保温层对墙体温度场的延迟和衰减

基于有限差分法,建立了考虑环境温度变化的外墙外保温体系的温度场数值计算模型。利用该模型,对比了混凝土墙体和聚苯板外墙保温体系的温度场,并分析了保温层材料的热物理性能的变化对墙体的延时和削弱作用。计算结果表明,聚苯板保温层对墙体的保温效果较好;其次,随保温层材料的导热系数的减少或热容的增加,墙体的延迟时间和衰减因子呈指数增长。     

考虑温度效应的界面层对混凝土热学参数影响分析

温度场是影响混凝土结构耐久性评价的重要因素之一,密度、质量热容、导热系数是混凝土材料的主要热学参数,决定于混凝土组成及细观结构。基于混凝土二维三相细观几何模型,考虑各相材料热学参数温度依赖性,得到了混凝土宏观热学参数并与试验结果比较。在验证该数值方法有效性的基础上,开展了升温过程中界面层厚度、界面层材料属性对混凝土热学参数的影响规律及影响程度分析。研究表明:随着温度升高,混凝土密度、导热系数逐渐降低,混凝土质量热容逐渐升高;随着界面层厚度增加,混凝土密度、导热系数逐渐减小,混凝土质量热容略微增大;界面层厚度的变化对混凝土导热系数影响最大,密度次之,对质量热容影响不显著;随着界面层导热系数、密度、质量热容的增加,混凝土的热学参数随之增加,但增幅有差异。     

基于热延长线系数的自保温砌块孔型设计方法与试验研究

建立了基于热延长线系数的自保温砌块孔型设计方法,采用ANSYS有限元软件分析了自保温砌块的热延长线系数、封闭空腔尺寸、芯体材料厚度、基体材料和芯体材料导热系数对自保温砌块热工性能的影响。研究表明：自保温砌块的热阻随着封闭空腔尺寸比的增大先增加后减小,并与热延长线系数和芯体材料厚度呈正相关,与基体材料和芯体材料的导热系数呈负相关;自保温砌块的热阻与孔肋热延长线系数、材料导热系数存在清晰的关系公式,并借此建立了适用于本模型的自保温砌块热阻计算公式;经试验测试,复合自保温砌块的热工性能和力学性能均满足高性能墙体材料的要求,所得结果可为墙体自保温系统的推广提供支持。     

空心砖导热系数影响因素的研究

随着国家墙体材料改革对墙体材料要求达到第二步节能目标政策的实施 ,“禁实”工作已在全国各地逐步的落实 ,砖瓦生产企业必须生产符合国家能源政策的、以空心砖为代表的新型墙体材料。要提高空心砖墙体的保温性能 ,节约能源 ,就要降低空心砖及墙体的导热系数。如何降低空心砖的导热系数 ?空心砖的导热系数受哪些参数的影响 ?是每一个砖瓦生产企业很关注的问题 ,也是我们研究的重大课题。本人多年来对空心砖的孔型排列及孔型结构与导热系数的关系 ,进行了大量研究 ,部分进行了热电模拟测试 ,通过计算、分析、测试 ,现将已经成为产品或可能成…     

高孔洞率复合保温砌块设计及热工性能影响因素

提出了高孔洞率复合保温砌块孔型的设计方法,同时采用ABAQUS有限元软件进行数值模拟,分析了复合保温砌块的孔型排布、孔洞率和材料导热系数对其热工性能的影响.结果表明:复合保温砌块的热阻随孔洞率的提高而增加,随实体材料导热系数的降低而增加,随填充的保温材料导热系数的降低而增加;通过数值模拟计算,得到了复合保温砌块热阻与孔洞率、实体材料导热系数、保温材料导热系数的关系公式;在灰缝对墙体传热影响很小的情况下,当砌块孔洞率为60%时,240mm厚单一砌块墙体的传热系数能达到0.29W/(m2·K),满足砌块和墙体热工性能大幅提升的需求.     

轻质水泥基墙体材料的火灾性能实验研究

利用热线法和液压伺服机,通过轻质水泥基墙体示范材料的现场测试测定火灾作用之后轻质竹纤维墙体的导热系数、残余抗压强度和弹性模量,研究了火灾温度对墙体保温、力学性能的影响。结果表明,温度在350℃时,剩余弹性模量最大,超过400℃之后,剩余弹性模量急剧下降;200℃时,材料的强度开始下降,400℃时,材料强度下降剧烈,600℃左右的高温作用会使材料严重破坏,并损失76%左右的抗压强度;200～350℃时,导热系数短暂下降,温度超过500℃时,少量开口气孔的存在使得材料的导热系数达到最大。     

次轻混凝土组合砌块墙体热阻分析

提出了用“分块平均法”来计算组合砌块墙体的热阻,并计算分析了组合砌块墙体在不同含湿状态、不同骨料导热系数、由于骨料导热系数和孔洞材料变化引起的不同修正系数条件下的热阻及其变化规律,给出了在不同修正系数时热阻的相对误差,并进行了修正。     

