地下水渗流对竖直U型地埋管周围土壤温度场的影响

为了探究地下水渗流对竖直U型地埋管周围土壤温度场的影响,基于多孔介质传热传质和热渗耦合作用,建立了二维地下渗流条件下的传热模型。分析了有无渗流作用,地埋管周围土壤温度场的变化规律,在此基础上探究了地下水渗流速度、土壤热物性参数、热泵运行模式等因素对土壤温度场的影响,研究表明:地下水渗流的作用导致地埋管周围土壤温度场沿渗流方向产生了拉伸,且拉伸幅度随渗流速度的增加而增加;渗流速度越大土壤温度场稳定所需的时间越短且稳定后温度越低;在其他条件不变时,土壤导热系数越大土壤温度场拉伸的幅度愈大;热泵间歇运行模式下在渗流影响区内土壤温度呈现等幅波动,沿渗流方向随振幅径向距离增加而降低,对于渗流影响区以外土壤温度基本不受影响。     

地埋管地源热泵热水供应系统运行性能的影响因素

建立了地埋管地源热泵热水供应系统实验平台,研究了环境温度、间歇/连续运行工况、管内循环液流速等对地埋管换热器换热能力的影响,并研究了地埋管换热器周围土壤温度场的变化.结果表明,地埋管地源热泵热水供应系统基本不受环境温度的影响;采用间歇运行,有利于提高地埋管换热器的换热能力;地埋管换热器平均单位井深换热量随管内循环液流速的增大而增大,但当流速增大到一定程度时,其增幅趋于平缓.     

无渗流条件下U形地埋管换热器能效特性研究

选取无穷远边界值,利用三维数值模型对无渗流条件下地埋管换热器传热过程进行动态模拟,研究了地埋管换热器能效系数的主要影响因素.结果表明,增大岩土体导热能力和埋设深度及适当减小管内流速能够提高地埋管换热器的能效系数,而加大支管间距仅能在较短换热时间内提升地埋管的换热能效;采用间歇运行模式,特别是小周期循环和较长时间温度恢复期,有利于提高地埋管换热器的能效系数;岩土体初始温度和地埋管进口温度的变化并不影响地埋管换热器的能效系数.     

竖直U形地埋管换热器热短路现象及换热性能研究

针对影响地埋管换热器热短路现象及换热性能的主要因素(回填材料导热系数和热泵运行方式),建立了U形地埋管换热器的三维非稳态数值模型,通过热响应实验验证了该模型。采用FLUENT软件进行模拟分析,得到不同导热系数土壤条件下地埋管换热器的热短路损失系数和每延米换热量随回填材料导热系数的变化规律,推荐采用导热系数比周围土壤稍大的回填材料。对比了地源热泵连续与间歇两种运行方式,得出当回填材料导热系数小于或等于周围土壤导热系数时,间歇运行对热短路现象基本无影响;当回填材料导热系数大于周围土壤导热系数时,间歇运行可使热短路损失系数降低51.6%~74.5%,每延米换热量提高32.6%~34.0%。     

热渗耦合作用下地下埋管换热器的传热分析

为确定地下水渗流对U型地下埋管换热器的影响,基于热渗耦合作用下的数学模型,采用整体求解方法求得管内流体、地下埋管换热器及周围土壤的温度场数值解。分析了地下水渗流对传热过程的影响,结果表明地下水流动对原温度场的影响明显,而且地下水流速越高影响越大。进一步分析了有渗流时不同土壤类型对地下埋管换热器的影响情况,在饱和状态下导热系数是主要的影响因素。     

间歇运行下土壤源热泵性能及土壤温度模拟

采用动态仿真软件TRANSYS建立土壤源热泵空调系统模型。针对供热工况,模拟地埋管换热器连续运行模式、不同间歇运行模式(日运行时间不同)下,土壤源热泵蒸发器出水温度、土壤温度随时间的变化以及供暖期能效比。地埋管换热器日运行时间越短,越有利于土壤源热泵的高效运行。     

地下水渗流条件下地埋管换热器的传热模型

提出了有限长线热源渗流传热模型,根据获得的解析解分析了地埋管换热器周围介质的温度响应。比较了有限长线热源和无限长线热源两种渗流模型,分析了地下水渗流速度及地埋管相关参数对热扩散的影响。研究表明,地下水渗流可改善地埋管换热器的换热性能,提高换热量,从而可降低系统的初投资。     

地下水渗流对地埋管换热器传热效率的影响

基于垂直单U型地埋管换热器的实际形状,建立了三维非稳态地下水渗流传热模型,分析了夏季工况下地下水渗流速度、渗流温度、地埋管进水温度以及管内流速对地埋管换热效率的影响。引入换热效率系数来量化地下水渗流对地埋管换热能力的影响程度。结果表明:考虑地下水的渗流可以有效的强化换热效率,对地埋管的传热影响显著;增大地下水渗流速度和减小渗流温度可加强地埋管的换热能力;选取合适的地埋管进水流速可降低系统能耗,增加换热量;根据不同的空调房间负荷,合理设计地埋管进水温度能保证热泵主机的高效运行。     

垂直地埋换热器非饱和岩土温度场分析

垂直地埋管换热器周围非饱和土壤的特性对埋管换热具有重要影响,目前地埋管换热器设计中多假设岩土为均匀介质,并未深入考虑非饱和岩土对埋管换热的影响。基于岩土的非饱和特性,通过数值模拟,对比分析岩土非饱和特性下温度响应的变化,为地埋管换热器设计提供更为准确模型。     

