并联模型法测量不规则泡沫塑料导热系数

稳态热流计法是测量保温材料导热系数的常用方法之一,但由于方法和仪器设备的限制,难以测量不规则保温材料的导热系数。本文以硬质聚氨酯泡沫为研究对象,首先在不同平均温度下验证和分析了不同拼接方式下并联模型法与整体测试结果。为了验证并联模型的可靠性和可重复性,按模型对聚苯乙烯泡沫及聚氨酯泡沫试样重复测试,并对测试结果和计算结果进行比较,结果表明,利用并联模型法计算所得的导热系数值与实测值误差小,重复性好。     

串联模型热流计法测薄层泡沫塑料导热系数

稳态热流计法因方法简单,广泛应用于测量保温材料的导热系数。但因仪器设备和方法的限制,难以测试薄层材料的导热系数。本文分别以聚苯乙烯泡沫和硬质聚氨酯泡沫为研究对象,首先在不同平均温度下测试不同厚度聚苯乙烯材料的导热系数,再利用串联模型法推导计算多层材料的导热系数。为了验证串联模型的可靠性和可重复性,按模型对聚苯乙烯泡沫及聚氨酯泡沫试样重复测试,并对测试结果和计算结果进行比较,结果表明,利用串联模型法计算所得的导热系数值与实测值误差小,重复性好。     

串联模型法测量泡沫塑料导热系数

采用串联模型热流计法,即通过叠加试样间接测量的方式,对硬质聚氨酯泡沫塑料、橡塑泡沫塑料及挤塑聚苯乙烯泡沫塑料在平均温度10℃、15℃、25℃下的导热系数进行了测试,并分析比较了导热系数测试值与模型计算值。结果表明:在不同平均温度及材料条件下,导热系数的串联模型计算值与测试值的误差均较小,因此该串联模型可用于薄层材料导热系数的测试。     

水泥石导热系数的计算模型

测试了不同水灰比、不同养护龄期水泥石的导热系数,并对比了并联模型、串联模型、Maxwell模型、Mori-Tanaka模型、有效介质理论模型和Self-consistent模型对水泥石导热系数的预测效果。利用分子动力学方法计算了水泥石中各相的导热系数。结果表明:水泥石的导热系数随着养护龄期和水灰比的增大而减小。SC模型适用于不同水灰比和养护龄期水泥石导热系数的计算,其计算结果与试验值的相对误差在0.3%～4.7%之间。Maxwell模型和MT模型可以用于对水灰比较大且养护龄期较长的水泥石的导热系数进行计算。     

基于激光热成像技术的耐火材料导热系数测试新方法

为了满足耐火材料对导热系数测试快速、准确的需求,提出了基于激光加热耐火材料、结合红外热成像技术的材料导热系数测试新方法——激光热成像法,并与现有国家标准的闪光法测试导热系数常用的耐驰公司激光导热仪FLASHLINE-500进行数据对比,探讨了两种不同方法测试不同成分耐火材料导热系数的差异。结果表明:相比闪光法,采用激光热效应结合红外热成像技术的新测试方法能快速、准确地测量出不同耐火材料的导热系数;对材料的导热情况显示直观、明确,测试方法操作简单,抗干扰能力强,大大降低了测试的成本投入。     

PE-XC材料导热系数的测量

文章采用瞬态热线法测试PE材料的导热系数,介绍了瞬态热线法的优势,并使用TC3000导热系数仪更加快捷、精确、高效的测试PE材料的导热系数。     

生产低导热系数的聚氨酯闭孔硬泡沫的方法

聚氨酯硬泡沫材料的导热系数相当程度上取决于发泡剂的类型或所使用的气体。可以在多元醇配方中采用不同的发泡剂体系来生产低导热系数的硬泡沫材料，而无需改变配方或机械装备参数，以利于降低成本。该文详细介绍了低导热系数的聚氨酯闭孔硬泡沫的多元醇组分和多异氰酸酯，以及发泡过程的要诀。     

五种保温材料的耐久性性能试验研究

为研究外墙外保温材料的耐久性能,对聚氨酯泡沫,硅酸铝陶瓷,铝箔玻璃棉,橡塑保温板和挤塑聚苯板进行抗冻性、耐老化、抗压强度和抗拉强度测试.根据测试结果得出:20次冻融循环后,聚氨酯泡沫的导热系数增长81.25％,硅酸铝陶瓷的导热系数增长57.78％,铝箔玻璃棉的导热系数增长28.95％,橡塑保温板的导热系数增长34.48...     

