复合空调室内气态污染物对流输运模拟

利用CFD数值模拟方法分析了复合窗式空调系统对建筑室内气态污染物输运过程的影响.采用雷诺应力模型(RSM)描述了室内空气和污染物对流输运过程,并详细探讨了复合窗式空调系统的送风速度、新风比、净化效率和室内热源强度等对室内气态污染物对流输运过程的影响.计算结果表明,提高送风速度、新风比以及净化效率都能有效降低室内气态污染物平均浓度.值得注意的是,当送风速度超过0.75 m/s后,室内气态污染物浓度水平维持恒定;空调系统即使按全新风模式运行,也不能彻底排除室内污染物.     

生土建筑围护结构表面吸放湿过程实验研究

陕南地区的生土建筑是一种独特的民居建筑 .为了定量地研究生土建筑室内热湿环境 ,确定生土建筑围护结构表面吸放湿过程质交换系数是一项基础工作 .建筑围护结构表面的热湿迁移过程是一个典型的边界层内的流动、传热和传质过程 ,该过程的微分控制方程比较复杂 ,求解困难 .首次实验研究了生土建筑材料的等温吸放湿过程 ,提出了生土建筑围护结构表面质交换系数实验测试方法 ,实测分析计算结果与利用对流质交换相似关系计算得到的表面质交换系数比较吻合 .本研究为定量地分析生土建筑室内热湿环境奠定了科学基础     

热质墙体在我国的热适应性研究

室外大气综合温度通过热质墙体传入室内,波动大大衰减,波峰延迟,在节能降耗中具有重要意义。本文首先建立了热质墙体的一维非稳态传热模型,对应用在一栋零能耗建筑中的热质墙体传热性能进行了模拟,模拟结果与实际检测的墙体温度和热流率吻和良好。而后进一步利用该模型分析了热质墙体在我国5类典型气候区域代表城市的适应性,结果表明在昼夜温差大、室内外平均温差大的地区较适宜采用厚重围护结构,而在冬暖夏凉地区现象相对不明显。     

室内空气对流热运动的RNG改良模型及其验证

本文针对室内普遍存在的空气热分层流现象及其空间湍流基本特征,提出了一种适用的湍流模型——改良型的RNG双方程模型,并配以改良的复合型壁面函数,以适应空气热分层对流运动中产生的空间湍流衰减问题,精确求解高、低Re数湍流共存的室内流场。在此基础上,采用方腔混合对流和AR=1/2双跨空间高Re数流动的实验数据,对湍流改良模型进行了充分的验证,为相关问题的研究及工程应用提供了有效手段。     

室内自然对流数值模拟分析

研究建筑围护结构传热与流体流动综合作用下室内自然对流数值模拟,建立了一套同时在固体-流体区域整体求解连续性方程、动量方程和能量方程的数值模拟方法。具体分析了瑞利数变化范围为104到106时建筑围护结构传热对室内自然对流的影响。数值预测结果表明:该方法能够真实反映室内自然对流问题。为室内自然对流问题数值模拟找到了一种实用有效的方法。     

实现非定常物性围护结构与基于状态空间法建筑热过程耦合计算方法研究

双层皮玻璃幕墙、种植屋面、蓄热相变墙体等新型围护结构具有良好的保温隔热、维持舒适的室内热环境的特征,其节能潜力得到了广泛的认可。随着新型围护结构方面的研究日益增多,此类技术也日益完善,在建筑中得到一些应用,因此,在建筑能耗模拟过程中需要考虑到新型围护结构。新型围护结构热(质)传递等物理过程均为非定常物性的动态热(质)传递过程,常采用有限差分法进行求解。应用有限差分法实现采用新型围护结构建筑的热过程模拟计算,存在计算量大、计算时间长等问题。为提高计算速度、保证计算稳定性,本文提出了实现建筑本体中非定常物性围护结构模拟与基于状态空间法的建筑热过程耦合计算的方法,并将此算法在建筑能耗模拟DeST软件中进行实现和案例计算及校核。     

严寒地区铜铟镓硒光伏墙体的热效能研究

为研究光伏墙体在严寒地区的热效能,在沈阳地区搭建实验平台,通过监测安装铜铟镓硒光伏墙体的光伏建筑与普通建筑的室内温度、围护结构温度和采暖设备耗电量等参数,比较两者室内热环境和采暖能耗。研究表明安装铜铟镓硒光伏墙体的光伏实验建筑室内温度更高,且采用自然循环热利用方式的室内热环境优于密闭空腔热利用方式,光伏实验建筑至少能够节约20%的采暖能耗。     

墙体特性与自然通风耦合作用的墙体传热模型

对单面墙体自然通风房间的传热过程进行数值模拟.主要讨论了不同自然对流强度时墙内侧对流换热系数的影响,并分析了不同墙体结构的室内空气温度变化情况.结果表明:墙内侧值的变化会随瑞利数(Ra)的增加而增加,室内平均温度随房间通风量增加振幅不断减小,房间热环境随通风量增加而改善.绝热层总厚度不变时,绝热层位置离热源越近隔热效果越好.     

