Demos: 3E-02 Cryophorous


This demonstration illustrates cooling by rapid evaporation. Two glass bulbs, each containing a small amount of water, are connected by a glass tube. One bulb is cooled by immersing it in a slush of dry ice and acetone. As this bulb cools, the vapor pressure is reduced and vapor from the other bulb is rapidly drawn in the cooled bulb. This rapid evaporation from the initially uncooled bulb causes the water in that bulb to freeze.

Directions: Make sure that each bulb has the same amount of liquid initially. Keep the tube level so that liquid doesn’t drain from one side to the other. Place one end in the slush and wait until the water freezes in the other bulb. For whole class visibility, use the camera and overhead projection system.

Suggestions for Presentation: Ask how one might go about freezing water. After the obvious answers, inquire as to whether one might do it simply by evaporation (assuming you have discussed evaporation as a cooling process). Students will likely not believe that sufficient cooling could take place by evaporation to actually freeze water.

Applications: Many processes in industry and homes use evaporation for cooling.

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Last Updated: May 9, 2016 11:44 AM