动态环境作用下螺旋型地埋管的传热模型与换热特性

发布时间：2018-04-11 23:16

本文选题：螺旋型地埋管 + 土壤源热泵　；参考：《重庆大学》2014年博士论文

【摘要】：土壤源热泵利用地下岩土作为热泵机组的低品位热源（汇），具有高效节能、环境友好的优点，但是由于传统垂直U型土壤源热泵系统钻孔费用较高，特别是重庆、成都等岩石地质结构，初投资高，经济性差，在技术推广过程中阻力较大。对于螺旋型地埋管换热器而言，，由于其能够依托建筑基础，可较大程度节约钻孔费用，减少了系统初投资，有利于技术推广应用。但是由于螺旋型地埋管换热器几何结构较为复杂，且具有埋深浅、桩径大的特点，其传热机理与换热特性有异于传统垂直U型地埋管，传统的地埋管传热模型不能正确描述其传热现象；此外，土壤表面环境参数（空气温度、太阳辐射等）的动态变化对埋深较浅的螺旋型地埋管的传热过程具有较大的影响，但是目前描述螺旋型地埋管传热过程的物理模型未深入考虑上述影响，故在上述工程实际问题及研究现状的基础上，本文对螺旋型地埋管换热器的传热模型及换热特性进行了研究。首先，对螺旋型地埋管换热器的导热模型进行了研究，建立了区别回填料与岩土热物性差异的螺旋型地埋管换热器实心圆柱热源一维导热数值解模型及线圈热源二维导热数值解模型，并与忽略热物性差异的导热解析解模型做了定量对比，分析了一维及二维模型的温度空间分布特征及温度时间变化特征。其次，在研究导热模型的基础上，提出了螺旋型地埋管在柱坐标系统下的单元体离散方法，并在此基础上建立了动态环境作用下螺旋型地埋管换热器的三维数值传热模型，该模型了考虑了回填料与岩土热物性差异及动态土壤边界条件对传热的影响，采用visual studio程序开发平台中C#程序设计语言，编制了螺旋型地埋管换热器设计与动态模拟软件；利用提出的螺旋型地埋管三维数值传热模型，模拟分析了地埋管设计参数、运行工况、螺旋形式、覆土深度、初始温度分布对传热特性的影响，提出了螺旋型地埋管沿流动方向上的4个典型换热阶段：进口换热换热阶段、回填区域热短路换热阶段、小温差换热阶段及出口换热阶段，分析了设计参数与运行工况等因素对4个换热阶段换热特性的影响。然后，考虑管群作用对螺旋型地埋管换热效果的影响，将传热区域分为单桩传热区域与管群传热区域，采用导热解析解模型与三维数值解模型分别描述管群传热区域与单桩传热区域传热过程，提出“动态土壤径向边界热流”的概念，将单桩传热区域与管群传热区域进行耦合，从而建立了考虑管群作用下适合系统长期模拟的螺旋型地埋管换热系统的传热模型；另外，考虑机组负荷率、冷凝器水温及水量、蒸发器水温及水量等5个因素，建立了螺杆热泵机组变工况能效模型；在螺旋型地埋管换热系统的传热模型及机组能效模型的基础上，模拟分析了重庆气候条件下，无辅助散热措施情况下地埋管系统的典型月响应特性、过渡季节温度恢复特性及典型年动态响应特性；然后通过调整夏季负荷，模拟了考虑辅助散热措施情况下的地埋管系统响应特性。最后，以贵阳城乡规划展览馆螺旋型地埋管热泵系统为案例项目，进行了实验性测试，分析了系统原始工况的运行特性，并提出了优化运行模式，在次日对优化运行模式进行了测试，发现冷热源系统能效提高了26.1%。另外，基于本文提出的三维传热模型与原始工况测试数据，确定得出测试项目埋管区域的岩土热物性参数，利用得出的热物性参数，预测了螺旋型地埋管换热器在优化运行工况条件下的出水温度，预测结果表明：本文提出的螺旋型地埋管三维传热模型具有较高的精确度，能够可靠的预测地埋管水温变化情况。
[Abstract]:The use of underground rock soil source heat pump for low grade heat source heat pump (sink), has the advantages of high efficiency and energy saving, environment friendly, but because of the traditional vertical U type ground source heat pump system of drilling cost is higher, especially in Chongqing, Chengdu and other geological structure of rock, the high initial investment, poor economy, resistance in the promotion process larger. For heat exchanger tube spiral type ground, because it can rely on the building foundation, can greatly save drilling cost, reduce the system initial investment, is conducive to the promotion and application of technology. But because the exchanger geometry of complex spiral type ground, and has the characteristics of large buried depth, pile diameter. The mechanism of heat transfer and heat transfer characteristics are different from traditional U vertical U-tube, traditional underground pipe heat transfer model cannot correctly describe the heat transfer phenomenon; in addition, the soil surface environmental parameters (air temperature, solar radiation). Has a great influence on the heat transfer process of spiral pipe the dynamic changes of the shallow depth, but the physical model describing the heat transfer process of spiral type buried pipe without a thorough consideration of the above effects, so the situation based on the problems mentioned above and the research on the spiral U-tube heat exchanger and heat transfer model the heat transfer characteristics were studied.
First of all, the research on spiral pipe heat conduction model of heat exchanger, a spiral type ground between backfill and rock soil thermal properties of different heat exchanger solid cylindrical heat source model and numerical solution of one-dimensional heat conduction numerical solution of two-dimensional heat conduction coil heat source model, and thermal analytical ignore differences in thermal properties the solution model to do quantitative comparative analysis, the distribution characteristics of temperature and time temperature change characteristics of one-dimensional and two-dimensional space model.
