含湿多孔介质应用于建筑墙体的制冷性能分析

在建立多孔介质墙体热湿平衡的基础上,采用描述非饱和多孔介质热质迁移的数学模型,分析了多孔介质墙体方位及结构、多孔介质层的材料及孔隙率对床层制冷特性的影响,为多孔介质蒸发制冷墙体的推广和应用提供理论依据.     

汲液式多孔介质应用于被动蒸发制冷墙体的性能分析

本文将汲液多孔材料管组合成被动蒸发制冷墙,通过多孔材料的主动吸水、被动蒸发产生制冷效果。应用描述非饱和多孔介质热质迁移的数学模型,分析环境参数对多孔床内部非饱和场量的影响,以及它们与蒸发制冷量之间的内在联系,所得结果与实验结果相符合。实验分析了含湿多孔材料管的排列组合方式对墙体制冷性能的影响,以及多孔材料管的汲液特性。研究结果表明:室外环境参数对多孔介质表面和内部热质迁移影响较大。在遮阳、低的空气相对湿度和有天空辐射时有利于多孔介质表面的蒸发。含湿多孔管内部水分蒸发和水蒸气凝结,与其内部温度高低、温度梯度、含湿量和湿含量梯度相关联。受含湿多孔管排列方式的影响,通过组合墙体的气流分布,气流绕过多孔材料管方式,以及气流与多孔管表面之间的接触时间等存在差异,从而影响组合墙体的制冷特性。汲液多孔材料管的汲液高度受其倾斜角的影响较小。     

多孔建筑材料含盐被动蒸发降温研究综述

本文通过梳理多孔建筑材料热质迁移研究现状,寻找适用含盐被动蒸发的数学模型案例,总结现有研究的优点与不足,为建筑围护结构被动蒸发降温技术充实理论基础。     

建筑中庭制冷屋面传热传质特性

设计了一种新型的,利用多孔介质制冷的建筑中庭节能屋面.应用标准K-ε紊流模型、焓-能量方程、组分方程和"多场-相变-扩散"模型,计算并分析了中庭内环境参数和屋面结构尺寸对多孔介质屋面内温度场、蒸发量场及气相速度场的影响.并从建筑结构设计的角度,提出了优化多孔介质屋面运行工况的技术措施.     

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。     

汲液式被动蒸发多孔墙体制冷性能及汲液特性分析

将汲液多孔陶瓷管组成被动蒸发制冷墙,干燥空气与含湿多孔管表面进行热湿传递,产生蒸发制冷效果,通过多孔材料主动吸水补充散失的水分。沿气流方向,邻近各排多孔陶瓷管分别以交错排列和平行排列方式组合。本文以数值分析与实验相结合的方法分析了含湿多孔管的组合方式、排数和邻近管之间的间距等组合墙体的结构形式以及空气的相对湿度、温度、风速和太阳辐射等气候条件对组合墙体制冷特性的影响。非饱和多孔介质含湿多孔陶瓷管的汲液特性即毛细升高特性,受含湿多孔介质孔隙率、粒径和饱和度的影响。在含湿多孔陶瓷管中填充含湿砂石后,对其制冷特性的变化进行了实验研究。所得结果为汲液式被动蒸发多孔墙体推广和应用提供一定的指导。     

多孔介质中悬浮颗粒迁移–沉积特性研究进展

研究多孔介质中悬浮颗粒的迁移–沉积特性对地下水回灌、石油开采、污染物迁移等问题具有重要意义。从数学模型和物理试验2个方面介绍和总结多孔介质中悬浮颗粒迁移–沉积特性研究现状。提出以现场监测及大量室内试验为手段,以不同条件下悬浮颗粒迁移–沉积特性研究为基础,以建立考虑颗粒速度修正系数、孔隙率修正系数、颗粒捕获率及孔隙率变化的颗粒迁移数学模型为前提的颗粒迁移–沉积特性研究方法。当前无论是物理试验还是数学模型研究,均存在很多不足:如未能准确描述多孔介质内部孔隙结构,没有考虑到颗粒在多因素耦合作用下的迁移–沉积特性,未能将宏观尺度下的过滤现象与细观尺度下的颗粒运动很好地结合等。因此认为以下4个方向是今后研究的重点和趋势:(1)开发动态三维试验装置;(2)建立完善的多孔介质空间模型;(3)建立多因素耦合影响下的颗粒迁移–沉积数学模型;(4)建立多孔介质多尺度颗粒分析方法与理论。     

