黄河冲积平原(鲁西北)浅层岩土体综合热导率研究——以临清市为例

现场热响应试验测试是获取换热深度内岩土体综合热导率最直接的方法,能够快速、直观的体现岩土体换热能力.通过分析研究临清市钻探获取的地质、水文地质参数,结合热响应试验成果资料,分析在一定条件下岩土体综合热导率与初始地温、含水层厚度、渗流速度、地下水位埋深等相互关系,发现综合热导率与初始地温、含水层厚度、渗流速度正相关,与地下水位埋深反相关.在黄河冲积平原(鲁西北)地埋管地源热泵系统开发利用应选择初始地温较高、含水层厚度大(古河道带)、地下水位埋深浅、地下水径流条件好的区域.     

地层初始温度及结构对地埋管换热能力影响分析

不同地质条件下,地埋管的换热能力有所不同,热能采集和扩散能力存在差异。为给地埋管地源热泵系统工程提供科学合理的设计依据,本文利用现场热响应测试数据分析了地层初始温度以及地层结构对地埋管换热能力的影响。结果表明:地埋管换热能力与地层初始温度呈较好的线性相关性,地埋管夏季延米换热量随地层初始温度的升高而减少,冬季延米换热量随地层初始温度的升高而增加;不同地层结构,地埋管换热能力有所不同,在富水性相对较好、岩性颗粒粗、地下水径流速度快的区域,地埋管换热效果要优于富水性相对较差、岩性颗粒细、地下水径流速度慢的区域。     

北京平原区地源热泵换热能力现场测试研究

岩土体不仅决定地温场的展布形态,而且也是浅层地温能资源评价和工程设计的关键因素,掌握区域岩土体的热物性及换热性能,是保障热泵高效稳定运行的关键。根据北京地区在施地源热泵工程对现场换热能力测试结果,系统地研究了地层结构及岩性、水文地质条件、回填材料等因素对综合热导率的影响。研究结果表明:在相同条件下选择适当回填材料有利于提高系统换热性能,膨润土和水泥基作为回填材料,比中细砂作为回填材料的换热性能分别提高了17.6%和19.7%;岩土体和地下水是热能赋存和传播的物质基础,地下水与地层结构决定着地温场分布形态和换热效率,地埋管换热器的换热能力与土壤颗粒、地下水位、地下水渗流存在直接关系,土壤颗粒越大,地下水位埋深越浅,渗流越快,对地埋管换热器换热能力具有明显的强化作用。     

沈阳市典型岩土体组合热响应试验及结果分析

岩土热物性参数是地层热响应特征的直接表征,也是地埋管地源热泵系统设计主要影响因素.热响应试验是获取岩土热物性参数的重要手段之一.针对沈阳市不同地貌单元,选择3种典型岩土体组合地段开展5组热响应试验,综合研究分析了沈阳市典型岩土体组合的综合热响应特征,包括地层初始温度、地层综合导热系数及地层的地温恢复时间,提出了沈阳市西部地区可优先发展地埋管地源热泵系统.这些结果将为沈阳市地埋管地源热泵系统的规划部署及工程的开发利用提供借鉴.     

河南省主要城市浅层地温能特征及开发利用建议

河南省浅层地温能资源具有分布广泛、资源量丰富、开发利用方便等特点,发展前景广阔。通过对河南省主要城市的地质、水文地质条件和岩土体结构特征等浅层地温能赋存特征的分析,采用数理统计和对比分析等综合研究的方法,对比研究了不同地貌类型城市200m以浅的岩土体热物性特征、浅层地温场分布特征和岩土热响应特征等的异同及其分布与变化规律。结果显示:河南省主要城市浅层地温能的赋存层位主要为第四系及新近系上部的各类松散堆积物,这些松散的堆积物和储存于其孔隙内的地下水为浅层地温能的载体;岩土导热系数会随着孔隙率的增加而减小,随岩性颗粒变粗而增大;城市地层综合导热系数和换热能力与地下水径流条件呈正相关;位于盆地和山前地带水文地质条件优越的城市或地段,浅层地温能开发利用宜采用地下水换热方式,松散堆积物厚度较大且以细粒相沉积为主的城市或地段,宜采用竖直地埋管换热方式。     

