stuff to do.
Crossfire: "Thank you! That explains it very nicely, and in a language that someone other than a physicist can understand..."
Denial is not falsification. You can't avoid a fact just because you don't like it.
"Data" is not the plural of "anecdote"
I cut a very tiny notch so that I could run the thermometer wire through without having to leave the door ajar at all, and did get some good washers that are a close fit to the concave bottom of a soda can.
Still, it's dropped only 2.6 degrees farenheight in 95 minutes. That's no speed record.
Hmm.... I'm gonna have fun with this. I want to squeeze out several degrees in an hour. The math says it's possible...
Crossfire: "Thank you! That explains it very nicely, and in a language that someone other than a physicist can understand..."
Denial is not falsification. You can't avoid a fact just because you don't like it.
"Data" is not the plural of "anecdote"
