Low—E玻璃对建筑节能的贡献

在《玻璃》2011年第7期《低辐射玻璃的概念与应用问题的讨论》的基础上,进一步讨论了Low-E玻璃的辐射系数对Low-E中空玻璃、Low-E充气中空玻璃和Low-E真空玻璃的隔热保温性能的影响,给出了有关计算结果,说明了Low-E中空玻璃的中间层厚度不应小于6mm。采用辐射系数E=0.25、中间层6mm的Low-E玻璃,可以满足北京地区建筑节能65%的要求。充填氩气等低导热气体取代空气,中空玻璃的保温性能有所提高。Low-E玻璃的辐射系数对Low-E真空玻璃传热系数的影响更大,真空玻璃虽然厚度比中空玻璃小很多,但传热系数更小,建筑节能效果更好。     

透明真空平板玻璃

透明真空隔热玻璃运用了与保温瓶相同的原理,即由真空层杜绝了气体传导和对流,又由于其内部镀有低辐射膜,因而辐射传热也就很小了。隔热结构由两块边部密封的玻璃板构成,为了保证在外界大气压力影响下真空层的存在,两片玻璃板之间必须放置圆柱支撑。上述设计应考虑圆柱支撑传导体热与机械应力的协调一致。现已开发了确定支柱分布的工艺。应用分析法计算出了由于结构温差而产生的应力和弯曲,计算结果与试验检测相当吻合。在较宽     

基于真空玻璃特性的节能定制方案

基于真空玻璃优良的保温隔热、抗结露、防噪音等的特性,根据国家关于门窗幕墙规范、居住建筑节能设计标准、被动房建筑对玻璃传热系数的要求等,从满足人体舒适度的角度出发,对国内寒冷区代表城市北京、夏热冬冷地区代表城市上海的典型户型,设计了最佳真空玻璃配置,并计算出使用定制真空玻璃后的节能数据。     

基于有限元分析的真空玻璃传热性能数值模拟研究

真空玻璃是具有优异保温、隔热、降噪性能的新型绿色建筑材料。本研究运用COMSOL Multiphysics 5.6软件建立了相关物理模型,探究不同规格真空玻璃的性能差异及不同玻璃在节能建筑中的应用情况。结果表明：500 mm×500 mm规格的真空玻璃的保温性能强于200 mm×200 mm及100 mm×100 mm规格的真空玻璃。随着真空玻璃规格的增大,真空腔体积变大,导致边缘密封层占整个真空玻璃表面面积百分比减小,边缘密封层的传热对真空玻璃的传热影响减少,真空玻璃的保温性能因而得到增强。节能建筑中使用真空玻璃替换普通平板玻璃和中空玻璃可以达到更好的节能效果。建筑物在冬季使用真空玻璃7 d时室内平均温度比使用平板玻璃高出3.91 K,比中空玻璃高出2.25 K。     

基于有限元分析的真空玻璃传热性能数值模拟研究

真空玻璃是具有优异保温、隔热、降噪性能的新型绿色建筑材料。本研究运用COMSOL Multiphysics 5.6软件建立了相关物理模型,探究不同规格真空玻璃的性能差异及不同玻璃在节能建筑中的应用情况。结果表明：500 mm×500 mm规格的真空玻璃的保温性能强于200 mm×200 mm及100 mm×100 mm规格的真空玻璃。随着真空玻璃规格的增大,真空腔体积变大,导致边缘密封层占整个真空玻璃表面面积百分比减小,边缘密封层的传热对真空玻璃的传热影响减少,真空玻璃的保温性能因而得到增强。节能建筑中使用真空玻璃替换普通平板玻璃和中空玻璃可以达到更好的节能效果。建筑物在冬季使用真空玻璃7 d时室内平均温度比使用平板玻璃高出3.91 K,比中空玻璃高出2.25 K。     

凝心聚力谋质量 奋楫杨帆启新程——访沃卡姆(山东)真空玻璃科技有限公司

真空玻璃作为一种新型玻璃深加工产品,具有传热系数低、隔音性能好、适用范围广泛等优点,能够起到保温隔热、防止结露、节能降耗、隔声降噪的作用。近年来,随着我国中央和地方政府大力推动建筑节能,性能优异的真空玻璃迎来了前所未有的发展机遇,在政策和市场的推动下,更是改变了“独木不成林”的产业局面,越来越多的企业和科研人员投入到真空玻璃研发生产的队伍中来。这其中,成立于2019年的沃卡姆(山东)真空玻璃科技有限公司(下称沃卡姆)正开启新的真空玻璃产业化征程。     

