共查询到20条相似文献,搜索用时 31 毫秒
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For the purpose of decreasing the peak electricity, balancing the on and off-peak electric load and utilizing the renewable geothermal energy, a new integrated system with cooling storage in soil and a ground-coupled heat pump is presented. In the integrated system, the moist soil acts as the material for cooling storage, and pipes serve as the cooling storage devices and geothermal heat exchangers simultaneously. In the cooling season, the cooling energy is stored in soil during the off-peak period and is extracted for space cooling during the on-peak period. While in other seasons, the system works as a ground-coupled heat pump for heating or cooling. A mathematical model which describes the charging and discharging processes of the integrated system has been developed and validated, and a computer code has been implemented to simulate the operational performance of cooling charging and discharging in soil. A parametric study indicates that the charging inlet temperature, tube diameter, moisture content of soil and pipe distance are important factors in determining the cyclic performance of the integrated system. 相似文献
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初步建立了土壤高温储热热湿迁移过程的数学模型,并进行了数值求解.结果表明,土壤热湿迁移过程中的湿度场稳定时间明显滞后于温度场,且与土壤类型和水力传导特性等有关.对于水力传导性较差的土壤,在高温储热初期,靠近热源的地方容易产生湿份聚集,使得湿度曲线出现一个短期峰值.与低温储热相比,土壤高温储热时湿度迁移对温度场的影响较大,温度场呈整体降低趋势,降低幅度顺序为:砂土>壤土>粘土.在该文模拟条件下,粘土的热湿迁移过程对于初始湿度的变化不敏感,而砂土的热湿迁移过程则依赖于初始湿度,且影响程度随着初始湿度的增加而增大. 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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《Applied Thermal Engineering》2014,62(1):256-266
A transient heat transfer model has been development for a thermal response test (TRT) on a vertical borehole with a U-tube. Vertical borehole heat exchangers are frequently coupled to ground source heat pumps, which heat and cool buildings. The model provides an analytical solution for the vertical temperature profiles of the circulating fluid through the U-tube, and the temperature distribution in the ground. The model is verified with data sets from a laboratory sandbox and field TRTs, as well as a previously reported numerical solution. Unlike previous analytical models, the vertical profiles for the circulating fluid are generated by the model without any assumption of their functional form. 相似文献
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《International Journal of Heat and Mass Transfer》2005,48(21-22):4579-4589
Mathematical model for describing simultaneous heat and moisture transfer in the porous soil with a dry surface layer was developed by using the volume-averaging method. Numerical simulation was conducted to investigate water evaporation, transient distributions of temperature and moisture in the porous soil at environmental conditions, which might be useful for agricultural application. In order to validate the mathematical model and numerical method, an experiment was conducted under natural environmental conditions. An additional experiment was conducted in a closed-loop wind tunnel to investigate the temperature effect on soil moisture transport. Theoretical and experimental results indicate that the dry surface layer has an important effect on heat and moisture migration in soil and the influence of temperature on moisture transport in unsaturated soil is significant. 相似文献
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The imbalance of heat extracted from the earth by the underground heat exchangers in winter and ejected into it in summer is expected to affect the long term performance of conventional ground source heat pump (GSHP) in territories with a cold winter and a warm summer such as the middle and downstream areas of the Yangtze River in China. This paper presents a new multi-function ground source heat pump (MFGSHP) system which supplies hot water as well as space cooling/heating to mitigate the soil imbalance of the extracted and ejected heat by a ground source heat pump system. The heat transfer characteristic is studied and the soil temperature around the underground heat exchangers are simulated under a typical climatic condition of the Yangtze River. A three-dimensional model was constructed with the commercial computational fluid dynamics software FLUENT based on the inner heat source theory. Temperature distribution and variation trend of a tube cluster of the underground heat exchanger are simulated for the long term performance. The results show that the soil temperature around the underground tube keeps increasing due to the surplus heat ejected into the earth in summer, which deteriorates the system performance and may lead to the eventual system deterioration. The simulation shows that MFGSHP can effectively alleviate the temperature rise by balancing the heat ejected to/extracted from underground by the conventional ground source heat pump system. The new system also improves the energy efficiency. 相似文献
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M. Piechowski 《国际能源研究杂志》1998,22(11):965-979
Validation of ground heat exchanger (GHE) model is presented using the experimental data obtained for both single and double pipe horizontal GHE. Sensitivity analysis of the GHE model shows the influence of the variation in the soil thermal conductivity, specific heat and density on the thermal performance of a GHE. Finally, the thermal performance of a GHE is analysed using both heat and mass transfer models, and conduction only model, as well as the influence of the initial soil moisture content on the thermal performance of a GHE. © 1998 John Wiley & Sons, Ltd. 相似文献
