4C20.10 - Super Cooling Water

Code Number:
Demo Title:
Super Cooling Water
Temperature & Pressure Relationships
Area of Study:
Heat & Fluids
Vacuum pump and bell jar unit, Petri dish, watch glass, thermocouple probe with digital thermometer. Small Test Tube Filled with Water, Thermometer, and Dry Ice and Ethyl Alcohol Bath.

The vacuum pump method works extremely well for this demonstration. 

Some advanced prep is necessary:  Place the watch glass in the Petri dish and fill the watch glass with water.  Place the thermocouple probe into the center of the water in the watch glass.  Open the gas ballast on the vacuum pump.  Start the vacuum pump and pump on the water until it freezes.  This cycle will draw the air out of the water sample and a great deal of this will splash into the Petri dish.  Close the gate valve, keep the water sample under vacuum, and allow it to warm up to room temperature again.  

Once the above prep is done, keep the demo under vacuum and move it into the classroom.  Position the water sample and the digital thermometer so that you can see them both clearly with the video camera.  When ready, start the vacuum pump and open the gate valve fully.  Monitor the temperature.  When the temperature approaches +5 degrees C close the gate valve until the second (Red) arrow mark on the gate valve is pointed straight up.  (The closing of the gate valve is necessary to reduce the pumping speed.  Too fast and the water sample will freeze before it is supercooled.)  It will take several minutes from this point, but the temperature should go to somewhere between -5 and -9 degrees C before the water sample freezes.  Observe that when this happens the temperature of the frozen water sample instantly rises to 0.0 degrees C.  


It helps if you boil and filter the water that you are trying to super cool to get rid of the air and the dust particles that act as nucleation sites.  Put about 5 cc of that water in the test tube and lower into the dry ice alcohol bath.  Observe the temperature over time and if things are very quiet and you don't shake the test tube you should get down to -4 degrees C.  Shake the test tube and the water should freeze instantly and the temperature should come up to 0 degrees C.

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Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.