上海地区岩土体分层导热特征及其计算模式研究

由于不同土层、不同岩性的导热系数存在差异,分层导热系数的精准计算利于地埋管换热器优化设计,提高地热利用率,降低地源热泵系统长期运行造成的岩土体热不平衡。热响应测试得到的导热系数较为准确,然无法体现岩土体的分层特性。室内测试法获取的导热系数能够体现岩土体的分层特性,但不够准确。本研究结合上海地区地下岩土体的分层特征,将地下岩土体分层细化、岩性归类,结合室内测试和现场测试结果,利用权重系数法建立岩土体分层导热系数与综合导热系数的相关关系,得到的导热系数更能反映地下岩土体分层特征也更精确。     

上海地源热泵系统对地质环境的热影响分析

根据地源热泵工程试验场两年监测数据,分析了地下换热区地温场分布特征以及地源热泵系统短期运行对地质环境的热影响效应。换热区地温场分布主要受气温、建筑冷热负荷、原始地温、岩土导热系数、与换热孔距离等因素影响。在吸排热比基本平衡的条件下,地源热泵系统对地质环境的热影响较小。选择合理的埋管间距,充分利用地源热泵的热回收功能,采用冷却塔—地埋管、地表水—地埋管等复合系统,有助于消除吸排热比不平衡现象。     

现场热响应试验测试数据对比及应用分析

勘查评价浅层地热能地质条件及换热能力是高效开发浅层地热能资源的关键基础,对高效、可持续利用浅层地热能起着举足轻重的作用。不同区域地质条件千差万别导致地下换热效果不同,目前现场热响应试验,是地埋管地源热泵系统区域调查评价和应用项目场地勘查中,采用的重要勘查手段。通过现场热响应试验获得地温场初始地温、岩土体的热物性参数,计算得出每个地埋孔的换热能力即换热功率,可为评价地埋管地源热泵系统适宜区域的浅层地热换热功率提供依据,指导地埋管地源热泵系统地下换热系统设计。本文主要对地层初始地温、不同测试功能测试所得数据,进行了对比及应用分析,对指导现场热响应试验的科学合理应用,具有重要的参考意义。     

天津中新生态城地源热泵原位热响应试验研究

介绍了天津中新生态城地源热泵原位热响应试验的方法和步骤,对实验数据进行了整理和分析,得出了单孔的换热能力和地层的导热系数,试验结果：生态城100 m深钻孔换热能力为6.13~6.98 kW,散热能力为12.03~12.7 kW,岩土体的导热系数为2.11w/m.k。     

地质条件及埋管形式对地埋管换热器换热性能影响研究

利用北京市35个现场换热孔岩土热响应试验数据,分析了地质条件和埋管形式对地埋管换热器换热性能的影响。研究结果表明地质条件对地埋管换热性能具有显著影响:地层初始平均温度每变化1℃,换热能力相差8%左右;基岩地层的地埋管换热能力平均比松散层高35%;换热孔处地下水流速从0.14 m/d增至0.91 m/d, Pe值从18增加至113,由于热对流换热作用加强,延米换热量提升13%。在相同地质条件下,套管式换热器冬季延米取热量比双U型换热器高约40%;换热深度从150 m增加至300 m时,双U型和套管式换热器延米取热量均略有升高。     

Negative thermal expansion in beta-quartz

Computer modelling and theoretical analysis are used to explain the nearly zero and slightly negative coefficients of thermal expansion in β-quartz well above the α-β phase transition temperature. Quartz was selected for study as an archetypal material with a framework structure of stiff units, namely SiO₄ tetrahedra, linked through shared oxygen atoms as very flexible hinges. The contributions of the soft mode, the Vallade mode, the TA_z phonon branch and the phonon spectrum as a whole are discussed in detail. The results fully support and illustrate a recent theory of the negative contribution to thermal expansion in framework structures. It is a geometrical effect due to the rotation of the tetrahedral units, folding together as they vibrate. The very rapid increase in the lattice parameters for about 20 K above the transition temperature is well accounted for within quasiharmonic theory, and is therefore not evidence for critical fluctuations or fluctuating patches of α ₊, α ₋ structure. Received August 14 1997 / Revised, accepted January 26 1998     

