热屏障井对地下水源热泵换热影响模拟

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。     

地下水源热泵系统布井方案分析

对于地下水源热泵而言,"热突破"现象普遍存在。但不同的布井方案,即抽、灌井间距和井位的不同,可能引起抽水井的温度变化差异很大,进而影响地温空调系统采能功效。本文结合郑州市儿童医院地温空调实例工程,应用HST3D程序对细颗粒含水层地区1抽2灌模式下不同布井方案进行了分析。结果表明,该区的最佳井间距为50m左右;选择直线型布井,抽、灌井连线平行于天然水力坡度方向,且天然水力坡度由抽水井指向回灌井的方式效果最好。     

水源热泵抽灌井布局及其运行过程中地下温度变化

本文以某水源热泵空调系统为例,建立了抽灌场地及周边地下水动力场与温度场的耦合数学模型,运用数值法求得系统运行过程中地下水的温度变化,分析了场地"热短路"效应和不同含水层中温度场的影响范围,以定量化的手段科学评价了场地抽灌井的布局及其可行性。分析结果表明,由于抽灌井之间的"热短路"程度较轻,场地的抽灌井布局可保证系统的高效运行。     

地源热泵系统抽灌模式对地下水流场和温度场的影响

通过建立三维水热耦合数值模型,对地下水地源热泵系统井群平行抽灌(即抽水井与回灌井平行布置)以及交叉抽灌(即抽水井与回灌井交错布置)两种调度运行模式下,系统运行后的含水层地下水流场及温度场情况进行了模拟计算、分析。结果表明:平行抽灌模式对含水层地下水流场、温度场的影响范围、程度均大于交叉抽灌模式,从系统运行效率以及对地温场的影响方面考虑,交叉抽灌模式均优于平行抽灌模式。     

含水层采能区热渗耦合三维数值模型研究

以西安市某水源热泵系统为例,建立三维热渗耦合数值模型,对研究区渗流场和温度场的演化进行模拟研究。结果表明:水源热泵系统运行初期,抽灌井水位变化明显,1. 5 h后趋于稳定;随着热泵系统的运行,在水动力的驱动下,回灌井冷热锋面逐渐到达抽水井,发生热贯通后抽水井温度变化显著;含水层渗透系数越大,温度锋面的移动速度越快;抽灌井连线上渗透速度最大,温度变化最明显,随着热泵系统的运行,温度场的影响范围逐渐增大。     

咸阳地区地热采灌井最佳井距分析

采灌井合理井间距的确定是对井采灌,资源可持续利用的关键性问题[1]。采灌井间距过大,不利于发生水力联系,间距过小容易产生"热突破"[2]。对采灌井合理井间距的确定提供依据,以咸阳采灌区为例,在建立地下水流场和温度场耦合数学模型的基础上,借助Feflow软件以咸阳地区WH2为回灌井中心,开采井呈东西南北向排布的方式模拟。模拟分析表明:在采灌过程中地下水水位稳定时间随抽、灌水量的增加相应减少。水流连通的时间缩短,主要是由于抽、灌水共同作用下,地下水发生强迫对流作用加强,使天然流场的作用被忽略。在强迫对流作用的影响下,经过一定的时间形成新的渗流稳定场,当新的渗流稳定场形成之后,水流连通也将出现。以回灌使含水层下降2℃视为出现"热突破"现象,运行3 650天时,在防止抽灌井发生"热突破"的前提下,抽水井距灌水井合理的间距的下限为400 m左右。结合水力联系影响下的合理井距上限500 m,得出的研究区采灌井间合理的井间距范围为400~500 m。     

区域流场作用下地下水地源热泵系统抽灌模式对地温场的影响

通过建立三维水热耦合数值模型,对区域流场作用下,地下水地源热泵系统运行一个采暖、制冷周期后,不同的抽灌井布局以及交替方式下,地下水地源热泵系统地温场的演变趋势进行模拟分析。结果表明,地下水的天然流速越大,越有利于热量的运移,有助于抽灌井连线垂直于地下水流方向的垂直布局以及地下水流向由抽水井指向回灌井的平行布局下的地温场演化,但不利于地下水流向由回灌井指向抽水井的平行布局下的地温场演化和温度恢复。一般的天然地下水流速条件下,由于含水层储能效应,进行抽灌井季节性交替模式的系统运行效率较高。     

