共查询到20条相似文献，搜索用时 31 毫秒
1.
A simple three-dimensional heat transfer model is developed to consider the hindering effect of cracks on heat transfer. The 3D heat transfer model can also be applied to numerical methods such as the combined finite-discrete element method (FDEM), discrete element method (DEM), discontinuous deformation analysis (DDA), the numerical manifold method (NMM), and the finite element method (FEM) to construct thermo-mechanical coupling models that allow these methods to solve thermal cracking problems and dynamically consider the hindering effect of cracks on heat transfer. In the 3D heat transfer model, the continuous-discontinuous medium is discretized into independent tetrahedral elements, and joint elements are inserted between adjacent tetrahedral elements. Heat transfer calculations for continuous-discontinuous media are converted to heat conduction in tetrahedral elements and the heat exchange between the adjacent tetrahedral elements through the joint element. If the joint element between adjacent tetrahedral elements breaks (ie, a crack generates), the heat exchange coefficient of the joint element is reduced to account for the hindering effect of cracks on heat conduction. Then the model and the FDEM are combined to build a thermo-mechanical coupling model to simulate thermal cracking. The thermally induced deformation, stress, and cracking are investigated by the thermo-mechanical coupling model, and the numerical results are compared with analytical solutions or experimental results. The 3D heat transfer model and thermo-mechanical model can provide a powerful tool for simulating heat transfer and thermal cracking in a continuous-discontinuous medium. 相似文献
2.
A geometrical model, including different geometrical shapes influencing thermal conductivity of snow is proposed. The geometrical
model has been assumed to comprise of unit cells having solid (ice) inclusion as an aggregation of spherical, cylindrical
or cubical shapes with vertical connection, arranged in a cubic packing. From the geometrical model and one-dimensional heat
transfer theory, the effective thermal conductivity has been computed. For this purpose, coupled one-dimensional heat transfer
equations have been solved for steady-state condition to account for conduction in ice, conduction in air and latent heat
transfer due to water vapour sublimation through air. The model demonstrates the dependency of thermal conductivity on density,
grain-spacing, grain contact ratio and temperature. Spherical inclusions give highest conductivity while cubical inclusion
estimates lowest value for the same density. Thermal conductivity has been found increasing sharply near to the packing density
for all three shapes. Empirical model results and results obtained from existing microstructure based models have also been
compared with the present model. 相似文献
3.
增强型地热系统(EGS)中高温岩石与流体之间的对流换热特征一直以来是干热岩(HDR)研究的重要基础内容。岩石导热热阻对裂隙对流换热特征具有重要影响。为研究其具体影响,综合运用理论解析与数值模拟2种研究方法,通过对解析解讨论以及建立数值模型,研究两平行光滑平板之间的换热规律。结果表明：流体速度、传热边界层充分发展时,局部努塞尔特准数Nux为定值,与其他因素无关;局部对流换热系数hx仅与流体热导率k和裂隙开度e有关,与其他因素无关。上下平板壁面热流恒定时,Nux为8.235;温度恒定时,Nux为7.54。然后建立多组导热热阻不同的岩石裂隙对流换热数值模型,发现岩石导热热阻增大,温度场进口段延长,对流换热系数h增大。岩石长度显著影响进口段占比,进而影响h的大小。h随着长度增大而减小;当岩石长度足够长时,进口段占比足够小,此时除k与e之外的参数对h基本没影响。并且发现实验室常用岩石长度为100 mm,而典型EGS工程中裂隙长度是米级的,建议室内实验重视岩石长度对裂隙对流换热特征的影响。 相似文献
4.
