共查询到19条相似文献,搜索用时 250 毫秒
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介绍了土壤源热泵竖直埋管换热器钻孔外的传统的无限长线热源模型,无限长圆柱模型,有限长线热源模型以及改进后的热湿传递的线热源模型,变热流的线热源模型,土壤分层的线热源模型。分析了各种模型之间的联系、区别以及优缺点。提出了完善土壤源热泵竖直埋管换热器钻孔外传热模型需进一步研究的内容。 相似文献
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对地热换热器竖直埋管的非稳态传热模型进行了分析讨论。采用虚拟热源和格林函数法给出了半无限大介质中有限长线热源产生的非稳态温度场的解析解表达式。与稳态温度场的解进行比较,讨论了温度场达到名义上的“稳态”所需的时间,同时对于达到稳态时的温度场也进行了分析,指出了现行教科书中关于该问题的错误,提出了稳态时两个地热换热器孔壁代表性温度的定义,并对两者进行了比较,进而给出了可供工程应用的简化计算公式,并对两者进行了比较,进而给出了可供工程应用的简化计算公式。基于以上分析,进一步讨论了全年冷热负荷不平衡对地热换热器长期性能的影响。 相似文献
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地下水运动对地埋管换热器具有重要的影响,通过对比分析渗流无限长与有限长线热源模型,指出考虑轴向传热的有限长线热源更为合理。基于温度场的叠加原理,建立渗流有限长线热源的管群换热模型,并通过耦合管内流体流动,构建管群换热的优化模型。采用位置布置优化措施后,18孔梅花布置比16孔正方形布置的面积利用率提高12.5%,承担相同的负荷其系统的COP值提高7%-10%;16孔管群采用负荷分配优化策略后,其管群的土壤温度场不平衡率大大降低,管群平均温度约降低7.6%,COP提高约10%。 相似文献
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针对双螺旋或多螺旋换热器的非稳态传热问题,提出一种获得换热器水箱温度分布的解析解模型。该模型将水箱传热问题简化为基于线圈模型的有限大空间内的二维绝热边界传热问题。采用虚拟热源法和热源温度场叠加法,推导出有限长线圈热源在有限大绝热空间内进行非稳态导热的水箱温度场解析解表达通式。以直热式空气源热泵热水器为例,在不同环境温度条件下,对蓄热水箱的非稳态温度场进行实验测量,实验结果与理论解析解模型获得的计算结果一致,从而验证解析解模型的可靠性和准确性。该文提出的螺旋换热器水箱导热解析解模型为研究该问题提供一种快捷而有效的分析方法。 相似文献
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建立了垂直埋管地源热泵地热换热器的传热模型,采用有限差分法建立了垂直U型埋管换热器瞬态传热模型的解析解;并且在不同的工况下进行实验测试,与模拟结果进行了对比,结果表明模拟与实验能较好地吻合,从而使模型的正确性得到了验证。可为地源热泵的设计和运行提供理论指导。 相似文献
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Nairen Diao Qinyun Li Zhaohong Fang 《International Journal of Thermal Sciences》2004,43(12):1223-1211
In order to estimate the impact of groundwater flow on performance of geothermal heat exchangers in ground source heat pump systems, an equation of conduction–advection is established for heat transfer in porous media, and an analytical transient solution is obtained for a line heat source in an infinite medium by means of the Green function analysis. An explicit expression has also been derived of the mean temperature on circles around the heat source. Dimensionless criteria that dictate the process are summarized, and influence of the groundwater advection on the heat transfer is discussed accordingly. Computations show that water advection in the porous medium may alter significantly the conductive temperature distribution, result in lower temperature rises and lead to a steady condition eventually. The hydraulic and thermal properties of soils and rocks influencing the advection heat transfer are briefly summarized. The analytical solution has provided a theoretical basis and practical tool for design and performance simulation of the ground heat exchangers. 相似文献
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A large number of ground-coupled heat pump (GCHP) systems have been used in residential and commercial buildings throughout the world due to the attractive advantages of high efficiency and environmental friendliness. This paper gives a detailed literature review of the research and developments of the vertical-borehole GCHP technology for applications in air-conditioning. A general introduction on the ground source heat pump system and its development is briefly presented first. Then, the most typical simulation models of the vertical ground heat exchangers currently available are summarized in detail including the heat transfer processes outside and inside the boreholes. The various design/simulation programs for vertical GCHP systems primarily based on the typical simulation models are also reviewed in this paper. Finally, the various hybrid GCHP systems for cooling or heating-dominated buildings are well described. It is found that the GCHP technology can be used both in cold and hot weather areas and the energy saving potential is significant. 相似文献
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In ground-coupled heat pump systems, accurate prediction of transient ground heat transfer is important to establish the required borehole length and to determine precisely the resulting fluid temperature. Three analytical solutions to transient heat transfer in the vicinity of geothermal boreholes are presented. These solutions are referred to as the infinite line source (ILS), the infinite cylindrical source (ICS) and the finite line source (FLS) models, which vary in complexity and are based on simplifications of the borehole geometry. The results of these models are compared and their validity domains are determined. 相似文献
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A two-region simulation model of vertical U-tube ground heat exchanger and its experimental verification 总被引:2,自引:0,他引:2
