Simulation of buoyancy-driven natural ventilation of buildings—Impact of computational domain

Two computational domains have been used for simulation of buoyancy-driven natural ventilation in vertical cavities for different total heat fluxes and wall heat distributions. Results were compared between cavities with horizontal and vertical inlets. The predicted ventilation rate and heat transfer coefficient have been found to depend on the domain size and inlet position as well as the cavity size and heat distribution ratio. The difference in the predicted ventilation rate or heat transfer coefficient using two domains is generally larger for wider cavities with asymmetrical heating and is also larger for ventilation cavities with a horizontal inlet than those with a vertical inlet. The difference in the heat transfer coefficient is generally less than that in the ventilation rate. In addition, a ventilation cavity with symmetrical heating has a higher ventilation rate but generally lower heat transfer coefficient than does an asymmetrically heated cavity. A computational domain larger than the physical size should be used for accurate prediction of the flow rate and heat transfer in ventilation cavities or naturally ventilated buildings with large openings, particularly with multiple inlets and outlets. This is demonstrated with two examples for natural ventilation of buildings.     

地埋管地源热泵制热性能测试与分析

理论分析地埋管地源热泵相比空气源热泵的节能率。结合工程实例,对地埋管地源热泵地埋管换热器进出水温度、冷凝器进出水温度、热泵机组日能效比、供暖期能效比进行了实测计算。在测试期,地埋管换热器进出水温度、冷凝器进出水温度均在正常范围内波动。日能效比基本不随室外温度的变化而波动,说明热泵机组的制热性能比较稳定。供暖期能效比为3.05,说明该项目地源热泵的制热性能比较理想。     

隧道等截面通风系统均匀送风特性研究

针对地下建筑长大隧道均匀通风的工程需求,提出了一种基于通风均流器的等截面通风系统,为获得主风管风速、宽高比与通风系统送风均匀性的关系,采用CFD数值模拟分析方法对通风系统的送风均匀性和阻力性能进行了研究。研究发现,主风管风速为9.7 m/s时,各风口最低风速4.45 m/s,最高风速4.96 m/s,平均风速4.63 m/s,最大偏差7%,各风口风速标准差为0.16,等截面通风系统能实现均匀送风。通风均流器阀片角度恒定时,系统送风均匀性随着主风管风速的增大而小幅降低,各风口风速标准差范围为0.12～0.24;随着主风管宽高比的增加,各风口风速标准差波动范围为0.22～0.34,主风管风速、宽高比对系统送风均匀性影响较小。风速大于6.5 m/s时,通风均流器阻力系数ξ随着阀片角度β的增大而减小,与Re无关;阀片角度β一定时,通风均流器阻力系数ξ随主风管宽高比的增加而减小。     

Experimental study on fluidisation behaviour and pressure drop across the centrifugal fluidised bed with static geometry by varying inlets,inlet width and mass of bed particles

Centrifugal fluidised bed with static geometry (CFBSG) is the novel approach of fluidisation which has not yet attracted the attention of IC engine researchers to remove particulate matter. This requires necessitating an understanding of the nature of fluidisation and pressure drop in CFBSG. The present study describes an experimental study on the effect of a number of inlets, inlet width, and mass of bed particles silicon carbide (SiC) on fluidisation and pressure drop across the fluidised bed chamber using air as a medium. Low pressure drop and better partial fluidisation were observed for three- and four-inlet chambers, especially at a higher loading of bed particles. The accumulation of bed particles near inlet and outlet is also drastically reduced as the number of inlet increases. When compared to 5?mm inlet slot chambers, 3?mm inlet slot chambers for any inlet gives better fluidisation with higher pressure drop.     

Assessment of Numerical Simulation Capabilities of the Fire Dynamics Simulator (FDS 6) for Planar Air Curtain Flows

Computational Fluid Dynamics (CFD) results are discussed for momentum driven planar jet flows, resembling configurations in use for air curtain in the context of smoke control in building fire. The CFD package Fire Dynamics Simulator (FDS) is used. Special focus is given to the impact of grid resolution, synthetic turbulent inflow boundary condition and sub-grid scale eddy viscosity models. The computational results are compared with summarized literature data. Investigation of different set-ups of inlet boundary conditions, including the inlet duct length, velocity profile and method of generation of turbulence at the level of the inflow, reveals that the inlet boundary condition is the most influential factor governing the flow downstream. The FDS results successfully reproduce the planar jet flows, both in terms of mean variables and second-order statistics. ‘Reference’ results have been obtained with a fully developed turbulent flow emerging from a long inlet duct. By reducing the inlet duct length and applying the Synthetic Eddy Method (SEM) at the inflow boundary condition, the ‘reference’ results have been reproduced with a reduction in the computing times of approximately 20%. However, care must be taken when choosing the parameters of SEM, in particular the number of eddies and their length scale. The impact of turbulent viscosity model is noticeable, but not of primary importance for the flow at hand, provided that a sufficiently fine computational mesh is used.     

