软土地区竖直地埋管换热器回填材料性能研究

竖直地埋管换热器回填材料性能对地源热泵换热系统的换热能力有直接影响。对不同配比的水泥基回填材料的导热性能进行测试分析。对不同配比的膨润土基回填材料的导热性能、抗渗性能以及充填性能进行测试分析。得出不同配比下导热系数、渗透系数、析水率的变化曲线,建立膨润土基回填材料导热系数与加压养护压力关系式及膨润土基回填材料水灰比与析水百分比关系式。     

竖直U型埋管地热换热器热短路现象的影响参数分析

通过引入换热器出口最高流体温度的概念,对地源热泵竖直U型埋管地热换热器的热短路现象进行了量化,基于竖直U型埋管周围的瞬时有限元模型,对影响热短路现象的主要参数(支管间距和回填料导热系数)进行了模拟分析,得出了量化结果。结果表明,增大支管间距可降低换热器出口最高流体温度,减小由热短路现象引起的热损失;回填料的导热系数对热短路现象的影响较大,当回填料导热系数小于周围土壤的导热系数时,增大回填料导热系数对减小热短路损失有较大作用,而当回填料导热系数大于土壤导热系数时则作用不大,推荐使用导热系数与周围土壤导热系数接近的回填材料。     

基于TRNSYS模拟的地埋管换热效果影响因素分析

通过原位热响应试验数据验证了TRNSYS软件中U型地埋管换热器模块Type557计算模型的可靠性,应用TRNSYS软件建立地埋管换热模型。基于正交试验的研究方法,综合分析了埋管壁、回填材料、埋管周围岩土的导热系数对埋管换热器换热效果的影响规律。得到影响地埋管换热过程的最主要因素是岩土导热系数,回填料导热系数对其影响程度略低于岩土导热系数,埋管壁导热系数对其影响不大的结论。     

含水率对工程常用土导热系数影响的试验研究

岩土的导热系数对工程施工和工程运行有较大影响,研究不同含水率条件下的导热系数变化规律对岩土的导热理论和工程实践具有重要意义。根据《土工试验规程》制备出粗砂、中砂、细砂、粉砂和粘土等5种工程常用土,试验分析了不同含水率时的导热系数变化规律,并根据试验结果得到5种土导热系数随含水率变化的拟合公式。结果表明,5种土的导热系数均随含水率的增加呈非线性增加。含水率在0~15%时,导热系数由大到小顺序依次为粗砂、中砂、细砂、粉砂和粘土;含水率超出20%时,中砂、细砂、粉砂的导热系数变化趋于平缓并呈轻微下降趋势;含水率大于25%时,粘土导热系数呈下降趋势。     

常温土壤导热系数的试验及预测研究

探究土壤导热系数的变化规律，对地源热泵系统和土壤储热等领域具有重要意义。利用TEMPOS热性能分析仪对不同干密度、不同饱和度下黄土和砂土导热系数变化规律进行研究。结果表明，饱和度、干密度均对土壤导热系数影响显著，黄土、砂土的导热系数随饱和度的增加总体呈增大趋势，但黄土和砂土的导热系数变化规律差异明显；黄土和砂土的导热系数随干密度的增大而增加，但黄土较砂土变化幅度较小。根据试验数据对16种预测模型进行评价，结果表明，CCM模型表现最好。     

地热井保温水泥导热系数影响因素研究

选择合适的测试方法探究不同因素对保温水泥导热系数的作用规律和方式。研究表明：随着保温材料加量和水灰比的增大，水泥石导热系数先迅速减小，随后下降速率降低并逐渐趋于稳定；随着养护温度的升高和时间的增长，导热系数逐渐减小，并在7 d后基本稳定；随着含水率的增大和测试温度的升高，导热系数显著增大；其中，含水率、测试温度、保温材料加量和水灰比等因素对导热系数的影响逐级递减。低密度和具有类蜂窝状结构的保温材料在降低导热系数和维持抗压强度等方面具有较大优势，且保温材料的推荐加量为15%～20%。     

