We all know the situation.
The party is about to begin, it's really hot outside and we forget to put the beer (or similar drink) into the fridge...
What is your way to chill beer really fast?
The mythbusters actually did this one once, and their conclusion was that the best and easiest way was indeed to simply add some salt to the water.
I've used this for chilling wine and long necks.
This works for cans of beer.
Using this method I can cool a beer that's been sitting out in the sun in under two minutes.
Here comes the science!
The Goal: Transfer heat from the warm object to the surrounding environment, as quickly as possible.
Discussing point 3, the corollary is that when ice melts at 0 degrees C, it takes a whole lot of heat to break the crystal lattice and convert to liquid. This means that melting ice will "grab" heat out of the beer faster than solid ice warming up, or liquid water warming up.
So at this stage, what we want is ice mixed with water, just below the melting point. Add beer cans, and the beer will "suck the cold" out of the ice as it melts, bringing the entire system near to freezing fairly quickly. (in a matter of 10 -15 minutes).
Still not fast enough? Then we need to go to a different universe where the melting point of water is colder. (Or add salt to the water, which will lower the melting point, causing the whole reaction to occur at a lower temperature, giving us a speed boost as to Bullet #2.)
Still not fast enough? -- Well, if you've got liquid nitrogen on hand, you're over prepared for your unpreparedness. You could have just stuck the beers in the fridge.
Wrap the beers in wet paper towels or wet rags and put in the freezer. Its really is quite effective and doesn't need salt or ice. This video shows what a difference it can make: http://youtu.be/Nf8rKvZWQrY
Water bath is best as suggested (I am not going to write that out again), but if you want to do it even faster then get the water moving around too.
A small pump that just pumps the water back in at an angle will do (I am thinking large fish tank one OR water fountain). A good whirl pool effect is fine if it is white wine but not so much as to fizz up the beer mind!
You should be abel to cool a whole case in just a few minutes.