Thermally driven refrigerators: Equivalent low-dissipation three-heat-source model and comparison with experimental and simulated results

Abstract

In order to investigate the performance of a class of thermally driven refrigerators, usually driven by low-grade thermal energy, a generic thermodynamic model of three-heat-source refrigerator without involving any specific heat-transfer law is put forward by adopting low-dissipation assumptions. Based on the proposed model, the analytical expressions for the coefficient of performance (COP) and cooling power of the system are derived in terms of well-defined dissipation parameters and contact time durations between the system and heat reservoirs. One essential parameter accounting for the size ratio of the two coupled subsystems inside the overall system is introduced in light of the practical meaning of the reversible entropy change. With the help of the aforementioned parameter, the optimal relation between the COP and cooling power is obtained. The optimal operation region and optimal construction of the overall system are further determined for the first time. In addition, the influences of the dissipation and temporal symmetries are discussed in detail, according to which the upper and lower bounds of the COP at maximum cooling power are firstly obtained under two extreme situations. Experimental and simulated data from previous reported works are collected to illustrate the validity and practical significance of the proposed model and associated results. A limit case is presented to highlight the generality of the model.

The equivalent low-dissipation combined cycle system and optimal analyses of a class of thermally driven heat pumps

“…It is worth to point out that the above relations between Rm , R max , and C ( ) are well different from the thermally driven refrigerators [46] in which the maximum cooling power is not a monotonic function of size ratio and the corresponding COP. Namely, there exists an optimal design which makes the cooling power of thermally driven refrigerator attain its globally maximum value and the corresponding COP can be determined.…”

“…Accordingly, different strategies in the design of practical devices should be selected. In particular, all values of the size ratio between 0 and C r are physically acceptable for thermally heat pump, while for thermally driven refrigerator the size ratio should be controlled in the region between the optimal size ratio and the size ratio under reversible limit [46]. Based on the data in Fig.…”

“…11 (b). Specifically, the upper bound of [46] due to the lack of optimal value of size ratio, even though some of the curves look alike. Specifically, in Ref.…”

“…Specifically, in Ref. [46], every point in the COP bounds at maximum cooling power were generated for optimal…”

“…In Ref. [46], low-dissipation model has been firstly adopted to construct a combined cycle model of thermally driven refrigerators coupled to three heat sources simultaneously. As a counterpart of thermally driven refrigerator, thermally driven heat pumps have similar operating principle but well different technological applications, different operating temperatures, and different objective functions.…”