墙体特性与自然通风耦合作用的墙体传热模型

对单面墙体自然通风房间的传热过程进行数值模拟。主要讨论了不同自然对流强度对墙内侧对流换热系数的影响,并分析了不同墙体结构的室内空气温度变化情况。结果表明：墙内侧值的变化会随瑞利数（Ra）的增加而增加,室内平均温度随房间通风量增加振幅不断减小,房间热环境随通风量增加而改善。绝热层总厚度不变时,绝热层位置离热源越近隔热效果越好。     

严寒地区冬季室内结露问题分析

本文结合严寒地区的几种典型墙体结构及室内温湿度情况 ,分析了墙体和热桥部位的热工状况对于相关标准规范的满足情况。提出了对建筑热桥部位保温处理的若干建议 ,认为外保温墙体是最适合严寒地区节能建筑的墙体形式     

地下道路污染物对流扩散反问题伴随同化研究

在反问题框架内,基于偏微分方程最优化控制理论的伴随同化方法,建立了融合动力模型和观测信息的地下公路隧道污染物对流扩散反问题的计算模型,并给出了模型求解方法。以对流扩散方程中的源项为例进行了反演计算,并利用反演计算出的源项对污染物浓度进行了预测。研究表明,与传统的正问题模型相比,反问题模型反演计算得到的源项可以动态地反映隧道内车流量、车速、排放特性等因素的综合影响,并且计算得到的污染物浓度场精度更高。应用该方法,通过有效的对各类污染物观测资料进行客观利用,可以识别一些不确定参数,从而更好地实现对污染物浓度分布的分析与预测。     

Detailed numerical simulation of coupled heat transfer by conduction,natural convection and radiation through double honeycomb walls

The aim of the present work is to study numerically 2-D steady state coupled heat transfer by conduction, free convection and infra-red radiation through two honeycomb walls separated by a vertical air layer. Airflow in both holes and separating air layer is laminar. The limiting vertical sides of the double honeycomb wall are assumed to be isothermal but at different temperatures while the upper and lower horizontal surfaces of the structure are insulated. The FVM method and the SIMPLE algorithm are used to solve numerically the equations of conservation of mass, momentum and energy in both air filled cavities and solid partitions. It is found that the global heat flux across the entire wall varies almost linearly with the difference between the outside and the inside temperatures. Based on this linear thermal behaviour, appropriate overall heat exchange coefficients are derived. These coefficients can be used easily in practice to predict the global heat transfer across the studied honeycomb walls without solving the detailed and complex equations that govern the different heat transfer mechanisms. Effect of the thermal conductivity of the construction material on the overall heat transfer through double honeycomb walls is studied.     

不同热源位置下室内自然对流换热数值模拟

以不同热源位置下室内自然对流换热过程为研究对象,采用有限容积数值方法对质量守恒方程、能量守恒方程进行离散求解,研究了瑞利数Ra在10 3~10 6之间,不同热源位置情况下,室内的流体流线、等温线的分布特征和Nu数的变化。分析结果表明：Ra=10 3时,等温线以热源为中心向外扩散呈均匀拱形,随着Ra数的增加,等温线逐渐弯曲变形,在冷壁和热壁附近形成薄边界层;流线呈现为两个反向对称的涡,随着Ra的增大,涡的大小改变并发生运动;Ra=10 3时,D=0情况下的Nu最大;热源的位置对换热量的影响较大,D=0.5时,Nu数曲线最陡,D=0时最平缓;Nu数与Ra数呈幂数关系,拟合的线性相关性可达90%。结论为研究室内复杂传热机理提供理论依据。     

Thermal plumes of kitchen appliances: Idle mode

In the kitchen environment, pollutant fumes of the cooking process are released into the ambient air by the convection plumes. The practical problem is to compute the requested extract air flow rate to maintain good indoor air quality in an energy efficient manner. In the most accurate design method, the design of a kitchen ventilation system is based on the flow rate of the thermal plume. In this method, the amount of heat carried in a convective plume over a cooking appliance at a certain height is calculated. The heat load is then assumed to be a point heat source and the velocity and temperature profiles are approximated to be Gaussian distributed. In commercial kitchens, the location of the extraction point is at a height of 0.9–1.4 m above the heat source where the convection flow is not yet fully developed. This paper demonstrates that the generic plume equation, derived in the region of complete flow similarity, is not accurate in this intermediate zone. However, it gives a reasonable accuracy for practical applications when an individually adjusted empirical factor of the virtual origin is applied. The power intensity of the heat gain has a much more significant effect on the plume characteristic than the previous studies indicate. The plumes are narrower and the spreading angle is smaller with higher heat gains.     