空调气流组织对卷烟高大厂房内温度场的影响

本文对具有高发热量烟机的4～5米高的大面积空调厂房进行流场和温度场的数值模拟。比较了不同的送、回风口布置方式对厂房内的温度分布的影响。研究发现卷烟高大厂房内温度沿高度分层明显。而中等高度下送风和上回风可以有效地利用温度分层,不仅在工作区保持较均匀工作温度,而且可以节省能源。     

Tracer gas experiment for local mean ages of air from individual supply inlets in a space with multiple inlets

We investigate the supply characteristics of incoming air via individual inlets in a ventilated space with multiple inlets. Theoretical considerations are given to determine the relations between the local mean age (LMA) of the total supply air and the individual LMA of each supply air inlet. Tracer gas experiments are conducted in a simplified livestock model with two supply inlets and one exhaust outlet. Transient concentration responses at internal points are measured after tracer gas injection one inlet at a time, and for simultaneous tracer injection at both inlets. The spatial distributions of LMAs and steady concentrations are obtained by tracer injections from each supply inlet, which demonstrate the supply characteristics of the individual inlets in the space. We have found that the overall LMA is the weighted average of the LMA by each inlet, and the weighting factor for the average is the corresponding steady state concentration at a given point. Experiments repeated for various airflow rates show that the nondimensional steady concentrations remain nearly constant regardless of the total airflow rate, but are greatly influenced by the airflow ratio between inlets. The local mean ages are found to increase proportionally with respect to the nominal time constant. Experimental procedures and results are verified by the fact that the total LMA measured at the exhaust is in good agreement with the theoretical nominal time constant of the space.     

初沉池集气罩内气流形态的预测与通风方案的研究

采用有限体积法和SIMPLE算法对某污水厂初沉池集气罩内的三维湍流进行了模拟。研究了进风口的形式、位置、尺寸以及排风口的位置等因素对速度场的影响。通过对几种不同形式流场流动特性的分析,得出了一些定性的结论。     

大型给水泵站进、出水流道数值模拟及优化设计

根据某给水泵站设计参数要求,设计具有相同进、出口尺寸的肘型和簸箕型2种进水流道方案,以及7种不同龟背形式和倒圆弧半径的出水流道方案。数值计算采用压强连接的隐式修正SIMPLEC算法,并结合雷诺平均法的RNGκ-ε模型和壁面函数法。计算结果表明,在相同进、出口尺寸条件下,肘型进水流道的水力损失比簸箕型进水流道小73.7%;有龟背和圆弧的出水流道的水力损失最小。该研究实现了进、出水流道的优化设计。     

严寒风沙地区金字塔形建筑呼吸式双层幕墙关键技术

银川宁东煤化工基地综合办公楼呈金字塔形,采用呼吸式双层幕墙,幕墙设计时需要解决换气层的宽度、进出风口的选用、防火及成本等问题.主要介绍了双层呼吸幕墙结构形式选择、通风和保温设计及主要系统设计.通过详细设计,幕墙工程满足国家和地区建筑节能的相关规范要求,并最大程度上降低建筑物的运行能耗,充分体现绿色建筑的设计理念.     

地铁车厢内气流组织的回风负压模拟

由于地铁列车回风是靠风机的抽吸完成的,因此回风口是处于负压状态下的,为了弄清这个负压对车厢内部气流组织和温度分布的影响,建立了地铁列车三维k-ε模型,利用Fluent软件模拟了不同回风压力、排风口宽度和热负荷下车厢的内渗透风量、压力分布.结果表明：车厢内压降△P随着排风口宽度和车厢热负荷的增大而增大;当回风压力一定时,渗透风量随负荷增加而增加;当热负荷一定时,渗透风量随着压力增大而减小;当车厢负荷小于额定负荷即负荷100％时,可通过减小排风口宽度来减少渗透风量;当车厢热负荷大于100％时,可增大回风口压力来减少渗透风量.     

Study of a passive scalar transport in a pipeline x-junction

The transport processes of a passive scalar generated in the mixing of two fluids in a pipeline x-junction are analysed in this paper. The turbulent flow field is computed for the merging of streams using a method of computational fluid dynamics. Two- and three-dimensional simulations are achieved employing both Cartesian and BFC co-ordinates. The numerical model is validated from an experimental set-up. Different parameters are measured for various operating conditions. The influence of the angle between pipe inlets is studied, to establish the optimal condition where the passive scalar concentration in both outlets is similar.     

