Prediction of effective thermal conductivity of moist porous materials using artificial neural network approach

An artificial neural networks (ANNs) approach is presented for the prediction of effective thermal conductivity of porous systems filled with different liquids. ANN models are based on feedforward backpropagation network with training functions: Levenberg–Marquardt (LM), conjugate gradient with Fletcher–Reeves updates (CGF), one-step secant (OSS), conjugates gradient with Powell–Beale restarts (CGB), Broyden, Fletcher, Goldfrab and Shanno (BFGS) quasi-Newton (BFG), conjugates gradient with Polak–Ribiere updates (CGP). Training algorithm for neurons and hidden layers for different feedforward backpropagation networks at the uniform threshold function TANSIG-PURELIN are used and run for 1000 epochs. The complex structure encountered in moist porous materials, along with the differences in thermal conductivity of the constituents makes it difficult to predict the effective thermal conductivity accurately. For this reason, artificial neural networks (ANNs) have been utilized in this field. The resultant predictions of effective thermal conductivity (ETC) of moist porous materials by the different models of ANN agree well with the available experimental data.     

多孔材料导热系数影响因素分析

导热系数是多孔材料的一个重要参数,影响多孔材料导热系数的因素很多,不同的材料有不同的导热系数。在多孔材料的组成固定之后,其导热系数主要随着温度、容重和含水率的变化而变化,其中对其影响最大的是含水率。     

基于Ansys的复合砌块孔型布置热分析研究

文中籍Ansys热分析技术原理,较为详细地讨论了具有相同孔型布置的砌砌块和具有相同导热系数的砂浆,因为砂浆敷设方式的不同对墙体传热系数的影响,同时也分析了不同孔型布置方式对砌块本体传热系数的作用。通过研究,认为只有合理设计砌块的孔型布置,选择正确的砌块间砂浆敷设方式,才能够有效地降低墙体围护材料的传热系数,提高墙体围护材料的阻热能力。Ansys热分析技术实质上是一种数值计算方法,可广泛地应用于空心砌块以及多孔烧结制品材料,能够在墙体制品(含烧结制品)材料的体型设计阶段,为有效地降低制品的传热系数、提高阻热能力提供科学、有效的佐证。     

稳态法和瞬态法对测试无机泡沫材料的适应性

泡沫材料导热性能评价与测试方法密切相关,为阐明瞬态法和稳态法对测试无机泡沫材料导热系数的适应性,在介绍两种导热系数测试方法原理基础上,以干密度200～300 kg/m3的自制泡沫地质聚合物和市售泡沫混凝土为研究对象,比较了两种测试方法对含宏观气孔（φ≥0.5 mm）的无机泡沫材料导热性能测试结果及其差异。结果表明：（1）在测试不同干密度等级无机泡沫材料导热系数时,稳态法比瞬态法低0.0085～0.0205 W/（m·K）,而且这种差别随材料干密度增大（导热系数增大）而增大;（2）干密度等级相同时,自制泡沫地质聚合物具有与市售泡沫混凝土相当或更低的导热系数,可望用于新型建筑保温材料;（3）稳态法比瞬态法更适用于具有宏观气孔无机泡沫材料导热性能测定。     

On the effective thermal conductivity of building bricks

This study contains computational and experimental investigation of the effective thermal conductivity of porous type building bricks. Internal heat transfer (conduction, convection and radiation) is considered in the numerical study under steady state condition. Experiments have been conducted to compare the numerical results with the experimental ones. Practical formulae are obtained and presented for a realistic estimation of the effective thermal conductivity of the building bricks. Present formulations include the effect of all of the parameters of the heat transfer mechanisms.     

A composite sphere assemblage model for porous oolitic rocks: Application to thermal conductivity

The present work is devoted to the determination of linear effective thermal conductivity of porous rocks characterized by an assemblage of grains (oolites) coated by a matrix. Two distinct classes of pores, i.e. micropores or intra oolitic pores (oolite porosity) and mesopores or inter oolitic pores (inter oolite porosity), are taken into account. The overall porosity is supposed to be connected and decomposed into oolite porosity and matrix porosity. Within the framework of Hashin composite sphere assemblage (CSA) models, a two-step homogenization method is developed. At the first homogenization step, pores are assembled into two layers by using self-consistent scheme (SCS). At the second step, the two porous layers constituting the oolites and the matrix are assembled by using generalized self-consistent scheme (GSCS) and referred to as three-phase model. Numerical results are presented for data representative of a porous oolitic limestone. It is shown that the influence of porosity on the overall thermal conductivity of such materials may be significant.     

