Random Heat Transfer And Reliability Theory On Ground-Coupled Pipe Of Ground Source Heat Pump

The applications of ground-source heat pump(GSHP) technology are showing a greater momentum of development in China. The function quality of the ground-coupled pipe, as a key device of air-conditioning system, is directly related to the operating results of GSHP. In recent years the heat transfer problems in rock and soil medium for ground-coupled pipe are an interdisciplinary research field of HVAC and geotechnical engineering, concerning the complex issues on heat and mass transfer in porous media, underground non-steady state heat transfer, temperature field random distribution. For a long time, the inherent nature of rock and soil with random composition and structure having been neglected, and the heat transfer phenomenon in rock and soil is explained by deterministic theory emphatically, and as a basis for engineering design, so that the problems on large investment and lack of function, and so on are aroused. Practically the impact factors of GSHP systems operation are extremely complex, many factors have significant uncertainties (mostly randomness). It is the random heat transfer phenomenon in geotechnical medium resulting in no universally agreed GSHP heat exchanger design and calculation methods, that the popularization and application of GSHP technology have been seriously constrained. Recently, more attention to ground-coupled pipe and environment, geological conditions and the complexity of system operation, especially the random effects are concerned. Considering buried pipe heat transfer problems of GSHP in rock and soil as an object of study, the random heat transfer analysis, stochastic finite element method, reliability theory are applied to analyse systematically the random distribution of composition and structure of rock and soil porous media, statistical methods of random thermal parameters, random heat transfer model, heat transfer stochastic finite element method, ground-coupled pipe reliability theory and design method in this dissertation. Main results completed are as follows:The heat transfer research status on ground-coupled pipe of GSHP at home and abroad is discussed, the existing heat transfer models of GSHP with buriedpipe heat exchanger are analyzed, the concept on buried pipe reliability of GSHP and necessity of random heat transfer research are put proposed. The the basic concept and principle of GSHP system are introduced, the form of ground heat exchanger and heat transfer mechanism are discussed, multiple factors effecting on the performance of GSHP, also ground-coupled pipe design problems and defects are analyzed.The heat transfer random characteristics in rock and soil medium are studied, the geotechnical heat conduction parameters field tests and the drawback of deterministic calculation method, as well as random effect factor on ground-coupled pipe are analyzed. The methods on randomness analysis of thermal properties of geotechnical parameters, the calculation and random temperature field of geotechnical materials, the discrete model and the local averaging theory on random field are studied. Based on geotechnical characteristics of heat transfer, the random heat transfer models and statistical analysis method of temperature field on ground-coupled pipe are given. By analyzing steady-state and non-steady-state heat transfer, the stochastic finite element theory for ground-coupled pipe is set up.The basic concepts of reliability of GSHP, reliability index system, stochastic analysis methods on total energy consumption are studied, function equation of state is given, also the reliability design and analysis method, as well as the reliability calculation are proposed.The engineering examples of computer simulation are discussed on the theory and methods givn in this dissertation. The resultes show that the methods are significance in theory and valuable in engineering.In short, using field test analysis, computer simulation technology, and interdisciplinary theory, the complex random heat transfer models of GSHP are studied.The random heat transfer nature of rock and soil media, and its relationship with non-steady-state heat transfer coupling characteristics are initially revealed. The random heat transfer mechanism and random distribution of temperature field on ground-coupled pipe in rock and soil are analyzed. The results establish a new area in GSHP research. Based on study of random heat transfer model of GSHP buried pipe, the random stochastic finite element analysis method is set up for analysis of random heat transfer of GSHP, wich provides a new theory and calculation method for random heat transfer study in rock and soil. The reliability analysis theory is proposed, which provides a new design method for GSHP technology.