竖直U型地埋管换热性能主要影响因素数值研究

发布时间：2018-02-06 01:21

本文关键词： 地埋管换热器换热性能热渗耦合土壤分层热响应试验数值模拟　出处：《长安大学》2014年硕士论文　论文类型：学位论文

【摘要】：土壤源热泵技术作为一种可再生能源利用技术，利用土壤这一天然的蓄热体可实现能源的跨季度利用。其以节能环保、机组能效系数高、运行管理稳定方便等优点广泛应用于工程实践中。采用竖直U型地埋管换热器的土壤源热泵系统更适合我国人均占地面积小的国情。土壤源热泵系统的综合性能主要取决于地埋管换热器的换热性能，研究地埋管换热性能的影响因素以强化埋管与土壤之间的换热可以有效提高热泵系统的综合性能。在进行岩土热响应试验时，这些影响因素直接表现在对试验结果造成一定偏差，而岩土热物性参数是土壤源热泵系统地埋管换热器设计的基础依据，应准确测量。鉴于此，本文对竖直U型地埋管换热性能的影响因素进行了探讨研究。首先建立了耦合地下水渗流和岩土热物性分层的竖直U型地埋管换热器全尺寸三维模型，利用专业数值模拟软件Fluent对岩土热响应试验过程进行数值模拟。对数值模拟过程中地埋管内流体进出口温度的变化及周围土壤温度的变化进行了监测和分析，并对比分析现场热响应试验和热响应数值模拟的结果，验证了该模型的合理性和可靠性。本文应用此数值模型对地下水位变化、同一水位下不同地下水渗流速度及岩土导热系数分层等不同条件下的热响应试验进行数值模拟，分析其对地埋管换热性能的影响；并通过解析计算模型，对模拟所得数据进行分析，得到岩土综合热物性参数，研究这些因素对热响应试验的影响。此外，本文还针对土壤源热泵系统初期运行对系统性能存在不利影响的现象，进行量化分析，研究起始运行时间不同对土壤源热泵性能的影响。结果表明，地下水位埋深越大，地埋管换热性能越差；地下水渗流作用可增强埋管的换热性能，且速度越大，作用越显著；在平均导热系数相同时，分层条件下埋管换热性能比均匀土质条件下要差；地下水位、地下水渗流速度及岩土导热系数分层的变化都会对热响应试验结果产生一定影响；在供冷季，热泵系统从5月1日开始运行时的机组COP不如热泵系统从11月15日开始运行时，，比其低1.8%；在供暖季，热泵系统从5月1日开始运行时的机组COP比热泵系统从11月15日开始运行时要好，比其高1.3%。
[Abstract]:As a kind of renewable energy utilization technology, the ground-source heat pump technology can realize the inter-seasonal utilization of energy by using the soil as a natural regenerator, which is energy saving and environmental protection, and the unit energy efficiency coefficient is high. The advantages of stability and convenience of operation and management are widely used in engineering practice. The ground-source heat pump system with vertical U-type ground heat exchanger is more suitable for the situation of small per capita occupation of land in China. The comprehensive performance of ground-source heat pump system. It mainly depends on the heat transfer performance of buried tube heat exchanger. In order to enhance the heat transfer between buried pipe and soil, the comprehensive performance of heat pump system can be improved effectively by studying the influencing factors of heat transfer performance of buried pipe. These influencing factors are directly reflected in the deviation of the test results, and the geotechnical thermal properties are the basis for the design of ground-buried heat exchangers in the ground-source heat pump system, which should be measured accurately. In view of this. In this paper, the factors affecting the heat transfer performance of vertical U-type buried pipes are studied. Firstly, a full-scale three-dimensional model of vertical U-type buried pipe heat exchangers is established, which is coupled with groundwater seepage and thermal stratification of rock and soil. The thermal response test process of rock and soil was simulated by the professional numerical simulation software Fluent. The variation of the inlet and outlet temperature of the fluid in the buried pipe and the change of the soil temperature around the buried pipe during the numerical simulation were monitored. And analysis. The results of field thermal response test and thermal response numerical simulation are compared to verify the rationality and reliability of the model. In this paper, the numerical model is used to simulate the thermal response tests under different conditions, such as the variation of groundwater level, the different seepage velocity of groundwater and the stratification of thermal conductivity of rock and soil under the same water level. The influence on the heat transfer performance of buried pipe is analyzed. Through the analytical calculation model, the simulated data are analyzed, the comprehensive thermal physical parameters of rock and soil are obtained, and the influence of these factors on the thermal response test is studied. Aiming at the phenomenon that the initial operation of ground-source heat pump system has adverse effect on the performance of the system, quantitative analysis is carried out to study the effect of different initial operating time on the performance of ground-source heat pump. The deeper the groundwater level is, the worse the heat transfer performance of the buried pipe is. Groundwater seepage can enhance the heat transfer performance of the buried pipe, and the greater the velocity, the more obvious the effect. When the average thermal conductivity is the same, the heat transfer performance of buried pipe under stratified condition is worse than that under homogeneous soil condition. The variation of groundwater level, groundwater seepage velocity and thermal conductivity of rock and soil will have a certain effect on the results of thermal response test. In the cooling season, the COP of the heat pump system is lower than that of the heat pump system from November 15th when the heat pump system starts to run on May 1st. In the heating season, the COP of the heat pump system when it started operation from May 1st is better than that of the heat pump system from November 15th, and is 1.3 times higher than that of the heat pump system.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU83

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