超低能耗建筑墙体内外表面温差对传热系数测试的影响分析

对严寒地区某超低能耗建筑采用热流计法进行墙体传热系数现场检测,通过对测试数据归纳整理发现墙体内外表面温差与传热系数呈幂指数散点分布特征,通过数据回归分析建立两者回归方程,为超低能耗建筑墙体围护结构传热系数检测技术方法提供依据。     

混凝土砌块墙体检测中的几个问题

墙体主体传热系数通常使用热流计进行测量.本文分析了热流计的使用条件,提出对于砌块墙体等表面温度分布不均匀的墙体,不适宜使用热流计测量其主体传热系数的观点.而后以混凝土砌块墙体为例,分别模拟了不同室外温度时,不保温、外保温和内保温3种情况下,墙体内外表面温度分布的情况.并针对保温墙体改变其保温层厚度.得出墙体内外表面温度及温差变化的趋势,进而得到应将热流计粘贴在保温层一侧对保温墙体进行检测的结论.模拟结果还显示,当室外温度大于0℃时,对于保温层厚度大于70 mm的内保温墙体,也可将热流计贴在不保温的一侧进行检测.     

湿热地区墙体传热系数实验室测试温度研究

通过对湿热地区常用墙体构造传热系数测试温度对比研究,得到如下结论:传热系数测试的冷热箱温差越大,结果准确度越高。适合湿热地区墙体传热系数实验室测试的温度范围为:冷箱温度介于0℃～10℃,冷热箱温差不小于25℃,最好超过30℃。     

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。     

围护结构传热系数现场检测影响因素探讨

本文主要讨论了在围护结构传热系数现场检测过程中,检测周期、内外表面温差以及围护结构含水率等因素对其检测结果的影响情况。     

自保温砌块墙体在夏热冬冷地区的传热性能研究

对陶粒泡沫混凝土砌块、加气混凝土砌块、黏土砖以及细石空心混凝土砌块(填充聚苯板/未填充聚苯板)5种砌体材料进行研究,并建立了多材料围护结构模型,采用热流计法同步测试了各墙体的传热系数。此外,还对墙体的热稳定性以及温差、环境温度以及温度传感器的分布对传热系数的影响进行了分析。结果表明,190mm厚陶粒泡沫混凝土砌块和加气混凝土砌块墙体以及290mm厚填充聚苯板的细石空心混凝土砌块墙体的传热系数均1.0W/(m2·K);虽然陶粒泡沫混凝土砌块的传热系数与填充聚苯板的细石空心混凝土砌块基本相同,但前者块体容重却远比后者低。此外,还得到了陶粒泡沫混凝土砌块墙体传热系数的线性预测模型。     

墙体传热系数检测结果的不确定度评定

本文主要从传热面积、传热功率、传热温差的测量及人员操作等方面因素,来分析墙体传热系数检测结果的不确定度,以供建筑行业同行参考。     

墙表换热系数与风速风向的关系

用实验测量了不同风速、风向下的温差和热流数据，给出了从实测温差和热流中提取表面换热系数的辨识方法，分析了风速、风向对墙体表面换热系数的影响，并最终得到了墙体表面换热系数随风速、风向变化的关系武。     

建筑维护结构表面换热过程辨识数学模型

采用了动态系统的随机型输入,输出离散差分方程,分别建立了以建筑围护结构表面与空气间的温差作为输入信号,建筑围护结构表面热流作为系统输出信号的单输入,单输出建筑维护结构表面换热过程系统辨识离散数学模型;和以辐射强度,墙体表面温度和空气温度作为输入信号,墙体表面热流作为系统输出信号的多输入,单输出建筑维护结构表面换热过程系统辨识数学模型,得出了建筑墙体表面换热过程相应的Z传递函数模型描述。为研究建筑围护结构表面换热过程找到了一种新的方法。     

基于PMV的空调外区进深确定

利用室内外温差和围护结构传热系数等参数,计算室内温度的变化,提出用表征人群对热环境平均投票值的PMV确定不同条件下空调房间内外分区界线。     

火灾下钢筋混凝土剪力墙温度场数值模拟

为了研究配筋率、升温曲线、多面受火、传热系数等因素对钢筋混凝土剪力墙温度场的影响,利用COMSOL多物理场建模与仿真软件对火灾下钢筋混凝土剪力墙温度场进行模拟,并得到不同因素变化条件下的剪力墙的温度场分布规律,模拟结果与试验结果符合良好.对温度场模拟中各参数对温度场的影响进行了讨论,结果表明:受火时间越长,钢筋混凝土剪...     

地源热泵地埋管换热器传热研究(2):传热过程的完全数学描述

建立了管内流体换热和土壤换热的耦合模型,并在此基础上建立了与地面热泵模型耦合的地源热泵系统仿真模型.给出了边界条件和计算参数的确定方法,计算参数包括:流体与管内壁面的表面传热系数、地面的表面传热系数、大气温度、不同埋深土壤温度、多孔介质土壤有效导热系数.     

