不同形式地埋管换热器换热性能数值计算分析

采用ANSYS软件对水平、竖直、桩基螺旋地埋管换热器进行建模。在定加热负荷、定入口水温两种设计工况下,对3种地埋管换热器的出口水温进行了数值计算,以评价地埋管换热器的换热性能。在设定条件下,竖直地埋管换热器的换热性能最优。     

U型地埋管换热器换热性能分析

为了探索U型地埋管换热器的换热规律,文章采用数值仿真模拟对二维U型地埋管换热器换热性能进行了分析,并模拟钻孔内、外换热过程。结果表明:钻孔内部瞬态换热模拟刚开始的少许时间内,温度变化仅发生在U型管附近,随着时间的增加,温度变化覆盖整个钻孔区域,U型管内水的温度与回填材料温度接近一致,系统趋于稳定;钻孔外部瞬态换热模拟之初,温度变化主要发生在钻孔内部,随着时间的推移,钻孔壁外温度逐渐降低,钻孔壁以内的温度逐渐增加,钻孔壁内、外温度接近一致,系统趋于稳定。     

灌注桩基埋管换热性能测试与对比分析

以江苏省昆山市地源热泵桩基一体化工程为研究对象,通过传统地埋管换热器与能量桩桩埋管换热器的换热试验对比,分别对传统并联双U垂直地埋管、并联双U灌注桩基埋管和并联双螺旋灌注桩基埋管等形式的换热器进行换热性能测试,得出3种埋管形式的平均换热量、单位管长平均换热量和单位埋管深平均换热量等因素的比对结果,并通过数据得出并联双U灌装桩基埋管换热器和并联双螺旋灌装桩基埋管换热器的每延米换热量分别是传统地埋管换热器的近2.5倍和5倍。     

竖直单U型地埋管传热模拟分析

针对地源热泵系统中的竖直单U型换热器的传热问题,利用FLUENT软件对其传热特性进行了稳态数值模拟。计算了管内流速,回填物导热系数,支管间距等因素对竖直单U型地埋管换热器换热性能的影响。通过数值模拟发现,管内流速过小时,地埋管换热器会出现严重的热短路现象。对比分析得出管内最佳流速为0.6 m/s～0.8 m/s;进回水支管间距越大,地埋管换热器换热性能越好;回填物的导热系数是影响地埋管换热器换热性能的一个重要因素,其最佳值与管内流速和管间距有关。综合考虑上述3个因素对地埋管换热器换热性能的影响,得出了支管间距为86 mm,管内流速为0.6 m/s～0.8 m/s,回填物导热系数为土壤导热系数的1～2倍时,竖直单U型地埋管的换热性能最好的结论。     

垂直地埋换热器非饱和岩土温度场分析

垂直地埋管换热器周围非饱和土壤的特性对埋管换热具有重要影响,目前地埋管换热器设计中多假设岩土为均匀介质,并未深入考虑非饱和岩土对埋管换热的影响。基于岩土的非饱和特性,通过数值模拟,对比分析岩土非饱和特性下温度响应的变化,为地埋管换热器设计提供更为准确模型。     

中深层套管式埋管换热性能的研究

地源热泵系统由于节能环保的优势广受关注。相较于传统的浅层地埋管换热器,中深层地埋管换热器具有单位面积取热量大、取热稳定等优势。本文建立了中深层套管式地埋管换热器的数值传热模型,对不同钻孔深度、岩土层导热系数、大地热流密度下,套管式地埋管换热器的换热性能进行了研究。并得出如下结论:加深钻井深度、岩土层导热系数分层递增、在土层导热系数分层递增的情况下大地热流密度越大,均能使得套管式地埋管换热器换热性能越好。研究结论可以为提高中深层地埋管地源热泵系统的换热性能提供一定参考价值和指导意义。     