多年冻土是含有冰的特殊土体,在自然环境变化及工程扰动下易发生冻胀融沉变形,严重威胁着青藏高原工程建筑物的安全稳定,特别对青藏铁路的畅通运营提出了严峻挑战。以青藏铁路五道梁地区路基断面为研究对象,采用颗粒离散单元法,通过建立热-力离散元计算模型,对路基的温度场和变形进行了计算和预测。结果表明：离散单元法克服了有限元方法无法模拟颗粒间导热与接触粘结作用的瓶颈,能够从微观层面阐释宏观变化,较为真实地反映冻土的导热和力学变形;离散单元法数值计算分析发现,随着运营时间的增加,路基存在冻土退化问题,而且路基中颗粒间热交换复杂,在0 ℃等温线区域和路基坡脚处,颗粒间相互作用更为突出。热-力耦合离散元为冻土工程研究提供了新思路,可更好地为寒区工程服务。 相似文献
5.
This paper describes a three-dimensional random network model to evaluate the thermal conductivity of particulate materials. The model is applied to numerical assemblies of poly-dispersed spheres generated using the discrete element method (DEM). The grain size distribution of Ottawa 20–30 sand is modeled using a logistic function in the DEM assemblies to closely reproduce the gradation of physical specimens. The packing density and inter-particle contact areas controlled by confining stress are explored as variables to underscore the effects of micro- and macro-scales on the effective thermal conductivity in particulate materials. It is assumed that skeletal structure of 3D granular system consists of the web of particle bodies interconnected by thermal resistor at contacts. The inter-particle contact condition (e.g., the degree of particle separation or overlap) and the particle radii determine the thermal conductance between adjacent particles. The Gauss–Seidel method allows evaluation of the evolution of temperature variation in the linear system. Laboratory measurements of thermal conductivity of Ottawa 20–30 sand corroborate the calculated results using the proposed network model. The model is extended to explore the evolution of thermal conduction depending on the nucleation habits of secondary solid phase as an anomalous material in the pore space. The proposed network model highlights that the coordination number, packing density and the inter-particle contact condition are integrated together to dominate the heat transfer characteristics in particulate materials, and allows fundamental understanding of particle-scale mechanism in macro-scale manifestation. 相似文献
6.
A modeling study was carried out to evaluate the influence of aquifer heterogeneity, as represented by geologic layering, on heat transport and storage in an aquifer thermal energy storage (ATES) system in Agassiz, British Columbia, Canada. Two 3D heat transport models were developed and calibrated using the flow and heat transport code FEFLOW including: a “non-layered” model domain with homogeneous hydraulic and thermal properties; and, a “layered” model domain with variable hydraulic and thermal properties assigned to discrete geological units to represent aquifer heterogeneity. The base model (non-layered) shows limited sensitivity for the ranges of all thermal and hydraulic properties expected at the site; the model is most sensitive to vertical anisotropy and hydraulic gradient. Simulated and observed temperatures within the wells reflect a combination of screen placement and layering, with inconsistencies largely explained by the lateral continuity of high permeability layers represented in the model. Simulation of heat injection, storage and recovery show preferential transport along high permeability layers, resulting in longitudinal plume distortion, and overall higher short-term storage efficiencies. 相似文献
7.
对于场地受限的地下水源热泵项目,随着系统运行时间的增加易引发热贯通现象进而降低机组运行效率。地下水源热泵设计中,在抽灌水井连线间布设热屏障井可改变地下水流场,降低热量在抽灌井间的运移速度,有利于延长热贯通发生时间并缓解热贯通程度。通过构建地下水换热模型,模拟计算夏季制冷工况条件下36组热泵运行场景,分析了热屏障井的位置,过滤管长度及回灌量对热贯通和含水层温度场的影响规律。结果表明:热屏障井回灌量的增加有利于提升热屏障效果,但提升幅度随回灌量的增加逐渐减弱;最大水位降深值随着热屏障井回灌量的增加呈线性增长;增加热屏障井滤管长度可提升热屏障效果,提升效果随屏障井回灌量的增加逐渐增强。通过模型多周期、长时间模拟计算发现,热屏障井的运行可促使回灌的冷热量集中在回灌井一侧,对于采用冬夏季抽灌井交换运行模式的热泵系统,可充分利用含水层储能,提升机组运行效率。 相似文献
8.