污泥干化过程中导热系数的试验研究

在对上海竹园生活污泥和绍兴印染污泥进行试验测试的基础上,得到污泥的表观导热系数与污泥含水率、温度、密度间的关系。结果表明,所研究的两种污泥在含水率低于50%时,导热系数值很低,随含水率变化缓慢,而当含水率高于50%时,污泥导热系数会随含水率的增加而迅速增大;低含水率(5.03%和12.06%)的污泥随温度的升高导热系数呈缓慢上升趋势;而含水率较高(36.70%和51.70%)的污泥,导热系数随温度的增加呈迅速增大趋势,密度小于0.4 kg/m3时导热系数随密度变化不明显,密度大于0.4 kg/m3后,导热系数随密度增加而迅速增大。     

地埋管回填材料传热性能的研究与分析

当回填材料导热系数大于周围岩土层,对地埋管换热器换热性能提升效果开始逐步递减。研究回填材料增益效果递减的原因,对提高总系统运行效率具有重要意义。通过软件平台Workbench对地埋管换热器在回填材料导热系数不同的情况下进行模拟。结果显示,回填材料在整个传热过程中主要起到疏导热量,扩大导热面积的作用。回填材料导热系数较高时,可通过提高进水管水温进一步开发系统换热效率。     

聚氨酯预制直埋保温管道散热损失研究

针对聚氨酯预制直埋保温管道散热损失开展实验与数值模拟研究。通过实验测试了聚氨酯预制直埋保温管道的散热损失,同时对输送介质温度、聚氨酯导热系数、土壤温度及其导热系数进行了测试,对影响聚氨酯预制直埋保温管散热损失的相关因素进行分析。并根据实验数据开展数值模拟研究,分析了不同条件对聚氨酯预制直埋保温管道散热损失的影响。研究结果表明:聚氨酯预制直埋保温管道散热损失随输送介质温度的升高而增加,保温管道周围土壤温度与保温管道径向距离成反比,聚氨酯保温材料导热系数对保温管道的散热损失影响较大,土壤导热系数在1.082-1.561 W/m·K时,土壤导热系数与保温管道散热损失成正比,但对保温管道散热损失产生影响较小。     

不同形式地埋管换热器运行性能影响因素研究

为研究单U和双U地埋管换热器运行性能的影响因素,运用能耗模拟软件TRNSYS建立地埋管换热器模型对其运行特性进行仿真模拟后,与实际工程数据对比,验证模型有效性,继而以换热器能效系数为评价指标,分别对钻孔深度、U型管两管间距和回填材料导热系数等影响因素进行分析研究,得到:双U地埋管换热器的单位延米换热量为106.72 W/m,单U地埋管换热器的单位延米换热量为86.39 W/m;适当增加钻井深度、埋管间距和回填材料导热系数对整体换热效果有促进作用,且在双U埋管情况下促进作用更显著的结论.     

Experimental performance evaluation of a closed‐loop vertical ground source heat pump in the heating mode using energy analysis method

An experimental study is performed to determine the performance of a ground source heat pump (GSHP) system in the heating mode in the city of Erzurum, Turkey. The GSHP system using R‐134a as refrigerant has a single U‐tube ground heat exchanger (GHE) made of polyethylene pipe with a 16 mm inside diameter. The GHE was placed in a vertical borehole with 55 m depth and 203.2 mm diameter. The average coefficients of performance (COP) of the GSHP system and heat pump in heating mode are calculated as 2.09 and 2.57, respectively. The heat extraction rate per meter of the borehole is determined as 33.60 W m^?1. Considering the current gas and electric prices in Erzurum city, the equivalent COP of the GSHP system should be 2.92 for the same energy cost comparing with natural gas. The virgin ground in Erzurum basin has high permeability and low thermal conductivity. In order to improve the thermal efficiency of GHE and thus improve COP of a GSHP in the basin, the borehole should be backfilled with sand as low‐cost backfill material and a 1 to 2 m thick surface plug of clay should be inserted. Copyright © 2007 John Wiley & Sons, Ltd.     

