Investigation On The Performance Characteristics Of Two Classes Of Energy Conversion Systems

The energy conversion systems are some of the important equipments that are widely used in daily lives and industry productions, which have various categories and have been noted. In the last years, because of the emergence of the shortage of energy sources, more and more countries have paid attentions to searching new energy sources, and the problems of how to apply new energy sources are universally noticed. In the mean time, energy conversion fixings become something that people focus. By using finite time thermodynamic and optimal control theories, the new models of energy conversion systems may be established, the effects of multifarious irreversibilities in the models may be considered, the inherent mechanism of the systems may be revealed, the operating characteristics of the systems may be analyzed, the various performance parameters may be optimized, the whole performance of the systems may be improved, and it is expected that the results obtained may provide some theoretical bases for the practical researches and application of new energy sources. The research works mentioned above are very significant subjects to be worthy studied further.In this thesis, the performance characteristics of two classes of thermodynamic systems, the fluid flow systems and energy conversion combined systems, are investigated. In Chapter 1, the development of the theory of finite thermodynamics and the applications of some new energy sources are introduced briefly. In Chapter 2, a general model of an irreversible fluid flow system is established, in which the linear and nonlinear fluid flow resistances and the friction forces with different types are taken into account. The influence of the piston speed and friction force on the instantaneous power output and efficiency of the system is analyzed. The instantaneous power output is maximized. The instantaneous power outputs versus efficiency characteristics are revealed. The optimum criteria of some important parameters are given. Some special cases are discussed in detail. The results obtained here can include the important conclusions obtained in literature. In chapter 3, on the basis of Bejan's model of an irreversible turbine, the influence of the dissipative losses resulting from friction on the performance of the system is analyzed. The maximum power output and efficiency are calculated. The characteristic curves of the system are presented for a set of given parameters. The optimally operating regions of some important parameters are determined. Analytic expressions of the main parameters are derived under some approximate conditions. In Chapter 4, Performance characteristics of a class of energy conversion combined systems are investigated. The heat leak loss, non-perfect regeneration, irreversibility of heat transfer and endo-irreversibility of the cycle existing in real energy conversion combined systems are considered and a general model of a class of energy conversion combnined systems is established. The synthetic influence of the main irreversibilities on the efficiency and power output of the system is analyzed. The maximum efficiency and power output and the corresponding parameters are calculated. The optimal characteristics of the system are revealed. Some significant special cases are discussed in detail. The important conclusions in the models of energy conversion combined systems established by Began and Peterson are directly derived. Some relevant results obtained here are generalized to apply to solar-driven heat engine systems.The results obtained here may provide some theoretical bases for the deep investigation on the performance characteristics of some relevant energy conversion systems as well as some references for the optimal design of some relevant energy conversion systems...