荒煤气在焦炉上升管内的流动与传热研究

采用热平衡原理,计算了荒煤气在上升管传热量的大小和温度的变化趋势。通过计算得到,辐射传热对上升管的传热过程有较大影响,辐射传热的存在显著提高了传热系数。与仅对流传热存在的情况相比,混合传热促进了荒煤气在管内温度场的变化,截面平均温度比纯对流情况下的温度低,辐射传热的存在导致截面平均温度下降。     

真空玻璃传导和对流传热机理研究

利用传导和对流传热原理,建立了真空玻璃热量的流动和传递数学模型,推导了真空玻璃自由分子状态的导热量、支撑柱及边料的固体导热及真空玻璃的外表对流换热方程.分析了自由对流传热、纯气体、稀薄气体、支撑柱及边料的固体导热机理,探讨了真空玻璃的外表对流换热问题.研究结果表明,在低真空状态下的真空玻璃夹层厚度越小,越有利于由自由对流向纯气体导热方向发展,越有利于真空玻璃传热系数的降低.真空玻璃结构只要保持夹层真空度小于0.313 Pa就使得夹层内成为自由分子导热状态.     

基于STC89C52R设计真空玻璃传热系数测量仪

参照国标研制开发了一套以STC89C52R单片机为核心的真空玻璃传热系数测量仪,运用一线式温度传感器DS18B20对真空玻璃两侧的温度进行采样,由PID计算和修正后达到控制冷、热板温度的目的,实现了对其传热系数的测量.     

Low-E玻璃U值及其影响因素的计算分析

应用传热学原理,分析了Low-E玻璃构件传热基本过程,给出了总传热系数U值计算的详细表达式,并在计算机上进行了数值计算,研究了各种参数对U值的影响。计算结果表明:玻璃厚度对U值影响不明显;影响U值的主要因素是气体间隔层厚度和玻璃的辐射率;随着气体间隔层厚度增加,U值逐渐降低,达最低值后缓慢上升,有一个最佳的厚度;随着辐射率降低,U值逐渐降低,但U值与辐射率并不呈现简单的线性关系,对给定的Low-E玻璃构件,有一个极限U值。     

Heat transfer control by dispersed metallic particles in glassy mold flux film for continuous steel casting

To assess the effect of metallic particles (MPs) on heat transfer in glassy mold flux, a structurally stable glassy mold flux system composed of CaO–Al₂O₃–CaF₂ was examined with 0, 2, or 5 wt% of FeO or Fe MPs. The change of extinction coefficient by Mie Scattering of the Fe particles and absorption by FeO was quantified using Fourier transformation infrared ray spectroscopy and an Ultraviolet/Visible spectrometry. Thermal conductivity of mold flux film with dispersed MPs was quantified using laser flash technique. One-dimensional Debye temperature was calculated, and particle morphology and size distribution were observed using image analysis to explain variations in thermal conductivity among the glass samples. Finally, to simulate the heat transfer ratio by both the conduction and radiation, the actual heat flux through mold flux film was measured using an Infrared Emitter Technique. The overall heat transfer rate across liquid flux film could be reduced significantly by a dispersion of MPs.     

周向非均匀加热水平圆管内超临界正癸烷换热特性

针对超燃冲压发动机再生冷却热防护问题,开展了顶部加热和底部加热水平圆管内超临界压力正癸烷换热的模拟研究。探究了两种加热模式下的换热特征和换热差别,阐述了通道外表面热通量、质量流速、运行压力及通道热导率对换热的影响机制。实现了周向平均换热的预测。结果表明：两种加热模式下的浮升力作用不同,通道内壁面周向呈现了不同的管壁温度和热通量分布情况。顶部加热时随周向角增大传热恶化逐渐减弱,底部加热时二次流更强,周向始终存在传热恶化问题。高温流体拟膜态热阻是传热恶化的原因。采用高热导率通道、增加运行压力、降低热质比可以缩小周向壁温和热通量差别。提出的关联式能合理预测周向平均换热情况,满足热防护设计的工程应用。     

Numerical study on non-uniform heat transfer deterioration of supercritical RP-3 aviation kerosene in a horizontal tube

