The Theory Study And Engineering Application Of Exergy Transfer Process For Multi-potential Fields

This paper is the main content of "Engineering Exergy Transfer Study" (Serial Number: G2000026307), which is the study task of "The Key Science Issue for Efficient Energy Saving" subsidized by National Key Item of Basic Research, Development and Plan. With the complex exergy transfer system for multi-potential fields being the main study object, the field synergy mechanism being the core study content, the field system of the intensity parameters being study medium, the exergy transfer phenomenological equation of multi-potential fields is constructed and the concept of field influence factor of exergy transfer coefficient is defined respectively in this paper. The application example study is done with pipeline transportation in the oil and gas storage and transportation engineering, crude oil thermal driving process and the heat transfer between the gas-injected well and oil layer. Thus many new thoughts and measures are provided for uncovering and improving the actual production processes. Started with the scientific definition of energy and the two basic thermodynamic laws, the dialectic relations between enthalpy, entropy and exergy, between energy analysis and exergy analysis, between energy transfer and exergy transfer are discussed. Thus some disputed learned questions, such as the impersonal existence and subject ascription of exergy transfer, are clarified. It is also stressed that exergy transfer can demonstrate the irreversible essence of practical process more directly and deeply than energy transfer does, exergy transfer has more" profound meaning and can provide more; new and more valuable information for analyzing and improving those practical processes. The study method of using field as the medium is obtained by discussing the philosophic university and identity of exergy transfer phenomenon. The present general describing method of exergy transfer is analyzed and compared. The relation between field synergy principle and exergy transfer study is explained. Then it is indicated that exergy transfer can be used to solve those complicated engineering questions of field synergy by considering exergy as uniform item and transforming multi-goals to single one. According to the dynamic transport law of energy, momentum and mass, with consideration of the related theory of non-equilibrium thermodynamics, the exergy transfer phenomenological equation of multi-potential fields is derived. On the basis of that, the concept of field influence factor of exergy transfer coefficient is defined. In this way the engineering exergy transfer questions of multi-fields can be analyzed fundamentally from the point of field synergy mechanism and single field action ratio. On the basis of summing up the features and analysis objectives of different engineering exergy transfer, the evaluating rules respectively suit for exergy transform process, steady and unsteady exergy transfer are consummated and used to judge the leading field of these processes. Also the corresponding approaches are provided. Thus theory research and engineering application are combined organically. The exergy transfer analysis model of pipeline transportation is established. Numerical simulation is finished for oil transferring pipeline, gas transferring pipeline and heat water transferring pipeline. The results can not only describe the space-time change law of exergy transfer of the leading field for the pipeline processes, but also explain rationally the synergy mechanism of pressure field and temperature field, the single field action ratio. The technical approaches of improving the pipeline transferring processes are provided, such as increasing pressure can increase effectively the pressure exergy transfer coefficient of oil and gas transferring pipeline, decreasing the radial temperature difference can decease effectively the heat exergy transfer coefficient of heat water transferring pipeline. As for the complex substance driving process concerned with multi-fields, the exergy transfer model of field synergy is established on the premise of using the driving exergy as uniform feature item and sorting the fields. Based on this model, the mechanism study of crude oil thermal driving can reasonably illuminate the mechanism of some technical measures, such as high temperature decreases viscosity, high pressure gradient increases driving force, high temperature and low water rate decreases driving resistance. It is well elucidated in theory that their combination can lead to increase driving power, or increase oil extraction rate, even transfer pressure farther and increase recovery ratio. Based on the equivalent thermal exergy transfer model of gas-injected well in situ combustion, according to the metrical temperature of well wall in different air velocity and heat flux, three kinds of thermal exergy transfer coefficient are measured and compared with the relevant theoretic answers by numerical simulation. The results show that, they change in the same way with time and the change trends both accord with the theoretic explanation of the second law of thermodynamics. In the end it is illuminated that the equivalent thermal exergy transfer model can be used to describe the convective heat transfer process between the hot air and oil layer in situ combustion.