地铁隧道围岩内温度分布规律的模型试验及其热导率反算研究 总被引：1，自引：0，他引：1
为能精确计算地铁隧道围岩内的传热量,模拟了地铁隧道围岩内的热传导,研究了地铁围岩内的温度分布规律,并通过试验结果对土体热导率进行反算。分析表明：同一时刻,距隧道壁面不同距离处的温度以指数形式进行变化,距离越远,温度越小;时间越久,隧道内流体的温度影响范围越大。除隧道外壁面外,距隧道壁某距离处的温度,随时间的增长而逐渐增长,距隧道壁较近处土体温度较高,温度增长速率随时间的增长而逐渐减小;距隧道壁面距离较远处温度较低,其增长速率随时间的增长而逐渐增大。传热时间超过某一值后,围岩内温度增长率逐渐平稳趋于一定值。根据模型试验结果能较精确得到土样的热导率数值。 相似文献
9.
为研究填充裂隙水流速度对岩体温度和应力的影响，选取甘肃北山地区的花岗岩，制作了稀疏非正交裂隙岩体模
型，采用河砂填充裂隙后进行模型试验；并对模型试验进行离散元数值模拟，分析了模型试验所测岩体温度和热应力与数
值模拟结果的差异和原因。结果显示：填砂裂隙强化了裂隙介质的热导能力，无填充时岩体温度和热应力比填砂时低；模
型试验和离散元模拟均表明，岩体温度和岩体应力随裂隙水流速度增大而减小，但是系统达到稳态所需要的时间变短；模
型试验中斜裂隙水流对温度场起主要作用；由于现有3DEC软件不能考虑水的热物性参数随温度的变化，进而产生自然对
流换热，斜裂隙水流和靠近热源侧的竖裂隙水流对温度场起主要作用。 相似文献
10.
为研究填充裂隙水流速度对岩体温度和应力的影响,选取甘肃北山地区的花岗岩,制作了稀疏非正交裂隙岩体模
型,采用河砂填充裂隙后进行模型试验;并对模型试验进行离散元数值模拟,分析了模型试验所测岩体温度和热应力与数
值模拟结果的差异和原因。结果显示：填砂裂隙强化了裂隙介质的热导能力,无填充时岩体温度和热应力比填砂时低;模
型试验和离散元模拟均表明,岩体温度和岩体应力随裂隙水流速度增大而减小,但是系统达到稳态所需要的时间变短;模
型试验中斜裂隙水流对温度场起主要作用;由于现有3DEC软件不能考虑水的热物性参数随温度的变化,进而产生自然对
流换热,斜裂隙水流和靠近热源侧的竖裂隙水流对温度场起主要作用。 相似文献
11.
长期非稳态的桩土热交换使得桩周土温度不断上升,产生热堆积效应,影响桩土换热效率,甚至也可使能源桩系统失效。为此,利用复合相变材料制备了相变混凝土能源桩,并在饱和粉土中开展了相变桩和普通桩热力响应模型试验,对比研究了相变桩的桩周温度分布、桩身应力−应变、桩顶位移和桩身换热效率的变化规律。结果表明：相变桩土热交换方向以径向交换为主,影响区域在2D范围以内,土体温度变化表现出滞后效应;相变桩的桩土温度变化幅度小于普通桩,具有缓解桩周土体热堆积效应的作用;在温度循环过程中,相变桩体累积了不可恢复的塑性应变。经过多次温度循环后,相变桩比普通桩的塑性累积位移更小;在夏季工况相变桩换热功率比普通桩增长约20%,冬季工况两者换热功率基本一致,随着运行时间增加,两者换热效率趋同。 相似文献
12.
针对新技术热排水固结法,采用非等温管道流模拟竖井中U型导热管的传热过程,考虑温度对竖井扰动区和未扰动区渗透性的影响,在COMSOL Multiphysics有限元软件中进行二次开发,建立了竖井地基热排水固结法的有限元模型。以热排水固结软基处理原型试验为例,重点分析了模型耦合、部分耦合和不耦合情况下软土地基的固结度。结果表明,相对于传统排水固结法的不耦合模型,部分耦合模型下因温度产生的孔压增量延缓了地基固结的发展,固结速率有所减慢;耦合模型下温度虽也产生一定的孔压增量,但温度有效地改善了竖井涂抹区土的渗透特性,地基的固结速率加快,固结周期缩短,与试验结果一致。 相似文献
13.
