Abstract
Thermally driven heat pump systems play important roles in the utilization of low-grade thermal energy. In order to evaluate and compare the performances of three different constructions of thermally driven heat pump and heat transformer, the low-dissipation assumption has been adopted to establish the irreversible thermodynamic models of them in the present paper. By means of the proposed models, the heating loads, the coefficients of performance (COPs) and the optimal relations between them for various constructions are derived and discussed. The performances of different constructions are numerically assessed. More importantly, according to the results obtained, the upper and lower bounds of the COP at maximum heating load for different constructions are generated and compared by the introduction of a parameter measuring the deviation from the reversible limit of the system. Accordingly, the optimal constructions for the low-dissipation three-terminal heat pump and heat transformer are determined within the frame of low-dissipation assumption, respectively. The optimal constructions in accord with previous research and engineering practices for various three-terminal devices are obtained, which confirms the compatibility between the low-dissipation model and endoreversible model and highlights the validity of the application of low-dissipation model for multi-terminal thermodynamic devices. The proposed models and the significant results obtained enrich the theoretical thermodynamic model of thermally driven heat pump systems and may provide some useful guidelines for the design and operation of realistic thermally driven heat pump systems.
Highlights
The generalized models and the associated performance boundaries of thermodynamic devices are desired for researchers
The low-dissipation assumption has been used to construct the combined cycle models of thermally driven refrigerator and heat pump by considering the constraint of reversible entropies inside two subsystems in the last two years [33,34], which obtains the bounds of the coefficient of performance (COP) at maximum cooling power and heating load for the first time and extends the application scope of low-dissipation model to multi-terminal thermodynamic systems
Based on the low-dissipation assumption, when the three-terminal heat pump is constructed as models A, B and C the heats exchanged between the system and the three heat reservoirs in four heat transferring processes can be expressed as [7]
Summary
The generalized models and the associated performance boundaries of thermodynamic devices are desired for researchers. Multi-terminal thermodynamic systems play the important roles in the utilization of lowgrade energies [27,28,29,30] and the energy resources at microscopic scale [31,32] In this regard, the low-dissipation assumption has been used to construct the combined cycle models of thermally driven refrigerator and heat pump by considering the constraint of reversible entropies inside two subsystems in the last two years [33,34], which obtains the bounds of the COP at maximum cooling power and heating load for the first time and extends the application scope of low-dissipation model to multi-terminal thermodynamic systems. The low-dissipation assumption will be used to esand explore the performance characteristics and differences of various constructions in tablish more practical models of three-terminal heat pump and heat transformer and exthe following.
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