Experimental unsteady characterization of heat transfer in a multi-layer wall including air layers—Application to vertically perforated bricks

Vertically perforated bricks were developed with a view to building environmentally friendly houses since they make insulating materials unnecessary. By an experimental approach, this study proposes to analyze the propagation of a temperature signal in this kind of brick, in order to characterize the thermal inertia of the brick. The steady-state knowledge is completed by the determination of properties like influence functions or characteristic depth concerned by a surface temperature variation. This allows to validate a simple unsteady surface model to be validated for this heterogeneous material which is classified as an insulating structural material. Furthermore, this study supplements the steady-state knowledge in local heat transfer through the air layers of the brick. Indeed, it is verified that convection heat transfer can be ignored in an unsteady heat transfer in this kind of brick, even in extreme conditions such as a sudden temperature fall.     

数值模拟技术在多孔砖墙传热性能研究中应用

本文总结了多孔砖的数值设计优化步骤。通过例子介绍了多孔砖墙传热数值模拟过程,以及砖孔可视表面辐射的模拟和墙体表面温度、热流密度的计算方法,并给出了有关结果。     

防护热箱法测定墙体传热系数影响因素研究

通过对防护热箱法测定墙体传热系数影响因素的研究,找出影响防护热箱法测定墙体传热系数的若干因素,以保证实验质量,提高墙体传热系数检测的准确性。     

地下洞室多孔墙体热湿传递的数值模拟

提出了一种以温度与相对湿度为驱动势的多孔墙体热湿耦合传递的数学模型,该模型同时考虑了水蒸气与毛细孔内液态水的传递。采用控制容积法将理论方程组离散并编制了计算程序,对深埋地下洞室的墙体进行了热湿传递的数值模拟,得到了墙体温度、相对湿度、热流率、湿流率的变化规律。结果表明,墙体传热过程趋于稳定的时间远小于传湿过程。     

回弹法检测砌体中烧结多孔粘土砖抗压强度技术研究

1前言 　　我国目前对砌体中烧结多孔粘土砖的砖材强度的测定,主要采用将砖从砌体中取出,按GB 13544-2000<烧结多孔粘土砖>和GB/T 2542-2003<砌墙砖试验方法>的检验和评定方法,确定砖的强度等级,这样既费时费工,又要局部破坏砌体结构的整体性,而且在掏掘砌体砖时不可避免的对试验砖进行扰动而影响其准确性.本课题拟采用的方法,不需从砌体上取出砖样,而是直接用回弹仪对砖墙上砖的表面进行弹击,不会损伤砖墙,而且可以对建筑物的砌体砖进行大面积普查.……     

Transfer function coefficients for time varying coupled heat transfers in vertically heated hollow concrete bricks

This paper describes a two step numerical procedure to determinate empirical transfer function coefficients (TFCs) for vertically heated hollow concrete bricks. For such systems TFCs cannot be generated using the analytical techniques available in the literature such as the z-transfer function method or the space state representation method because of the nonlinear local character of the heat transfer by natural convection and radiation in the air cells of the hollow concrete bricks. The first step of the procedure consists in predicting coupled heat transfer by conduction, convection, and radiation in realistic time varying conditions using a detailed numerical simulation. In the second step, the results of the simulation (the time-varying heat fluxes at the hollow brick surfaces) are used to obtain empirical transfer function coefficients using an identification technique. Transfer function coefficients are generated for three different types of hollow concrete bricks mostly used in practice. It is shown that the empirical transfer function coefficients permit fast and accurate prediction of heat transfer for thermal excitations that differ markedly from those used to generate these coefficients without solving the complex system of equations governing the coupled heat transfer mechanisms.     

Numerical and experimental study of conjugate heat transfer in a horizontal air cavity

The demand for general reduction of the energy consumption in civil engineering leads to more frequent use of insulating materials with air gaps or cavities. Heat transfer through a constructional part can be decreased by adding an air gap and low emissivity reflective foils to the structure. In the first part of this paper, the impacts of cavity thickness and inner surface emissivity on combined conduction, convection and radiation heat transfer was experimentally explored in the case of constructional part with a horizontal cavity subjected to constant downward heat flux. The heat flow meter Netzsch HFM 436 Lambda was used for steady-state measurements. Results suggest that the studied parameters seriously affect the combined heat transfer in the composed structure. In the second part the paper reports the numerical study of two-dimensional conjugate heat transfer in closed horizontal cavity having air as the intervening medium. Numerical models validated by related experimental results were performed to further investigate the effect of radiation heat transfer. It was found that in general, the total heat flux through the composed structure decreases with increasing air cavity thickness, which is significant especially when low emissivity inner surfaces are taking into account. The direction of heat flow (downward or upward heat flow) has a significant impact on the convection heat transfer. An important contribution from the present work is the analysis of the optimal thickness of the cavity at different boundary conditions. The optimal thickness of the enclosure with low emissivity surfaces is 16 mm when subjected to upward heat flux.     

基于Ansys的相变墙体传热特性计算分析

基于Ansys软件建立数学模型,计算分析了不同厚度相变储能材料、不同相变墙体结构的传热特性.计算结果表明,相变储能材料越厚,相变墙体内层与室内环境界面温度随外界温度变化幅度越小,能够有效降低室内空调设备的能耗;相变储能材料厚度一定时,不同结构的相变墙体从节能降耗角度差别不大:相变储能材料位于墙体中心位置时节能效果较好.     

