Does wrapping a beer in a wet paper towel increase the rate of cooling

In summary: I'm not sure. A short time I think. I'm not familiar with the physics behind it.Not true. The towel will have more surface area than the can does. (I think it does at least) This allows more air to be in contact with it and increases the total amount of heat transferred into the air over...I'm not sure. A short time I think. I'm not familiar with the physics behind it.
  • #1
axiom1
10
0
It is commonly said (based on a quick Google search) that wrapping your beer in a wet paper towel and placing it in the freezer will allow it to cool faster than placing it in the freezer without said paper towel.

Newton's Law of Cooling suggests otherwise. The fact that water releases energy when it freezes (the paper towel tends to freeze) suggests otherwise (although this effect is probably minimal). Specific heat capacity doesn't seem to be relevant here because the water is initially above the temperature of the air in the freezer (so it is likely detrimental). Perhaps it could be that water has better "thermal conductivity" (is that even a thing?) but then its still just an intermediate layer between the air and the glass, so we'd still be bound by the rate at which the air cools the water.

Anyway, I'd love to hear a definitive answer to I can put an end to this (likely) urban myth.

Thanks.
 
Physics news on Phys.org
  • #2


Hi axiom1. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

I'd be pleased to give you my thoughts on this, but I'm hesitant to do so as it sounds suspiciously like a science question that you are supposed to think about yourself. http://physicsforums.bernhardtmediall.netdna-cdn.com/images/icons/icon6.gif [Broken]
 
Last edited by a moderator:
  • #3


Ummm, this isn't a homework problem if that's what you're implying.

The physics of cooling beer just happen to be of great interest to me.

I guess I went overboard in trying to make the question sound professional.
 
  • #4


Why not try it out as an experiment first? You can drink the results.
 
  • #5


As a mathematician I've always preferred theory to experiment. But regardless, the experiment is underway, but I'd rather just hear a good theoretical argument.
 
  • #6


I think it's supposed to work by evaporation. The air in the freezer is probably 100% saturated at -18C, but the water (or ice) will rapidly evaporate while it's still at a temperature above this. The temperature of the outside of the bottle will probably rapidly decrease to 0C, and this will take longer without a towel, because the air around the bottle doesn't conduct heat well.
Freezing of the water produces heat, but evaporation uses up about 8 times the amount of heat that freezing produces.
 
  • #7


So you're saying the cooling you get through evaporation is enough to account for the fact that the water is initially warmer than the surrounding air (which decreases initial rate of cooling) and the release of latent heat when some of the water on the towel freezes (which tends to happen from my own experience).

And what do you mean by "air doesn't conduct heat well"? What is it about air that makes it a worse conductor?
 
  • #8


axiom1 said:
And what do you mean by "air doesn't conduct heat well"? What is it about air that makes it a worse conductor?

Air is a gas and as such isn't very dense. Compared to many solids and liquids it simply doesn't conduct heat as well.

From here: http://en.wikipedia.org/wiki/Heat_conduction

Fluids (and especially gases) are less conductive. This is due to the large distance between atoms in a gas: fewer collisions between atoms means less conduction. Conductivity of gases increases with temperature. Conductivity increases with increasing pressure from vacuum up to a critical point that the density of the gas is such that molecules of the gas may be expected to collide with each other before they transfer heat from one surface to another. After this point conductivity increases only slightly with increasing pressure and density.
 
  • #9


Ok. So even if the air in the freezer doesn't conduct heat as well as water then that doesn't make the towel better, because the towel still has to be cooled by the surrounding air. In other words, the air is the still the weakest link and is the limiting factor here.

The only thing that seems to make sense here is evaporative cooling and I'm not convinced its significant enough to make a noticeable difference. There's not much water on the towel, and even if it gets cooled very fast by evaporation it will eventually reach a steady state (no more evaporative cooling) and we are again bound by the conductivity of the air.
 
  • #10


axiom1 said:
Ok. So even if the air in the freezer doesn't conduct heat as well as water then that doesn't make the towel better, because the towel still has to be cooled by the surrounding air. In other words, the air is the still the weakest link and is the limiting factor here.

Not true. The towel will have more surface area than the can does. (I think it does at least) This allows more air to be in contact with it and increases the total amount of heat transferred into the air over time.
 
  • #11


How much surface area are we talking here?

The paper towel adds some small amount of radius to this cylinder-like structure, so 2*pi*r*L changes insignificantly (but this is assuming the surface is smooth).

Is the surface of the paper towel full of little "folds" (crevasses, ridges, etc) while the surface of the glass is comparatively smooth? If so, that would make sense.
 
  • #12


axiom1 said:
How much surface area are we talking here?

The paper towel adds some small amount of radius to this cylinder-like structure, so 2*pi*r*L changes insignificantly (but this is assuming the surface is smooth).

Is the surface of the paper towel full of little "folds" (crevasses, ridges, etc) while the surface of the glass is comparatively smooth? If so, that would make sense.

That is how I am seeing it.
 