Seepage-heat transfer coupling process of low temperature return water injected into geothermal reservoir in carbonate rocks in Xian County,China 
下载免费PDF全文
下载免费PDF全文 WANG Yan LIU Yan-guang BIAN Kai ZHANG Hong-liang QIN Shen-jun WANG Xiao-jun 《地下水科学与工程》2020,8(4):305-314
Fracture seepage and heat transfer in the geothermal reservoir of carbonate rocks after the reinjection of low temperature geothermal return water is a complex coupling process,which is also the frontier of geothermal production and reinjection research. Based on the research of cascade comprehensive development of geothermal resources in Beijing-Tianjin-Hebei (Xian County),the carbonate geothermal reservoir of Wumishan formation in the geothermal field in Xian County is investigated. With the development of the discrete fracture network model and the coupling model of seepage and heat transfer,the numerical solution of seepage field and temperature field with known fracture network is reached using the finite element software COMSOL,and the coupling process of seepage flow and heat in carbonate rocks is revealed. The results show that the distribution of temperature field of fractured rocks in geothermal reservoir of carbonate rocks has strong non-uniformity and anisotropy. The fracture network is interpenetrated,which constitutes the dominant channel of water conduction,and along which the fissure water moves rapidly. Under the influence of convective heat transfer and conductive heat transfer,one of the main factors to be considered in the study of thermal breakthrough is to make the cold front move forward rapidly. When the reinjection and production process continues for a long time and the temperature of the geothermal reservoir on the pumping side drops to a low level,the temperature of bedrocks is still relatively high and continues to supply heat to the fissure water,so that the temperature of the thermal reservoir on the pumping side will not decrease rapidly to the water temperature at the inlet of reinjection,but will gradually decrease after a long period of time,showing an obvious long tail effect. The distribution of fractures will affect the process of seepage and heat transfer in carbonate reservoirs,which should be considered in the study of fluid thermal coupling in carbonate reservoirs. 相似文献
14.
A mathematical model is developed for simulating the thermal energy transfer in a confined aquifer with different geological properties in the underlying and overlying rocks. The solutions for temperature distributions in the aquifer, underlying rock, and overlying rock are derived by the Laplace transforms and their corresponding time-domain solutions are evaluated by the modified Crump method. Field data adopted from the literature are used as examples to demonstrate the applicability of the solutions in modeling the heat transfer in an aquifer thermal energy storage (ATES) system. The results show that the aquifer temperature increases with time, injection flow rate, and water temperature. However, the temperature decreases with increasing radial and vertical distances. The heat transfer in the rocks is slow and has an effect on the aquifer temperature only after a long period of injection time. The influence distance depends on the aquifer physical and thermal properties, injection flow rate, and injected water temperature. A larger value of thermal diffusivity or injection flow rate will result in a longer influence distance. The present solution can be used as a tool for designing the heat injection facilities for an ATES system. 相似文献
15.
Stress-induced evolution of anisotropic thermal conductivity of dry granular materials 总被引：1，自引：1，他引：0
Jinhyun Choo Young Jin Kim Jung Hwoon Lee Tae Sup Yun Jangguen Lee Young Seok Kim 《Acta Geotechnica》2013,8(1):91-106
Various factors, such as the volumetric fraction of constituents, mineralogy, and pore fluids, affect heat flow in granular materials. Although the stress applied on granular materials controls the formation of major pathways for heat flow, few studies have focused on a detailed investigation of its significance with regard to the thermal conductivity and anisotropy of the materials. This paper presents a numerical investigation of the stress-induced evolution of anisotropic thermal conductivity of dry granular materials with supplementary experimental results. Granular materials under a variety of stress conditions in element testing are analyzed by the three-dimensional discrete element method, and quantitative variations in their anisotropic effective thermal conductivity are calculated via the network model and conductivity tensor measurements. Results show that the directional development of contact area and fabric under anisotropic stress conditions leads to the evolution of anisotropy in thermal conductivity. The anisotropy induced in thermal conductivity by shear stress is higher than that induced by compressive stress because shear stress causes more significant changes in microstructural configurations and boundary conditions. The shear-stress-induced evolution of anisotropy between principal thermal conductivities depends on dilatancy as well as shearing mode, and the shear-driven discontinuity localizes the conductivity. Factors involved in the stress-induced evolution and their implications on the thermal conductivity characterization are discussed. 相似文献
16.