Secondly, based on the heat conduction model, put forward the element discretization method in cylindrical coordinate system of spiral pipe under the ground, and on this basis to establish a 3D numerical model of heat transfer of heat exchanger spiral type ground dynamic environment under the action of tube, the model considers the effect of backfill and rock soil thermal properties. The difference of soil and dynamic boundary conditions on heat transfer, by using C# programming language Visual Studio programming platform, the spiral pipe for heat exchanger design and dynamic simulation software; using spiral buried pipe is proposed for three-dimensional numerical heat transfer model, simulation analysis of the design parameters, operating conditions of buried pipe, helical form. The depth of overlying soil, effect of initial temperature distribution on the heat transfer characteristics, puts forward 4 typical spiral pipe along the flow direction on heat transfer stage: imported heat exchanger, the heat exchanger backfilling area short circuit order The effect of the design parameters and operating conditions on the heat transfer characteristics of the 4 heat exchange stages is analyzed.
Then, considering the effect of tube tube group affect the heat transfer effect of spiral type ground, heat transfer area is divided into single pile heat transfer area and pipe group heat transfer zone, solution model and 3D numerical solution model to describe the heat transfer region of single pile and pipe group heat transfer heat transfer by conduction region analysis, the concept of "dynamic soil radial boundary the heat will be coupled heat transfer zone and single pile pipe group heat transfer area, so as to establish a long-term simulation of buried spiral tube for group action system considering the heat transfer model of heat exchanger system; in addition, considering the load rate, condenser and evaporator temperature and water temperature, water and other 5 factors. The working efficiency model of variable heat pump is established; energy efficiency model based on the tube heat transfer model and unit heat exchanger system in spiral buried, simulated and analyzed the climate condition of Chongqing, no auxiliary cooling measures. The typical monthly response characteristics of the buried pipe system, the temperature recovery characteristics in the transitional season and the typical annual dynamic response characteristics are presented. Then the response characteristics of the buried pipe system considering the auxiliary cooling measures are simulated by adjusting the summer load.
Finally, taking Guiyang urban and rural planning exhibition hall type spiral pipe heat pump system as the case project, experiment test, analyzes the operating characteristics of the original operating system, and puts forward the optimized operation mode, in the test of optimal operation mode, found the cold and heat source system of improving energy efficiency of 26.1%. in addition, the three-dimensional heat transfer model the original condition based on the test data, determine the thermal parameters of soil and rock that buried pipe test project area, using thermal parameters obtained, to predict the water temperature of heat exchanger under optimized operating conditions under the condition of the spiral pipe buried, the forecast results show that three-dimensional heat transfer model of spiral type ground is proposed in this paper. The tube has high accuracy, can predict the change of water temperature of buried pipe reliable.

【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU831

【参考文献】