The convective heat transfer of supercritical-pressure RP-3(Rocket Propellant 3) aviation kerosene in a horizontal circular tube has been numerically studied, focusing mainly on the non-uniform heat transfer deterioration along the circumferential direction. The governing equations of mass, momentum and energy have been solved using the pressure-based segregated solver based on the finite volume method. The re-normalization group(RNG) k-ε turbulence model with an enhanced wall treatment was selected. Considering the heat conduction in the solid wall, the mechanism of heat transfer deterioration and the buoyancy effect on deteriorated heat transfer were discussed. The evolution of secondary flow was analyzed. Effects of the outer-wall heat flux,mass flux, pressure and tube thermal conductivity on heat transfer were investigated. Moreover, the buoyancy criterion and the heat transfer correlation were obtained. Results indicate that the poor flow performance of near-wall fluid causes the pseudo-film boiling, further leads to the heat transfer deterioration. The strong buoyancy has an effect of enhancing the heat transfer at the bottom of tube, and weakening the heat transfer at the top of tube, which results in the non-uniform inner-wall temperature and heat flux distributions. Decreasing the ratio of outer-wall heat flux and mass flux, increasing the pressure could weaken the heat transfer difference along the circumferential direction, while the effect of thermal conductivity of tube on the circumferential parameters distributions is more complicated. When the buoyancy criterion of(Gr_q/Gr_(th))_(max)≤ 0.8 is satisfied, the effect of buoyancy could be ignored. The new correlations work well for non-uniform heat transfer predictions.     

真空闪蒸冷却换热机制及流量影响

通过对真空闪蒸冷却机理的分析,基于膜-渗透理论建立了以水为工质的真空闪蒸冷却换热模型,并利用实验研究和模型模拟相结合的方法,对闪蒸冷却的换热特性进行了研究。模型分析结果和实验结果误差小于10%,证明了所建模型的准确性。研究结果表明：液膜闪蒸换热在高热通量闪蒸冷却中占主导地位;随着工质流量的增加,闪蒸冷却换热性能提高;工质流量越小,液膜闪蒸换热所占份额越大,即工质闪蒸所带来的潜热利用率增加。研究结果为真空闪蒸冷却在航天热控方面的应用提供了理论基础。     

Measuring properties for material decomposition modeling

Thermal properties were measured on coupon size samples for use in predicting the temperature response and mass transfer during fires exposures. The thermal properties were determined up to temperatures of 800°C through inverse heat transfer analysis on temperature response and mass loss data. Temperature response and mass loss data were determined using a high heat flux decomposition apparatus with controlled oxygen environment. Data included thermal conductivity, specific heat capacity, and density as a function of temperature as well as heat of decomposition and Arrhenius kinetic decomposition constants. Properties for inert materials (no decomposition) compared well with manufacturer reported values and values using other methods. Properties for two decomposing materials, woven glass vinyl ester composite and balsa wood, were measured and compared well with data from other methods. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Particle-fluid heat transfer and dispersion in fluidised beds

The dynamic response of a gas fluidised bed has been measured for a range of particle sizes of lead glass ballotini and a range of particle Reynolds numbers. A dispersion model has been formulated that includes the effects of gas and particle mixing, fluid-to-particle heat transfer and intraparticle thermal conductivity, and the dynamic thermal response in theory has been found by solving the partial differential equations in the Laplace transform domain. The coefficient of thermal dispersion, the particle-to-fluid heat transfer coefficient and the intraparticle thermal conductivity have been found for the experimental response by non-linear regression. The coefficient of axial dispersion was found to be large and the particle to fluid heat transfer coefficients agreed with an established correlation for fixed and fluidised beds. The intraparticle thermal conductivity agreed with literature values for lead glass, the estimates showed no trend with flowrate, and the standard deviation of the estimate was three times smaller than the deviation found from similar experiments in fixed beds.     

A DEM study on the effective thermal conductivity of granular assemblies

A discrete element method (DEM) is developed to simulate the heat transfer in granular assemblies in vacuum with consideration of the thermal resistance of rough contact surfaces. Average heat flux is formulated by the positions and heat flow rates of particles on the boundaries of the granular assemblies. Average temperature gradient is given as a best-fit formulation, which is computed from the relative position and temperature of particles. With the thermal boundary condition imposed on the border region, the effective thermal conductivity (ETC) of granular assemblies can be calculated from the average heat flux and temperature gradient obtained from DEM simulations. Moreover, the effects of particle size, solid volume fraction and coordination number on the ETC are also investigated. Simulation results show that granular assemblies with coarse particles and under large external compression forces exhibit a better heat conduction behavior. The effects of particle size and external compression forces on the ETC are in good agreement with experiment observations.