Discrete fracture model for simulating waterflooding processes under fracturing conditions 下载免费PDF全文
下载免费PDF全文 In our study, we develop a model for simulating fracturing processes in a poroelastic medium. The proposed approach combines the discrete fracture model enriched with contact plane mechanics. The model captures mechanical interactions of fractures and a deformable medium, fluid, and heat transfer in fractures and in a porous medium. Both effects of poroelasticity and thermoelasticity are accounted in our model. Mass and heat conservation equations are approximated by the finite volume method, and mechanical equilibrium equations are discretized by means of the Galerkin finite element approach. Two‐dimensional grid facets between 3‐dimensional finite elements are considered as possible fracture surfaces. Most of these facets are inactive from the beginning and are activated throughout the simulation. A fracture propagation criterion, based on Irwin's approach, is verified on each nonlinear iteration. When the criterion is satisfied, additional contact elements are added into finite element and discrete fracture model formulations respectively. The proposed approach allows modeling of existing natural and artificially created fractures within one framework. The model is tested on single‐ and multiple‐phase fluid flow examples for both isothermal and thermal conditions and verified against existing semianalytical solutions. The applicability of the approach is demonstrated on an example of practical interests where a sector model of an oil reservoir is simulated with different injection and production regimes. 相似文献
17.
Kun Sang Lee 《Hydrogeology Journal》2014,22(1):251-262
Numerical investigations and a thermohydraulic evaluation are presented for two-well models of an aquifer thermal energy storage (ATES) system operating under a continuous flow regime. A three-dimensional numerical model for groundwater flow and heat transport is used to analyze the thermal energy storage in the aquifer. This study emphasizes the influence of regional groundwater flow on the heat transfer and storage of the system under various operation scenarios. For different parameters of the system, performances were compared in terms of the temperature of recovered water and the temperature field in the aquifer. The calculated temperature at the producing well varies within a certain range throughout the year, reflecting the seasonal (quarterly) temperature variation of the injected water. The pressure gradient across the system, which determines the direction and velocity of regional groundwater flow, has a substantial influence on the convective heat transport and performance of aquifer thermal storage. Injection/production rate and geometrical size of the aquifer used in the model also impact the predicted temperature distribution at each stage and the recovery water temperature. The hydrogeological-thermal simulation is shown to play an integral part in the prediction of performance of processes as complicated as those in ATES systems. 相似文献
18.
19.
20.
基于有限元分析法,建立了准三维非稳态传热模型。在试验验证的基础上,分析了跨季节蓄热型地源热泵蓄热过程中土壤温度、单位井深换热量、热作用半径随热泵运行时间的变化规律,讨论了土壤结构、入口水温、入口质量流量、热泵运行模式等对土壤传热规律的影响,并研究了土壤热平衡问题。结果表明:同一半径不同深度处,土壤温度增长幅度随土壤热扩散率的增加而增大;土壤热作用半径随热泵运行时间及入口水温的升高而增加,并逐渐趋于稳定;间歇运行模式下,地埋管附近土壤温度及换热量均呈波动式变化,且当径向距离大于0.3 m时,与连续模式一致;在满足换热量的情况下,流体质量流量不宜过大;系统运行一个周期（360 d）后土壤温度基本可以恢复,且流体入口温度不宜低于40 ℃。 相似文献