Research On Thermal-fluid System Modeling Method And Application With The Object-oriented Technology

Thermal-fluid systems are widely used in industrial production and daily life, and affect human activities deeply. After the method of experience combining experiment, simulation becomes one of the important design means for thermal-fluid systems gradually. However, the current thermal-fluid system simulators have shortages as follows:model is described as a black box which is not open to the end-user; model in different simulators could not be shared with each other; only supporting reuse of knowledge on the unit model level. There are also some general simulation platforms, like Matlab/Simulink, could be used to model and simulate the thermal-fluid system. In these tools, the model is usually expressed in procedural form. So the topology of the system gets lost and any future extension and reuse of the model is tedious and error-prone. To solve the problems mentioned above, the modeling strategy and framework construction of the model library are intensively studied based on the unified multi-domain modeling and simulation technology, around the following three key points:abstraction of thermal-fluid system, non-causal expression and reuse of model, in the themes of the basic thermal-fluid system, two-phase equilibrium system and one-dimensional distribution parameters thermal-fluid system. The main contribution includes the following.Firstly, with the unified multi-domain language Modelica as an example, the principle and technical characteristics of unified multi-domain modeling and simulation are analyzed. Combined with the characteristics of thermal-fluid system, system decomposition and level progressive construction of thermal-fluid system are explored based on the unified multi-domain technology. And then, the non-causal expression and reuse mechanism of thermal-fluid system model are researched. The decoupling mechanism between the device model and the media model is proposed. The above research provides the modeling method and principle for thermal-fluid system.Secondly, the method of basic thermal-fluid library is explored and the framework of the library is constructed. The library is divided into four levels:the connection level, basic physical level, unit abstraction level, and unit level. The abstraction process and implement of model in each level is discussed. The library covers the basic unit of thermal-fluid system, such as physical phenomena, the correct equation of heat transfer and fluid flowing, pipe, pump, valve, heat exchanger and so. A vehicle engine cooling system is modeled and simulated to reveal the engineering value of the library.Thirdly, the modeling method of distillation system is studied. The decoupling and coupling mechanism between the distillation system devices and the mixture media model is presented. Structured level progressive modeling strategy is proposed in order to solve that there are many phase equilibrium prediction methods, the mixture rules and kind of mixture. The mixture media model has three levels:base level, method level and case level. The prediction methods, components’information of mixture and the mixing rules are separated into the three different levels. A new media could be introduced by changing the component information of mixture and mixing rules. The distillation system model is decomposing and the unit models of distillation system are modeled. Based on the media models and unit models, a model of air distillation column is constructed and simulated. The results agreed well with that simulated in Aspen Plus.Finally, based on the methods of line, the method transformed the thermal-fluid system described by partial differential equation to differential algebraic equations is researched. The following three key issues are discussed:discreting of one-dimensional space solving domain, differential expression of first and second derivative on the node and boundary conditions. The unified modeling of thermal-fluid systems described by partial differential equation and differential algebraic equations is achieved. With the heat transfer model of the human body as an example, body segment dividing, model describing and implement of the model are discussed in detail. The simulation results are agreed well with the experimental results. It is indicated that the transforming method is effective for modeling the one-dimensional distribution parameters thermal-fluid system.