大空间建筑室内热环境CFD模拟中壁温及室温的求解

应用PHOENICS软件模拟某体育馆的室内热环境,将壁温作为模拟的第一类边界条件。建立了室内表面对流辐射耦合换热方程,着重讨论了采用表面换热分析法求解表面传热系数以求解壁温的方法。因壁温计算和室温计算互相耦合,采用迭代计算的方法求解壁温和室温。模拟计算结果与实测结果基本吻合。     

建筑门窗玻璃幕墙传热系数现场测试研究

建筑门窗玻璃幕墙是建筑围护结构节能最薄弱部位,其传热系数目前只能在实验室通过热箱法测定,在现场准确、快捷地测试该值对于建筑的节能评估改造具有重要意义。在现场测试门窗幕墙内外空气温度和表面温度的基础上,推导出了基于"准稳态"测试原理和"热阻法"、"表面温度法"、"传热系数法"3种传热系数现场测试方法,现场测试值与实验室检测值的较高一致性表明了该现场测试方法的准确性,连续测试数据与平均值的较小偏差表明了该测试方法的稳定性。研究结果表明,建筑门窗玻璃幕墙传热系数可通过该方法在现场准确、快捷地测试得到。     

Performance of phase change material boards under natural convection

The high thermal storage capacity of phase change material (PCM) can reduce energy consumption in buildings through energy storage and release when combined with renewable energy sources, night cooling, etc. PCM boards can be used to absorb heat gains during daytime and release heat at night. In this paper, the thermal performance of an environmental chamber fitted with phase change material boards has been investigated. During a full-cycle experiment, i.e. charging–releasing cycle, the PCM boards on a wall can reduce the interior wall surface temperature during the charging process, whereas the PCM wall surface temperature is higher than that of the other walls during the heat releasing process. It is found that the heat flux density of the PCM wall in the melting zone is almost twice as large as that of ordinary wall. Also, the heat-insulation performance of a PCM wall is better than that of an ordinary wall during the charging process, while during the heat discharging process, the PCM wall releases more heat energy. The convective heat transfer coefficient of PCM wall surface calculated using equations for a normal wall material produces an underestimation of this coefficient. The high convective heat transfer coefficient for a PCM wall is due to the increased energy exchange between the wall and indoor air.     

Coupled heat transfer modes for calculation of cooling load through hollow concrete building walls

A CFD model was developed to study thermal performance of hollow cement wall constructions of buildings under hot summer conditions. The approach employed couples conjugate, laminar natural convective flow of a viscous fluid in hollow building blocks with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the wall. A state-of-art building energy simulation program, ESP-r, was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the wall domain. A detailed parametric study showed that using a wider cavity within a building block does not necessarily reduce heat flux through the block. Radiation heat transfer between cavity sides may account for a significant fraction of heat flux through the block and neglecting its effect can lead to errors that could be as large as 46%. The geometry of the hollow blocks was demonstrated to affect the heat flux by as much as 30%.     

Convection heat transfer in the cone calorimeter

Estimates of the convection heat transfer coefficient (HTC) in the cone calorimeter are obtained from a near-steady-state analysis of the temperature histories of horizontal coated steel plates. Corrections are applied to the derived HTC values to account for changes of the surface emissivity as a function of temperature. Furthermore, estimates are obtained of the additional heat losses through the sides of the sample holder and the insulation layer on which the test sample rests. The derived HTC values are analysed and correlations presented in the form of Nu=f(Ra) as well as h=f(T), where Nu is the plate Nusselt number, Ra is the plate Rayleigh number, h is the HTC and T is the plate temperature.     

The effect of surface roughness and emissivity on radiator output

The effect of altering the emissivity and the roughness of a wall behind a radiator on the radiator heat output has been studied experimentally and by using computational fluid dynamics.The results of a 3D RNG k–? turbulent model agree well with, and have the same trend as, the experimental results. The results indicate that the presence of large scale surface roughness and a high emissivity surface increases both the heat flow rate and the air velocity behind the radiator compared to a smooth shiny surface. The former increases the wall surface emissivity which causes the surface temperature of the wall to increase, effectively creating additional convective heat transfer surface. The surface roughness will increase both the surface area for heat transfer and the turbulent intensity which increase the mass transfer and free convective heat flux through the air gap.The results indicate that the heat transfer can be increased by about 26% through the use of a high emissivity saw-tooth surface compared to a smooth shiny one. This means that using a wall surface with high roughness and emissivity behind the radiator will increase the heat output from the radiator.     

热工参数对混凝土结构温度场影响研究

根据热学基本原理,结合结构设计需要,以上海地区某桥梁为对象,分析了各基本热工参数对混凝土结构温度场和温度效应的影响,重点阐述了表面热交换系数和太阳辐射吸收系数的影响。旨在为混凝土结构温度问题的研究和为考虑温度作用的结构设计提供参考。