Refrigeration By NON-CYCLIC PROCESS

REFRIGERATION BY NON-CYCLIC PROCESSES

Refrigeration is the cooling of a system below the temperature of its surroundings. The melting of ice or snow was one of the earliest methods of refrigeration and is still employed. Ice melts at OOC. So when ice is placed in a given space warmer than OOC, heat flows into the ice and the space is cooled or refrigerated. The latent heat of fusion of ice is supplied from the surroundings, and the ice changes its state from solid to liquid. Another medium of refrigeration is solid carbon dioxide or dry ice. At atmospheric pressure C02 cannot exist in a liquid state, and consequently, when solid C02 is exposed to atmosphere, it sublimates. i.e. it goes directly from solid to vapour, by absorbing the latent heat of sublimation (620 kJ/kg at I atm. —78.5'C) from the surroundings (Fig. 14.1). Thus dry ice is suitable for low temperature refrigeration.

 

 

In these two examples it is observed that the refrigeration effect has been accomplished by non-cycle processes. Of greater importance, however, are the method in which the cooling substance is not consumed and discarded, but used again and again in a thermodynamic cycle.