icecream

Ice Cream

Background

Sensible people will make ice cream using either a low tech approach (by churning a mix in a bowl surrounded by a salt and ice mixture) or by using a fancy household machine. See the basics in Wikipedia.

There is another approach, which is far less efficient, but way more spectacular. One can place the mixture in intimate contact with an inert and very cold gas, thus freezing the mixture almost instantly. The most common "cold" gas to use is nitrogen, commercially available as a saturated liquid at room pressure. At these conditios, liquid nitrogen is at around -196 C . Liquid nitrogen is not particularly expensive or difficult to come by, and it can even be obtained by refrigerating air in a small Linde plant. Another gas that could be used is CO2. While it is impractical to liquify CO2 using the same process as the with nitrogen, one can use a common CO2 extinguisher to provide the same effect.

But first the proof:

The thermodynamics

Some interesting links

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Warnings

As usual, I must warn you not to try this yourself, to be sensible with fire-fighting equipment, and to not be so stupid to use foam or powder extinguishers for this purpose.