Experimental Verification to Estimate Ground Thermal Conductivity Using Spiral Coil Type Ground Heat Exchangers

This paper presents an experimental study on the evaluation of thermal response of a spiral coil type GHE （ground heat exchanger）. This GHE was installed on partially saturated landfill ground that was composed of silt and clay in the runway area of Incheon International airport. TRT （thermal response test） was conducted for more than 65 hours under continuous operation conditions. Ground thermal conductivity was derived based on line source theory, which has usually been found to be appropriate for line type GHEs such as U, W and 2U types. A reasonable method to derive ground thermal conductivity using the infinite line source theory for a spiral coil type GHE was introduced. Ground thermal conductivity from the TRT using spiral coil type GHE was compared with those from the analytical equivalent model of ground thermal conductivity.

Theoretical and Experimental Study on Ground Coupled Heat Pump with Vertical Spiral Coil

The numeric al simulation study on the temperature distribution of underground field for the ground coupled heat pump (GCHP) with vertical spira l coil was carried out by using finite element. The distribution and recovery of undergroun d field temperature under different operation ratio and the optimal operation ratio were simulated.The performance parameters, i.e. inlet and outlet temperature of the ground spiral coil in heating and cooling modes were tested, the heat extracted or emitted by the heat pump to the ground was calculated, and the coefficients of performance (COP) of GCHP at heat ing and cooling modes were analyzed.

Numerical Simulation of Heat Transfer Characteristics of Horizontal Ground Heat Exchanger in Frozen Soil Layer

A simplified numerical model of heat transfer characteristics of horizontal ground heat exchanger (GHE) in the frozen soil layer is presented and the steady-state distribution of temperature field is simulated. Numerical results show that the frozen depth mainly depends on the soil′s moisture content and ambient temperature. The heat transfer loss of horizontal GHE tends to grow with the increase of the soil′s moisture content and the decrease of ambient temperature. Backfilled materials with optimal thermal conductivity can reduce the thermal loss effectively in the frozen soil. The applicability of the Chinese national standard “Technical Code for Ground Source Heat Pump (GB 50366-2005)” is verified. For a ground source heat pump project, the feasible layout of horizontal GHE should be determined based on the integration of the soil′s structure, backfilled materials, weather data, and economic analysis.

Experimental Analysis of Horizontal Ground Heat Exchanger for Northern Tunisia

The aim of this study is first to evaluate the Tunisian geothermal energy and second to test the performance of horizontal ground heat exchanger. An experimental set-up has been constructed for climatic condition of Borj Cedria located in the north of Tunisia for space cooling. Results obtained during experiment were presented and discussed. The ground temperature at several depths was measured, the overall heat transfer coefficient (U) was determined. To evaluate the system efficiency, the energy analysis was applied;the energy efficiency was found to range from 14% to 28%. The heat exchange rate was quantified, the pressure losses were calculated. The total heat rejected by using the ground heat exchanger (GHE) system was compared to the total cool requirements of a tested room with 12 m2 surface. The results showed that the GHE, with 25 m of length buried at 1 m depth, covers 38% of the total cool requirement of the tested room. This study showed that the ground heat exchanger provide a new way of cooling buildings, it also showed that Tunisia have an important thermal potential. This favorable circumstance allows Tunisia to be a pioneer in the exploitation of geothermal energy for the installation of ground source heat pump systems.

Fluid flow and heat transfer characteristics of spiral coiled tube: Effects of Reynolds number and curvature ratio

Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12n. As the varying radius of curvature became a dominant flow parameter, three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field. From the analysis, centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer. The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube. Even then, friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number. Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.

Experiments Using Capillary Mat as Ground Heat Exchanger for Ground Source Heat Pump Heating Application

The cooling and heating of spaces are among the largest sources for household’s energy demand. Ground Source Heat Pump (GSHP) is a promising technology to reduce the energy for cooling and heating purposes. However, the major obstacle hindering the utilization of this technology is the high initial cost, especially for the installation of ground coupled heat exchanger. The horizontal closed-loop system offers lower installation cost, as it requires no vertical borehole construction. Instead, the heat exchangers can be installed in shallow trenches that may be excavated, by small excavator or even by human labor. This paper presents the comparison of two different heat exchangers, namely, the capillary mat and the widely used slinky pipe. Both heat exchangers are connected to a heat pump, where continuous heating tests were carried out for 165 hours (~7 days) for each configuration. The purpose of this research is to show the performance of capillary mat in comparison to slinky pipe. Despite during the entire test for capillary mat required 6% higher electricity consumption, compared to slinky heat exchanger, the results still suggest the potential use of capillary mat as alternative to slinky heat exchanger. Additionally, the results also highlight the high hydraulic resistance of installed capillary mat heat exchangers may become the major disadvantage of the capillary mat.

