竖直单U型地埋管换热器热短路现象研究与分析
发布时间：2019-02-11 16:45
【摘要】：当今世界,能源短缺和环境污染已成为制约全球可持续发展的重要问题之一。以可再生地热源为能源的地源热泵技术,受到了国内外政府、高校和研究机构的高度关注,并且展开了大量的理论研究和实际工程的应用。地埋管换热器设计不仅是地源热泵研究的重点,也是地源热泵空调系统的应用基础和理论核心。如何在狭窄的钻孔内减少热短路的影响并且提高换热器的性能,研究抑制热短路的措施就显得尤为重要。本文从换热器传热模型和管内循环流体的湍流模型两个方面对地埋管传热模型进行介绍,为研究地埋管换热器做了理论准备。介绍了数值模拟相关CFD软件,利用Gambit软件建立地埋管换热器三维模型,用Fluent进行数值仿真模拟。通过对影响地埋管换热器热短路现象的三个因素:循环流体的速度、埋管深度和运行时间分别进行模拟,通过对比循环流体出口水温、不同深处的换热器温度分布云图和近出口温差以及单位井深换热量对热短路现象进行分析和研究。得出如下结论:管内流速推荐值为0.6 m/s,埋管深度在80 m最佳,采取缩短机组连续运行的时间或者间歇运行的策略更加合理。在研究不同因素对换热器的影响时,发现两支管间必然发生热短路现象,而且越靠近地表现象越严重。本文研究了抑制地埋管热短路现象的两种措施,即在垂直于两支管间中心线处添加一定深度和厚度的隔热板或在回水管敷设不同深度和厚度的保温材料。通过比较添加不同深度隔热板、不同深度保温层和不同保温层厚度三种情况,对热短路现象进行定性研究,并通过对出水温度和单位井深换热量对换热器热短路现象和换热器性能进行定量分析。当未添加任何抑制措施即换热器正常换热时,循环流体出水温度为304.44 K,单位井深换热量为56.1 W/m:当采取添加隔热板抑制措施时,最佳工况点隔热板深度为40 m时,出口温度最低为304.35 K,单位井深换热量最高为57.5 W/m;当采取敷设一定深度和厚度保温层时,最佳工况点为敷设10m深保温层厚度为4 mm,出口温度最低为304.16 K,单位井深换热量为60.5 W/m。通过比较单位井深换热量,在两支管间添加隔热板单位井深换热量最高可以提高为2.5%,在回水管敷设保温层最高可以提升7.8%。通过对地埋管换热器热短路现象的研究,并提出了两种抑制措施,为提高换热器性能提供理论支撑,希望为地源源热泵的技术推广起到积极的作用,使该技术更加节能环保。
[Abstract]:In today's world, energy shortage and environmental pollution have become one of the most important problems restricting global sustainable development. Ground-source heat pump (GSHP) technology, which uses renewable geothermal source as energy source, has been highly concerned by governments, universities and research institutions at home and abroad, and a large number of theoretical research and practical engineering applications have been carried out. The design of ground heat exchanger is not only the focus of ground source heat pump research, but also the application basis and theoretical core of ground source heat pump air conditioning system. How to reduce the influence of hot short circuit and improve the performance of heat exchanger in narrow borehole is very important. In this paper, the heat transfer model of underground tube is introduced from two aspects: heat transfer model of heat exchanger and turbulence model of circulating fluid in tube. This paper introduces the related CFD software of numerical simulation. The 3D model of underground tube heat exchanger is established by Gambit software, and the numerical simulation is carried out by Fluent. Through the simulation of three factors that affect the hot short circuit phenomenon of the ground buried tube heat exchanger: the velocity of the circulating fluid, the depth of the buried pipe and the running time, the water temperature at the outlet of the circulating fluid is compared. The thermal short-circuit phenomenon is analyzed and studied in different depths of heat exchanger temperature distribution cloud map and near outlet temperature difference as well as heat transfer in unit well depth. The conclusions are as follows: the recommended value of flow velocity in the tube is 0.6 m / s and the depth of buried pipe is 80 m. It is more reasonable to adopt the strategy of shortening the continuous operation time or intermittent operation of the unit. When studying the influence of different factors on the heat exchanger, it is found that the phenomenon of thermal short circuit between the two branch tubes is inevitable, and the phenomenon is more serious with the closer to the surface. In this paper, two kinds of measures to restrain the phenomenon of thermal short circuit of buried pipe are studied, that is, adding heat insulation plate with certain depth and thickness perpendicular to the center line between two pipes or laying insulation material of different depth and thickness in backwater pipe. The phenomenon of thermal short circuit is studied qualitatively by comparing the three conditions of adding different depth insulation plate, different depth insulation layer and different insulation layer thickness. The thermal short-circuit phenomenon and heat exchanger performance of heat exchanger were analyzed quantitatively by water temperature and heat transfer per well depth. Without adding any inhibition measures, that is, the heat transfer of the heat exchanger, the outlet temperature of the circulating fluid is 304.44 K, the heat transfer of the unit well depth is 56.1 W / m: when the heat insulation board is added, the heat transfer rate is 56.1 W / m. When the depth of the insulation plate is 40 m, the lowest exit temperature is 304.35 K, and the maximum heat transfer per well depth is 57.5 W / m; When a certain depth and thickness insulation layer is laid, the optimum operating point is that the thickness of 10 m deep insulation layer is 4 mm, the lowest exit temperature is 304.16 K, and the heat transfer of unit well depth is 60.5 W / m. By comparing the heat transfer of unit well depth, the maximum heat transfer of unit well depth can be increased to 2.5 by adding heat insulation board between two pipes, and the maximum value of heat transfer can be increased to 7.8 by laying insulation layer in backwater pipe. Through the study of heat short circuit phenomenon of ground heat exchanger, two kinds of restraining measures are put forward to provide theoretical support for improving heat exchanger performance. It is hoped that it will play an active role in popularizing the technology of ground source heat pump and make the technology more energy saving and environmental protection.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU83
