Abstract: The non-Carnot refrigerators are composed of two polytropic and two adiabatic processes. It is assume that Newton’s heat transfer law is obeyed during heat transfer processes, the expressions for the coefficient of performance(COP) and cooling rate of the refrigerator are derived. The characteristic curves between the cooling rate and the COP are plotted. Moreover, the optimal COP of the refrigerators at maximum figure of merit are analyzed by the numerical calculation and graphic method. The optimal COP is analyzed at two special limit cases of long and short contact times, and compared with that of the classical Curzon-Ahlborn COP. The results show that, for the long thermal contact time limit, the optimal COP is equal of the CA COP when the ratio of heat capacity between the heat capacities of the working medium during hot and cold contact process. In the case of , the optimal COP is less than the CA COP, however, in the case of , the optimal COP is larger than the CA COP. For the short contact time limit, the optimal COP is larger than the CA COP when . In both cases, the optimal COPs increases as the heat capacities ratio increases. This model can be applied to Otto, Joule-Brayton, Dissel and Atlinson thermodynamic cycles. This might provide guidance for designing real refrigerators.

Key words: Figure of merit, Finite time thermodynamics, Newton’s heat transfer law, Non-Carnot refrigerators, Performance optimazation