桩基螺旋型埋管换热器换热性能的数值研究

发布时间：2018-11-20 18:57

【摘要】：桩基埋管换热器依托于建筑地下热工结构,具有桩径大、埋深较浅等特点,比传统钻孔埋管换热器具有更为明显的优势,如占地面积小、节省钻孔费用及换热器性能稳定等,符合我国可持续发展战略目标。其中,与桩基U型、W型等桩基埋管换热器相比,桩基螺旋型埋管换热器在同一桩基中不仅埋管长度较长、换热面积更大,而且还可以防止气体集聚在管道顶部。但是,桩基螺旋型埋管换热器传热机理有异于传统钻孔埋管换热器且几何结构复杂,关于其传热性能的研究尚不够充分。首先,本文利用ANSYS软件建立桩基并联双螺旋型埋管换热器三维动态传热的仿真模型,通过其对现场试验的仿真复现以及与实心圆柱源热源模型解析解的对比验证了模拟结果的正确性。然后,由于不同埋管形式对换热器与土壤换热有重要影响,在管材、回填材料和土壤热物性及边界条件均相同的情况下,以实际尺寸的换热器为原型,分别建立了桩基单螺旋型、并联双螺旋型与双螺旋型埋管换热器三维仿真模型,对以上模型在土壤中的非稳态传热过程进行了模拟。结果表明:埋管形式不同,桩基埋管换热器的换热效果呈现差异,桩基双螺旋型埋管换热器的换热性能最好,而单螺旋型优于并联双螺旋型。然后,采用桩基单螺旋型埋管换热器数值模型模拟了进口流速、进口水温、土壤初始温度、管径及螺距对换热器换热性能的影响,得到各主要参数的传热变化规律。此外,结合建筑空调工程负荷特点,选定三种运停比,探讨了各种间歇运行模式下桩基并联双螺旋型埋管换热器的传热性能以及沿桩深和径向不同位置桩基内部、桩壁及土壤温度的变化规律,提出了以温度恢复百分比为指标对桩基的温度恢复特性进行定量评价的方法。最后,建立了桩基双螺旋型桩基换热器的热湿耦合传热数值模型,利用该模型来研究地下水渗流作用下土壤温度场分布情况及不同流速、土壤类型对周围土壤的影响规律,并利用单位管长换热量指标来评估渗流作用下桩基双螺旋型换热器的传热性能。本文的研究结果可为桩基螺旋型埋管换热器实际工程设计及应用提供参考。
[Abstract]:The pile-base buried tube heat exchanger relies on the underground thermal structure of the building and has the characteristics of large pile diameter, shallow buried depth and so on. It has more obvious advantages than the traditional borehole buried tube heat exchanger, such as small area, low drilling cost and stable performance of the heat exchanger, etc. In line with the strategic objectives of sustainable development in China. Compared with the pile foundation U-type and W-type pile-embedded tube heat exchangers, the pile-foundation spiral buried tube heat exchangers not only have longer length and larger heat transfer area in the same pile foundation, but also prevent gas accumulation on the top of the pipe. However, the heat transfer mechanism of the pile-foundation helical buried tube heat exchanger is different from that of the traditional drilled buried tube heat exchanger and the geometry structure is complicated, so the research on its heat transfer performance is not enough. Firstly, the three-dimensional dynamic heat transfer simulation model of parallel double-helical buried tube heat exchanger with pile foundation is established by using ANSYS software. The correctness of the simulation results is verified by the simulation reappearance of the field test and the comparison with the analytical solution of the solid cylindrical heat source model. Then, because of the important influence of different buried tube forms on heat exchanger and soil heat transfer, the heat exchanger with actual size is used as prototype under the same conditions of pipe material, backfill material and soil thermal properties and boundary conditions. Three dimensional simulation models of single spiral parallel double helical and double helical buried tube heat exchangers are established respectively. The unsteady heat transfer process of the above models in soil is simulated. The results show that the heat transfer efficiency of pile based buried tube heat exchanger is different with different buried pipe types. The heat transfer performance of pile foundation double helical buried tube heat exchanger is the best, while that of single spiral heat exchanger is better than that of parallel double helical heat exchanger. Then, the effects of inlet velocity, inlet water temperature, soil initial temperature, pipe diameter and pitch on the heat transfer performance of the single spiral buried tube heat exchanger on pile foundation are simulated, and the heat transfer changes of the main parameters are obtained. In addition, combined with the load characteristics of building air conditioning engineering, three kinds of operation stop ratio are selected to discuss the heat transfer performance of parallel double-helical buried tube heat exchanger with pile foundation under various intermittent operation modes, as well as the different positions of pile foundation along pile depth and radial direction. Based on the variation of soil temperature and wall temperature, a quantitative evaluation method for the temperature recovery characteristics of pile foundation is put forward, which is based on the percentage of temperature recovery. Finally, a numerical model of heat and moisture coupling heat transfer in pile foundation double-helical pile heat exchanger is established. The model is used to study the distribution of soil temperature field and the influence of different velocity of flow and soil type on surrounding soil under the action of groundwater seepage. The heat transfer index of unit tube length is used to evaluate the heat transfer performance of double helical heat exchanger with pile foundation under percolation. The results of this paper can be used as a reference for the practical engineering design and application of spiral buried tube heat exchanger on pile foundation.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU83

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