Chapter 7 - Refrigeration

Abstract

Refrigeration is the process of removing thermal energy (or heat) from a low temperature reservoir and transferring it to a high temperature reservoir requiring the input of energy. A fluid or refrigerant repeatedly circulating through the refrigeration system's components accomplishes the heat transfers. One complete circulation of the refrigerant completes a cycle. Vapor compression refrigeration systems contain at least four components: evaporator, compressor, condenser, and an expansion device. At each location in the vapor compression cycle, the refrigerant maintains its operating condition under a steady-state operation. Vapor compression systems are prevalent in refrigeration applications, but in special situations absorption refrigeration cycles may be preferred. The coefficient of performance (COP) is a measure of how well the refrigeration cycle is using the supplied energy to provide refrigeration. The standard vapor compression cycle is an idealized refrigeration cycle resulting from several simplifying assumptions that yield some useful performance results. With actual compressor efficiency incorporated into the standard vapor compression cycle, realistic operating characteristics of the vapor compression refrigeration system may be computed. Several configurations of secondary cooling loops using propylene glycol and water mixtures are examined in conjunction with vapor compression cycles showing postharvest cooling applications.