砌筑灰缝对蒸压加气混凝土砌块墙体热阻的影响

采用ABAQUS有限元软件进行数值模拟,分析了砌筑砂浆和灰缝厚度、蒸压加气混凝土砌块、抹面砂浆等因素对蒸压加气混凝土砌块墙体传热性能的影响。结果表明,加气砌块墙体的热阻随加气砌块导热系数的增大而降低;砌筑灰缝对加气砌块墙体热阻的影响程度与灰缝厚度、砂浆导热系数和加气砌块导热系数均有关系,是三者综合影响的结果;抹面砂浆增加了墙体热阻,同时也影响了砌筑灰缝处的热流分布。     

广州地区围护结构传热系数简化计算研究

目前,国内主要依据GB/T13475-2008《建筑构件稳态热传递性质的测定标定和防护热箱法》进行墙体传热系数测试,然而防护热箱法检测需要样品在自然状态下养护28d以上,试验周期太长,不利于工程实际。本文针对广州地区目前工程上常用的墙体材料加气混凝土砌块与混凝土空心砖,组成不同的构造,进行传热系数简化计算研究。通过对理论计算得到当量导热系数,寻找当量导热系数与传热系数的变化规律,通过数值拟合,得到当量导热系数与传热系数的关系式,通过关系式计算得出的传热系数与测试结果对比,发现对于非匀质材料结果非常吻合。一方面方便墙体生产厂家对新型墙体材料特别是非匀质材料的研究与开发,另一方面为设计师进行墙体构造优化设计提供依据。     

含水率对轻质烧结页岩砖及墙体热工性能的影响

通过含水率对轻质烧结页岩砖、保温砂浆、普通砂浆导热系数影响试验和理论分析,并研究含水率对抹灰厚度为10、20mm的普通砂浆和保温砂浆墙体的传热系数影响。提出符合3种墙体材料导热系数与含水率的拟合计算公式,当含水率平均每增加1%时,则1~#、2~#、3~#、4~#墙体的传热系数分别增大1.75%、1.55%、1.65%和1.73%;抹灰厚度每增加10 mm,普通砂浆和保温砂浆抹面砌筑的墙体传热系数平均减小0.52%、7.07%。     

Effects of wall's insulation thickness and position on time lag and decrement factor

In this study, effects of wall's insulation thickness and position on time lag and decrement factor have been investigated numerically. For this purpose, one-dimensional transient heat conduction equation was solved using Crank-Nicolson scheme under convection boundary conditions. To the outer surface of the wall, periodic boundary conditions were applied. The total wall thickness (insulation + thermal mass = 20 cm) was kept constant in a such a way that when the insulation thickness was increased, the thermal mass thickness was decreased in the same amount. The insulation was placed in four different locations of the wall. These locations were the inner surface, the outer surface, the center plane and half of the insulation in the inner surface and half of the insulation in the outer surface of the thermal mass. For all these wall configurations, the computations were repeated and effects of wall's insulation thickness and position on time lag and decrement factor have been investigated. It was found that insulation thickness and position have a very profound effect on the time lag and decrement factor. Computations were repeated for three different insulation materials namely polyurethane foam, cork board and rubber and for two different thermal masses namely brick and wood and the results were discussed.     

Effects of Wall's thermophysical properties on time lag and decrement factor

In this study, the effects of thermophysical properties and thickness of a wall of a building on time lag and decrement factor have been investigated. For this purpose, one dimensional transient heat conduction equation was solved using Crank-Nicolson scheme under convection boundary conditions. To the outer surface of the wall, periodic boundary conditions were applied. A very general code which can take care of composite walls under any kind of boundary condition was developed. Single and combined effects of the thickness and thermophysical properties on the time lag and decrement factor were investigated. It was found that thermophysical properties have a very profound effect on the time lag and decrement factor. The computations were repeated for different building materials and the results are discussed.     

Numerical computation of time lags and decrement factors for different building materials

In this study, time lags and decrement factors for different building materials have been investigated numerically. For this purpose, one dimensional transient heat conduction equation was solved using the Crank–Nicolson scheme under convection boundary conditions. To the outer surface of the wall, periodic boundary conditions were applied. Twenty-six different building materials were selected for analysis. The computations were repeated for eight different thickness of each material and the effects of thickness and the type of material on time lag and decrement factor were investigated. It was found that thickness of material and the type of the material have a very profound effect on the time lag and decrement factor. The results of present study are useful for designing more effective passive solar buildings and other related areas.     