Heterogeneous shock-induced thermal radiation in minerals

A 500 channel optical imaging intensifying and spectral digital recording system is used to record the shock-induced radiation emitted from 406 to 821 nm from transparent minerals during the time interval that a shock wave propagates through the sample. Initial results obtained for single crystals of gypsum, calcite and halite in the 30 to 40 GPa (300 to 400 kbar) pressure range demonstrate greybody emission spectra corresponding to temperatures in the 3,000 to 4,000 K range and emissivities ranging from 0.003 to 0.02. In the case of gypsum and calcite, distinctive line spectra, are superimposed on the thermal radiation. The observed color temperatures are a factor of 2 to 10 greater than the Hugoniot temperature, calculable on the basis of continuum thermodynamics and equation of state models for the shock states achieved in the three minerals. These observed high temperatures are believed to be real. We conclude that we are detecting a large number of closed spaced high temperature shear-band regions immediately behind the shock front. A shear instability model, such as proposed independently by Grady (1977, 1980), Ananin et al. (1974), and Horie (1980), in which small zones of highly deforming and melted material are produced which are the source of the detected thermal radiation and have a fractional effective area approximately numerically equal to the measured emissivity, can be used to predict an effective emissivity of 0.0065 directly behind the shock front. If shear band instability arises from viscous flow processes, Grady's model and mineral thermal properties yield for the shocked mineral viscosities values in the range of 10⁹ to 10¹⁵ P immediately behind the shock front.     

Compositional and thermal convection in magma chambers

Magma chambers cool and crystallize at a rate determined by the heat flux from the chamber. The heat is lost predominantly through the roof, whereas crystallization takes place mainly at the floor. Both processes provide destabilizing buoyancy fluxes which drive highly unsteady, chaotic convection in the magma. Even at the lowest cooling rates the thermal Rayleigh number Ra is found to be extremely large for both mafic and granitic magmas. Since the compositional and thermal buoyancy fluxes are directly related it can be shown that the compositional Rayleigh number Rs (and therefore a total Rayleigh number) is very much greater than Ra. In the case of basaltic melt crystallizing olivine Rs is up to 10⁶ times greater than Ra. However compositional and thermal buoyancy fluxes are roughly equal. Therefore thermal and compositional density gradients contribute equally to convection velocities in the interior of the magma. Effects of thermal buoyancy generated by latent heat release at the floor are included.The latent heat boundary layer at the floor of a basaltic chamber is shown to be of the order of 1 m thick with very low thermal gradients whereas the compositional boundary layer is about 1 cm thick with large compositional gradients. As a consequence, the variation in the degree of supercooling in front of the crystal-liquid interface is dominated by compositional effects. The habit and composition of the growing crystals is also controlled by the nature of the compositional boundary layer. Elongate crystals are predicted to form when the thickness of the compositional boundary layer is small compared with the crystal size (as in laboratory experiments with aqueous solutions). In contrast, equant crystals form when the boundary layer is thicker than the crystals (as in most magma chambers). Instability of the boundary layer in the latter case gives rise to zoning within crystals. Diffusion of compatible trace elements through the boundary layer can also explain an inverse correlation, observed in layered intrusions, between Ni concentration in olivine and the proportion of Ni-bearing phases in the crystallizing assemblage.     

Isotopic composition of thermal waters in Chukotka

Twenty three groups of thermomineral springs in eastern Chukotka with the discharge temperature of 2 to 97°C and mineralization of 1.47 to 37.14 g/l are studied and compared with surface freshwater from their localities. The δD and δ¹⁸O values in surface waters vary from ?121.4 to ?89.5‰ and from ?16.4 to ?11.1‰, respectively, while respective values in thermomineral waters range from ?134.2 to ?92.5‰ and from ?17.6 to ?10.5‰. The δD value in surface waters decreases from the east to west, i.e., toward interior areas of the peninsula. Hydrothermal springs most depleted in deuterium (δD < ?120‰) are localized in the geodynamically active Kolyuchinskaya-Mechigmen Depression. According to the proposed formation model of Chukotka thermomineral waters, their observed chemical and isotopic characteristics could result from the mixing (in different proportions) of surface waters with the deep-sourced isotopically light mineralized component (δD ≈ ?138‰, δ¹⁸O ≈ ?19‰, M = 9.5?14.7 g/l). The latter originates most likely from subpermafrost waters subjected to slight cryogenic metamorphism.     

