We have microwave ovens that can re-heat leftovers in a matter of seconds.
Why can’t we have a device that can, say, cool a can of beer in a matter of seconds? Or freeze ice cubes in minutes? Is it a matter of cost? Is the available technology not (at present) adaptable for the home?
This topic came up on a morning-drive radio show the other day, and one caller stated that most better wine stores have a gizmo that you insert a bottle of wine into, and it’s properly chilled in a matter of seconds.
And while we’re on the subject, how do water coolers so quickly chill the water when you press the little spout?
let’s see now, there are three general methods of heat transfer… convection, conduction, and radiation.
convection generally doesn’t go very quickly in any situation… convection ovens generally take longer to cook than the usual kind, IIRC.
Radiation is the principle on which microwaves work, but though that can be increased on the supply side, I can’t think of any way that you’d be able to coerce an object into radiating its heat away faster than usual. So that’s out for our instant-cool device.
Generally then, we’d need to find some way of putting the object to be cooled in contact with a very large, very cold surface (conduction,) or forcing a large quantity of frigid fluid past it.
I can’t think of any particular reason that devices like this couldn’t be constructed… ones that would work more quickly than your everyday household freezer at least. The question of expense is probably very relevant… it’s a lot easier to introduce heat into a system from a ready source of energy, (electric current or natural gas combustion,) than to pump heat from a cool object into a warmer object. You’re fighting the second law of thermodynamics when you’re running a refrigerator or an air conditioner, and that means that you’ve got to expend energy compressing and expanding coolant fluid or some such thing.
We could, but it would be cost prohibitive in most circumstances. Flash cooling water for ice would have to be one of the most inefficent methods imaginable unless time was the only real premium.
They dont, there is a little resorvoir (sp?) of water under the bottle that is kept chilled. This is pretty easily handled because you usually only dispense a few ounces at a time.
The device at wine stores is a smallish bucket filled with water that is below freeing temperature, kept from freezing by (if I recall correctly what I was told years ago) circulating and some kind of additive – salt, perhaps?
Not only does the low temperature bring the wine’s temperature down, the rapid circulation ensures that the water in contact with the wine bottle is always really cold, rather than allowing the bottle to stay in an envelope of warmer water. In essence, it’s wind chill in action.
I would really like one of these in a home bar – being able to store my beverages outside of the fridge and then rapid-cool them would be very handy.
When heating or cooling something through conduction, the speed at which the temperature of the target changes will be proportional to the size of the heat differential.
So if you take something at room temperature and put a 2,000 degree flame under it, it’ll heat up pretty fast.
In contrast, if you put something in your freezer, the temperature differential will be less than 100 degrees. So it takes a lot longer to chill it down.
If you want something flash-frozen, gets a dewar of liquid nitrogen, and dip your can of beer in it. It’ll freeze quickly.
Google for [wine chiller]. They’re readily available now for $80. Even Home Depot is selling a version. Cooling times appear to be 15ish minutes. Not so good for individual beers, but fine for bottles of wine.
Peltier devices (heat pumps) allow for solid-state, high performance cooling based on the amount of power you throw at them. The problem is that they tend to require a lot of power and produce a LOT of heat that needs to be disposed of. Some smaller refridgerators use Peltiers because a full vapor phase cooling system is too bulky.
One problem with very rapid cooling, how do you keep from ending up with a can of beer with a layer of ice along the inside of the can and warm beer in the center? You can’t stir liquids inside the container without opening the container…
“First there was Bud. Then we made Bud Ice. Now there’s Bud B.E.C!!! Brewed from the coldest substance in existance to give it that crisp clean flavor!”
Never mind that in your two examples, one is adding heat and one is removing it from the subject.
Never mind that you didn’t specify how much heat in calories is being added or removed per unit of time.
If it takes “a lot longer” to chill something 100 degrees than raise something 2000 degrees, then, using your logic, if we try to chill something only 50 degrees, it will take longer yet. Only 10 degrees, even longer. Logically, then, if I try to chill something one degree, I’ve got a near-infinite wait.
And it’s unlikely that I can ever boil water, because before it gets really hot, it has to get one degree hotter first, and it’ll never get there in my lifetime.
I service and recharge fire extinguishers and was always surprised to find the CO2 extinguishers at the forest service offices completly empty, while the dry chemical ones were just fine.
Took a few years before someone clued me in to the fact that the folks on the fire lines use them to rapid cool their six-packs.
Now I can attest that you can cool a lot of six packs with a single 20 pound CO2 extinguisher.