地下水源热泵抽灌井优化布置及参数灵敏度

为了确定地下水源热泵的最佳布井方式,探明含水层温度场变化特征以及水文地质参数灵敏性,以石家庄地下水源热泵适宜区肖家营—东兆通为研究区,基于热储层的地热地质条件和热物性参数,利用FEFLOW软件构建了三维水-热耦合数值模拟模型。在2 000 m³/d的抽灌量下对不同井间距、不同布井模式-含水层温度场变化进行模拟,探讨发生热突破的可能性,并探讨温度场关于热导率、渗透系数、孔隙率等参数的灵敏度。研究结果表明：1)在单抽双灌模式下,方案C(两眼回灌井连线与地下水流向垂直,一眼回灌井位于抽水井正下游,另一眼回灌井位于沿地下水流向45°方向,即两回灌井与抽水井组成等腰直角三角形,抽水井正下游的回灌井为直角顶点)的布井方案对含水层温度场影响最小,为最优方案;2)单抽双灌模式下,抽灌量为2 000 m³/d时,方案C抽灌井间距设置在40～50 m较为合理;3)抽灌过程中,温度场对于渗透系数的改变灵敏度较高,而对孔隙率以及热导率的改变灵敏度较低。     

基于FEFLOW的水源热泵水热耦合数值模拟研究

以西安市北郊经济开发区某水源热泵系统为例,采用基于有限元的FEFLOW软件,建立三维水热耦合数值模型,对该区域渗流场和温度场的演变进行模拟。结果表明:水源热泵运行之初,抽灌井水位变化明显,1.5 h后趋于稳定;随着系统的运行,回灌井冷热锋面到达抽水井后,抽水井温度变化显著;含水层渗透系数越大,温度锋面的移动速度越快;抽灌井连线上渗透速度最大,温度变化最明显,随着热泵系统的运行,温度场的影响范围逐渐增大。     

场地地下水源热泵系统抽灌实验及数值模拟研究

基于野外实际地下水源热泵系统和长时间抽灌实验,构建场地水文地质概念模型和水热耦合模型,进行场地地下水温度场数值模拟研究。利用场地群井观测数据对所建模型进行验证,诸观测孔各时段的绝对误差均值为0.38℃,平均相对误差率为2.00%,表明模型模拟结果良好。模型经验证后,预测不同抽灌模式下温度场分布,发现季节性交替抽灌结果优于正常抽灌,但均产生热贯通现象,说明现状抽灌井距(30 m)偏小。设计不同抽灌井距情况模拟回灌井对抽水井的影响,得到研究场地合理井距为50 m。进一步研究渗透系数、热弥散度、抽灌水量和回灌水温差对合理井距的影响,发现抽灌水量和回灌水温差的影响最大。     

水源热泵井群布置方案对地下水流场影响分析

以某地下水源热泵系统工程为例,依据工程场地实际抽水-回灌试验数据,建立研究区地下水流数值模拟模型,分析该地区适宜的井群布置方案,并定量研究不同井群布置方案对地下水流场的影响范围与程度,为确定合理的井群布置方案提供技术支撑。研究表明：对于同一含水层回灌,随着抽水-回灌时间的延长,就有利于抽水-回灌能力及尽量减小对周边地下水开采的影响而言,抽水井、回灌井交叉布置,部分回灌井集中布置的方案较为合理。     

北京地区地下水源热泵利用现状及存在问题

本文综合国内外地下水源热泵研究现状,通过对北京地区地下水源热泵利用现状调查分析,重点分析了地下水水源热泵利用过程中存在的不能完全回灌、回灌水温差过大、水井布设不合理等问题。结合北京平原区第四系水文地质条件,分析了不同含水层结构下如何合理布设地下水源热泵系统的用水井,尽量避免水源热泵系统的使用对地下水的影响。     

Groundwater flow and capture zone analysis of the Central Passaic River Basin, New Jersey

Delineating capture zones of pumping wells is an important part of safe drinking water and well protection programs. Capture zones or contributing areas of a groundwater extraction well are the parts of the aquifer recharge areas from which the wells draw their water. Their extent and location depend on the hydrogeologic conditions such as groundwater recharge, pumping scenario and the aquifer properties such as hydraulic conductivity, porosity, heterogeneity of the medium and hydraulic gradient. Different methods of delineation can be used depending on the complexity of the hydrogeologic conditions. In this study, a 3-dimensional transient numerical MODFLOW model was developed for the Central Passaic River Basin (CPRB), and used with a MODPATH particle tracking code to determine 3-dimensional transient capture zones. Analytically calculated capture zones from previous studies at the site were compared with the new numerically simulated capture zones. The study results revealed that the analytical solution was more conservative, estimating larger capture zones than the numerical models. Of all the parameters that can impact the size, shape and location of a capture zone, the hydraulic conductivity is one of the most critical. Capture zones tend to be smaller in lower hydraulic conductivity areas.     

The Role of Groundwater Leakage through Deep Wells for the Deformation of Groundwater Flow: a Case Study in Cangzhou Area

Overexploitation of groundwater in Cangzhou area has attracted wide attention. Different layers of the aquifer may be connected through wells, since most wells of the deep aquifer have screens in several layers. This study proved the existence of vertical flow through wells, calculated the flow velocity and quantity of vertical flow in wells with methods of both field measurement and numerical simulation. Further, the recharge of deep groundwater by vertical flow through wells was estimated. An annual recharge of 1.5×108-2.8×108m3 from the third aquifer to the forth aquifer in Cangzhou area was estimated, according to the in-well measurement by heat pulse flowmeter sonde.     