Origin of components in Chilean thermal waters

Thermal waters of northern (18°–27°S) and southern (37°–45°S) Chile occur in two very different climatic, geologic and hydrologic environments: arid closed basins with abundant evaporites in the north; humid climate and well drained valleys in the south. The origin and behavior of the main components of the two groups of waters are examined and compared to each other. The modeling of the alteration of volcanic rocks leads to water compositions very different from those observed both in the north and south. In addition to hydrothermal alteration and deep emanations, the Cl/Br ratio reveals a major contribution of saline waters to the two groups: infiltrating brines from salt lakes in the north; seawater in the south.In the north, concentrations of Cl, Br, Na, K, Ca, SO₄, Li, B, Si result from the mixing of alteration waters with recycled brines. Hydrothermal alteration is obscured by this massive saline input, except for Mg. δ³⁴S values are consistent with an origin of sulfate from salar brines, which are themselves derived from deep Tertiary gypsum. In the south, two processes account for the composition of thermal waters: mixing of alteration waters with seawater and deep magmatic contribution. The mixing process controls the concentration of Cl, Br, Na, Alk, Si, K, Ca, Mg. Magmatic inputs are detectable for SO₄, Li and B. δ³⁴S suggests that sulfate stems from the mixing of alteration waters with either marine SO₄ in coastal waters or with deep SO₂ in inland waters. In both the north and south, the Mg concentration is drastically lowered (<1 μmol/L) by the probable formation of a chlorite-type mineral. In the south, very small amounts of seawater (<1% in volume) are sufficient to imprint a clear signature on thermal waters. Not only coastal springs are affected by seawater mixing, but also remote inland springs, as far as 150 km from the sea. Subduction of marine sediments in the accretive margin could be the source of the marine imprint in thermal waters of southern Chile. Seawater may be expelled from the subducted lithosphere and incorporated into the mantle source.     

Granites and thermal structures in the lithosphere

The production of melts of the granite clan on a significant scale requires participation of continental crust. Such crust will melt when heated from below by a mantle thermal anomaly, or when thickend to 40 km or more. Sites of melting, and the time sequences of melting associated with subduction and underplating processes, and collision processes, are complex. In both these processes, at least six melting sites may be involved. The final chemical and isotopic composition of granitic melts depends on a very complex array of processes, which include: source composition, composition of subducted materials, magma mixing, magma underplating, assimilation-fractionation-cooling processes. Resolution of granite melt dynamics requires an integrated attack, using modern seismic and electrical measurements, in regions where the continental crust is abnormally thick or hot.

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Zusammenfassung Die Produktion von Granitschmelzen im grö\eren Ausma\e erfordert die Beteiligung kontinentaler Kruste. Die Kruste wird aufgeschmolzen, wenn sie von unten durch eine Wärmeanomalie des Mantels aufgeheizt wird oder wenn sie mächtiger als 40 km wird. Der Ort des Aufschmelzens und die Zeitabfolge des Schmelzens, die im Zusammenhang mit Subduktion Plattenstapelung und Kollisionsprozessen ablaufen, sind äu\erst komplex. Diese Prozesse sind mindestens auf sechs verschiedene Areale zu lokalisieren, in denen Aufschmelzung möglich ist. Die endgültige chemische und isotopenchemische Zusammensetzung von Granitschmelzen hängt von einer sehr komplexen Proze\abfolge ab, wobei zu berücksichtigen sind: Die Zusammensetzung des Ausgangsmaterials, die Zusammensetzung subduzierten Materials, Magmenmischung, Magmenunterströmung und Proze\e der Assimilation, Fraktionierung und Abkühlung. Um die Dynamik einer Granitschmelze zu erkennen, bedarf es moderner seismischer und geoelektrischer Methoden in Gegenden, wo die kontinentale Kruste ungewöhnlich dick oder hei\ ist.

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Résumé La production en quantité importante de liquides de la famille granitique requiert la participation de la croûte continentale. Celle-ci fond lorsqu'elle est chauffée d'en bas par une anomalie thermique du manteau, ou quand son épaisseur s'accroÎt jusqu'à 40 km ou plus. Les endroits où se développe la fusion, ainsi que son déroulement temporel, associé aux processus de subduction et d'underplating, sont complexes. Pour chacun de ces deux processus, six sites de fusion ou moins peuvent Être définis. Les compositions chimique et isotopique finales des liquides granitiques dépendent d'un ensemble de processus très complexes, qui comportent: la composition de la source, la composition des matériaux subductés, le mélange de magmas, les processus d'assimilation, de fractionement et de refroidissement.La compréhension de la dynamique de la fusion granitique requiert une approche intégrée qui comporte la mise en oeuvre de méthodes sismiques et géoélectriques modernes dans des régions où la croûte continentale est anormalement chaude ou anormalement épaisse.

