physics question #110



Jonjon, a 16 year old male from the Internet asks on January 2, 2000,

Q:

How does a pressure cooker work?

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the answer

Barry Shell answered on January 2, 2000, A:

A pressure cooker is a pot of boiling water which has been sealed shut. Because the water vapour cannot escape to the atmosphere at the boiling point, 100 degrees C, the temperature and pressure increase above that temperature. This means that food cooks faster in a pressure cooker. Pressure cookers all have pressure release valves so that the pressure does not build up too much and blow up the whole pot. To understand fully the relationship between Temperature, Pressure and Volume, read about the gas law (PV=nrt) in an introductory chemistry or physics book.

Mike Davidson answered on October 20, 2005, A:

You can determine the temperature of the water in a pressure cooker by looking at a steam table in an introductory thermodynamics textbook. A good quality pressure cooker that you would use at home operates at a gauge pressure of 103 kilopascals (kPa) [15 pounds per square inch (psi)]. To see a sample construction of a modern new generation pressure cooker have a look at the site Fastcooking.ca and click on “How It Works”. The cooking times of foods are decreased dramatically when using a pressure cooker. The steam pressure breaks down the fibres of the food a lot faster than just boiling the food would do. Because the food is cooked so quickly, the energy needed to cook the food is 50-75% less than other cooking methods.

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