Thermal inertia of newspaper sandwiched aerated lightweight concrete wall panels: Experimental study

A short term experimental investigation on the thermal inertia: time lag and decrement factor of aerated lightweight concrete (ALC) wall panels is the main purpose of this study. ALC wall panels of different density and different aerial intensity of newspaper sandwiched were produced and erected on a prototype house. All wall panels were installed facing east direction and subjected to natural environment or tested under transient condition. The inner and outer surface temperatures of the wall panels were recorded at 3 min interval, 24 h a day. Time lag and decrement factor were computed from the surface temperatures recorded. The results showed that newspaper sandwiched ALC panel has greater time lag and lower decrement factor compared to ordinary ALC panel. It is found that time lag and decrement factor were influenced by the thermal diffusivity value of the wall panel. The thermal inertia property of the panels was negatively related to its thermal diffusivity.     

Optimum location and distribution of insulation layers on building walls with various orientations

In this study, to determine optimum location and distribution of insulation in a wall, an analysis was made of 12 different wall configurations with different configurations of insulation layers. The investigation was carried out by using an implicit finite difference method for multilayer walls during typical summer and winter days in Elaz??, Turkey. For this purpose, the location of insulation layers was varied across the wall thickness for each configuration while the masonry thickness and the total insulation thickness were held constant. The optimum location of insulation for the configurations analysed was obtained from consideration of time lag and decrement factor for various wall orientations in both summer and winter conditions. Results showed that the best thermal performance was obtained in the case that one of three equal pieces insulation layers was placed in the outdoor surface of wall, the second piece of insulation was placed in the middle of wall and third piece of insulation was placed in the indoor surface of wall. Furthermore, it was found that equal thicknesses of insulation layers placed in the indoor and outdoor surface of wall was better than different thicknesses from the point of view of maximum time lag and minimum decrement factor.     

土坯热物性对储热装置充放热性能影响研究

储热系统的充放热能力直接关系到对太阳能的热利用率,对以土坯为储热材料的储热装置充放热性能进行了分析。对储热装置进行简化处理,并建立土坯二维、流体一维非稳态传热模型,利用该模型考察储热块密度、导热系数及比热容对储热装置储放热时长的影响。结果表明:储放热时长随着储热块密度的增大呈线性增大;随着导热系数的增大储放热时长先明显减小,增大到1.4 W/(m·K)后其对储放热时长的影响变小;储放热时长随着比热容的增大一直增大,热物性对储放热时长的影响可为合理选取储热材料提供参考。     

The effect of south wall's outdoor absorption coefficient on time lag,decrement factor and temperature variations

In this study, the effect of outdoor absorption coefficient of an opaque wall on time lag, decrement factor and temperature variations is investigated by employing a dynamic thermal-network model. The model simulates heat transfer by conduction through the wall and considers convection boundary conditions under detailed forcing functions on the wall outer and inner surfaces. The transient analysis is based on the fundamental principles of thermal circuits and the well-known analogies between the thermal and electrical laws are employed. The effect of the solar absorptivity, is examined for representative wall formations including masonry, insulation and coatings on both surfaces. The insulation is placed as one or two layers on the outer, the inner or in the mid-center of the masonry. The investigation is carried out for a wall with south orientation during the cooling season in the Mediterranean region. The analyses presume a non-sinusoidal periodical excitation that simulates precisely the effect of the outdoor environmental conditions. Computer results show how these varied aspects affect thermal inertia parameters and outdoor/indoor temperature peaks.     

热传导与墙材厚度之间的关系

本文分析了墙体厚度与热传导之间的关系,热传导与优化的墙体厚度之间的关系是一个非线性函数,函数形式为x=a+bk+ck2。这个公式对于估计墙体的优化厚度,减少穿过墙体的热量是很有用的。     

Thermal storage and nonlinear heat-transfer characteristics of PCM wallboard

For the materials with constant thermophysical properties, the thermal performance of wallboards (or floor, ceiling) can be described by decrement factor f and time lag φ. However, the phase change material (PCM) may charge large heat during the melting process and discharge large heat during the freezing process, which takes place at some certain temperature or a narrow temperature range. The behavior deviates a lot from the material with constant thermal physical properties. Therefore, it is not reasonable to analyze the thermal performance of PCM wallboard by using the decrement factor f and time lag φ. How to simply and effectively analyze the thermal performance of a PCM wallboard is an important problem. In order to analyze and evaluate the energy-efficient effects of the PCM wallboard and floor, two new parameters, i.e., modifying factor of the inner surface heat flux ‘α’ and ratio of the thermal storage ‘b’, are put forward. They can describe the thermal performance of PCM external and internal walls, respectively. The analysis and simulation methods are both applied to investigate the effects of different PCM thermophysical properties (heat of fusion H_m, melting temperature T_m and thermal conductivity k) on the thermal performance of PCM wallboard for the residential buildings. The results show that the PCM external wall can save more energy by increasing H_m, decreasing k and selecting proper T_m (α < 1); that the PCM internal wall can save more energy by increasing H_m and selecting appropriate T_m, k. The most energy-efficient approach of applying PCM in a solar house is to apply it in its internal wall.