Theory of heat transfer-irreversible refrigeration plants
This study questions the view that the degree of thennodynamic imperfection (second law efficiency, η11) of the refrigeration and liquefaction plants that have been built does not depend on the refrigeration load temperature Tl. It is shown first that when plotted correctly, the empirical ηII values decrease as Tl 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 Tl. 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 ηII generally decreases as Tl. decreases. © 1989.
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