竖直双U地埋管换热器分层换热模型研究

发布时间：2018-06-03 08:57

本文选题：土壤源热泵 + 可再生能源　；参考：《重庆大学》2015年博士论文

【摘要】：土壤源热泵系统是以岩土体为低温热源,由热泵机组、地埋管换热系统、建筑物内系统组成的空调系统。它充分利用低品位地热能源,可夏季供冷、冬季供热,高效节能,被称为21世纪非常具有发展前途的可再生能源应用空调技术。地埋管换热器是用于传热介质与岩土体在地埋管换热系统中进行换热的载体,其换热性能是制约土壤源热泵技术发展关键因素之一。全面认识和掌握地埋管换热器的热量传递过程,可以正确指导地埋管换热器的设计,提高换热效率,保证系统安全可靠运行,降低系统能耗,有利于土壤源热泵技术的良性发展和应用。本文依托重庆某土壤源热泵工程,针对实际工程中地埋管换热器所处岩土体由多种地质层组成且存在地下水渗流的情况,采用理论分析和现场实测相结合的方法,对地埋管换热器的换热性能开展研究。论文综合考虑地质分层和地下水渗流等因素,建立竖直双U型地埋管分层换热模型;根据工程热响应测试及实际运行结果,通过理论推导,求解出各分层的综合热物性参数;并以此热物性参数为边界条件,利用现代CFD技术进行动态数值模拟,对所建模型进行流速、回填料、埋深等因素,冬夏季取、排热等工况全面对比分析,验证其计算精度及可靠性。并将常规均匀换热模型和本文研究的分层换热模型计算结果分别与工程实际运行数据进行了对比。利用验证后的分层换热模型分析流速、回填料、埋深、井间距等因素对地埋管换热器的影响,并合理确定各因素水平。以正交试验理论为基础,合理设置模拟试验方案,分析地埋管换热器各种条件下的换热特性及其影响因素的显著性。最后基于地埋管分层换热模型,分析其在工程中的应用方法,提出应用于工程的简化分层换热模型。实测研究表明,土壤各分层内热物性参数存在一定的差异,即使是同一地质层也存在差异。该实验工程实测各分层热阻在0.1344~0.1717(m·K)/W之间变化,变化幅度达20%以上,因此模型分层具有必要性。实测及模拟研究表明,在同一地质层岩土导热热阻与地下水渗流流向、流速及地下孔隙率有关,结合地质分层及测点分布对地埋管换热器模型进行竖向分层具有合理性。以实际工程实测数据和不同流速、埋深及回填料导热系数以及季节取、排热过程的模拟结果对比验证,发现各验证工况下,各深度、各时刻管壁温度模拟值与实测值最大平均相对误差仅为1.82%。分层换热模型综合考虑地质分层、地下水渗流等因素,更加合理完善、可靠,且计算精度高。实测及模拟研究还表明,常规均匀换热模型与实测值之间存在较大差距,常规均匀模型单位井深换热量与实测值误差为7.83%,分层换热模型单位井深换热量与实测值误差为1.56%,分层换热模型与实测值更接近。通过模拟,发现地埋管换热的影响因素中,流速的显著性最大,其次为埋深和井间距,回填料导热系数为非显著性因素。研究表明,根据热响应测试原理,在工程应用中采用简化分层换热模型进行热响应测试及分析,可更准确分析土壤的热物性参数。用于设计计算,可更准确地求解合理的单井埋深及埋管总长度,方法可靠,简单可行。分层换热模型在工程中具有较好的应用前景。
[Abstract]:Soil source heat pump system is an air conditioning system composed of heat pump unit, buried pipe heat exchange system and inner building system. It makes full use of low grade geothermal energy, can supply cold in summer, heating in winter, high efficiency and energy saving. It is called as a very promising renewable energy application technology in twenty-first Century. Heat exchanger is used as the carrier for heat transfer medium and rock mass in the heat transfer system of buried pipe. The heat transfer performance is one of the key factors restricting the development of soil source heat pump. The overall understanding and mastery of the heat transfer process of the buried pipe heat exchanger can correctly guide the design of the heat exchanger of the buried pipe, improve the heat transfer efficiency and ensure the system safety. Fully reliable operation, reducing the energy consumption of the system, is beneficial to the benign development and application of the soil source heat pump technology. Based on a soil source heat pump project in Chongqing, this paper combines the theoretical analysis and field measurement for the rock and soil mass of the buried pipe heat exchanger in the actual project. The heat transfer performance of the buried pipe heat exchanger is studied. The paper takes into consideration the factors of geological stratification and groundwater seepage, and establishes a vertical double U type buried pipe stratified heat transfer model. According to the engineering thermal response test and the actual operation results, the thermal physical parameters of each layer are solved by theoretical derivation, and the thermal physical parameters are the boundary. Conditions, using the modern CFD technology to carry out dynamic numerical simulation, carry out the flow velocity, back filling, buried depth and other factors of the model, compare and analyze the working conditions such as winter and summer, heat discharge and so on, to verify the calculation accuracy and reliability. And the conventional uniform heat transfer model and the calculated results of the sub layer heat transfer model in this paper are separately from the actual operation data of the project. The effect of flow rate, back filling, depth, well spacing and other factors on the heat exchanger of buried pipe is analyzed and the level of various factors is rationally determined. Based on the orthogonal test theory, the simulation test scheme is set up reasonably, and the heat transfer characteristics and its influencing factors under the various conditions of the buried pipe heat exchanger are analyzed. In the end, based on the stratified heat transfer model of buried pipe, the application method in the engineering is analyzed, and a simplified stratified heat transfer model applied to the engineering is put forward. The experimental study shows that there is a certain difference in the thermal property parameters in the soil layers, even in the same geological layer. The experimental engineering measured the thermal resistance of each layer in 0.1344~0.1 The variation of 717 (M. K) /W is more than 20%, so the model stratification is necessary. The measurement and simulation study shows that the vertical stratification of the buried pipe heat exchanger model in the same geological layer is reasonable with the geological stratification and the measurement point distribution. According to the actual engineering data and different velocity, the thermal conductivity of the buried depth and the backfill and the simulation results of the heat transfer process, it is found that the maximum average relative error of the depth and the maximum average temperature of the tube wall temperature and the measured value is only the 1.82%. layer heat transfer model, which considers the geological stratification and the groundwater seepage. Flow and other factors are more reasonable, reliable, and with high calculation precision. The measurement and simulation study also shows that there is a big gap between the conventional uniform heat transfer model and the measured value. The error of the unit well depth change and the measured value of the unit well depth of the conventional uniform model is 7.83%, and the depth of the unit well depth change and the measured value is 1.56%, and the stratified heat transfer die is a stratified heat transfer model. The model is closer to the measured value. Through the simulation, it is found that the velocity is the most significant in the influence factors of the buried pipe heat transfer, followed by the buried depth and the well spacing, and the thermal conductivity of the backfill is not significant. The study shows that the thermal response test and analysis are carried out in the engineering application by the simplified stratified heat transfer model in the engineering application. It is more accurate to analyze the thermal physical parameters of soil. It is more accurate to solve the reasonable buried depth of single well and the total length of buried pipe in the design and calculation. The method is reliable and simple and feasible. The model of stratified heat transfer has a good application prospect in the project.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU831

【引证文献】