水平多层spiral型地埋管数值模拟研究及换热特性分析

本文基于COMSOL软件建立了水平spiral型多层地埋管群传热三维数值模拟模型,并对其换热性能和温度场进行分析研究。结果表明:对比水平spiral多层并联管群来说,远离注入端的地埋管管内温度相对较低。地埋管群周围地层温度有所升高,远离注入端的地层温度变化相对较小。地埋管群的换热量随循环流体的流速增加而增加,但增幅降低。在进行换热器设计时,应合理控制循环水的流速。3层螺旋地埋管群的换热量略高,但层间干扰明显,建议选用2层并联螺旋管群。

不同螺旋缠绕异形管换热器壳程性能数值研究

缠绕管的形状对螺旋缠绕管换热器的传热能力有重要影响,本文建立了具有不同截面形状的螺旋缠绕管换热器模型,数值研究了八种不同截面形状的缠绕管对螺旋缠绕管换热器壳程流动与传热性能的影响。相比于传统圆管,三叶管和水滴管对壳程流体造成的扰动较大,增强了螺旋缠绕管换热器的综合换热性能,而三叶管则具有最大换热能力。进一步分析了不同冲刷方式对螺旋三叶管换热器和螺旋水滴管换热器壳程性能的影响,结果表明:在相同的进口工况下,螺旋三叶管换热器壳程努塞尔数相比于传统圆管提高了11.8%~15.5%,阻力系数增大了41.9%~49.6%;螺旋水滴管换热器壳程努塞尔数相比于传统圆管提高了2.8%~4.3%,阻力系数增大了3.2%~6.8%;在雷诺数为2 603~5 206的工况条件下,管截面与流动方向夹角为0°的三叶管换热器综合换热性能最好,而管截面与流动方向呈逆流形式的水滴管换热器综合换热性能优于顺流形式。

铅-超临界二氧化碳换热器耦合流动传热特性研究

为探究螺旋盘管式主换热器内的耦合流动传热机理,基于等长度分段模型,构建了以液态铅和超临界二氧化碳为工质的螺旋盘管式主换热器原型及模化比例样件的理论设计方法,并利用相似性原理完成了主换热器小比例样件设计。以主换热器小比例样件为研究对象,通过SST k-ω湍流模型数值分析了液态铅和超临界二氧化碳在螺旋盘管换热器内的流动传热特性。计算结果表明:螺旋盘管换热器内耦合流动传热性能主要受壳侧质量流量、管侧质量流量和壳侧工质入口温度影响;管侧超临界二氧化碳质量流量对螺旋盘管换热器内耦合流动传热性能的影响最为显著,在超临界二氧化碳质量流量增加52.4%的条件下,螺旋管的平均表面换热系数增大了21.2%;在壳侧液态铅的质量流量和入口温度分别增大94.6%、20 K的情况下,螺旋管内的表面传热系数分别增大了5.5%、3.3%。该研究可为螺旋盘管式换热器的工况选择和高效设计提供理论指导。

超强吸水树脂与源土混合作为地源热泵供热系统回填材料的实验研究

在热泵制热工况下,超强吸水树脂与源土混合作为回填材料,分别对螺旋盘管、U型管以及整个系统进行了实验研究,得出系统性能变化曲线。实验结果表明,超强吸水树脂与源土混合作为回填材料,特别是螺旋盘管换热器,可明显增大地下换热器换热量,提高地源热泵系统的效率和稳定性,适用于干旱、土壤非饱和以及地下水位比较低的地区。

地源热泵地下环路的设计方法

介绍了地热换热器的形式 ,提出了竖直埋管地热换热器的设计方法及地下环路循环泵的选择方法。

水平埋管周围土壤温度场数值模拟研究

建立了应用于地源热泵系统的水平埋管的传热数学模型,并采用 ANSYS 软件模拟了埋深为 3 m 的水平埋管在冬夏运行工况下周围土壤的温度场变化。根据选取的特定时间比较了单管和双管水平埋管在相同工况下周围土壤温度场,得出各自的影响半径,为水平埋管换热器的埋设提供了参考。

闭环地源热泵系统设计研究

闭环地源热泵系统与传统空调系统的区别在于增加了地热换热器,因此地热换热器的合理设计是提高热泵系统效率和经济性的关键.文章介绍了地热换热器的形式,提出了竖直埋管地热换热器的传热模型、设计方法以及地下环路循环泵的选择方法.