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This paper presents a new computerized procedure for dealing with the design of horizontal ground heat exchangers (HGHE). The computer program is based on the transient model of coupled nonlinear partial differential equations governing heat and mass flow in soils. The model is two-dimensional and delineates the operation of ground heat storage with the HGHE and such phenomena as freezing/thawing and drying/rewetting of soil moisture. Comprehensive climatological data, such as ambient temperature, solar radiation, wind velocity, rainfall, snowfall, snow characterstics, and water vapour pressure is used to simulate conditions at the ground surface over any required length of time. The package can be applied to any geographical location by changing climatic and soil data input. The designer has the possibility of selecting any of 12 types of soils from sand to clay, 12 commercial heat pumps, nine different configurations of the HGHE, 16 plastic pipes for ground coils, and 13 ground coil fluids. The program, however, does not calculate the length of the HGHE but it evaluates the thermodynamic performance of a ground heat pump system and provides comprehensive data on thermal and hydraulic conditions in ground heat storage. The length of the ground heat exchanger is obtained from a line source theory model or from site dimensions and pipe spacing. Computed results for ground heat exchanger operation correlate fairly well with experimental data. Simulation of temperature and moisture content in the ground for natural conditions (no heat extraction/deposition) showed a fair agreement with field data. The entire computer program is user-friendly, interactive, menu-driven, and written in FORTRAN 77. 相似文献
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A new complete numerical model for the prediction of thermal performance of the earth-to-air heat exchangers is presented. The model describes the simultaneous heat and mass transfer inside the tube and into the soil accounting for the soil natural thermal stratification. The model is validated against an extensive set of experimental data and it is found accurate. The proposed algorithms are suitable for the calculation of the temperature and humidity variation of the circulating air and for the temperature and humidity distribution inside the ground. The presented model was developed within the TRNSYS environment and can be easily coupled with building or greenhouse simulation codes in order to describe the impact of the earth-to-air heat exchangers to indoor environments. 相似文献
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V. R. Tarnawski 《国际能源研究杂志》1989,13(2):137-148
A one-dimensional model of ground heat storage is used to simulate complex heat and moisture processes in the vicinity of double-and single-layer ground heat exchangers. Simulated results indicate that a ground heat pump with the double-layer heat exchanger has certain advantages over the single-layer system in terms of a higher seasonal performance factor, smaller ground area, and reduced ecological risk in the soil subsurface region. Solar energy injection into the ground improves the seasonal performance factor both in the single and in the double layer heat exchanger system. Latent heat released by the freezing of soil moisture is an important component in the total amount of heat extracted from the ground when a phase change takes place. 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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Mohammad Hossein Jahangir Mahyar Ghazvini Josua P. Meyer 《Numerical Heat Transfer, Part A: Applications》2018,73(7):466-481
In this article, a numerical model for simulation of the heat and mass transfer phenomena in unsaturated soil is presented. The system is provided to evaluate its behavior as a thermal storage system. The model includes a single pipe that is buried under unsaturated media which is connected to a source with the constant heat rate of 20 W/m3 in sandy soils during a specific time. All the numerical results show good agreement with previous results, thus excellent correlation was achieved. Additionally, sensitivity analysis is done to clear up the role of the thermal and isothermal properties respect to volumetric water content and temperature and to assess the effects of related parameters on heat transfer in the media. The results show that as getting far away from the source, in addition to reduce the collected energy, the intensity of increasing the temperature and decreasing the moisture diminished will be more. Generally over time, the cumulative stored energy for each point will tend to a constant quantity. 相似文献
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The energy analysis of ground source heat pump systems is based on the instantaneous fluid temperature at the ground heat exchanger outlet. This temperature defines the ground source heat pump coefficient of performance (COP) and hence the electricity consumption required in order to fulfill the energy demands of the building. The aim of this work is to present a model able to predict the fluid temperature at the ground heat exchanger outlet, taking into account the heat transfer phenomena in the soil and the temporal variation of the thermal load of the ground heat exchanger. The model developed was verified using experimental data, expanding over a three years period, of a vertical ground heat exchanger. It is proved that the model is able to satisfactorily predict the recorded temperature values throughout the verification period. The differences between measured and estimated outlet water temperatures impose a deviation between the estimated and the actually recorded electricity consumption of less than 4%. 相似文献
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Efficiency of Vertical Geothermal Heat Exchangers in the Ground Source Heat Pump System 总被引:1,自引:0,他引:1
Taking the fluid temperature distribution along the borehole depth into account, a new quasi-three-dimensional model for vertical ground heat exchangers has been established, which provides a better understanding of the heat transfer processes in the geothermal heat exchangers. On this basis the efficiency of the borehole has been defined and its analytical expression derived. Comparison with the previous two-dimensional model shows that the quasi-three-dimensional model is more rational and more accurate to depict the practical feature of the conduction of geothermal heat exchanger, and the efficiency notion can be easily used to determine the inlet and outlet temperature of the circulating fluid inside the heat exchanger. 相似文献
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通过井筒向某地质结构内注入冷介质时,由于地温与冷介质之间存在温差,冷介质将通过井筒结构与土壤进行热量交换,最终导致冷介质冷量损失进而温度升高而达不到所需温度要求。因此,在施工前,需要对井筒进行冷量损失和沿井筒的温度分布的预测,为保冷结构设计以及井筒结构材料选型提供数据支持。由于注入冷介质的过程中,热量交换过程是一个非稳态传热过程,通常只能采用数值模拟来进行预测。为了简化数值模拟复杂的计算过程,采用准稳态的传热方法来构建单相冷介质通过井筒注入时的流动换热的物理数学模型,并开发了一个数值仿真软件。将仿真结果同商业软件FLUENT模拟结果进行了比较,表明温度分布和冷量损失基本一致,由此验证了所提模型的正确性和可靠性,为非工程热物理专业的工程技术人员提供能够预测低温工质在井筒流动与换热过程的仿真软件。 相似文献