单井循环地下换热系统地下水流动及其传热特性研究

发布时间：2018-04-29 04:03

本文选题：地下水源热泵 + 循环单井　；参考：《哈尔滨工业大学》2014年博士论文

【摘要】：单井循环地下换热系统作为一种新型的地下水源热泵系统热源井，目前共有三种形式，即循环单井、抽灌同井和填砾同井。它们均将抽水管和回水管置于一口井内，在井的下部抽水，上部回水。循环单井是在基岩层中直接开孔，大部分水在井孔之内循环，与井壁发生热量交换；少部分水进入井孔，并进入含水层与其进行原水交换；抽灌同井在井孔内部加设了隔板，将热源井分为三个部分，上部为回水区，中间为隔断区，下部为抽水区；填砾同井的形式和抽灌同井类似，不同之处在于，填砾同井的井孔较井管的直径要大很多，其空隙采用分选性较好的砾石进行回填。本文针对以上三种热源井开展了相关的理论和实验研究工作，主要研究工作及结果如下：设计并搭建了单井循环地下换热系统的物理模拟砂箱实验台，选取了实验测量仪器和数据采集系统，计算了实验误差。结果表明，所搭建实验台的测量误差在可接受的范围之内，能够准确真实地反映物理现象。通过更换不同的预制井来实验模拟三种类型热源井的特性。针对三种不同的热源井，分别进行不同抽回间距、不同初始地温和不同负荷的实验研究。并对循环单井和填砾同井进行了不同排放比例的实验研究。研究表明，增大抽回间距能够显著改善三种热源井的抽水温度、提高换热量。三种热源井中循环单井承担负荷的能力最低，抽回水温度变化最大，热影响范围最小。在取热工况下，排放能够提高循环单井和填砾同井的抽水温度及取热量，小排放比对于提高热源井承担负荷能力的效果较好，随着排放比的增加，这种改善效果减弱。针对不同运行模式下抽灌同井特性进行实验研究，，按照三个具有代表性的地区——北京、沈阳和上海采暖期和空调期时间分配来设计实验。实验包括四种工况，即连续取热、连续放热、先夏后冬和先冬后夏。研究表明，抽灌同井在寒冷地区运行过程中，系统在该实验条件下，仅靠自然恢复期内的恢复，地下含水层不能使自身恢复至最初状态。必须采用辅助设备，对地下含水层进行热量补给，保证系统长期可靠的运行。在冷热负荷相当的地区，采用先夏后冬的运行模式，可以提高系统运行的稳定性；在寒冷地区应先进行放热工况，继而进行取热工况，保持热源井的抽水温度处在较高水平。相反，在较暖和地区则应先进行取热工况，保持热源井的抽水温度处在较低水平。建立了多区域耦合CFD仿真模型。通过纳维-斯托克斯方程和伯努利方程对多孔介质中运动方程进行分析推导，得到了多孔介质内的流动模型，并通过实验确定了该流动模型中的经验系数。利用单井循环地下换热系统砂箱实验台测得的实验数据对数值模拟结果进行了对比，验证了仿真模型的准确性。针对三种热源井进行了不同孔隙度、不同初始地温及不同抽水流量三个方面的仿真研究，并分析了三种热源井含水层的流场以及不同流量下的温度场变化情况。研究表明，孔隙度对含水层参与换热较多的抽灌同井和填砾同井影响稍大，对循环单井的影响则较小，但总体上看孔隙度对三种热源井的特性影响不大。抽水流量对单井循环地下换热系统的影响较大，增大抽水流量使得三种热源井的抽水温度变化加大，并能显著提高热源井的热影响范围。初始地温的变化并不影响含水层温度的变化趋势，抽水温度的变化趋势也几乎相同，只是各工况间存在一定温差。但提高初始地温能够显著提高热源井的平均抽水温度和累计取热量，可见初始地温是影响单井循环地下换热系统的关键因素之一。本文为国家自然科学基金“单井循环地下换热系统多流态流动与传热耦合机理研究”(41002085)的部分研究内容。本文的研究工作，为全面的掌握单井循环地下换热系统的运行特性、为该系统的设计及应用提供了重要的理论基础和技术储备。
[Abstract]:As a new type of heat source well of underground water source heat pump system , the single well circulation underground heat exchange system has three forms , namely circulation single well , pumping well and gravel with same well . Both pumping pipes and water return pipes are placed in a well . They are pumped in the lower part of the well . The circulating single well is directly open in the bedrock layer . Most of the water circulates inside the well bore , and heat exchange occurs with the well wall ;
a small part of water enters a well hole and enters a water - containing layer and carries out raw water exchange ;
a partition board is additionally arranged inside the well hole of the pumping well , the heat source well is divided into three parts , the upper part is a water return area , the middle is a partition area , and the lower part is a water pumping area ;
The form of gravel and well is similar to that of pumping irrigation . The difference lies in that the diameter of the well bore of gravel and well is much larger than the diameter of the well pipe , and the void is backfilled with gravel with better sorting property . In this paper , the relevant theoretical and experimental research work is carried out for the above three heat source wells , and the main research work and the results are as follows :

The physical simulation sand box experiment platform of single well circulation underground heat exchange system is designed and built , the experimental measurement instrument and the data acquisition system are selected , and experimental error is calculated . The results show that the error of the experiment table is within the acceptable range and can accurately and truly reflect the physical phenomena .

In this paper , the characteristics of three types of heat source wells are simulated by replacing different prefabricated wells . Experimental research on different pumping intervals and different initial conditions and different loads is carried out for three different heat source wells . The results show that increasing the pumping distance can significantly improve the pumping temperature of three heat source wells and increase the heat exchange rate .

The experiments were carried out on the characteristics of pumping and irrigation in different operating modes . The experiments were carried out according to three representative areas _ Beijing , Shenyang and Shanghai heating period and air conditioning time distribution . The experiment included four working conditions , namely , continuous heat removal , continuous heat release , first summer and summer after winter . The research shows that the system can not restore itself to the original state only by the restoration of the natural recovery period . The auxiliary equipment is used to make the system run reliably . In the area where the cold and heat load is equivalent , the operation mode of the first summer and the winter is adopted to improve the stability of the system operation .
In the cold area , the heat release working condition should be carried out firstly , then the hot working condition should be carried out to keep the water pumping temperature of the heat source well at a higher level . In contrast , the hot working condition should be firstly carried out in the warmer regions , so that the pumping temperature of the heat source well is kept at a lower level .

A multi - zone coupled CFD simulation model is established . The motion equations in porous media are derived by Navier - Stokes equation and Bernoulli equation . The flow model in porous media is obtained . The empirical coefficients in the flow model are determined experimentally . The results of numerical simulation are compared with the experimental data measured by the experiment table of the sand box of the single - well circulation underground heat exchange system , and the accuracy of the simulation model is verified .

Three heat source wells are simulated and studied with different porosity , different initial ground temperature and different pumping flow . The results show that the influence of porosity on the flow field of three heat source wells and the change of temperature field in different flow rates is small .

This paper is a part of the research on the mechanism of multi - flow state flow and heat transfer coupling mechanism of single - well circulation underground heat transfer system of the National Natural Science Foundation ( 41002085 ) . The research work of this paper provides an important theoretical basis and technical reserve for the design and application of this system in order to master the operating characteristics of the single well circulating underground heat exchange system .

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU83

【参考文献】