严寒地区土壤源热泵地下水平埋管换热性能影响研究

针对严寒地区地源热泵水平埋管换热器的传热规律及其制约因素,建立加土壤保温层水平埋管换热器周围土壤不稳定温度场的物理和数学模型,并对所建立的模型进行模拟计算及实验验证。研究加保温层前后埋管周围土壤的温度变化以及不同运行方式下埋管周围土壤的温度场。结果显示:加土壤保温层后,单埋管换热器周围土壤温度提高1.30℃,双埋管换热器周围土壤温度提高约1.20℃。间歇运行比连续运行更有利于土壤温度的恢复,埋管换热量也得到提高。

气象波动对水平埋管换热器传热影响的数值模拟

应用气象学方法和传热传质理论,建立考虑气象因素和土体传热共同作用的大气-土壤相互作用模型;针对桂林红粘土地层,模拟分析气象波动对水平埋管换热器传热的影响。研究结果表明：1）在1.0～2.0 m埋深范围内,水平埋管换热器的换热效果明显受到地表气象波动的影响,大气温度、蒸发、辐射是主要因素;2）对于红粘土地层,降雨形成的浅层渗流对换热效果的提高幅度约为5.6%;3）通过开展不同设计埋深及埋管间距的换热效果分析,确定桂林红粘土地区水平埋管布置方式的合理值：埋深为2.5 m,埋管间距为2.0 m。

地源热泵中U型埋管传热过程的数值模拟

以钻孔壁为界将U型埋管的换热区域划分为钻孔内外两部分,并分别采用稳态与非稳态传热来分析求解,两区域模型间通过钻孔壁温耦合连接,以构成完整的埋管传热模型.对于钻孔以外部分,采用变热流圆柱源模型来求解钻孔瞬时壁温.钻孔以内部分,在考虑埋管流体温度的沿程变化及U型管2支间热干扰的基础上,基于能量平衡建立了钻孔内U型埋管的稳态传热模型.用所建U型埋管传热模型对地源热泵系统的运行特性进行了动态模拟,得出了埋管出口流体温度、钻孔瞬时壁温、单位埋管吸热量及热泵COP随运行时间的变化规律.所建埋管模型可为地源热泵系统的动态模拟、优化设计及其改进提供参考.

地源热泵桩基螺旋埋管换热性能实验研究

实验研究了不同螺旋形式和流速对桩基螺旋埋管换热性能的影响。结果显示,不同埋管方式导致埋管的换热热阻不同,螺距越小,热阻越大,单螺旋埋管的热阻比三螺旋小34.58%,双螺旋的比三螺旋小25.71%;管内流速越大,热阻越小,单螺旋埋管0.8m/s工况时的热阻比0.6,0.4m/s工况分别小3%和9%;当管内为湍流时,流速对单位管长换热量的影响较小。

桩埋螺旋管式地热换热器的传热模型

针对现有桩埋管地热换热器构造形式的不足,提出了桩埋螺旋管式地热换热器。在分析竖直钻孔埋管地热换热器传热模型的基础上,提出了适合桩埋螺旋管式地热换热器的实心圆柱面热源模型,并用格林函数法求得了该模型的两个一维解析解表达式。计算分析表明:新的实心圆柱面模型不仅适用于桩埋螺旋管换热器的传热分析,在应用于竖直钻孔埋管地热换热器的短时间传热分析时,也优于传统的线热源模型和空心圆柱面模型。

制冷工况下水平埋管换热器运行试验研究

通过夏季工况的地源热泵运行试验,对运行过程中水平埋管的换热性能参数、试验场地周围气象因素和换热过程中土体的温湿度变化等因素进行实时监测,探讨了地源热泵运行过程中水平埋管换热器热交换性能及其周围土壤的温、湿度场变化规律。研究结果表明,地源热泵间隙运行有利于土壤温度场的恢复,随着停机时间的增加,水平埋管与周围土壤的热交换能力明显提高;气候变化对水平埋管周围土壤的温度场分布具有显著影响,随着埋深的递减,土壤温度受气候变化的影响越明显;水平埋管周围土壤温度的变化幅度随着与埋管距离的增加呈递减趋势,其影响半径为1.0m左右;热交换对水平埋管周围土壤湿度场的影响不明显,但大气降雨引起的地表水入渗对土壤湿度场的分布具有显著影响。

水平埋管换热器地热源热泵实验研究及传热模型

介绍了于 1 998年所建成的埋深分别为 0 .9m和 1 .8m的双层水平埋管地热源热泵系统 ,内容包括实验装置、换热器几何尺寸、测试仪表及测试数据的处理方法等 ,并用典型日分析了该系统的制冷和制热性能。同时 ,又对影响地热源热泵系统性能的诸多因素中的埋管尺寸及热泵运行方案等因素作了分析。另外 ,本文参考 VC.