地源热泵间歇运行对地埋管换热器性能的影响

运用二维非稳态导热模型对地源热泵夏季间歇运行模式地埋管换热器的换热特征进行了数值模拟,分析了间歇运行模式对地埋管换热器性能的影响。热泵停机后各处平均温度及平均线热流密度在穿透时间内将延续换热器正常运行时的变化规律;在总运行时间相同的条件下,开停机次数适当增加,可以有效改善地埋管换热器的性能。     

Thermal performance of borehole heat exchanger under groundwater flow: A case study from Baoding

The performance of ground source heat pumps (GSHPs) depends strongly on the heat transfer between the soil and borehole heat exchangers (BHEs). In the present work, a thermal performance experiment of a BHE under groundwater flow was conducted in Baoding, China. Based on the measurement of the natural ground temperature profile, a simplified theoretical model was presented to estimate the characteristics of groundwater flow. The results showed that the presence of groundwater had an obvious influence on the temperature profile in the aquifer. Due to the strong groundwater advection, the thermal performance of the BHE was enhanced. The enhanced effect depends to a great extent on the distribution and thickness percentage of the ground layer with the greatest groundwater flow. In the present case, the heat injection and heat extraction of the BHE were enhanced on average by 9.8% and 12.9%, respectively, compared with the case without groundwater flow, when the total thickness of coarse sand and gravel layer as a percentage of the borehole depth was 10.6%. This enhanced effect is favorable for reducing the possible imbalance between heat injection and extraction from and to the ground, which is helpful for the long-term operation of GSHP systems.     

地埋管换热器传热模型的回顾与改进

回顾了国内外关于地埋管换热器的设计计算理论、传热模型及其计算方法,发现几乎所有的模型都未考虑地下水渗流的影响。举例说明地下水流动对地埋管换热器有较大的影响,建立了考虑热传导和地下水流动共同作用的地埋管换热器的传热模型,并且对单井地埋管进行了初步分析,结果表明地下水渗流能增强盘管的换热能力。     

竖直单U形地埋管换热器单因素敏感性分析

基于竖直单U形地埋管换热器的热渗耦合传热模型,分析了岩土导热系数、岩土体积热容、岩土孔隙率、原始地温、地下水渗流速度、埋管深度、管内流体流量、地埋管进口水温及运行模式等因素对地埋管换热器换热性能的影响。进行了单因素回归分析,拟合得到了单位井深换热量及地埋管出口水温与各个参数的回归方程。     

Biodegradability and ecotoxicity of commercially available geothermal heat transfer fluids

Commercially available heat transfer fluids used in borehole heat exchangers were investigated for their composition, their biodegradability as well as their ecotoxicity. The main components of the fluids are organic compounds (often glycols) for freezing protection. Biodegradation of the fluids in laboratory studies caused high oxygen depletion as well as nitrate/iron(III) reduction under anaerobic conditions. Additives such as benzotriazoles for corrosion protection were persistent. Ecotoxicity data show that the commercially available fluids caused much higher ecotoxicity than their main organic constituents. Consequently, with regard to groundwater protection pure water as heat transfer medium is recommended. The second best choice is the usage of glycols without any additives. Effects on groundwater quality should be considered during ecological-economical cost-benefit-analyses of further geothermal energy strategies. The protection of groundwater as the most important drinking water resource must take priority over the energy gain from aquifers.     

Wall heat loss from intermittently conditioned spaces—The dynamic influence of structural and operational parameters

The intermittent daily operation of the HVAC equipment is currently a method usually adopted for reasons of proper building energy management in geographical regions with temperate climatic conditions. Under these conditions, the influence of the building envelope and the specific operational schedule of the mechanical equipment under the effect of time-varying ambient temperature and incident solar radiation is responsible for the development of complex transient heat transfer phenomena, which leads to continuous heat exchange with the environment. The heat exchange through the building envelope, which determines its energy efficiency, is strongly influenced by several parameters along with the thermal characteristics of the building elements like the wall thermal resistance and heat capacity as well as the thermal time constant and operational conditions of mechanical equipment. In the present investigation, an analysis is developed for the evaluation of the daily quasi steady-state energy losses from composite walls under the effect of time-varying meteorological driving forces, when heating at the room side is intermittent.The effect of various significant design and system operational parameters like wall heat capacity, thermal time constant and the insulation layer configuration, daily heating cycle duration and phase, as well as room heat capacity and net heating power input are investigated on the quasi steady-state energy loss and daily room temperature swing under typical winter conditions.     

中深层套管式地埋管换热器换热性能模拟研究

建立套管式地埋管换热器数值模型,采用FLUENT对制热工况下套管式地埋管换热器的换热性能进行模拟,研究运停比、岩土热导率、地温梯度等因素对单位钻孔深度换热量的影响.岩土热导率为2.5 W/(m·K),地温梯度为0.03℃/m条件下:不同运停比的单位钻孔深度换热量均随时间推移而下降.相同供暖期,单位钻孔深度换热量由大到小...     

福建省地源热泵适宜性研究

为了使该省地源热泵系统能健康有序地发展,对当地的地表水资源、地下水资源、浅层土壤热能源等地质情况进行了调查。依据调查资料的分析、研究,认为这一地区较适宜采用地表水和地下水地源热泵系统,不适宜采用地埋管地源热泵系统。提出了地下水地源热泵的适宜性分区,可供该地区暖通空调工程设计参考。     

地源热泵地埋管换热器传热研究(4):系统耦合运行特性

采取数值计算与解析计算相结合的方法,在构建地埋管换热器与地上机组耦合模型的基础上,研究了夏季变热流边界条件下单U形地埋管换热器与地上机组耦合运行的非稳态特性。分析了连续运行工况和间歇运行工况下地源热泵机组COP、单位管长换热量、埋管进出口流体温度及钻孔壁面平均温度随运行时间的变化规律。