Heat and moisture transport in durian fiber based lightweight construction materials

This paper presents result on heat and moisture transport in durian (Durio zibethinus) fiber based lightweight construction materials composed of cement, sand and waste fiber from durian peel and the performance of the material was simulated with the surface treatment by using a computational tool. The commercial research software (WUFI 2D) was used to calculate heat and moisture transfer through a durian fiber based lightweight construction material. The materials were exposed to a climate condition similar to the one in Bangkok and the hygrothermal characteristics of the materials were investigated. The investigation reveals that the weekly mean water content on the surface of material was quite low. The effect of moisture on the apparent thermal performance of the composite was found to be higher as water absorbed in the pore structure contributed to higher thermal conductivity than the air it replaced. However, the mean value of thermal conductivity in material is still rather low as the mean value of water content in material is low. Coating the surface reduced the flow of moisture to or from the structure considerably. The results of simulation confirmed that the manufactured composite satisfied the requirement of construction materials. It is then reasonable to conclude that the use of such materials in the design and construction of passive solar buildings is promising. Laboratory investigation is undergoing to validate the simulated performance.     

Performance of solid particles flow thermal storage material made of desert sand

It is a safe and low-cost new heat storage method to realize sensible heat storage at medium and high temperature by using flowing inorganic inert solid particle materials. The cost and performance of granular heat storage medium are very important for this kind of heat storage technology. The yellow sand in southeast of Tenggri Desert in Ningxia is studied. By thermal shock and grinding methods, the tests of thermal shock-resistance and wear resistance were carried out, under laboratory conditions, for the unscreened raw sand and the screened sand samples with three grain sizes (40–60 mesh, 60–80 mesh, and 80–100 mesh). The particle size of the raw sand is 150–300 µm (60–100 meshes) accounts for 60% (wt %) or more and meets the requirement of heat storage material. The density, thermal conductivity, and specific heat of raw sand are higher than those of three kinds of screened sand. Thermal shock and grinding affect the particle size distribution, density, specific heat, and thermal conductivity of the particles. The degree of influence varies with the particle size. The volume ratio heat capacity is used to measure the heat storage performance of the particles. Thermal shock results in a better thermal storage performance of the screened sand than the original sand. After comprehensive analysis of the properties of three kinds of screened sand, it is found that the content of 60–80 mesh-screened sand (31.75%) is the highest in the original sand. After thermal shock and grinding, the screened sand not only has good heat storage performance (average volumetric specific heat capacity 3.232 J· K^?3· K^?1), but also has the smallest change of particle size (breaking rate is less than 24, and agglomeration rate is less than 6), and the thermal shock resistance and wear resistance are outstanding. It is suggested that the screened sand with the particle size range of 200-300µm (60–80 mesh), also the particles with the highest content in the original sand, should be selected as the solid particle flowing heat storage medium.     

Mechanical and thermal properties of cement composite graphite for solar thermal storage materials

The comprehensive survey on an attractive thermal storage material consisted of aluminate cement and graphite is obtained in this paper. The effect of different water/cement (w/c) ratio and graphite content on compressive strength and thermal properties including thermal conductivity, volume heat capacity and thermal expansion coefficient of hardened aluminate cement pastes were investigated to pursue the optimum material design for solar parabolic trough power plant. It is observed that thermal conductivity and volume heat capacity were improved with the decrease of w/c and the increase of graphite content. The results show that w/c is a key factor affecting thermal properties of pastes and graphite even has some influence on the hydration process. After heat treatment at 350 °C for 6 h, compressive strength and thermal properties descended in a certain extent. XRD and FTIR were used to characterize the evolution of hydration products together. Furthermore, the properties obtained from the paper will lay the foundation for thermal storage materials of solar thermal power plants in the future.     

孔隙率与含水率对砂质土样导热系数的影响

鉴于研究岩土体导热系数的变化规律及影响因素,对岩土的导热理论和工程实践的现实意义,利用热探针测定了不同孔隙率和含水率条件下的砂质土样导热系数,分析其变化规律,并用1stOpt软件得到孔隙率、含水率与导热系数的拟合公式。计算结果与试验结果表明,导热系数随孔隙率的增加而减小,随含水率的增加而增大,且在一定含水率下,导热系数随孔隙率的增加呈线性减小,孔隙率为0.468~0.511时,导热系数降幅为20.19%;在一定孔隙率下,导热系数随含水率的增加呈非线性增长,含水率0~10%时,导热系数增幅为338.38%,含水率10%~15%时,导热系数的增幅为8.83%。     

Experimental performance of borehole heat exchangers and grouting materials for ground source heat pumps