Heat transfer around vertical ground heat exchanger (GHE) is a common problem for the design and simulation of ground coupled heat pump (GCHP). In this paper, an updated two-region vertical U-tube GHE analytical model, which is fit for system dynamic simulation of GCHP, is proposed and developed. It divides the heat transfer region of GHE into two parts at the boundary of borehole wall, and the two regions are coupled by the temperature of borehole wall. Both steady and transient heat transfer method are used to analyze the heat transfer process inside and outside borehole, respectively. The transient borehole wall temperature is calculated for the soil region outside borehole by use of a variable heat flux cylindrical source model. As for the region inside borehole, considering the variation of fluid temperature along the borehole length and the heat interference between two adjacent legs of U-tube, a quasi-three dimensional steady-state heat transfer analytical model for the borehole is developed based on the element energy conservation. The implement process of the model used in the dynamic simulation of GCHPs is illuminated in detail and the application calculation example for it is also presented. The experimental validation on the model is performed in a solar-geothermal multifunctional heat pump experiment system with two vertical boreholes and each with a 30 m vertical 1 1/4 in nominal diameter HDPE single U-tube GHE, the results indicate that the calculated fluid outlet temperatures of GHE by the model are agreed well with the corresponding test data and the guess relative error is less than 6%. 相似文献
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Despite ground source heat pump has been proven as highly efficient, high initial cost discourages homeowners and small-medium enterprises to opt for such systems. Horizontal ground heat exchangers offer relatively low-cost solution that may help promoting these systems usage worldwide. This study examines ways to optimize the designs for horizontal ground heat exchangers by using different layouts and pipe materials. CFD simulation of three dimensional models was performed to achieve this objective. All cases tested are able to yield comparable heat exchange rate for an equal trench length. However, the effective period differs one from the other. Additional initial and overhead costs are worthy as slinky ground heat exchangers prolongs heat transfer process when compared against straight configuration. Pipe materials with superior thermal conductivity also promote longer high efficiency operation. An improvement of 16% is reported when copper pipe is used instead of the conventional HDPE pipes. Effective period can be extended by 14% when ground heat exchangers are installed in vertical orientation. Thermal interference in slinky configuration is prevalent during initial operation. In a long run, the effect is observed to be minimal except in vertical orientation. However, it is avoidable beforehand at design stage. 相似文献
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One‐dimensional transient heat conduction in a bilayer finite slab: A case study in the printing process
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In this work, a typical case of heat distribution is examined during a paper printing process, based on one‐dimensional transient heat conduction in two‐layer finite slabs with an insulated free surface, and a constant temperature free surface. Analytical solutions were obtained in non‐dimensional form. Various examples of applying these solutions are presented. The accuracy of the solutions, with respect to time, is analyzed considering the eigenvalues of their infinite solutions. It is observed that the larger the number of eigenvalues in consideration, the better the accuracy of the solutions. The model related to a two‐layer slab describes the simplified case in which all heat transfer occurs only by conduction. The solutions obtained are finally compared with the solutions for heat conduction in two semi‐infinite solids. The comparison between the two solutions shows that results are in good agreement only during short time scales. The heat distribution study is expected to be helpful in knowing the effectiveness of various mediums to be used as the reciever during the printing process; however, there is scope for development of more robust models. 相似文献
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This paper investigates the transient heat conduction around the buried spiral coils which could be applied in the ground-coupled heat pump systems with the pile foundation as a geothermal heat exchanger. A transient ring-coil heat source model is developed, and the explicit analytical solutions for the temperature response are derived by means of the Green’s function theory and the image method. The influences of the coil pitch and locations are evaluated and discussed according to the solutions. In addition, comparisons between the ring-coil and cylindrical source models give that the improved finite ring-coil source model can accurately describe the heat transfer process of the pile geothermal heat exchanger (PGHE). The analytical solutions may provide a desirable and better tool for the PGHE simulation/design. 相似文献
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Improving parameter estimates obtained from thermal response tests: Effect of ambient air temperature variations 总被引:1,自引:0,他引:1
This paper presents a method of subtracting the effect of atmospheric conditions from thermal response test (TRT) estimates by using data on the ambient air temperature. The method assesses effective ground thermal conductivity within 10% of the mean value from the test, depending on the time interval chosen for the analysis, whereas the estimated value can vary by a third if energy losses outside the borehole are neglected. Evaluating the same test data using the finite line-source (FLS) model gives lower values for the ground thermal conductivity than for the infinite line-source (ILS) model, whether or not heat dissipation to ambient air is assumed. 相似文献