Analysis of Steady-State Flow To Multiscreened Wells Under Natural Vertical Flow Conditions

Water levels measured at multiscreened wells in unconfined aquifers may not coincide, in general, with the elevation of the water table. The presence of vertical gradients (as often is the case in recharge areas) or the existence of confining layers may cause the water levels to differ from local hydraulic heads in the aquifer. In these cases, a misinterpretation of water levels may lead to the erroneous conclusion that observed drawdowns are provoked by overpumping. In this paper, we analyze the effect that a natural vertical gradient has on water levels in wells screened over their entire saturated thickness. As one would expect, it is observed that, even without pumping, the water level in the wells lies below the water table. Type curves relating the steady-state drawdown to the vertical gradient and to the hydraulic conductivity anisotropy are presented. These curves were obtained using a groundwater flow numerical model (FREESURF: Neuman and Witherspoon, 1970). The theoretical results are checked with field data from deep wells in the detrital Madrid aquifer. In this particular aquifer, it is observed that the effect of vertical gradients is important both in terms of drawdowns and flow rates.

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The dependence of stream depletion by seasonal pumping on various hydraulic characteristics and engineering factors

Compensation pumping is used to alleviate deficiencies in streamflow discharge during dry seasons. Short-term groundwater pumping can use aquifer storage instead of catchment-zone water until the drawdown reaches the edge of the stream. The capacitance is a complex, dimensionless parameter of an aquifer system that defines the delayed effect on streamflow when there is groundwater pumping. This parameter is a function of aquifer hydraulic characteristics, pumping time, and distance between the well and stream edge; the latter can involve stream leakance and vertical leakance of an associated aquitard. Three typical hydraulic cases of combined water systems (major catchment-zone wells close to the stream and compensation pumping wells) were classified depending on their capacitance structure (i.e. the relationship between surface water and groundwater): (1) perfect hydraulic connection between the stream and aquifer; (2) imperfect hydraulic connection between the stream and aquifer; and (3) essentially imperfect hydraulic connection between the stream and the underlying confined aquifer. The impact of various hydraulic characteristics and engineering factors on stream depletion was examined by conceptual and numerical modeling. To predict the suitability and efficiency of a combined water system application, regression tests were undertaken on unit stream depletion and capacitance, and power dependencies were defined.     

含水层对地下水热泵承载力数值评价及其实用化:以北京平原区为例

针对北京平原区的水文地质条件,运用地下热传递数值法评价了年内地下热量均衡、失衡两种状态下,各水文地质亚区单位面积含水层对地下水热泵的承载力,并利用多元线性回归方法阐明了承载力、抽灌井间距与含水层各参数之间的关系。研究表明:承载力仅与含水层厚度显著正相关,而抽灌井间距与含水层的渗透系数和厚度均显著正相关。研究结果为类似地区的地下水热泵定量规划提供了简捷的估算方法及参考依据。     

Monitoring artificially stimulated fluid movement in the Cretaceous Dakota aquifer,western Kansas

Aquifer properties can be evaluated by monitoring artificially stimulated fluid movements between wells, if the fluid is heated. Changes in the temperature profile recorded in observation wells indicate the flow path of the heated fluid, which in effect acts as a tracer. A fluid-flow experiment in the Cretaceous Dakota Formation at the Hodgeman County site, west-central Kansas, demonstrated the advantage of using the distributed optical-fiber temperature sensing method for monitoring transient temperature conditions in this hydrological application. The fluid flow in the aquifer was increased by producing water from a pumping well and injecting heated water in an injection well 13 m (43 ft) distant from the pumping well. The time-temperature series data obtained and compared with results from previous pumping tests point to interwell heterogeneity of the aquifer and to a zone in the sandstone aquifer of high hydraulic conductivity. However, the experiment would have allowed further clarification of aquifer heterogeneity and thermal properties if at least one observation well had been present between the injection and production wells. Electronic Publication     

水力层析法与克立金法估算非均质含水层渗透系数场比较

含水层非均质性空间分布特征的识别,是准确模拟地下水流和污染物运移的前提.基于室内非均质含水层砂箱实验,分别利用水力层析法和克立金插值法刻画了非均质含水层渗透系数场.研究结果表明:(1) 水力层析法与克立金法相比,不仅可以更好地刻画非均质含水层渗透系数场,还可以更高精度地预测地下水流过程;(2) 水力层析抽水实验中,通过增加抽水实验组数可以有效地提高水力层析参数反演的精度,但是抽水实验组数增加到一定程度以后,再增加抽水组数不会显著提升参数反演的效果.后续需要进一步研究水力层析抽水实验合适的组数,进一步对抽水井进行优化布设.