地下水渗流对竖直埋管换热器的影响研究

发布时间：2018-05-03 05:10

本文选题：土壤源热泵 + 地埋管换热器　；参考：《重庆大学》2015年硕士论文

【摘要】：以节能和环保为特征的土壤源热泵技术是具有较大发展前途的制冷空调技术,正在受到各个国家和地区越来越多的关注。影响土壤源热泵系统性能的因素是多方面的,其中,地埋管换热器与土壤传热过程是土壤源热泵系统的关键研究内容之一。近年来,我国不论是在土壤源热泵系统的实际工程应用上,还是在对地埋管换热器数值计算分析、实验测试等方面均进行了相当多的研究工作,而关于地埋管换热器的传热研究大部分都是基于单一的热传导理论,忽略了土壤中地下水渗流的影响,这必然会使得地埋管换热器的设计与实际所需产生偏差。基于以上,本课题以多孔介质传热传质理论为基础,对地埋管换热器在地下水渗流下的换热性能进行了研究,建立了地下水渗流位于不同地下深度和不同水渗流方向作用下的热渗耦合影响下的地埋管换热器数值模型。依据实际工程勘探地质情况,以三维模型为基础,建立竖直双U埋管换热器与土壤热渗耦合换热模型,通过热响应测试得到数值计算模型的边界条件、初始条件及计算时间长度,并利用Fluent软件进行数值计算,根据数值计算结果分析了渗流速度、孔隙率对埋管换热性能的影响,同时对测试值和数值计算结果进行对比验证,结果显示特定地下水渗流条件下土壤饱和区热渗耦合换热模型与实际热响应工况接近,证明了数值计算模型的正确性,所建物理模型可以应用于实际工程,同时也近似的得到了热响应测试地区的渗流速度和孔隙率大小。以实际热响应测试地质情况为基础建立的竖直双U埋管换热器与土壤热渗耦合换热模型为基准模型,建立了不同深度地下水渗流条件下地埋管热渗耦合换热模型,分析地下水渗流位置的变化而引起的地下换热器换热性能的变化,分析结果发现在存在地下水渗流的区域,土壤的温度场发生了偏移,进水管水温下降明显大于无渗流区域中的水温降,出水管水温下降几乎等于无渗流区域中的水温降,同时相对于无渗流的情况,地下水渗流分别位于上层、中层、下层的换热量分别上升了5.8%、4.9%、2.6%,即地下水渗流位于上层时,最有利于地埋管换热器的良好运行,并侧面验证了层换热理论的正确性。以实际热响应测试地质情况为基础建立的竖直双U埋管换热器与土壤热渗耦合换热模型为基准模型,建立了不同方向地下水渗流条件下地埋管热渗耦合换热模型,分析地下水渗流方向的变化而引起的钻孔换热性能的变化,分析结果发现不论地下水渗流方向如何,渗流速度越大,越能促进循环介质与土壤之间的换热,而且地埋管换热器进水管的温降始终大于出水管的温降,但是当地下水渗流方向分别为进水管方向为上游、出水管方向为下游的渗流水方向;垂直于进出水管水平轴线的渗流水方向以及出水管方向为上游、进水管方向为下游的渗流水方向时,进水管换热量所占总换热量百分比逐渐下降,出水管换热量所占总换热量百分比逐渐上升,同时,换热系数的取值逐渐增大,即出水管方向为上游、进水管方向为下游的渗流水方向最有利于地埋管换热器的良好运行。
[Abstract]:The soil source heat pump technology, characterized by energy saving and environmental protection, is a promising refrigeration and air conditioning technology, which is being paid more and more attention from various countries and regions. The factors affecting the performance of soil source heat pump system are many aspects. The key research of soil source heat pump system is the heat transfer process of buried pipe heat exchanger and soil In recent years, our country has done quite a lot of research work on the practical engineering application of the soil source heat pump system, the numerical calculation and analysis of the buried pipe heat exchanger, the experimental test and so on, and the heat transfer of the buried tube heat exchanger is mostly based on the single heat conduction theory, neglecting the soil. The influence of groundwater seepage in the medium will inevitably make the design of the buried pipe heat exchanger deviate from the actual needs. Based on the above, the heat and mass transfer theory of porous media is used to study the heat transfer performance of the buried pipe heat exchanger under the seepage of groundwater, and the groundwater seepage is located at different underground depth and different water. The numerical model of the buried pipe heat exchanger under the influence of seepage flow under the influence of seepage direction. Based on the geological conditions of the actual engineering, the vertical double U heat exchanger and the soil thermal seepage coupled heat transfer model are established on the basis of the three-dimensional model. The boundary conditions of the numerical calculation model type are obtained by the thermal response test, the initial conditions and the long calculation time are obtained. The numerical calculation is carried out by Fluent software. According to the numerical results, the influence of the seepage velocity and the porosity on the heat transfer performance of the buried pipe is analyzed. At the same time, the test values and the numerical results are compared and verified. The results show that the thermal seepage coupled heat transfer model in the saturated zone of the soil is close to the actual thermal response condition under the specific groundwater seepage condition. It proves the correctness of the numerical calculation model. The physical model can be applied to the actual engineering, and the seepage velocity and porosity in the thermal response test area are approximated. The vertical double U heat exchanger and the soil thermal seepage coupled heat transfer model, based on the actual thermal response test, are based on the model of the coupled heat transfer model of the soil. The thermal seepage coupled heat transfer model of buried pipe under different depth of groundwater seepage is established, and the change of heat transfer performance of underground heat exchanger caused by the change of groundwater seepage position is analyzed. The results show that the temperature field of soil is offset in the area of groundwater seepage, and the water temperature drop of the inlet pipe is obviously greater than that of the non percolation zone. In the water temperature drop, the water temperature drop of the outlet pipe is almost equal to the water temperature drop in the non percolation area. At the same time, the heat transfer of the groundwater is 5.8%, 4.9%, 2.6% respectively, respectively, in the upper layer, the middle layer and the lower layer, respectively, relative to the non percolation condition, that is, the groundwater seepage is located at the upper level, which is most favorable to the good operation of the heat exchanger of the buried pipe and is verified side by side. The theory of layer heat transfer is correct. The model of vertical double U buried tube heat exchanger and soil thermal seepage coupled heat transfer model based on the actual thermal response test is established, and the thermal seepage coupled heat transfer model of buried pipe under different direction of groundwater seepage is established, and the change of the seepage direction of underground water is analyzed, and the heat transfer of the borehole is analyzed. The analysis results show that the greater the seepage velocity, the greater the seepage velocity, the greater the heat transfer between the circulating medium and the soil, and the temperature drop of the inlet pipe of the buried pipe heat exchanger is always greater than the temperature drop of the outlet pipe, but the direction of the water flow pipe is upstream and the direction of the outlet pipe is downstream. When the water flow direction of the water pipe is perpendicular to the horizontal axis of the inlet pipe and the direction of the outlet pipe is upstream and the direction of the inlet pipe is downstream, the total heat exchange percentage of the intake pipe decreases gradually, and the total heat exchange ratio of the outlet pipe is gradually rising, and the value of the heat transfer coefficient is gradually obtained. The direction of the outlet pipe is upstream, and the direction of the seepage pipe downstream of the inlet pipe is most conducive to the good operation of the ground heat exchanger.

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU831;P641.2

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