光学热带法测量固态材料热物性研究

针对接触式瞬态热带法测量导热系数时,加热丝和样品间接触热阻,会影响实验测量结果以及对固体样品形状大小要求较高的现状,根据瞬态热带法原理,本文提出了一种光学瞬态热带法来测量固体材料的导热系数。采用连续激光为加热源,通过透镜将光斑放大并聚焦照射在样品表面,实现样品非接触式测量。构建二维导热模型,采用红外热像仪记录样品表面温升随时间的变化关系,根据导热理论模型求出待测样品的热扩散系数及导热系数。以K9和石英玻璃为样品对本套测量方法进行验证,制备并测量了纯石蜡、0.5%和1%石墨烯-石蜡的固态复合相变材料的导热系数,探讨了影响实验结果的潜在因素。     

TPS法测定泡沫铜/石蜡复合相变材料热物性

运用瞬态平面热源法(Transient Plane Source-TPS)对4种孔隙率的泡沫铜/石蜡复合材料热物性进行了测量。以10μm厚的镍金属按双螺旋线布置作为测量探头。泡沫铜材料孔隙率分别为ε=97.79%、ε=96.17%、ε=94.94%和ε=93.26%,经线切割加工后向内灌入液态石蜡,凝固后作为测试样品。在室温(25±1℃)和常压下对复合材料的等效导热系数、热容及热扩散率进行了测量。测试结果表明:复合材料导热系数和热扩散率因泡沫铜的加入而大幅提高,在孔隙率ε=93.26%时,等效导热系数已达到单纯石蜡的25倍,而复合材料等效热容则由于铜金属加入的绝对量较少相对原石蜡热容变化较小。以比例加成的方法对泡沫铜/石蜡复合材料的等效热容进行了计算,并利用实验数据拟合了其等效导热系数的计算公式,运用这些公式对复合材料物性的计算结果与实验结果非常吻合。     

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%。     

温湿度对冰箱保温材料隔热性能影响研究

在不同工况下对冰箱保温材料聚氨酯发泡材料的导热系数及热工性能进行测试,结果表明:环境温湿度对冰箱保温材料的热工性能影响明显,保温材料的导热系数随温湿度的增大而增加;夏季高温工况时,保温材料隔热性能衰减4.11%;高低温交替变化条件下,保温材料隔热性能衰减为11.92%。研究结果可为今后冰箱隔热材料的制作过程提供理论指导,以达到降低能耗目的。     

Influence of 2-D nanofillers on the thermal conductivity of composite PCMs

为了探究两种不同二维纳米填料对复合相变材料导热系数的影响,分别制备了以石墨烯纳米片和六方氮化硼纳米片为填料的石蜡基复合相变材料.采用瞬态平面热源法在20 ℃时测量了不同添加量下复合相变材料的导热系数.结果显示,石蜡基复合相变材料的导热系数随纳米填料添加量近似线性增长;六方氮化硼纳米片对复合相变材料导热系数的提升远低于石墨烯纳米片.此外,利用基于有效介质模型的预测公式与试验值进行了比较,计算发现形状,大小和导热系数相近的两种纳米材料,六方氮化硼纳米片的界面热阻却高出石墨烯纳米片两个数量级,是后者具有更显著强化效果的原因之一.     

岩土热响应散热修正瞬态模拟及关键参数研究

提出一种带散热修正的地埋管储热的TRNSYS瞬态计算模型,考虑管道散热及地表空气对流散热损失;在山东省滨州市进行实地热响应测试,通过对实验测试井供回水温度的模拟,验证模型准确性。同时,模拟分析循环流量、加热功率等关键参数对岩土导热系数、钻孔热阻、延米换热量辨识精度的影响。研究结果表明,测试持续时间对岩土导热系数辨识精度影响高达24.88%,其次分别是加热功率、初始舍弃时间、循环流量、回填材料导热系数。加热功率对延米换热量影响最高达75.01%。     

