Heat Transfer Problem In Buried-Directly Pipes With Multi-Layer Insulation By Boundary Element Method

Directly buried pipes have been favored in recent years for its low cost, easily built and environmental factors. Technologies of directly buried hot water pipes have been mature and are widely used in thermal pipe network of a city. Now people are trying to apply those technologies into steam transportation. For its high temperature, multi-layer insulation is used. But as a result of lacking parameters about the form of layers and thickness of layers, insulation layers aren't used effectively and some accidents were caused as well. Developing a method of designing insulation layers is key to advance technologies of multi-layer insulation pipes.Effective forms of multi-layer insulation can't be gotten unless the temperature and the rate of heat flow in insulation layers, especially in the boundary of insulation layers can be calculated. In this paper, the heat transfer problem in directly buried pipes with multi-layer insulation was resolved by boundary element method and the corresponding computer program was designed.The first chapter presents the significance and its values in practice of the task. Briefly it introduces three widely used numerical methods and discusses their advantages and disadvantages. By comparison, it was clear that the BEM could solve the problem not only effectively but also precisely.In the second chapter the theory of weighted residual technique is illustrated and the boundary integral function of the potential problem is deduced by it. Methods of obtaining Green's function fundamental solutions in infinite region and semi-infinite region are presented. It also illustrates how to deal with inhomogeneous regions and the third boundary condition. At last the numerical solution of boundary integral function is presented.The third chapter is the major work of the paper. It deals with mathematic model construction of the problem and ideas of designing the computer program. It also presents interfaces of the program, the frame figure of a subprogram and explains how to use the program.The fourth chapter is the emphasis of the paper. At first the program calculates an instance that can be resolve by analytical method. By comparing the results obtained by the two methods it demonstrates that the program is credible and its result is precise. Then some rules are achieved by analyzing the results of many instances.Finally in the fifth chapter an overview of the paper is made and the research in future is foreseen.