[Abstract]:In today's world, energy shortage and environmental pollution have become one of the most important problems restricting global sustainable development. Ground-source heat pump (GSHP) technology, which uses renewable geothermal source as energy source, has been highly concerned by governments, universities and research institutions at home and abroad, and a large number of theoretical research and practical engineering applications have been carried out. The design of ground heat exchanger is not only the focus of ground source heat pump research, but also the application basis and theoretical core of ground source heat pump air conditioning system. How to reduce the influence of hot short circuit and improve the performance of heat exchanger in narrow borehole is very important. In this paper, the heat transfer model of underground tube is introduced from two aspects: heat transfer model of heat exchanger and turbulence model of circulating fluid in tube. This paper introduces the related CFD software of numerical simulation. The 3D model of underground tube heat exchanger is established by Gambit software, and the numerical simulation is carried out by Fluent. Through the simulation of three factors that affect the hot short circuit phenomenon of the ground buried tube heat exchanger: the velocity of the circulating fluid, the depth of the buried pipe and the running time, the water temperature at the outlet of the circulating fluid is compared. The thermal short-circuit phenomenon is analyzed and studied in different depths of heat exchanger temperature distribution cloud map and near outlet temperature difference as well as heat transfer in unit well depth. The conclusions are as follows: the recommended value of flow velocity in the tube is 0.6 m / s and the depth of buried pipe is 80 m. It is more reasonable to adopt the strategy of shortening the continuous operation time or intermittent operation of the unit. When studying the influence of different factors on the heat exchanger, it is found that the phenomenon of thermal short circuit between the two branch tubes is inevitable, and the phenomenon is more serious with the closer to the surface. In this paper, two kinds of measures to restrain the phenomenon of thermal short circuit of buried pipe are studied, that is, adding heat insulation plate with certain depth and thickness perpendicular to the center line between two pipes or laying insulation material of different depth and thickness in backwater pipe. The phenomenon of thermal short circuit is studied qualitatively by comparing the three conditions of adding different depth insulation plate, different depth insulation layer and different insulation layer thickness. The thermal short-circuit phenomenon and heat exchanger performance of heat exchanger were analyzed quantitatively by water temperature and heat transfer per well depth. Without adding any inhibition measures, that is, the heat transfer of the heat exchanger, the outlet temperature of the circulating fluid is 304.44 K, the heat transfer of the unit well depth is 56.1 W / m: when the heat insulation board is added, the heat transfer rate is 56.1 W / m. When the depth of the insulation plate is 40 m, the lowest exit temperature is 304.35 K, and the maximum heat transfer per well depth is 57.5 W / m; When a certain depth and thickness insulation layer is laid, the optimum operating point is that the thickness of 10 m deep insulation layer is 4 mm, the lowest exit temperature is 304.16 K, and the heat transfer of unit well depth is 60.5 W / m. By comparing the heat transfer of unit well depth, the maximum heat transfer of unit well depth can be increased to 2.5 by adding heat insulation board between two pipes, and the maximum value of heat transfer can be increased to 7.8 by laying insulation layer in backwater pipe. Through the study of heat short circuit phenomenon of ground heat exchanger, two kinds of restraining measures are put forward to provide theoretical support for improving heat exchanger performance. It is hoped that it will play an active role in popularizing the technology of ground source heat pump and make the technology more energy saving and environmental protection.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU83
【参考文献】
相关期刊论文 前10条
1 李志华;胡志高;康杰;王彦芳;胡平放;雷飞;;桩基地埋管地源热泵系统在湖北移动3G办公楼中的应用[J];制冷与空调;2015年12期
2 张行星;赵旭东;谭军毅;马世歌;;欧洲低温空气源热泵技术发展现状[J];暖通空调;2015年07期
3 胡平放;黄峙;孙心明;李成慧;李梦静;房美玲;江章宁;;地源热泵技术研究与应用发展状况[J];制冷与空调;2014年12期
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