双平板法测量建保浊湿材料导热系数

论述双平板法测量建筑保温材料导热系数的基本原理、操作步骤和技术性能，通过对一定数据的分析，讨论影响导热系数的主要因素。     

导热规律服用q∞（△T）^n广义不可逆卡诺热机的最优性能

考虑工质与热源间热阻损失,用一常数项表示热漏损失和常系数项表示循环中除热阻和热漏外其余不可逆性，建立不可逆卡诺热机模型。基于另一类较为普遍的导热规律Q∞（△T）^n，导出热机的功率和效率最佳特性关系，由详细数值计算分析了热漏、内不可逆性和导热规律的影响特点。     

岩芯导热系数测试

为了研究采油井筒附近地层传热状况，用防护热板法对岩芯的导热系数进行了测试，并对测试结果进行了分析。     

微纳米粒子对辛酸-肉豆蔻酸相变储能体系热物性的影响

该文通过添加3组同族(镍、铝、铜)亚微米级金属、纳米金属及纳米金属氧化物改善其传热性能,制备可用于空调蓄冷系统的新型相变储能材料;通过步冷实验、差示扫描量热法(DSC)及瞬态平面热源法(Hotdisk)对比添加剂对OA-MA在过冷度、相变温度、相变潜热、导热系数及热扩散率等方面的影响,研究添加剂种类与颗粒尺寸对上述热物性的影响规律;利用Maxwell及Zimmerman公式对比不同质量比例的纳米氧化铜(CuONP)对材料导热系数的影响,研究纳米流体传热传质机理,数据拟合得出其拟合公式。     

Determination of the thermal conductivities of building and insulating materials by the probe method

A simple and inexpensive electrical circuit based on the transient probe method has been developed for the determination of thermal conductivities of building and insulating materials namely limebrick, gypsum, rockwool and polystrene foam. The solution of the unsteady state heat conduction equation has been approximated by considering certain simplifying assumptions which have been justified by experimental observations. The overall accuracy of the thermal conductivity measurements is estimated to be within ± 3%.     

An experimental and theoretical study of the nonlinear heat conduction in dry porous media

Heat transfer in porous media is important in various engineering fields, including contaminated soil incineration. Most heat transfer models are theoretical in nature. Consequently, this study was undertaken to perform both theoretical and experimental studies of heat transfer in two different sand matrices. A mathematical model based on Fourier's law of heat conduction for a one‐dimensional system with the variable thermal conductivity was developed. The experimental part included heating sand samples placed in a small reactor within an infrared furnace. The transient temperature profiles of the sand layers were monitored by thermocouples. The bulk thermal conductivity was estimated to be linearly proportional to the temperature. The temperature profiles predicted by the model of heat conduction with a variable bulk thermal conductivity was compared by the observed temperatures in Quartz and Sea sands matrices up to 1300 K. Copyright © 1999 John Wiley & Sons, Ltd.     

正交各向异性相变材料的无网格法传热模型及应用

利用无网格迦辽金(EFG)法建立正交各向异性相变材料的传热计算模型,基于该模型编程完成各向异性材料太阳能相变蓄热水箱和管壳式相变蓄热单元的相变传热分析,并探讨热导率因子和材料方向角对复合材料相变传热特性的影响.研究表明:在相同节点布置下EFG法的温度场和相界面计算精度均高于有限元法,EFG法在动态相界面追踪方面具有明显...     

Experimental and theoretical study of the hot-wire method applied to low-density thermal insulators

The use of the hot wire method for thermal conductivity measurement has recently known a significant increase. However, this method is theoretically not applicable to materials where radiative heat transfer is not negligible such as low-density thermal insulators. In order to better understand the influence of radiative contribution, we developed a two dimensional simulation of transient coupled heat transfer and made hot-wire measurements on low-density Expanded PolyStyrene (EPS) foams. The analysis of theoretical and experimental results shows that classical hot-wire apparatus are poorly adapted to low-density insulators. However, if an appropriate hot-wire apparatus is used, the estimated equivalent thermal conductivity is in close agreement with that estimated by the guarded hot-plate method.     