热烈庆祝深圳汉光电子技术有限公司成立20周年

<正>2014年2月,深圳汉光电子技术有限公司(以下简称汉光公司)喜迎成立20周年庆典。汉光公司是一家专业从事城市基础能源(水、电、气、热、冷等)的能耗数据采集、运营监测、节能管理等产品与软件开发的国家级高新技术企业。在20年的发展历程中,公司取得了全面的发展。为在激烈的市场竞争中占据优势地位,汉光公司结合国家智慧城市、节能减排以及物联网产业政策,始终坚持开发具备自主知识产权的高新技术产品,并不断拓宽产品领域,逐渐形成了汉光品牌,依托深圳辐射全国市场,目前产品已遍布北京、天津、深圳、宁波、济     

Numerical investigation on the ingress of particulate matter from ambient air into the inlet of a building air handling unit

The transportation of ambient particulate matter (PM) from outdoor air into the inlet of a mechanical building ventilation system is poorly understood. No studies have examined the effect commonly used commercial air handling unit (AHU) inlet designs have upon the migration of PM from the ambient environment into the building ventilation system, and implications of this on energy consumption and indoor air quality (IAQ). Through the numerical analysis of commercial AHU inlets, the differences in concentration of PM in ambient air and that within AHUs were determined, more commonly referred to as Aspiration Efficiency (AE %). A 20–50% difference in particle concentrations between ambient air and the in-AHU concentration was observed between forward and rear-facing AHUs relative to ambient wind direction and speed, and at the maximum ventilation flow rate. Furthermore, a decrease in the ventilation flow rates resulted in a significant reduction in PM concentrations entering the rear-facing AHU. Increasing the Stoke number led to lower AE as a continuous decrease was observed for both rear-facing inlets. The findings of this paper show that AHU inlet design has significant implications on IAQ and building energy consumption, and scope exists to design these inlets to impact both aspects positively.     

Effects of inlet and exhaust locations and emitted gas density on indoor air contaminant concentrations

The steady-state distribution of contaminant concentrations in a workroom is a function of several factors, of which the types and relative position of air inlets and exhausts are some of the most important. Here several different inlet and exhaust locations and types (with or without diffuser) were investigated to determine the optimum inlet and exhaust positions. Room concentration patterns for a workroom were explored by computational fluid dynamics (CFD) simulations for various inlet locations, exhaust locations, contaminant gas densities, and dilution air flow rates. Average contaminant concentrations were calculated for the entire room, the breathing zone plane, and the near-source breathing zone (BZ).     

对空调系统送风量"基准风口调整法"的异议

认为教科书中所讲述的“基准风口调整法”的操作程序不具有普遍适用性。当“基准风口”不是系统末端送口时，则其后送风口调整将相互影响，不满足“流量等比分配”条件故而提出了确定“基准风口”的新原则，并分两种情况介绍新的送风量调整程序。     

Evaluation of an air-cleaning unit having photocatalytic sheets to remove acetaldehyde from indoor air

A photocatalytic oxidation (PCO) reactor to which newly developed photocatalytic sheets were applied to decontaminate indoor air was considered in this study. Firstly, the PCO reactor was designed to achieve efficient ultraviolet (UV) irradiation. Then the rate at which acetaldehyde, as a representative indoor air contaminant, was removed by the PCO reactor was calculated using a computational fluid dynamics (CFD) simulation. In this process, some alternatives that achieved higher removal performance using obstacles at the inlet and outlet openings were introduced. The results of the CFD simulation showed that the obstacles installed in the middle of the inlet and outlet openings helped to improve the removal performance of the PCO reactor as the degree of contact by the acetaldehyde on the PCO sheets was increased. Furthermore, the results of these experiments also showed some improvement in removal performance when obstacles were installed. However, the overall experimental performances were far lower than as had been suggested by the CFD simulation, which inferred that the oxidation rate on the surface of the PCO sheets was not 100%, as had been assumed in the CFD simulation. Nevertheless, CFD simulations are assumed to be a good method for selecting the optimal option from many alternative PCO reactors.     

ILES of flow over low-rise buildings: Influence of inflow conditions on the quality of the mean pressure distribution prediction

The paper presents an analysis of the deformation of the horizontal velocity profile in the flow approaching low-rise buildings for large eddy simulation on coarse grids. Build-up of velocity near the ground is observed as a consequence of momentum transfer from the outer flow to the ground level due to the fluctuating flow field. As a remedy, reduction of the turbulence intensity at the inflow boundary of the computational domain with respect to the experimental values is studied. The observation is that accurate prediction of the mean pressure distribution on the building surface is obtained when the inlet turbulence is reduced such that the deformation of the velocity profile in the flow approaching the building becomes small. For reliable mean pressure prediction, it is best not to reduce the inlet turbulence more than the minimum necessary to obtain a good velocity profile in the approaching flow.     

Nitrogenous compounds in facultative oxidation pond sediments

The protein content of sludge samples from facultative oxidation ponds was measured and was found to have even distribution in the pond floor. Proteolytic activity which degrades protein to intermediate compounds, was found to be slightly higher near the pond inlet region. It was also shown that proteolytic activity increased with increasing depth of overlying pond liquor.Ammonia content of, and ammonification by pond sludge appeared to be independent of locality. Urea and urease activity were restricted to the regions close to the pond inlet region.     

串联式双层平流沉淀池的工艺设计

以大连市三道沟净水厂一期串联式双层平流沉淀池的工艺设计为例,介绍和分析了该池型的主要设计参数、进出口布置、上下层排泥布置、放空与采光等主要设计内容。该双层沉淀池运行后,进水量达到甚至超过了设计水量,出水水质稳定可靠,排泥设备运行良好,实现了节省占地优化设计的预期目的,能为同行业相关设计提供借鉴和参考。