Die Wärmeübertragung in porösen Stoffen – Einfluss von Albedo und Extinktion

Heat transfer in porous materials – effect of albedo and extinction. In the context of European market harmonisation it is important to determine the properties of construction and insulation products with minimum measurement uncertainty. For insulation used for industrial equipment and building services the temperature‐dependent thermal conductivity has to be specified for the respective application. However, the established test methods for determining thermal conductivity are not designed for high temperatures. prEN 15548‐1:2006 [4] is a new technical specification designed to meet the requirements of such measurements. In order to be able to compare different types of insulation products, the measuring methods must have approximately the same measurement uncertainty, and the influence factors for the different measuring methods must be clear. For certain products the thickness is a significant influence parameter, which may have different causes. This paper focuses on the so‐called thickness effect.     

营造可持续建筑蓄能围护结构的新思路及新方法

随着能源供求失衡日益加剧,建筑蓄能节能的重要性不断凸显。营造具有高效蓄能及可调节能力的可持续蓄能围护结构,对于建筑节能具有重要意义。本文从居住者的热舒适需求出发,通过反问题思路,提出了被动式及主动式建筑中可持续室内环境营造的一些新思路和新方法。研究发现,被动式建筑围护结构理想热质体热性能具有相变材料的特征,即热容随温度的分布接近δ函数形式。并进一步开展了建筑用相变材料的研发及应用研究,研制了建筑用定形相变材料和微胶囊化相变材料,克服了传统相变材料易泄露和导热系数偏低等缺点。最后,提出了主被动式建筑围护结构和相变材料一体化的系统应用方案,并通过实验及模拟验证了其节能舒适效果,为相变材料和建筑蓄能围护结构一体化的设计及应用提供指导。     

多孔陶瓷材料增材制造

多孔陶瓷具有低密度、低导热率、高比表面积和耐腐蚀等优点,广泛应用于生物组织工程、催化剂载体、建筑材料等领域.多孔陶瓷的传统成型技术难以满足对多孔陶瓷个性化、结构复杂化、快速制造化、多级孔的要求.增材制造技术(3D打印)具有设计自由度高、制造周期短、制造成本低等优势,可以无需模具快速制造复杂结构多孔陶瓷零件.本文综述了粉...     

基于细观复合材料的混凝土导热系数模型

混凝土温度场分析是混凝土结构耐久性劣化、温度应力、火灾作用下结构破坏以及建筑节能分析的关键内容,而导热系数是确定温度场的重要参数。在细观尺度上,将混凝土看作由连续相水泥砂浆和分散相粗骨料组成的两相复合材料。分析了两相复合材料等效导热系数理论模型,将其用于混凝土等效导热系数的预测并与实测值进行比较,发现饱和混凝土即使采用不考虑界面热阻模型仍与实测结果吻合较好,而干燥混凝土必须考虑界面热阻的影响。为提高混凝土导热系数理论模型的预测精度,还应考虑粗骨料形状、级配、水泥砂浆与粗骨料间界面热阻以及孔隙率、含水率等方面的影响。     

Benchmark experiments for moisture transfer modelling in air and porous materials

The presence of hygroscopic materials has a large impact on the moisture balance of buildings. Nowadays, HAM (Heat, Air and Moisture) models are widely used to investigate the role of hygroscopic materials on the performance of buildings, i.e. on the building envelope, the indoor climate and valuable objects stored within the building. Recently, these HAM models are being coupled to CFD (Computational Fluid Dynamics) models to study the moisture exchange between air and porous materials on a local scale (microclimates), or to BES (Building Energy Simulation) models which focus on the interaction between air and porous materials at building level. Validation of these numerical codes is essential to gain confidence in the codes. However, available experimental data are rather scarce.     

Study of moisture transfer in a double-layered wall with imperfect thermal and hydraulic contact resistances

The objective of this work is to study the effect of taking into account interface contact resistance on the prediction of moisture distribution through multilayered building envelope. Therefore, two mathematical models to describe coupled heat and mass transfer in double-layered porous materials have been investigated: one that considers imperfect contact between layers and another that ignores this phenomenon. Both models are one-dimensional and were implemented using finite difference technique with an implicit scheme. Numerical results are presented in terms of moisture distribution for a double-layered wall and compared with the experimental data available in the current literature. The comparison has shown that the model that disregards interface contact resistance between layers cannot predict correctly one-dimensional heat and moisture transfer within double-layered porous materials. The sensitivity analysis of the simulation parameters and the impact of contact resistances at the whole building level are presented in detail and their effect on the whole building level was analysed. Our results suggest that the thermal contact resistance is the most influent parameter on the moisture flux across the hydraulic contact interface. On the whole building level, simulations indicate that taking into account contact resistances had a slight effect on the indoor relative humidity but a noticeable effect on heating input energy. A decrease of 10% in energy consumption is obtained when contact resistances are considered.     

