The present section deals with the heat transfer phenomena and the types of heat exchangers encountered in refrigeration cycles. Emphasis is given to vapour compression cycles because of their predominance in the household, commercial and industrial sectors (albeit gas and absorption cycles are also largely employed and dominate some specific applications). In the first part of this section, the thermodynamics of power and refrigeration cycles is reviewed. A description and a classification of vapour compression cycles, including aspects of refrigerant selection, are presented. In the second part of the section, design correlations and methodologies are presented with a particular focus on heat exchangers employed