Theory of heat transfer-irreversible refrigeration plants

This study questions the view that the degree of thennodynamic imperfection (second law efficiency, η 11) of the refrigeration and liquefaction plants that have been built does not depend on the refrigeration load temperature T l . It is shown first that when plotted correctly, the empirical η II values decrease as T l decreases. Two theoretical arguments are offered as explanations for this trend. The first argument is based on a refrigeration plant model the irreversibility of which is due solely to the ‘internal’ heat transfer that passes directly through the machine all the way to T l . The second argument is based on a more refined model in which the refrigeration plant irreversibility is due to three heat transfer phenomena: the internal heat transfer (retained also in the first model), the external temperature difference between refrigeration plant and ambient, and the external temperature difference between the refrigeration load and the cold end of the refrigeration plant. It is shown that there exist optimum ways of allocating heat transfer equipment to the distinct parts of the plant, if the objective is to maximize the refrigeration capacity of the plant. Both theoretical arguments lead to the conclusion that η II generally decreases as T l . decreases.