工业厂房自然通风热环境的数值研究

运用CFD技术对某典型工业厂房的自然通风进行了数值模拟。研究了热源、污染源参数一定时,不同进风口离地高度对厂房工作区热环境及污染物浓度分布的影响。分析了带热源工业厂房热环境的主要特点,认为评价这种高温环境时,应同时考虑工作区风速及建筑内壁面辐射的影响。为此,采用热应力指数HIS作为这类热环境的评价指标。结果可以看出,对于热源具有一定的高度的工业厂房,适当提高进风口位置,不仅可以增加自然通风量,提高工作区空气流速,改善工作区热环境,而且有助于降低厂房平均污染物浓度。随着H的增加,通风量和工作区风速增大,热应力指数和污染物浓度减小。当H增加到1.2 m后,通风量和工作区风速基本不再变化。     

An algorithm for calculating convection coefficients for internal building surfaces for the case of mixed flow in rooms

The treatment of convective heat transfer at internal building surfaces has a significant impact on the simulation of heat and air flow. Accurate approaches for the range of flow regimes experienced within buildings (buoyant flow adjacent to walls, buoyant plumes rising from radiators, fan-driven flows, etc.) are required, as is the ability to select an appropriate method for the case at hand and to adapt modelling to changes in the flow.A new approach — drawing upon previously published methods — has been developed for modelling mixed convection within mechanically ventilated rooms. It is applicable for rooms ventilated with ceiling mounted diffusers and is appropriate for both heating and cooling. ESP-r simulations performed with the mixed flow model indicate that the prediction of heating and cooling loads is highly sensitive to the treatment of surface convection and that significant errors can result if an inappropriate model is employed. The results also reveal that the choice of convection algorithm can influence design decisions drawn from a simulation-based analysis.     

不同通风条件下船舶舱室火灾热量分布研究

以某全尺度船舱火灾试验为基础,依据能量守恒定律定量分析了不同通风条件下火灾过程中舱壁升温、以辐射及对流方式向周围舱室传热、高温烟气传热等方式进行热量扩散的比重关系.结果表明,在该试验条件下,高温烟气扩散和舱壁升温占据主要部分,而经舱壁向相邻舱室扩散的热量最大不到10％.     

Modelling Radon Entry into Houses with Basements: Model Description and Verification

We model radon entry into basements using a previously developed three-dimensional steady-state finite difference model that has been modified in the following ways: first, cylindrical coordinates are used to take advantage of the symmetry of the problem in the horizontal plane, thereby increasing resolution and computing eficiency without signifiant loss of generality; second, the configuration of the basement has been made m e realistic by incorporating the concrete fmtm which sup ports the basement walls and floor; third, a quadratic relationship between the pressure and flow in the L-shaped gap between slab, footer, and wall has been employed; and fourth, the natural convection of the soil gas which follows from the heating of the basement in winter has been taken into account. The temperature field in the soil is determined fiom the equation of energy consmation, using the basement, surface, and deep-soil temperatures as boundary conditions. The pressure field is determined from Darcy's law and the equation of mass conservation (continuity), assuming that there is nofIow across any boundary except the soil surface (atmospheric pressure) and the opening in the basement shell (fixed pressure), Since the energy conservation equation includes both heat advection and conduction, the temperature and pressure equations must be coupled. After the pressure and temperature fields have been obtained, the velocity field is found fiom Darcy's h. Finally, the radon concentration field is found from the equation of mass-transport, assuming that diffusive entry through openings may be neglected. The convective radon entry rate through the opening or openings is then calculated. In this paper we describe the modified model, compare the predicted radon entry rates with and without the consideration of thermal convection, and compare the predicted rates with rates determined from data from seven houses in the Spokane River valley of Washington and Idaho. Although the predicted rate is much lower than the mean of the rates determined from measurements, er-TOTS in the measurement of soil permeability and variations in the permeability of the area immediately under the basement slab, which has a signifiant influence on the pressure field, can account for the range of entry rates inferredfiom the data.     

Indoor air environment: more structures to see?

A convection transport visualization technique is suggested to analyze the indoor air environment (IAE). A two-dimensional and laminar displacement ventilated room with discrete heat and contaminant sources is numerically investigated. Based on the governing equations, three convection transport functions, i.e. streamfunction, heatfunction, and massfunction, are derived to describe the fluid, heat, and contaminant transport processes, respectively. Main attentions are focused on the effects of the strength of heat source (Gr), the strength of contaminant source (Br), the strength of external ventilation (Re), and the positions of inlet/outlet openings on IAE. Numerical results illustrated that the abstract transport behaviors of the fluid, heat, and contaminant indoors are clearly exhibited by the convection transport functions which provides a simple but practical means of assessing IAE.