渗流作用下多孔介质内颗粒迁移与堵塞规律研究

渗流作用下细颗粒在多孔介质中的迁移穿透与堵塞规律对于防止岩土内部侵蚀、提高人工渗滤设施性能具有重要意义.为此,以砾石为填料,基于X-CT技术开展了多孔介质内颗粒在渗流作用下的迁移与堵塞规律研究.研究结果表明,颗粒在多孔介质中的穿透率总体上随着渗流流速的增大而增大,但不同粒径比工况下,渗流流速对穿透率影响呈现出较大差异....     

粒径对多孔介质中悬浮颗粒迁移—沉积特性的影响

粒径变化对悬浮颗粒在多孔介质中迁移—沉积过程影响的研究有重要意义。利用自主研发的砂层迁移—沉积模拟试验系统,研究不同粒径的悬浮颗粒在不同尺寸多孔介质中的迁移—沉积特性。结果表明,对于相同尺寸的多孔介质,随着悬浮颗粒粒径的增加,到达相对浓度峰值时间增加,而对应的相对浓度峰值降低;同时,对于相同粒径的悬浮颗粒,随着多孔介质尺寸增大,相对浓度峰值增加;另外,相对于多孔介质,悬浮颗粒粒径的变化对其迁移—沉积过程影响更为显著;随着多孔介质与悬浮颗粒粒径比增大,相对浓度的峰值和终值增大;根据粒径比不同将悬浮颗粒在多孔介质中的迁移—沉积类型划分为“滤饼过滤型”、“迁移—沉积型”、“自由迁移型”3种。研究结果为水源热泵回灌过程中悬浮颗粒在地层中的迁移—沉积特性进一步研究奠定了基础。     

建筑围护结构热湿传递控制方程

介绍了多孔介质热湿迁移的机理,在此基础上提出了多孔材料热湿耦合传递理论,介绍了一定假设条件下建筑围护结构热湿传递控制方程及其边界条件,指出建筑围护结构热湿传递的研究,对节能和更好地改善热湿环境具有极其重要的作用。     

太阳能多孔集热墙内传热与流动特性分析

分析了太阳能多孔集热墙内传热与流动过程，在局部非热力学平衡的条件下，采用双方程多孔介质模型对其进行数值模拟。获得了空气流速，多孔材料的当量导热系数，多孔介质骨架与气体间的对流换热系数以及多孔层厚度变化时的温度分布，分析这些因素对太阳能多孔集热墙性能的影响。结果表明，提高多孔材料的当量导热系数，多孔介质骨架与气体间的对流换热系数和增大多孔层的厚度对提高集热器的性能是有利的。降低空气速度可以提高空气的温升幅度，但是总的吸热量将会降低。     

Salt influence on evaporation from porous building rocks

The evaporation process of saline solutions within porous building rocks has been studied. Twelve different porous rocks saturated in pure water and a NaCl solution, were dried in a moisture balance. The influence of pore structure, environmental relative humidity and saline solution on the evaporation process has been studied from the experimental results. In order to explain the influence of these parameters simultaneously on the evaporation process, a detailed study of the thermodynamic equations is realised. This study explains the evaporation process in 0.01–100 μm pore size interval, predicting that saline solutions remain a long time within porous media, and therefore, intensify weathering processes.     

Roof cooling effect with humid porous medium

A method of laying a layer of humid porous medium on roof to gain free cooling effect by passive water evaporation is proposed. Numeric model for simulating cooling effect is built with the help of experimental results of physical properties for humid porous medium, which shows advantage over analytical solutions because of the supposition of constant physical properties in the latter. Through the comparison between simulated and experimental results, the model is validated. And the method of evaporation cooling effect with humid porous medium on the roof is tested to be feasible.     

热湿气候地区墙体内部冷凝分析

根据Motakef和E1-Masri的研究,将墙体分为“干-湿-干”3个区域.以多孔介质传热传质学为基础,将水蒸气冷凝看成是湿源、热源、蒸汽汇,建立起墙体湿区域内、热湿耦合传递方程.通过分析解得到了墙体内冷凝率和液态含湿量的分布曲线以及达到临界含湿量所需的时间.分析结果表明墙体内的冷凝率跟湿区域两侧的温差成正比,最大冷...     