The system performance of a ground source heat pump (HP) system is determined by the HP characteristics itself and by the thermal interaction between the ground and its borehole heat exchanger (BHE). BHE performance is strongly influenced by the thermal properties of the ground formation, grouting material, and BHE type. Experimental investigations on different BHE types and grouting materials were carried out in Belgium. Its performances were investigated with in situ thermal response tests to determine the thermal conductivity (λ) and borehole resistance (R_b). The line‐source method was used to analyze the results, and the tests showed the viability of the method. The main goal was to determine the thermal borehole resistance of BHEs, including the effect of the grouting material. The ground thermal conductivity was measured as 2.21 W m^?1 K^?1, a high value for the low fraction of water‐saturated sand and the high clay content at the test field. The borehole resistance for a standard coaxial tube with cement–bentonite grouting varied from 0.344 to 0.162 K W^?1 m for the double U‐tube with cement–bentonite mixture (52% reduction). Grouting material based on purely a cement–bentonite mixture results in a high thermal borehole resistance. Addition of sand to the mixture leads to a better performance. The use of thermally enhanced grouts did not improve the performance significantly in comparison with only a low‐cost grouting material as sand. Potential future applications are possible in our country using a mobile testing device, such as characteristics, standardization, quality control, and certification for drilling companies and ground source HP applications, and in situ research for larger systems. Copyright © 2011 John Wiley & Sons, Ltd.     

超强吸水树脂与源土混合作为地源热泵供热系统回填材料的实验研究

在热泵制热工况下,超强吸水树脂与源土混合作为回填材料,分别对螺旋盘管、U型管以及整个系统进行了实验研究,得出系统性能变化曲线。实验结果表明,超强吸水树脂与源土混合作为回填材料,特别是螺旋盘管换热器,可明显增大地下换热器换热量,提高地源热泵系统的效率和稳定性,适用于干旱、土壤非饱和以及地下水位比较低的地区。     

Study of different grouting materials used in vertical geothermal closed-loop heat exchangers

As a renewable source, low-enthalpy geothermal energy is becoming more relevant in heating and cooling buildings, by using an adapted heat pump to exchange thermal energy with the ground. Vertical closed-loop geothermal systems exchange heat with the ground through a closed buried pipe system, sealed with a grouting material that ensures the stability and thermal transmission of the borehole. Different grouting materials have been tested recently, which use cement or bentonite as a base material. However, the use of recycled materials, which might contribute to the sustainability of the project, has not yet been studied. This paper analyzes the use of different natural and recycled aggregates as main constituents in cement-based mortars. Results show that all mixes fulfill the minimum consistency and strength requirements. The use of any of the aggregates proposed improves the thermal conductivity compared to the cement mortar on its own, independently of the proportion used. Limestone sand, silica sand and electric arc furnace slag enhance the thermal conductivity of the grout as its proportion of use increases. However, no satisfactory results have been obtained for Construction and Demolition Waste-based mixes because of their high water requirement.     

Improvement of thermal performance of mortars by using heat storage aggregate made with industrial by-product to reduce cooling load

The usage of waste materials as building materials can be an important method to reduce energy consumption and decrease natural resource usage in the construction industry. In this work, phase change materials (PCMs) were incorporated with industrial by-product materials as an aggregate to produce mortars, which can improve the energy efficiency and improve the environment of buildings. Bottom ash (BA), a by-product from coal-fired power plants, was directly impregnated into paraffin, a PCM, to produce a heat storage aggregate (HSA). The raw materials of the HSA production were characterized by X-ray diffraction, scanning electron microscope, and differential scanning calorimeter. The mortar mixes had a water to cement ratio of 1:2 and a sand to cement ratio of 2.5:1. Six mixtures were prepared with different HSA amounts of 0%, 10%, 20%, 30%, 40%, and 50% by volume. The compressive strength, density, and thermal properties of the mortars were investigated. The results and analyses showed that the compressive strength and density of the mortars decreased with increasing HSA amounts. The thermal conductivity of HSA mortars slightly decreased for increasing levels of HSA. In addition, HSA mortars showed a significant increase in time lags when the HSA content increased, up to approximately 165% to 197% higher than that of the control mortars. HSA levels in mortars can play an important role in improving the heat conductance into buildings.