聚酯铵盐粉末发泡制备聚酰亚胺泡沫材料的研究

以芳香二酐和二胺为单体,采用聚酯铵盐前体粉末发泡的方法制备聚酰亚胺泡沫材料。考察了发泡温度、粉末大小对泡孔结构的影响。力学和热性能测试结果表明,该泡沫材料拉伸行为呈脆性,而压缩行为呈塑性,密度较大的聚酰亚胺泡沫表现出较好的力学性能。随着泡沫材料密度增大或测试温度升高,聚酰亚胺泡沫的导热系数增大。     

石墨泡沫材料性能研究的随机建模方法

石墨泡沫是一种新型多孔材料,具有内表面积大、低密度、高导热等优异热性能.基于泡沫类多孔材料内部孔隙空间位置及孔径分布的局部不均匀性质,提出了一种均匀随机几何模型的建模方法,用于石墨泡沫导热性能的数值模拟,并将容积导热系数的模拟结果与美国ORNL的实测数据作了比较.     

开孔泡沫金属复合材料有效热导率的研究进展

有效热导率是开孔泡沫金属复合材料热传输热性的重要参数,基于三维结构的复杂性,从边界模型和晶胞分析模型两个方面出发,较为全面地概述了有效热导率的研究现状。指出边界模型以均质化方法宏观分析热传导问题而忽略了微观孔结构的影响,重点阐述晶胞分析模型中立方体模型和开尔文模型的经验相关性分析方法,指出其关键点在于以孔隙率形式将多孔结构形状参数拟合成可调参数表达式。此外,3D断层扫描与数值模拟相结合,阐述lattice-Boltzmann方法对开孔泡沫结构的研究,突出真实孔结构对有效热导率的影响和规律。展望后期研究重点是经验相关模型的精确拟合方式及特征关联式的统一化,高精度数值模拟计算中的简化对比分析模型。     

Thermal conductivity of anisotropic,inhomogeneous high‐density foam calculated from three‐dimensional reconstruction of microtome images

An effective method is developed to predict the thermal conductivity of thick foam insulation on offshore oil and gas pipelines. High‐resolution three‐dimensional (3D) images (212 megavoxels) spanning macroscopic sample volumes (38 × 19 × 4 mm³) are obtained and used to create a 3D geometry of the foam. A gravimetric technique is developed to measure the mass density through the foam thickness and used to verify the 3D geometry. The local anisotropic thermal conductivity through the thickness of the foam is calculated using the finite element method on the 3D geometry and the results are verified against measurements and found to be in good agreement. Results show that thermal conductivity is dependent on morphology. For the highly anisotropic part of the foam where the long axes of the bubbles are oriented parallel to the axial direction of the pipe, the radial thermal conductivity is lowered significantly compared to more isotropic foam. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1020‐1028, 2013     

中铝质闭孔泡沫陶瓷砖的制备和性能研究

采用发泡法,以废石膏为发泡剂,通过干压成型工艺制备出了中铝质闭孔泡沫陶瓷砖。主要探讨了助烧熔剂和烧成制度等因素对闭孔泡沫陶瓷砖性能的影响。采用真空密度仪、万能测试机、导热仪分别测试了样品的真密度、抗压强度、导热系数,采用排水法测量了样品的体积密度、闭孔气孔率,通过SEM分析了样品的闭孔分布。实验结果表明:样品的真密度为2.691g/cm3,体积密度为1.324 g/cm3,抗压强度为4.82MPa,热导率为0.173 W/(m.k),闭孔气孔率为57.2%,,样品内闭孔分布均匀。     

Eggshells as agro-industrial waste substitute for CaCO3 in glass foams: A study on obtaining lower thermal conductivity

In this work, discarded glass bottles (GB) and eggshells (ES) were used to produce foam glass designed for thermal insulation. The literature on the thermal conductivity of foam glasses produced with eggshells is sparse. This material was used as pore-forming agent at 3% and 5% weight fractions to obtain a foam glass with low thermal conductivity. Homogenized powders were uniaxially pressed, and the compacts were fired at three temperatures (800, 850, and 900°C). Raw materials were characterized by chemical analysis and particle size distribution. The foam glasses were characterized by their porosity, phases, compressive strength, and thermal conductivity. The best insulating properties were obtained for the composition containing 5 wt% ES fired at 800°C. This sample displayed a porosity of 91.4% while its thermal conductivity was of 0.037 W/m.K, with a compressive strength of 1.12 ± 0.38 MPa. Crystalline phases were observed in samples fired at 850 and 900°C as a result of the devitrification process. The final properties of the materials are comparable to those of commercial foam glasses obtained from non-renewable, more expensive raw materials, a great indicator that the studied compositions could be used as an environmentally friendly substitute.     