  • #13


I just got a vision of an invention. An express beer cooler that is a cylindrical heat sink with a can/bottle shape in the center to slide your can/bottle into. And then fins sticking out.

The ambient air (in the fridge) will be cooler than the heat sink initially. But since the heat sink has higher thermal conductivity there will be some temperature greater than ambient which cools the can/bottle quicker than ambient. Just like the wet rag.

Better still, precool the heat sink and you will get the fastest cooling.

Cool thread! Experiments are certainly in order. It would probably be ok to open one and shove a thermometer into the can's center.
 
  • #14


Just to clarify some of the theory.

If the increase in surface area was negligible, would the towel still cool faster?

My guess is no, because we are still limited by how quickly the air cools the towel (which in turn cools the bottle).

And another question, what about a dry towel? Would it have good thermal conductivity? I'm assuming air pockets would form underneath it, defeating the purpose of it.
 
  • #15


axiom1 said:
...
And another question, what about a dry towel? Would it have good thermal conductivity? I'm assuming air pockets would form underneath it, defeating the purpose of it.

being dry... its full of tiny airpockets producing a good insulator and I would expect it to be worse than if the can was in the freezer uncovered

think of the big bulky jackets used by skiers, mountain climbers or those working in the polar regions. They are poor in heat transfer because they are full of air between the threads and filling of the internal fabric

Dave
 
  • #16


What about a hypothetical thin layer of water surrounding the bottle (that stays put).

The surface area isn't changed considerably.

Would it be better than having no such layer? It seems that the effect of the water "cancels out" because we are still limited by the conductivity of air (which has to cool the water).
 
  • #17


Could someone address my last question?

In general can you improve performance by inserting an intermediate layer with better conductivity assuming surface area is unchanged?
 
  • #18


But surely the metal of the can is a better conductor of heat then a towel. The additional service area of the wet towel would be defeated by the extra volume that needed to be cooled. Also, the conductivity of the air is irrelevant if the air is being blown around by the freezer fan. I'd always figured that the best thing to do is to have the can in as much contact with cold surfaces as possible.
 
  • #19


axiom1 said:
What about a hypothetical thin layer of water surrounding the bottle (that stays put).

The surface area isn't changed considerably.

Would it be better than having no such layer? It seems that the effect of the water "cancels out" because we are still limited by the conductivity of air (which has to cool the water).

Unlikely. The water isn't a better conductor of heat than aluminum is, so I don't think there would be any point.

Algr said:
But surely the metal of the can is a better conductor of heat then a towel. The additional service area of the wet towel would be defeated by the extra volume that needed to be cooled. Also, the conductivity of the air is irrelevant if the air is being blown around by the freezer fan. I'd always figured that the best thing to do is to have the can in as much contact with cold surfaces as possible.

A paper towel may be too bad of a thermal conductor to work well. Personally I'd add aluminum "wings" that you could attach to the can to increase the surface area.
 
  • #20


Drakkith said:
A paper towel may be too bad of a thermal conductor to work well. Personally I'd add aluminum "wings" that you could attach to the can to increase the surface area.

So it seems I've gotten a very mixed response to the question.

Some people are saying that evaporation allows the paper towel to cool faster. Some people say the increased surface area increases the thermal contact with the air, making the towel better.

Can anyone give me a definitive answer? Is wet paper towel better than no paper towel?

Or should I just do an experiment lol.
 
  • #21


There are too many variables to give a definite answer. The phenomena of conduction, convection, radiation, and change of state with evaporation condensation and possibly solidification all coming into play.
Consider an extreme case where there is near perfect thick insulating coat surrounding the can and where only the outer layer of the coat is wet. In this case cooling will be very slow due to the reduced conductive losses.
 
  • #22


axiom1 said:
so it seems I've gotten a very mixed response to the question.

Some people are saying that evaporation allows the paper towel to cool faster. Some people say the increased surface area increases the thermal contact with the air, making the towel better.

Can anyone give me a definitive answer? Is wet paper towel better than no paper towel?

Or should i just do an experiment lol.

Experiment!
 
  • #23
Still no experiment?! :( Sorry to drag up this old thread, but I was just looking up this very same question. I just tried it with a soda (my beer's already all cold :) ), and shortly after putting it in, the paper towel was frosting and turning to ice. Would encasing the liquid canister in a "paper towel ice cube" be responsible for quicker cooling? I didn't actually put a baseline soda in without the paper towel as I don't have a thermometer anyway, but just wanted to share what I did notice through trying it...
 
  • #24
Putting more water at room temperature around the bottle just increases the thermal mass of the object you are hurrying to cool down, even more so when you consider its latent heat when freezing. This sounds like nonsense to me.

The extra conductance from a very thin layer of ice would be about as negligible as putting your beer in a slightly thicker bottle and expecting it to cool down faster.
 