桩基螺旋埋管换热器的沿程换热特性

建立了桩基螺旋埋管换热器的三维数值传热模型,研究了流体沿程换热特性和岩土温度分布特性。结果表明:桩基螺旋埋管换热器沿流动方向有进口、回填料热短路、小温差及出口4个换热阶段,每个换热阶段具有相应的换热特性;进行优化设计时,需控制小温差换热阶段的长度,增加其他换热阶段的长度,以提高螺旋埋管换热器的整体换热能力。     

广州与另两类地区埋地换热器换热性能的比较

本文将广州地区与另两类不同气候类型地区的埋地管换热器的换热性能进行了对比分析。结果表明,放热性能．广州地区比其它两类地区低;取热性能。广州处于中间位置。文中给出了取放热时,广州与另两类地区埋管换热器换热能力的相对大小数值．可为不同地区埋管换热器的设计提供参考。     

地埋管换热器合理钻孔深度的选取

分别针对竖直单U形、双U形地埋管换热器,建立地埋管换热器数学模型。选取工程中常采用的内直径分别为20、26、32 mm的单U形地埋管(简称单U20、单U26、单U32)、双U形地埋管(简称双U20、双U26、双U32),在设定条件下进行换热性能模拟分析,筛选管材造价、换热性能相对合理的埋设形式与管径,对合理的钻孔深度进行确定。单U26、双U20、双U26的管材造价、换热性能优势各异,应结合实际条件进行选取,3种地埋管换热器合理的钻孔深度分别为70~120 m、80~100 m、70~110 m。     

桩基螺旋地埋管换热器模型与换热性能研究

以线热源理论为基础,结合格林函数法中的持续热源法,建立了桩基螺旋地埋管换热器准三维模型,采用Matlab程序对模型进行编程计算。在设定条件下,分析了土壤热导率、土壤初始温度、螺旋地埋管螺距、桩基半径、管内流体流速对桩基螺旋地埋管换热器换热性能的影响。     

地源热泵地下单管在大连地区的实验研究

地源热泵以其环保特性越来越受到空调界的重视。地下埋管换热器是地源热泵研究的重点和难点之一,不同的地质条件会有不同的换热效果。因此,大连理工大学针对大连地区地质为岩石这一特点建立了地源热泵实验系统。由于单管换热特性足研究地源热泵地下埋管特性的基础,所以实验采用电加热器控制单管的进口水温,使其保持恒定,得出了75m埋深地下换热器夏季2小时内单独运行时在不同进口水温和水流量情况下的换热特性。     

地热换热器U型埋管的传热模型及热阻计算

讨论了地源热泵地热换热器竖直U型埋管钻孔内的二维稳态传热模型。基于钻孔内的温度场的二维解析解，得出钻孔热阻表达式。分析了影响钻孔热阻的几个相关因素，通过与一维简化模型得到的钻孔热阻相比较，认为采用二维模型可以为工程设计提供更准确可靠的热阻数据。     

Simulation of a domestic ground source heat pump system using a three-dimensional numerical borehole heat exchanger model

Common approaches to the simulation of borehole heat exchangers (BHEs) assume heat transfer in circulating fluid and grout to be in a quasi-steady state and ignore fluctuations in fluid temperature due to transport of the fluid around the loop. However, in domestic ground source heat pump (GSHP) systems, the heat pump and circulating pumps switch on and off during a given hour; therefore, the effect of the thermal mass of the circulating fluid and the dynamics of fluid transport through the loop has important implications for system design. This may also be important in commercial systems that are used intermittently. This article presents transient simulation of a domestic GSHP system with a single BHE using a dynamic three-dimensional (3D) numerical BHE model. The results show that delayed response associated with the transit of fluid along the pipe loop is of some significance in moderating swings in temperature during heat pump operation. In addition, when 3D effects are considered, a lower heat transfer rate is predicted during steady operations. These effects could be important when considering heat exchanger design and system control. The results will be used to develop refined two-dimensional models.     