Applied research of reaction coefficient method for unsteady heat transfer in the wall

According to a building's characteristics, a wall may be divided into three categories (heavy, middle and light) from the aspect of heat transmission. Using theory on unsteady heat transmission of the wall and simulated calculation by computer, the influences on reaction coefficients (y_n) exerted by a series of roots (α_i) from the transcendental equation B(s)=0 and on heat transmission calculation exerted by the items (n) of reaction coefficients are analyzed. In this paper, when heat transfer reaction coefficients y₀ and y₁ are calculated, α_i⩽100 and when y_n are calculated, α_i⩽30. The definite values for the items of reaction coefficients for different wall types are introduced, that is, n=96 for heavy wall, n=72 for middle wall and n=48 for light wall. The work of calculation may be greatly simplified and the accuracy of reaction coefficients is guaranteed. The calculation method of heat transfer reaction coefficient was further perfected and the condition to use this method was improved.     

平流式沉淀池穿孔墙进水及隔板作用数值模拟

为改善实际运行平流式沉淀池悬浮物去除效率,借助计算流体力学软件FLUENT,利用标准k-ε两方程湍流模型和混合模型,对沉淀池底部进水、穿孔墙进水以及加入隔板后的穿孔墙进水3种运行条件进行了数值模拟,得到了沉淀池内流场分布及悬浮物体积分数分布。研究表明,穿孔墙进水较底部进水产生的回流区域小,水流均匀稳定,悬浮物去除率高;隔板的加入不但不会增加回流区域,而且对悬浮物具有显著的截留作用,可以减少沉淀池上部悬浮物浓度,提升沉淀池运行效率。     

Numerical analysis on heat transfer characteristics of ionic liquids in a tubular heat exchanger

ABSTRACT

The efficiency of the solar thermal system depends on the performance of the solar collectors. There is a need to operate solar collector at higher possible temperature to attain maximum efficiency limits. However, the performance of the collector system is limited by the heat transfer characteristics of the working fluid called as the heat transfer fluid (HTF). Water is widely used as the HTF in the solar collector, but the major problem of using water as the HTF is its limited operating temperature. The objective of the work is to investigate the heat transfer characteristics of ionic liquids in tubular heat exchanger (HE) suitable for the solar thermal application. The HE was designed for a heat duty of 1?kW based on the thermal transport property of available ionic liquids and the computational fluid dynamics (CFD) analysis was performed. The results indicate that there is only minimal deviation between the assumed and CFD data.     

建筑墙体表面传热系数辨识研究

对实验房间南向墙体内表面中心区域的换热过程进行实验，发现当风速在0－5．5m/s之间时，表面传热系数在8－18W（m^2.K）之间波动，而风向对墙体表面传热系数影响不大；用辅助变量法分析墙体表面传热过程，并结合实验推导出墙体表面传热系数。模型的预测结果与实测结果吻合良好。     

低温地板辐射供暖的传热模拟

建立了低温地板辐射供暖系统的传热数学模型,应用有限差分法对数学模型进行了求解;通过实测及理论计算,得出地板内及室内温度分布特点;计算值与实,测值相对误差小于5％。     

Numerical modeling of radiative heat transfer in water sprays

A numerical method is developed for the transport of polychromatic radiation in polydisperse sprays. The method is implemented within a wide-band radiation solver using the Finite Volume Method. Mie theory is used to compute the absorption and scattering characteristics of the water droplets. The solver is designed to be computationally effective because the simulations of fire scenarios are inherently time-dependent and the radiative transport equation must be solved many times. The model is compared with two sets of experimental data, and a discussion of the results is presented.     

新型节能墙体传热研究

建筑墙体负荷计算是建筑能源系统设计的基本依据，也是建筑能耗分析和能源管理的基础。根据反应系数法编程计算，得到适合工程技术应用的新型节能墙体冷负荷温度计算用表和动态传热特性基础数据，从而将节能建筑墙体改革成果应用于空调冷负荷计算，并为建筑新型节能墙体热工性能的深入研究和综合性能评价提供参考依据。     

室内空气自然对流换热的数值模拟研究

应用PHOENICS软件对自然对流换热条件下室内空气温度场和速度场进行了数值模拟，并对温度场的模拟结果进行了实验验证。结果表明，模拟计算值与实验值吻合得较好。     

泡沫玻璃外保温墙体窗口周边传热试验研究

采用大型耐候性试验装置实测2种泡沫玻璃外保温墙体窗口周边的热流密度的结果表明,2种泡沫玻璃外保温墙体的窗口周边热流密度偏差"面砖系统"窗口周边达29.59%";涂料系统"窗口周边热流密度差达34.51%,传热不均匀性较大。当试验温差△t≤10℃时,窗口周边的传热能力相差近35%,热应力及其衍生问题不容忽视。因此,在外保温墙体窗户设计、施工、材料选用时,应尽量采用断桥窗框,降低热桥效应,提高节能效果。     

中空玻璃传热系数的传热过程及检测方法

论述了中空玻璃的传热过程,对标定热箱法、防护热板法、热流计法三种中空玻璃传热系数的检测方法进行详细分析,阐明了各方法的适用范围、检测原理、检测设备及对样品的要求,为深入了解中空玻璃的传热过程奠定了基础。     

烧结多孔砖抗压强度测量结果的不确定度评定

通过对烧结多孔砖抗压强度不确定度的评估,分析了测量过程中存在的不确定度来源,并建立了测定过程的数学模型,量化不确定度分量,求出合成不确定度,最终给出了测定结果的表达式,找出影响抗压强度的主要因素。     

塑料毛细管换热器传热系数影响因素分析

毛细管席作为空调系统的辐射末端,得到逐步的重视和应用,但对于应用在闭式地表水源热泵系统中,作为地表水体的前端集热器的研究资料较少.建立毛细管简化的数学模型并通过大量数值计算,确定影响k值的各个参数,得出不同参数对k值的影响曲线,通过对影响曲线进行分析,区分出影响传热系数的主要、次要因素,对毛细管前端换热器的设计及应用提供理论基础.