  • #25
It may be that the icy layer makes the can just look cold, which then tricks the brain into thinking the content is also cold :)
 
  • #26
So, I found this trick a while back. I never used it before and sitting here on my night off with a case of warm beer I remembered it and decided to google it. I came across this forum and post and read it, ultimately agreeing with the heat sink theory. Since no one tested it, I felt it was my duty to do so. I put two beers in the freezer at the same time, one wrapped in a wet paper towel. The results are in, the beer with the paper towel is much cooler.

Now I did not take the temperature of the beers before hand (although from the same luke warm case), and I didnt not take the temperature afterwards, but the Coors light mounttain indicator was clear, and so was the taste test.

Im almost enticed to do a formal experiment, but the results seem clear enough to me, so I think I'll enjoy my beer and leave it to someone else.

Enjoyed reading the thoughts and theories, hope this provides some resolve to the issue. Happy physics and happy drinking, cheers.
 
  • #27
Let's neglect the effect of additional surface area of the paper towel (from the thickness), and let's assume the wet paper towel pulls heat from the warmer beer can very efficiently. The surface of the aluminum can is very smooth, and so heat transfer through strict convection will not be very efficient. Adding a wet paper towel will increase the heat transfer coefficient. There a few reasons for this, but one of them is that convective currents are slower at the surface of the (getting colder) wet paper towel than the warmer can.

If we put two aluminum surfaces in a freezer, one polished and one sandblasted, which will cool faster? Why?
 
  • #28
I have no knowledge to contribute here, all I know is I just did it, it works, and I stumbled on here looking for an answer to why.

Trying and then forming a theory probably makes some sense. Things might happen that you don't expect in your imagination.

I took a room temperature beer, wrapped it, put it in the freezer, and waited a few minutes. When I grabbed it the paper towel was mostly frozen and after removing it and testing, the beer was quite cold.

I've done no research at all but something makes me think a wet, and then rung out towel will work better then a sopping wet towel. I'm not actually a smart person, so I can give no justice to why I'm saying this. Maybe I'll try two side by side next time. One damp and one pretty wet.

This isn't the first time I've used this trick and I'm pretty pro at beer, so I can tell it works faster than just putting it in the freezer.

I wonder if somehow the freezing of the water in the towel draws energy from the warmth of the beer bottle. Different, but same sentiment as how salted ice and water cools beer faster than just ice or ice and water.

I haven't a clue, but I'd like to know why. This site makes an attempt at an explanation. http://gizmodo.com/5882160/3-ways-to-chill-your-superbowl-beer-fast
 
  • #29
People have been using this principle for cooling for centuries.

As long as the temperature of the towel is warmer than the dew point (as it when the beer first goes into the freezer) evaporative cooling will happen; and as long as the beer is warmer than the dew point it will transfer heat to the towel to keep it above the dew point. So the beer ends up moving fairly quickly to the dew point. If there's a decent breeze blowing or the air is very dry, you can easily cool the beer to below ambient temperature as long as the towel is holding enough moisture.
 

1. What is the science behind wrapping a beer in a wet paper towel to increase cooling?

When you wrap a beer in a wet paper towel, the water from the towel evaporates, causing the surrounding air to cool down. This is because the process of evaporation requires energy, which it takes from the surrounding area, resulting in a decrease in temperature.

2. How does the rate of cooling change when a beer is wrapped in a wet paper towel?

The rate of cooling increases when a beer is wrapped in a wet paper towel due to the added evaporation process. The water from the towel absorbs heat from the beer, causing the beer to cool down faster.

3. Does the type of paper towel used affect the rate of cooling?

Yes, the type of paper towel can affect the rate of cooling. Thicker and more absorbent paper towels will have a greater surface area to absorb and retain water, leading to a more effective cooling process. However, any type of paper towel will still have a similar cooling effect due to the process of evaporation.

4. Is wrapping a beer in a wet paper towel more effective than putting it in the fridge?

No, wrapping a beer in a wet paper towel is not more effective than putting it in the fridge. The fridge provides a much colder and controlled environment for cooling, while the paper towel method relies on ambient temperature and humidity. Additionally, the fridge also prevents the beer from getting warm again after the cooling process.

5. How long does it take for a beer to cool down when wrapped in a wet paper towel?

The time it takes for a beer to cool down when wrapped in a wet paper towel can vary depending on factors such as the initial temperature of the beer, the temperature and humidity of the surrounding environment, and the type of paper towel used. Generally, it can take anywhere from 5-15 minutes for a beer to cool down significantly using this method.

Similar threads

Replies
1
Views
1K
  • Materials and Chemical Engineering
Replies
12
Views
2K
Replies
152
Views
4K
Replies
16
Views
2K
Writing: Input Wanted Great Lakes Earth Map
  • Sci-Fi Writing and World Building
Replies
6
Views
2K
Replies
2
Views
7K
  • Introductory Physics Homework Help
Replies
4
Views
2K
  • MATLAB, Maple, Mathematica, LaTeX
Replies
5
Views
2K
  • MATLAB, Maple, Mathematica, LaTeX
Replies
5
Views
2K
Replies
3
Views
11K
Back
Top