地埋管换热器管内外耦合及相变换热性能编程研究

发布时间：2018-04-06 03:32

本文选题：地埋管换热器　切入点：蓄冷相变　出处：《长安大学》2017年硕士论文

【摘要】：随着社会经济的迅速发展,能源危机和环境污染问题已对人类的需求和健康构成了严重威胁。为响应节能环保政策,开发节能技术和寻求新能源已经迫在眉睫。土壤源热泵技术作为一种可再生能源技术,对降低建筑能耗和能源污染起着高效作用。为了推进土壤源热泵技术的发展,地埋管换热器与浅层岩土的换热问题成为研究的焦点。本文基于有限元的思想,结合多孔介质理论和流体动力学理论,采用Fortran语言工具,针对土壤源热泵地埋管换热问题,在等效直方管的基础上,将U型地埋管等效成真正意义上的U型方管,建立了考虑固液相变过程的土壤蓄冷模型和地埋管换热器管内外耦合换热模型,编制了三维动态数值计算程序。在应用地埋管换热器进行土壤蓄冷和为严寒地区冬天取热的过程中,地埋管换热器周围土壤中的地下水可能发生冻结的现象。为了描述地埋管换热性能,本文引出了线性热通量评价指标,对比分析了地下水固液相变过程对换热性能的影响。在管内紊流计算的基础上,分析了不同地下水渗流速度、不同地埋管的入口流速、不同地埋管的入口温度、不同回填材料及不同埋管管材对换热性能的影响。利用程序计算得出如下结论:(1)土壤地下水的渗流有利于地埋管的换热,渗流速度越大地埋管换热器换热性能越强,渗流速度每增加10m/a,线性热通量平均增加0.06%;(2)随着入口流速的提高,出口温度随之增加,线性热通量显著增大,但存在最佳入口流速;(3)在流量一定的条件下,随着入口水温的增加,埋管进出口温差会增大,线性热通量也随之增加;(4)导热系数越高的回填材料,换热效果越好,回填材料的导热系数应当接近土壤的导热系数。在低于土壤导热系数时,单位回填材料导热系数的增加对应线性热通量平均增加18.74W/m,增幅为15.3%;(5)采用导热性能较好的HDPE管和PE管管有助于地埋管换热器换热性能的提高;(6)土壤蓄冷时的固液相变过程有助于地埋管换热器的换热,出口温度在相变现象出现后会有一定的波动,有无相变过程的土壤蓄冷的线性热通量相对差值为5.4%。
[Abstract]:With the rapid development of social economy, energy crisis and environmental pollution have posed a serious threat to human needs and health.In order to respond to the policy of energy conservation and environmental protection, it is urgent to develop energy saving technology and seek new energy.As a kind of renewable energy technology, ground source heat pump technology plays an efficient role in reducing building energy consumption and energy pollution.In order to promote the development of ground source heat pump (GSHP) technology, the heat transfer between ground heat exchanger and shallow rock has become the focus of research.Based on the idea of finite element, combined with the theory of porous media and hydrodynamics, this paper adopts Fortran language tool, aiming at the heat transfer problem of ground buried pipe of ground source heat pump, on the basis of equivalent straight square tube.The U-type buried pipe is equivalent to the U-shaped square tube in real sense. The soil cold storage model considering the solid-liquid phase transition process and the coupled heat transfer model inside and outside the tube of the buried tube heat exchanger are established, and a three-dimensional dynamic numerical calculation program is developed.In the process of soil cold storage and winter heat recovery in cold regions with ground buried tube heat exchanger, the groundwater in the soil around the ground buried tube heat exchanger may be frozen.In order to describe the heat transfer performance of buried pipes, the evaluation index of linear heat flux is introduced, and the effect of the solid-liquid phase transition process of groundwater on the heat transfer performance is analyzed.On the basis of turbulent calculation in pipe, the effects of different groundwater seepage velocity, inlet velocity of different buried pipe, inlet temperature of different buried pipe, different backfill material and different buried pipe material on heat transfer performance are analyzed.The results obtained by the program are as follows: (1) the seepage of soil groundwater is beneficial to the heat transfer of buried pipes, and the greater the seepage velocity, the stronger the heat transfer performance of the heat exchangers.For every 10 m / a increase in the flow velocity, the average linear heat flux increases by 0.06 / a) with the increase of the inlet velocity, the outlet temperature increases and the linear heat flux increases significantly, but there is an optimal inlet flow rate of 3) when the flow rate is constant, with the increase of the inlet water temperature,The temperature difference between the inlet and outlet of the buried pipe will increase, and the linear heat flux will increase. The higher the thermal conductivity of the backfill material is, the better the heat transfer effect will be, and the thermal conductivity of the backfill material should be close to that of the soil.When the thermal conductivity of the soil is lower than that of the soil,The increase of heat conductivity per unit backfill material corresponds to an average increase in linear heat flux of 18.74 W / m, an increase of 15.3W / m) the adoption of HDPE tubes and PE tubes with better thermal conductivity will contribute to the improvement of heat transfer performance of buried tube heat exchangers, such as the heat transfer performance of buried tube heat exchangers, and the solid liquid phase of soil during cold storage.The change process is helpful to the heat transfer of the ground buried tube heat exchanger.The exit temperature will fluctuate after the phase change, and the relative difference of the linear heat flux of the soil with or without phase transition is 5.4.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU83

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