共查询到19条相似文献,搜索用时 78 毫秒
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《工业加热》2018,(6)
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。 相似文献
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通过对典型长期在役热力蒸汽管道保温材料导热系数和保温结构进行实地测量,并在此基础上进行数值建模,探究两种不同因素对热力蒸汽管道保温性能的影响机制。其中,保温材料导热系数通过现场采样并利用Hot Disk热常数分析仪进行实验测量,保温结构参数以结构偏心率和底部镂空夹层厚度为关键特征参数。研究结果表明,数值计算与实验测量的管道散热损失能够很好吻合,其保温性能恶化系数分别为1.65和1.64。进一步分析表明,对于所选取热力管道,保温材料导热系数、偏心和镂空结构对保温性能恶化所占比重分别为67.7%,13.8%和18.5%。 相似文献
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为研究保温管道不同保温材料在埋地敷设和架空敷设时的保温情况,通过Ansys软件建模计算架空管道和直埋管道在不同保温材料下运行前期和运行稳定后热损失随时间变化的情况,模型考虑了保温材料和土壤的比热容。数据结果表明:在管道运行初期,直埋管道和架空管道的热损失几乎一致,保温效果主要取决于保温材料的导热系数。当管道运行稳定在管壁周围形成一个稳定的温度场后直埋管道的保温效果稍好于架空管道的保温效果,且随着保温材料导热系数的增加,埋地管道的保温效果越明显。在管道架空敷设时,选用导热系数小的保温材料收益更高。 相似文献
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竖直U型埋管地热换热器热短路现象的影响参数分析 总被引:6,自引:0,他引:6
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。 相似文献
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文章建立了三维非稳态的全玻璃真空管太阳热水器的数值模型,分析了夜间散热时,该热水器内的流动和传热特征,并且在夜间同一工况下,模拟研究了贮热水箱保温材料的导热系数、保温厚度,以及真空管涂层的发射率对贮热水箱温度、真空管温度和该热水器夜间热损失的影响。分析结果表明:随着散热过程的持续进行,全玻璃真空管太阳热水器内温度分层情况越来越明显,内部流体的流速越来越小,真空管内静滞区域自下往上逐渐扩大;当贮热水箱保温材料的导热系数由0.035 W/(m·℃)减小至0.020 W/(m·℃)时,该热水器的夜间热损失减少了8.5%;当贮热水箱保温厚度由50 mm增加至60 mm时,该热水器的夜间热损失减少了5.0%;当真空管涂层的发射率由0.06减小至0.05时,该热水器的夜间热损失减少了4.0%。 相似文献
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本文通过计算透过热处理炉壁的热损失和预测炉子外壳温度的方法,介绍了热处理炉最常用材料的导热系数;论证炉子温度变化对热损失的影响;炉子上的金属构件、砂封、开炉门的时间与频率以及气氛加热等因素造成的热损失进行了详细阐述。 一、基本计算 首先研究以下两种情况: 在一台炉子的炉壁处于热平衡时,透过炉 相似文献
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孔隙率与含水率对砂质土样导热系数的影响 总被引:3,自引:0,他引:3
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%。 相似文献
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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%。 相似文献
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在国家规定的热网管道的每米热损失下,其保温层厚度随着保温材料的导热系数及工质温度的不同而不同。利用导出的计算公式,通过计算,将以上四个参数的关系用图表的形式表示出来,以供在热网管道的保温中予以应用。 相似文献
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含水率对工程常用土导热系数影响的试验研究 总被引:1,自引:0,他引:1
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。 相似文献
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The improvement of heat transport is a very important phenomenon in nuclear reactors, solar collectors, heat exchangers, and coolers, which can be achieved by choosing the nanofluid as the functional fluid. Nanofluids improve thermophysical properties; as a result, they have made great progress in engineering, biomedical, and industrial applications. Therefore, a numerical study has been proposed to analyze the flow and heat transport of nanoliquids over an extendable surface near a stagnation point with variable thermal conductivity under the influence of the magnetic field, due to their importance in the engineering field. Nanoliquid attributes explain the Brownian motion and the diffusion of thermophoresis. The effects of the chemical reaction and the uniform internal heat source/heat sink are also considered. The Nachtsheim‐Swigert shooting procedure based on the Runge‐Kutta scheme is used for numerical calculation. The impact of effective parameters on velocity, temperature, and volume fraction of the nanoparticles is shown in the graphs and reported in detail. The surface criteria are also estimated with respect to the shear stress and the rate of heat and mass transfer. The aspects of the Brownian moment and Lorentz force are positively correlated to the thermal field of the nanoliquid. Also, the variable thermal conductivity aspect favors the growth of the thermal boundary layer. 相似文献
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The idea of combining photovoltaic and solar thermal collectors (PVT collectors) to provide electrical and heat energy is an area that has, until recently, received only limited attention. Although PVTs are not as prevalent as solar thermal systems, the integration of photovoltaic and solar thermal collectors into the walls or roofing structure of a building could provide greater opportunity for the use of renewable solar energy technologies. In this study, the design of a novel building integrated photovoltaic/thermal (BIPVT) solar collector was theoretically analysed through the use of a modified Hottel-Whillier model and was validated with experimental data from testing on a prototype BIPVT collector.The results showed that key design parameters such as the fin efficiency, the thermal conductivity between the PV cells and their supporting structure, and the lamination method had a significant influence on both the electrical and thermal efficiency of the BIPVT. Furthermore, it was shown that the BIPVT could be made of lower cost materials, such as pre-coated colour steel, without significant decreases in efficiency.Finally, it was shown that by integrating the BIPVT into the building rather than onto the building could result in a lower cost system. This was illustrated by the finding that insulating the rear of the BIPVT may be unnecessary when it is integrated into a roof above an enclosed air filled attic, as this air space acts as a passive insulating barrier. 相似文献
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S.-A.B. Al Omari 《International Communications in Heat and Mass Transfer》2011,38(8):1073-1079
The present study is a numerical investigation on the flow and heat transfer in a mini-channel where both hot liquid water and mercury co-flow together in a direct contact manner. Results show that the presence of a high thermal conductivity liquid metal such as mercury enables the hot water to lose much more of its initial thermal energy content, than when only water alone flows in the channel. However, too unjustified excessive mercury co-flowing with the hot water can lead to adverse effects in regards to the heat loss from the hot water. The reason behind the enhanced heat transfer between the two liquids is due to the initiation of high temperature gradients sites inside the channel, especially in the region of the interface between the two liquids, in addition to the high thermal conductivity of mercury, as compared to water thermal conductivity. These two effects lead to effective conduction cooling in the transverse direction over the whole length of the channel. These aspects are quantified in this study. 相似文献
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叙述了胶粉聚苯颗粒保温浆料的保温效果达不到要求的直接原因是聚苯颗粒的数量不够,根本原因则是保温浆料的黏结力太差。指出,增多聚苯颗粒的体积,减少导热系数,增加保温性能,提高胶粉料的黏结性能,确保足够的聚苯颗粒含量,可保证保温浆料的保温性能。 相似文献