On the evaporation effect of a sprinkler water spray

A crude model for estimating the evaporation heat loss due to a sprinkler water spray in a smoke layer is reported. It is found that the evaporation heat loss lies below 11.2% of the convective loss when water travels through a hot gas layer 0.9 m thick and 160°C under normal sprinkler operating conditions. It is also found that the value may go up to 26% if the smoke layer reaches 1.5 m and 273°C.     

蓄热过程中非饱和土壤热湿迁移特性的数值研究

基于多孔介质传热传质理论,建立了在蓄热过程中关于非饱和土壤热湿迁移的数学模型,采用控制容积法,利用Matlab软件对模型进行了数值求解,得到了基本的传热传质机理及温湿度场间的关联性,为优化地下蓄/放热系统提供参考依据。     

饱和度对多孔介质中热–水–力耦合响应的影响

以湿-热弹性理论为基础,给出了非饱和多孔介质中热能传输、水分迁移和变形的耦合控制方程,并与已有试验结果进行了对比。模型计算结果与试验结果吻合较好。针对多孔介质中初始饱和度随深度呈不同分布的三维非对称热源问题进行了热–水–力耦合响应分析。分析表明:当初始饱和度沿竖向的梯度变化较小时,重力作用下孔隙水首先由多孔介质上部向下部流动,继而在温度荷载作用下产生回旋流动。当竖向梯度变化较大时,基质吸力作用下孔隙水先由饱和度较高的底部流向饱和度较低的顶部,然后产生回旋流动,且回旋中心位置随竖向梯度的减小逐渐向多孔介质中心位置靠近。     

Predicting suitability of different scale-dependent dispersivities for reactive solute transport through stratified porous media

In this paper,the behavior of breakthrough curves(BTCs) for reactive solute transport through stratified porous media is investigated.A physical laboratory model for layered porous media was constructed,in which thin layer of gravel was sandwiched in between two thick layers of natural soil.Gravel layer and natural soil layers were hydraulically connected as single porous continuum.A constant source of tracer was connected through gravel layer and elucidated at different sampling points in the direction of flow.Flexible multiprocess non-equilibrium(MPNE) transport equation with scale-dependent dispersivity function was used to simulate experimental BTCs of reactive solute transport through layered porous media.The values of equilibrium sorption coefficient and other input parameters were obtained experimentally.The simulation of BTC was performed using MPNE model with scale-dependent dispersivity.The simulation of different scale-dependent dispersivities was then compared and it was found that for field scale of estimation of dispersivity,asymptotic and exponential dispersivity functions performed better.In continuation to the comparison of simulated BTCs obtained using different models,spatial moment analysis of each aforesaid scale-dependent dispersivity model was also done.Spatial moment analysis provides the information related to mean solute mass,rate of mass travel,and mean plume dispersion.Linear and constant dispersivities showed higher variance as compared to asymptotic and exponential dispersion functions.This supports the field applicability of asymptotic and exponential dispersivity functions.The BTCs were also found to elucidate a nonzero concentration with time,which was clearly affected by physical non-equilibrium.In natural condition,such information is required in effective aquifer remediation process.     

A fully coupled thermo-hydro-mechanical model for simulating multiphase flow,deformation and heat transfer in buffer material and rock masses

This paper presents a numerical method for modeling coupled thermo-hydro-mechanical processes of geomaterials with multiphase fluid flow. A FEM code has been developed and validated for modeling the behavior of porous geological media, and is equally applicable for modeling coupled THM processes in rocks. The governing equations are based on the theory of mixtures applied to the multiphysics of porous media, considering solid phase deformation, multiphase fluid flow, and heat transport. New numerical techniques have been developed for more efficient FEM formulation and equation solution for modeling saturated or partially saturated water flow, gas flow and heat transfer in deformable porous media, as are commonly encountered in performance and safety assessment of underground radioactive repositories. The code has been validated against an experimental benchmark test, which involves bentonite under laboratory conditions, with good results. Several critical outstanding issues for modeling coupled processes of geomaterials are discussed in depth.