Investigation On The Influences Of Heat And Mass Transfer On The Performances Of Three-Source Thermodynamic Cycles

In this dissertation, the influences of the irreversibilities of heat and mass transfer, the irreversibility inside a cyclic working fluid, heat leakage and otlier irreversible effects on the performances of three-source thermodynamic cycles are studied. By using the methods of finite-time thermodynamics and optimal control theory, the fundamental optimal relations and a series of performance bounds for the concerned thermodynamic cycles are derived. The new results obtained here can not only make progress in modern thermodynamics but also develop some new applications of finite-time thermodynamics in chemical cycle engineering, especially in chemical pump cycle engineering. They can also provide some new theoretical bases for the optimal design and the performance improvement of real thermodynamic cyclic equipments.The thermodynamic cycle equipments considered in this dissertation include absorption refrigerators, solar refrigerators, two classes of three-source chemical pumps and so on. It should be pointed out that the optimal performances of the chemical engines and the two-source chemical pumps are also investigated in this dissertation because the study on them is the foundation of probing the optimal performances of three-source chemicalpump cycles.Absorption refrigerators are a class of currently developing refrigerator equipments. They can be driven by some low-grade heat and have great potential for saving energy and decreasing environmental pollution. In Chapter 2, a new irreversible cycle model is presented for an absorption refrigerator, in which not only the irreversibilities of heat conduction and heat leakage but also the irreversibilities resulting from the friction, eddy and other irreversible effects inside the working fluid are taken into account. The influence of these irreversibilities on the performance of an absorption refrigerator whose working fluid flows continuously is investigated. The optimal relation among the coefficient of performance, cooling rate and overall heat-transfer area of the refrigerator is derived, from which some important performance bounds of the refrigerator are determined. Moreover, the factors that have direct effects on the internal irreversibility are analyzed and discussedAbsorption refrigerators may be also applied in solar-driven refrigerators, which may directly utilize solar energy and is an important equipment of saving energy. Solar-driven refrigerators have a good prospect of application. In Chapter 3, a universal irreversible model of a solar-driven refrigerator is set up, in which not only finite-rate heat transfer and the heat loss of a solar collector but also the internal irreversibility described in Chapter 2 are considered. On the basis of the new model, one of the important parameters, called the optimal operating temperature of the collector of a solar-driven refrigerator, is derived. From the results, the maximum overall coefficient of performance of the refrigerator is determined and some significant problems are discussed. Moreover, the optimal operating temperature of the solar-driven refrigerator with a corrugated-sheet collector is analyzed further in this chapter. The results show that the conclusions obtained here not only include the important results appeared in the related literature but also are more general.From Chapter 4 to Chapter 7, the effects of the irreversibility of mass-transfer, the internal irreversibility inside a cyclic working fluid andmass leakage on the optimal performances of chemical cycle devices are investigated.In Chapter 4, the cyclic model of an irreversible chemical engine is established, in which the irreversibility of mass-transfer, the internal irreversibility and mass leakage are taken into account. The optimal relation between the power output and the efficiency for the chemical engine is derived. The effects of the internal irreversible parameter on the optimal performances of the chemical engine are analyzed and some important performance bounds are obtained. Besides, the minim...