Graphite foams infiltrated with phase change materials as alternative materials for space and terrestrial thermal energy storage applications

In this work, a numerical study is proposed to investigate and predict the thermal performance of graphite foams infiltrated with phase change materials, PCMs, for space and terrestrial energy storage systems. The numerical model is based on a volume averaging technique while a finite volume method has been used to discretize the heat diffusion equation. A line-by-line solver based on tri-diagonal matrix algorithm has been used to iteratively solve the algebraic discretization equations. Because of the high thermal conductivity of graphite foams, the PCM-foam system thermal performance has been improved significantly. For space applications, the average value of the output power of the new energy storage system has been increased by more than eight times. While for terrestrial applications, the average output power using carbon foam of porosity 97% is about five times greater than that for using pure PCM.     

基于导热形状因子的泡沫金属导热特性分析

通过理论分析引入用于定向计算泡沫金属等效热导率的导热形状因子（m）,并基于文献报道的大量实验数据对m进行了计算和分析。研究发现,m随泡沫金属材质、孔隙率及孔密度变化呈显著随机波动现象,无固定趋势或规律可循;泡沫金属等效热导率的准确预测需纳入多孔泡沫结构定向形变效应影响。鉴于此,通过直接数值模拟获得了m随孔胞形变参数（即沿泡沫金属宏观传热方向与其垂直方向的胞径比）变化的无量纲准则关联式,进而提出了基于m定向预测泡沫金属等效热导率的新方法。对比文献报道实验数据及基于各向同性结构假设的理论模型预测结果发现,上述方法可提高等效热导率的预测精度（平均偏差为0.77%）。     

Studies on thermal degradation kinetics and dielectric properties of polyether imide foam/nanosilica-based nanocomposites

ABSTRACT

In this paper, polyether imide (PEI) having properties such as a high glass transition temperature of 216°C, high heat resistance, high flame resistance, low smoke generation and a high melting point within the range of 400°C, having low thermal conductivity and low dielectric constant was chosen to be a polymeric foam. Water vapor-induced phase separation method was used to prepare PEI foams. PEI foams were reinforced with nano-silica (weight 1, 3 and 5%) in order to alter the dielectric properties, thermal conductivity and degradation kinetics of foamed polymer. The tested samples showed a reduction in dielectric constant than that of solid PEI but at a higher loading, it showed a higher value due to threshold percolation and a reduction in thermal conductivity was observed for foamed PEI. From thermogravimetric analysis, we can conclude that PEI with 3% filler loading showed better thermal stability compared to other PEI foam compositions.     

Thermal conductivity improvement of phase change materials/graphite foam composites

Effective thermal conductivity of composites of graphite foam infiltrated with phase change materials (PCM) was investigated numerically and experimentally. Graphite foam, as a highly-conductive, highly-porous structure, is an excellent candidate for infiltrating PCM into its pores and forming thermal energy storage composites with improved effective thermal conductivity. For numerical simulation, the graphite structure was modeled as a three-dimensional body-centered cube arrangement of uniform spherical pores, saturated with PCM thus forming a cubic representative elementary volume (REV). Thermal analysis of the developed REV was conducted for unidirectional heat transfer and the total heat flux was determined, which leads to the effective thermal conductivity evaluation. For experimental verification, a sample of graphite foam was infiltrated with PCM. The effective thermal conductivity was evaluated using the direct method of measuring temperature within the sample under fixed heat flux in unidirectional heat transfer. The results indicate a noticeable improvement in the effective thermal conductivity of composites compared to the PCM. Our numerical and experimental results are in agreement and are also consistent with reported experimental results on graphite foam. Moreover, the role of natural convection within the pores is found to be negligible.     

Polyethylene Foam Waste Utilization for Light-weight Concrete Production

Abstract

The utilization of construction materials based on polymers is considerably limited by their low fire-safety and insignificant durability. In this paper the investigations results of construction on composite including up to 30% of the volume of foam polyethylene waste are discussed. Its destruction during the fire action and also utilization is limited by a cement concrete matrix which has a traditional composition. The composition optimization to thermal conductivity value is carried out The aggregate of amorphous structure in the form of ash-slag waste is used to decrease concrete thermal conductivity.     

Thermal properties of copper-coated carbon foams

Carbon foams, with 97% porosity, were electroplated with copper for different periods of time to achieve desired copper thicknesses and foam porosity. A light flash diffusivity instrument was used to measure the thermal conductivity of the coated samples. An analytical model was developed to calculate the effective thermal conductivity of the coated foams. It was observed that the copper-coated carbon foam with 50% porosity can attain a thermal conductivity of 180 W/m K. The results from the analytical model were compared to the experimental results and they were in a very good agreement. The above analyses demonstrated the significance of copper coating in tailoring carbon foam thermal properties. The developed analytical model was adopted to predict the thermal conductivity of the copper-coated carbon foams.