地源热泵换热器随机传热及可靠性设计方法探讨

介绍了国内外地源热泵换热器技术的理论与试验研究现状,分析了地源热泵换热器传热基本理论,以及现有的各种常用传热设计理论和数值模型,并指出了确定性分析理论与设计方法存在的缺陷。针对地源热泵换热器的复杂实际工况,探讨了地源热泵换热器影响因素的随机特征,提出了地源热泵换热器的可靠度概念和定义、基于可靠性理论的地源热泵换热器研究方法,给出了地源热泵换热器设计步骤。     

Development of a numerical model to predict heat exchange rates for a ground-source heat pump system

Ground-source heat pump (GSHP) systems can achieve a higher coefficient of performance than conventional air-source heat pump (ASHP) systems. For the design of a GSHP system, it is necessary to accurately predict the heat extraction and injection rates of the heat exchanger. Many models that combine ground heat conduction and heat exchangers have been proposed to predict heat extraction/injection rates from/into the ground in the research field of heating, ventilation and air-conditioning systems. However, most analysis models are inaccurate in their predictions for long periods because they are based on a thermal conduction model using a cylindrical coordinate model or an equivalent diameter model. In this paper, a numerical model that combines a heat transport model with ground water flow and a heat exchanger model with an exact shape is developed. Furthermore, a method for estimating soil properties based on ground investigations is proposed. Comparison between experimental results and numerical analysis based on the model developed above was conducted under the conditions of an experiment from 2004. The analytical results agreed well with the experimental results. Finally, the proposed model was used to predict the heat exchange rate for an actual office building in Japan.     

土壤源热泵系统能效提升要素分析

随着近几年节能减排政策的不断出台,土壤源热泵的应用范围和项目规模不断扩大,但是由于设计、施工及运行中存在的各种原因,一些已经投入使用的土壤源热泵系统工程的节能效果并不如人意。因此,从系统的角度出发,全面分析土壤源热泵系统能效提升中需要把握的几个关键要素,包括:保证低位热源的能量平衡、提高机组自控级别、优化水力输配系统、减少热损失环节、因地制宜按质用能的配置辅助系统、选择适宜的"供冷高温化和供热低温化末端系统装置",以及加强运行监测管理及维护工作。通过这些对这些关键要素的把握,可以改善和提供土壤源热泵的能效情况,具有现实指导价值和意义。     

Modeling of foundation heat exchangers—Comparison of numerical and analytical approaches

Foundation heat exchangers (FHXs) are an alternative to more costly ground heat exchangers utilized in ground-source heat pump (GSHP) systems serving detached or semi-detached houses. Simulation models of FHX are needed for design and energy calculations. This paper looks at two approaches used for development of simulation models for FHX systems: a simplified analytical model and a detailed numerical model. The analytical model is based on superposition of line sources and sinks. The numerical model is a two-dimensional finite volume model implemented in the HVACSIM+ environment. Both the analytical and numerical models have been validated again experimental results from a test house located in Oak Ridge, Tennessee. Six geographically diverse locations are chosen for a parametric study; results of the two models are compared, and differences between the results are investigated.     

土壤源热泵系统的地埋管热平衡分析

主要针对土壤源热泵系统的垂直地埋管系统进行实际测试,从春夏秋冬4个季节分析单U管和双U管形式与土壤温度的关系,重点分析了土壤源热泵地埋管系统与土壤热平衡问题.     

基于线热源模型的地源热泵系统运行模拟

在比较地源热泵地埋管计算的2类线热源模型的基础上,本文采用有限长线热源模型与钻孔内热阻的准三维模型相结合的方式,在相应的建筑年逐时负荷条件下,进行地源热泵系统的逐时参数计算,通过与DST模型计算结果进行比较,验证了本文计算模型的准确性,为垂直U型地埋管的设计计算和热泵系统的运行模拟提供了必要的参考.     

地源热泵地埋管换热器传热研究(4):系统耦合运行特性

采取数值计算与解析计算相结合的方法,在构建地埋管换热器与地上机组耦合模型的基础上,研究了夏季变热流边界条件下单U形地埋管换热器与地上机组耦合运行的非稳态特性。分析了连续运行工况和间歇运行工况下地源热泵机组COP、单位管长换热量、埋管进出口流体温度及钻孔壁面平均温度随运行时间的变化规律。