增强石蜡相变材料传热性能的实验研究

添加高导热颗粒和增大换热面积是当前增强石蜡相变材料传热性能的主要研究方向。以此为基础搭建试验台结合数据采集系统对石蜡在圆管外的熔化凝固过程进行了实验测试,并对各测点的温度变化趋势进行分析,研究了添加不同纳米颗粒和加入金属肋片对换热过程的影响。结果表明:在石蜡溶液中添加纳米颗粒能够起到减小过冷度的效果同时有效增强相变材料的传热性能,添加纳米氧化铜颗粒的传热性能增强效果要优于添加氧化锌颗粒和二氧化硅颗粒;在储热系统中加入肋片能够显著提高相变储能系统的热性能,强化换热过程。     

Numerical simulation of the cooling of a hot disk rapidly subjected to combined convective and radiant heat losses

The development of a transient method for measuring the spectral directional emissivity of solid materials at high temperature is currently being completed by the analysis of the influence of various sources of error. A hot disk is subjected to mixed convective and radiant heat losses on one face after the rapid withdrawal of a shutter. The cooling is investigated during a short period of observation through numerical simulations of the transient temperature. The thermal problem is simulated using 3D and axisymmetric 2D codes. The progressive withdrawal of the shutter results in a delay for the transient temperature in comparison with the instantaneous withdrawal. For an insulating material, the influence of the side wall boundary conditions remains negligible at the center of the front face. The strong influence of the convective heat transfer is demonstrated.     

Research progress on heat transfer enhancement technology of phase change energy storage

相变储能是通过相变材料吸/放热过程来实现能量储存的技术,它能够解决热量供需时间、空间和强度上的不匹配,并以其高储能密度成为储能领域的研究热点,但由于相变材料的热导率较低,使其应用受到限制。针对相变储能材料熔化/凝固过程中热导率低引起的传热速率慢的问题,从优化储能设备结构、添加剂提高相变材料热导率以及联合强化传热技术三方面综述国内外相变材料储能强化传热技术的最新进展。通过比较各种强化传热方式的优劣,实验和模拟均显示复合强化传热即可解决相变材料热导率低,又增大传热面积,从而提高相变材料的传热性能;多孔金属作为导热添加剂增强导热效果更好;并提出了相变储能强化传热技术未来需要解决的相关技术难题。     

Heat-spreading analysis of a heat sink base embedded with a heat pipe

A simplified model predicting the heat transfer performance of a heat sink base with a high thermal conductivity was developed. Numerical analysis was performed using the commercial software FLUENT. The investigation indicates that for heat sink bases with a high effective thermal conductivity, such as the base embedded with a typical heat pipe, the entire heat sink can be modeled as a flat plate with a uniform temperature and an effective convection heat transfer coefficient. This simplified model can be used to determine the heat transfer performance of a heat sink embedded with a typical heat pipe or vapor chamber.     

The research applications of new heat insulation composite material in automobiles

With the rapid development of its unique advantages, nonwoven fabric has become the leading material of automotive textiles. Nonwoven fabric has become an ideal material for automobiles and replaced traditional textiles and plastic products. This paper takes a car as the research model. A DRL‐2B thermal conductivity tester was used to test thermal conductivity of the material based on the plate method. Material systems and structures of new types of heat insulation composite materials were determined according to test results and the theory of heat transfer. Then, the final new type of heat insulation material was determined by calculating and comparing average heat transfer coefficients and heat transfer between traditional insulation materials and new types of heat insulation materials. The calculated results were verified by experiments in this paper. All the test results show that the new type of composite insulation material is significantly better than traditional insulation materials, and the test results match the calculated results.     

强化太阳能相变蓄热技术的研究进展

为解决太阳能的间歇性问题,常将其与相变蓄热技术进行结合。与传统显热蓄热相比,相变蓄热可将蓄热能量提高数倍以上,具有巨大的研究和应用价值。本文总结分析了相变蓄热的传热机制及在强化太阳能相变蓄热技术上的研究手段,如变换蓄热结构、添加肋片、使用相变胶囊、充注多相变材料、蓄热材料中添加高导热物质等。分析结果显示,相变传热机制中,融化过程主要考虑对流换热,凝固过程热传导占主导;使用肋片、相变胶囊等,主要增大相变材料接触面与蓄热体的比值,进而改善传热;蓄热材料添加高导热物质,可以改善相变材料的团聚、结核及使用寿命,从而提高导热性能,其中添加泡沫金属效果最为显著。