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Based on a lecture presented at the Granit Symposium, Gie\en 1986. London     

Determination of ground thermal properties for energy piles by thermal response tests

Thermal properties of ground heat exchanger (GHE) such as effective thermal conductivity and borehole thermal resistance are commonly measured in the field by thermal response tests (TRTs). TRT has been proved to be a consolidated method to determine thermal properties of traditional borehole heat exchangers (BHEs). However, there is still lack of data for adopting TRT on energy piles with often a large diameter and deficiency in validation of TRT results with geological materials. In this study, ground thermal properties for typical configured GHEs of energy piles are investigated. Three TRTs are conducted and the obtained results are analyzed. Effective thermal conductivity, λ_eff, of the ground derived by following the traditional linear source model shows large deviation as compared to the thermal conductivity of the geological materials. In order to determine λ_eff properly, the linear source model is modified and an equivalent radius, r_eq, of energy piles is considered. The λ_eff estimated by the modified model shows a good agreement with thermal conductivity of the in situ geological materials. In addition, there has been no obvious correlation between borehole thermal resistances and thermal efficiency due to heat transport of energy piles that depends not only by borehole thermal resistance but also by the pile’s diameter and ground conditions. The findings drawn from this study indicate that the modified model is reasonable and useful in determining thermal properties of energy piles.     

Plate motion and thermal instability in the asthenosphere

This paper investigates the effect of shear heating in the asthenosphere on the thermal structure of the upper mantle. Equations describing the motion of the lithosphere over the asthenosphere in the presence of a strongly temperature-dependent stress-strain rate relation are derived and solved with the help of several approximations. These approximations are shown to be valid under conditions appropriate for the earth.Two sets of solutions are found. For one set (the “subcritical” solutions) a normal shear stress—velocity relation is found for small stresses. The velocity increases as the stress increases, reaching a maximum velocity σ_c for a critical stress σ_c. The subcritical solutions have a negligible effect on the thermal structure of the earth, even at the critical stress. The other set of solutions (the “supercritical” solutions) has the bizarre property that a decrease of applied shear stress leads to an increase of velocity. Thus, as the shear stress goes to zero, the velocity becomes infinite. At larger shear stresses the velocity decreases until it reaches σ_c at a stress σ_c (the two sets of solutions share this point in common). There are no steady solutions of any kind for shear stresses in excess of σ_c. We discard the supercritical solutions as candidates for the thermal structure of the earth on the basis of their instability to small perturbations of applied stress and temperature.The realm of subcritical solutions (stress less than σ_c, velocity less than σ_c) thus defines a regime of plate motion in which the thermal effects of shear heating are negligible. If the shear stresses acting on plates exceed σ_c, however, new physical processes must come into play to dissipate the excess heat generated. Assuming that the velocities of plates on the earth today are less than σ_c, relative to the deep mantle, a strict upper limit of a few tens of bars can be derived for σ_c, corresponding to effective viscosities of ca. 10¹⁹ poise in the asthenosphere.     

Adcumulus dunite growth in a laboratory thermal gradient

Laboratory experiments near 1450° C at 1 bar (QFM) on komatiite bulk composition show olivine and liquid in cumulus textures which evolve with experiment duration. Orthocumulus texture with settled olivine crystals separated by liquid matrix is developed within a day. Experiments quenched after a few days to a week show a progression of textures which include development of columns of olivine crystals separated by channels of liquid. Olivine grain sizes increase with the cube root of time suggesting that dissolution and reprecipitation of olivine may be involved in the organization into columns and channels. Experiments quenched after two weeks have well developed adcumulus texture. The basal polycrystalline granular olivine aggregate forms from the decay of the olivine columns. Melt expulsion from the aggregate can be virtually complete, leaving 1% or less of the melt originally present.Buoyancy-driven compaction of olivine is not the mechanism responsible for this textural evolution because the final basal aggregate sometimes contains vesicles. An addition proof of the inadequacy of buoyancy is provided by raising the crucible slightly above the thermal symmetry point of the furnace. The aggregate then compacts on top of a crystal-free liquid. The thermal gradients above and below the furnace hot spot are thought to be primarily responsible for the olivine redistributions observed. Diffusion of olivine components in the liquid is driven along a saturation gradient resulting from the temperature gradient. The process, called thermal migration in geological literature, is essentially the same as traveling solvent zone refining in metallurgy. Differential solubility and Soret fractionation both contribute to olivine redistribution to the cold region of the crystal-liquid aggregate. There may be some applications of these results to natural cumulate rock petrogenesis.