Sam Stone isn’t really wrong but he’s talking about cooling by simply exchanging energy from something hot with something that is already cold.
Refrigeration runs into tha told devil the second law of thermodynamics. There is no succinct way to state it, heck people make entire careers out of trying to understand it, but it isn’t too far off the mark to say there is no process where the only result is to move thermal energy from a cold place to a hot place. You ask, “isn’t that how a fridge works?” No, a fridge works by taking thermal energy from the inside plus the emergy being sucked from the wall socket to power the compressor and dumps it outside to make your kitchen hotter. Think of it as making energy go uphill, not letting it flow in the normal direction it wants to go. There are ways to make things cold fast but only at enormous energy costs.
Making things hotter is much easier in comparison because there are a lot of methods of taking the input energy and putting it directly into your pop tart. If you want a frozen banana dqauiri in a hurry you need a whole bunch more energy than you are removing from the drink because it is a wasteful process.
You misunderstand what I was saying. I was saying that the rate of energy exchange between two objects of different temperature will be proportional to the size of the temperature differential. In other words, if you place something that is 100 degrees against a material that is at 0 degrees, it will cool faster than if you placed it against a material that is at 50 degrees.
When heating things, the temperature differential can be very, very large. Generally when cooling things we’re dealing with much lower temperature differentials, on the order of a few tens of degrees. That’s why it takes longer (all else being equal, of course).
For example, put a can of lukewarm beer in a large vat of water that is childed to just above freezing. Put another one in a vat of liquid nitrogen. Which one do you think will chill 20 degrees faster?
I could give you the equations, but I haven’t cracked open a thermodynamics text in 15 years, and I’m already stretching the boundary of my memory.
This would be adiabatic expansion - the same reason butane comes out of a can freezing cold. It’s also the mechanism used in most refrigerators and air conditioners - compress the fluid with a compressor, which heats it up. Put the compressor outside, where the heat can be shed. Then run the compressed fluid into the fridge and let it expand. It will cool, chilling the pipes, which then conduct the cold into the fridge space (or into the house). Pump the fluid back out into the compressor, and repeat.
While we’re talking about this, why are refrigerators made that can vent to the outside? Those coils at the back of the refrigerator radiate the energy taken from the air inside the refrigerator. That radiated energy goes into my house air, then the energy has to be removed by the air conditioner and radiated to the outside air.
It’d be a lot more efficient (and therefore energy-conserving) if the refrigerator just vented and/or radiated its energy outside.
This has been discussed but I could not seem to find the thread. The energy savings would not be enogh to justify the added cost of building and installing a refrigerator this way. Even large commercial refrigerators and freezers that I have seen radiate into the inside of the building, however all the walk in refrigerators and freezers I have seen radiate the heat outside like an air conditioner.
Sam Stone, you may be confusing the rate of change with the time it takes to heat or cool an object.
When someone says, “A cools faster than B,” do they mean that the temperature change per unit of time for A is greater than B or that A reaches the end temp sooner (in fewer time units) than B?
If I put a tray of hot water (A) in the same freezer with a tray of cool water (B), assuming same-sized trays, no influence of one over the other, etc., which will cool faster?
If by “faster,” you mean rate of change, A.
If by “faster,” you mean sooner, B.
Since the temp differential between A and the freezer is greater, the rate of change of A is greater, initially. But B will probably reach the desired end temp first, that is, in a shorter time interval. It would be impossible for A to reach it first, since A has to pass thru the same temp as B at some point in time, and at that time, they are equal in all respects. It would be the same as putting two trays of equal temperature in the freezer and expecting one to reach the end temp faster than the other; not logical.
An old WWII vet once told me that in the South Pacific, they would cool beer with a pail of gasoline and a bicycle pump.
Basically, they put the cans of beer in the pail, put the hose of the pump at the bottom of the pail, and pump for a couple of minutes. Supposedly, the air moving throught the gasoline produced enough evaopration to chill the beer to near-freezing. They would then rinse the cans, and party.
I’ve never tried this. For one thing, I doubt that they could rinse the cans enough to get all of the gasoline taste off. On the other hand, if you were desperate enough…
(He also told me about building crude washing machines out of a five-gallon jerry can. Apparently it takes a very long time and a lot of agitation to clean clothes with salt water soap. So, they would put the clothes, salt water, and salt water soap in the can, and rig it to a small windmill to let it turn for a couple of hours. A quick rinse in fresh water (very limited on S. Pacific islands) and you were done. Johnson Island was apparently a major layover in mid-Pacific, and he claimed that there were hundreds of windmills running at any given time.)