有机相变蓄热复合材料导热性能的实验研究

以膨胀多孔石墨(EG)和硅藻土(DI)这2种多孔矿物介质与硬脂酸丁酯(BS)有机相变材料制备了有机相变蓄热复合材料,并采用调制差示扫描量热方法(MDSC)测试了复合材料的导热系数,借助层状复合材料热传导模型分析了多孔矿物介质内部结构特征对复合材料导热性能的影响.结果表明:采用EG和BS制备的有机相变蓄热复合材料具有明显的层状结构,其压制方向的导热系数更接近于层状复合材料热传导模型c轴方向的导热系数;采用DI和BS制备的有机相变蓄热复合材料的导热系数接近层状复合材料热传导模型a-b平面方向的导热系数,即该复合材料内部具有非常好的连通性.多孔矿物介质对有机相变复合材料导热性能的增强效果不仅受多孔矿物介质导热系数的作用,而且还受到复合材料内部结构特征的影响.当复合材料在热传导方向上形成连通性结构时有利于上述增强效果;而当复合材料形成与热传导方向垂直的层状结构时则不利于上述增强效果,即使多孔矿物介质具有很高的导热系数也是如此.     

外墙保温材料导热系数的试验研究

针对常用的XPS聚苯乙烯泡沫塑料、EPS聚苯乙烯泡沫塑料,以及水泥基复合保温砂浆和建筑垃圾为骨料的硅酸盐保温节能材料,试验研究材料的保温性能,得出不同保温材料密度与导热系数的关系。研究结果表明,XPS聚苯乙烯泡沫塑料、EPS聚苯乙烯泡沫塑料保温材料的表观密度和导热系数之间没有表现出特定的关系。水泥基复合保温砂浆和建筑垃圾为骨料的硅酸盐保温节能材料的导热系数随着密度的增大线性增加,大孔径材料比小孔径材料导热系数要大。通过研究,可以对建筑垃圾为骨料的硅酸盐保温节能材料配方及工艺的进一步改良提供理论依据和指导。     

两种常见墙体的热湿迁移特性分析

大多数建筑墙体均为多孔介质材料,多孔介质墙体中湿迁移与热迁移是互相耦合的过程,湿迁移对热迁移有着重要的作用,例如会使热导率明显增加,同时,热过程对湿过程也有着影响作用。基于Fourier定律、Fick定律、Darcy定律,以温度和空气含湿量为驱动势建立了多层多孔介质墙体热湿耦合迁移数学模型,对两种常见墙体（红砖墙体和加气混凝土墙体）进行计算分析。结果表明,加气混凝土墙体比红砖墙体具有更好的保温隔热性能,但更容易发生湿积累和引发湿破坏。     

The determination of the thermal properties of homogeneous and composite building materials by a dynamic method

A dynamic experimental method for the determination of thermal conductivity and diffusivity of homogeneous and composite building materials is presented. These thermal properties are determined by means of the analysis of termperature evolution in a board, which is a consequence of varying conditions of temperature and heat flux conditions produced by the transport of the board from one room to another with different fixed temperatures.     

可再分散乳胶粉及玻化微珠对泡沫混凝土性能的影响

泡沫混凝土(FC)作为一种轻质多孔材料具有优良的保温隔热效果,将其用作建筑保温墙体材料可以有效降低建筑能耗.利用可再分散乳胶粉(RDL)和玻化微珠(GB)改性FC,研究了RDL和GB单独取代以及RDL和GB共同取代快硬硫铝酸盐水泥对FC干密度、抗压强度、导热系数和拉伸黏结强度的影响.结果表明:RDL可以显著提高FC的拉...     

Factors affecting the thermal properties of concrete and applicability of its prediction models

In this paper an investigation on thermal conductivity of mortar, concrete and its major constituent aggregate is presented. Four different types of rocks were tested for their conductivities at dry and fully saturated states, which were further crushed and used as coarse aggregates in concrete. Thermal conductivity of mortar and concrete have been measured at various moisture contents. The applicability of Campbell-Allen and Thorne's model in assessing the influence of aggregate type has been investigated. Using a few advanced models for thermal conductivity of porous material, it has been demonstrated that there exists a possibility to gain insight into the nature of the pore that is likely to be encountered in the concrete. The relationship between concrete conductivity and aggregate conductivity at various degrees of saturation including at dry and fully saturated conditions have been developed. Further, equivalent conductivity of solid, which is a necessary input parameter for porous material models, has been evaluated for all the types of concrete under consideration.     

硅藻土的改性及深加工利用

本文介绍了硅藻土的起源、结构、性质,综述了国内外硅藻土产品在助滤剂、填料、建筑材料与保温隔热材料、载体方面的应用现状。重点从水处理、橡胶、多孔陶瓷、沥青、造纸、新型建筑材料等方面对硅藻土的深加工利用研究进展进行了综述,并对硅藻土的未来发展进行了展望。