Rui Long

Coefficient of performance and its bounds for general refrigerators with nonisothermal processes

An analysis of the coefficient of performance (COP) and its bounds at maximum figure of merit for refrigerators is conducted and the heat transfer processes are described using Newton?s law of cooling with a time-dependent heat conductance. The upper bound of the COP, , is independent of the time duration completing either process or the heat conductance. The optimal temperature profiles in the heat exchanging processes are analyzed under different dimensionless contact time limits. Provided the dimensionless contact times satisfy certain relations, the endoreversible model is recovered. Furthermore, numerical calculations are conducted to investigate the effect of different heat conductances on temperature profiles under the maximum criterion. This work can guide design and operation of actual refrigerators.

Coefficient of performance and its bounds with the figure of merit for a general refrigerator

A general refrigerator model with non-isothermal processes is studied. The coefficient of performance (COP) and its bounds at maximum figure of merit are obtained and analyzed. This model accounts for different heat capacities during the heat transfer processes. So, different kinds of refrigerator cycles can be considered. Under the constant heat capacity condition, the upper bound of the COP is the Curzon?Ahlborn (CA) coefficient of performance and is independent of the time durations of the heat exchanging processes. With the maximum criterion, in the refrigerator cycles, such as the reversed Brayton refrigerator cycle, the reversed Otto refrigerator cycle and the reversed Atkinson refrigerator cycle, where the heat capacity in the heat absorbing process is not less than that in the heat releasing process, their COPs are bounded by the CA coefficient of performance; otherwise, such as for the reversed Diesel refrigerator cycle, its COP can exceed the CA coefficient of performance. Furthermore, the general refined upper and lower bounds have been proposed.