TABLE OF CONTENTS Refrigeration is a process whereby heat is extracted from a system. In the past it was done by means of ice stored in an ice box. The heat of fusion of the ice as it melts, comes from the substance that is being cooled. This method has essentially been replaced by the mechanical refrigeration process which operates on the Clausius statement of the Second Law of Thermodynamics. Mechanical refrigeration extracts heat from a cold temperature reservoir and through the means of a work input deposits this heat into the high temperature reservoir. It is interesting to note that the old concept of melting ice is still with us in terms of the rating of refrigeration units. A ton of refrigeration is the amount of heat that is absorbed by a ton of ice as it melts in a 24 hour period. This term was defined in the English Engineering system of units by:
Mass of ice Heat of fusion = Heat required in a 24 hr day
(2000 lb ice)(144 Btu/lb) = 288,000 Btu/day which is equal to 12,000 Btu/hr
The most common term is in Btu/min which is 200 Btu/min.
The SI system this is 211 kJ/min or dividing by 60 s/min to get 3.517 kJ/sec.
Mechanical refrigeration is based upon the principle that as a liquid vaporizes at a specific pressure it will have a controlled absorption of the heat of vaporization. The principle of operation is patterned after the Carnot cycle with...
