水平送风工况下CRAC机组间距对机架散热的影响

本文研究架空地板数据中心CRAC水平送风方式下四种CRAC机组送风间距对机房内机架散热和穿孔地板气流分布的影响,分析四种CRAC送风间距的机房机架入口温度和通过穿孔地板的体积流量,比较四种工况的机架设备散热情况和热循环,为今后数据机房设计以及机房热管理和节能改造提供了依据。     

CO2-dispersion studies in an operation theatre under transient conditions

Maintaining air quality and thermal comfort inside an operation theatre equipped with horizontal jet flow type air-conditioning units, has been a challenge to engineers. The objective of this study is to analyze the airflow pattern in such operation theatres and the influence of location of the air-conditioners. The outcome of this study is expected to reduce the post-operation problems faced due to excess concentration of contaminants. Experimental studies were conducted in 10 different hospital operation theatres. Parameters such as air temperature and carbondioxide concentration were measured at discrete points chosen in the theatre. A 3D time-dependent numerical model was developed to simulate the airflow in terms of parameters such as velocity, temperature and CO₂ distributions in an operation theatre under transient conditions. The Eulerian approach using the volume fraction of the mixture of air and CO₂ was used to solve the numerical model. Finite volume approach was attempted in this work with PISO (pressure implicit with split operators) algorithm for the pressure correction equations. The simulated results were compared with the experimental results for validity. The locations of the air-conditioners were changed in the numerical model to analyze the airflow patterns and the contaminant distribution.     

Numerical analysis of diffuse ceiling ventilation and its integration with a radiant ceiling system

A novel system combining diffuse ceiling ventilation and radiant ceiling was proposed recently, with the aim of providing energy efficient and comfort environment to office buildings. Designing of such a system is challenging because of complex interactions between the two subsystems and a large number of design parameters encountered in practice. This study aimed to develop a numerical model that can reliably predict the airflow and thermal performance of the integrated system during the design stage. The model was validated by experiments under different operating conditions. The validated model was further applied to evaluate the effects of different design parameters, including the U-value of the diffuse ceiling panel, plenum height, plenum depth, and inlet configuration. In the integrated system, diffuse ceiling separated the radiant ceiling from the rest of the room and consequently changed the energy efficiency of the radiant system. The simulated results demonstrated that using ceiling panel with a higher U-value can minimize this impact and make the system to cool down space efficiently. Low plenum height was beneficial to the energy efficiency, but aggravated the non-uniformity air distribution and further led to the draught problem in the occupied zone. This system was recommended to apply in the small offices instead of large, open spaces.     

地板送风房间内流场、温度场及负荷特性的研究

地板送风系统通过安装于架空地板上的旋流或格栅型散流器送风,架空地板下的静压箱是其区别于置换送风系统和全混送风系统的重要特征之一。本文采用数值模拟的方法对有、无静压箱工况下的下送风系统进行了对比研究,通过对室内流场和温度场的分析,考察了静压箱对室内热平衡的影响。其次,通过负荷有效系数计算了温度分层环境下的空调负荷,并给出了负荷有效系数的数值计算方法,可为今后地板送风系统的工程设计提供参考。     

The Influence of Office Furniture,Workstation Layouts,Diffuser Types and Location on Indoor Air Quality and Thermal Comfort Conditions at Workstations

Abstract Many factors affect the airflow patterns, contaminant removal efficiency and the indoor air quality at individual workstations in office buildings. The effects of office furniture design and workstation layouts on ventilation performance, contaminant removal efficiency and thermal comfort conditions at workstations were studied. The range of furniture configurations and environmental parameters investigated included: 1) partition heights, 2) partition gap size, 3) diffuser types, 4) supply air diffuser location relative to the workstation, 5) return air grill location relative to the workstation, 6) heat source locations, 7) presence of furniture, 8) supply air temperatures, 9) adjacent workstations, 10) contaminant source locations, 11) supply air flow rates, and 12) outdoor air flow rates. The tracer gas technique was used to study experimentally the relative impact of these parameters on the air distribution and ventilation performance, as well as contaminant removal efficiency. Thermal environmental parameters such as air velocity and temperature were monitored at several locations to characterize the impact of these parameters on the thermal comfort conditions. The results showed that the outdoor air flow rate had a significant influence on the mean age of air. The air distributions at all the workstations were good even when the supply air flow rate was relatively low (i.e 5 L/s). At the same time, most of the parameters tested had a significant influence on contaminant removal efficiency when there was a contaminant source present somewhere in the office.     

高大空间喷漆作业环境漆雾控制的一种新方法

利用局部静压箱和条缝型百叶排风口在污染控制区形成上送风下排风的气流组织形式.因送排风口距离小可以形成强劲的吹、吸气流,能克服冬季送热风时浮力对气流的影响,同时由于控制区域小,不污染附近的作业环境,因此可取得漆雾控制的最佳效果.     

A review on the applied techniques of exhaled airflow and droplets characterization

In the last two decades, multidisciplinary research teams worked on developing a comprehensive understanding of the transmission mechanisms of airborne diseases. This article reviews the experimental studies on the characterization of the exhaled airflow and the droplets, comparing the measured parameters, the advantages, and the limitations of each technique. To characterize the airflow field, the global flow-field techniques—high-speed photography, schlieren photography, and PIV—are applied to visualize the shape and propagation of the exhaled airflow and its interaction with the ambient air, while the pointwise measurements provide quantitative measurements of the velocity, flow rate, humidity and temperature at a single point in the flow field. For the exhaled droplets, intrusive techniques are used to characterize the size distribution and concentration of the droplets' dry residues while non-intrusive techniques can measure the droplet size and velocity at different locations in the flow field. The evolution of droplets' size and velocity away from the source has not yet been thoroughly experimentally investigated. Besides, there is a lack of information about the temperature and humidity fields composed by the interaction of the exhaled airflow and the ambient air.     

天津图书馆新馆空调设计

介绍了该工程的冷热源系统、地板送风系统、紧凑型空调机组。模拟了地板送风系统的不同高度、不同风量地板静压箱内的压力分布,根据模拟结果合理地确定了静压箱的高度、风量、送风口的形式及外区空调形式。     

地板送风静压层内气流流动特性研究

通过实验测试和CFD模拟,研究了地板静压层内有一根横梁时,静压层内的气流流动特性及局部阻力系数的理论计算式.研究结果表明,横梁高与静压层高之比为0.3～0.7,静压层内速度为0.2～1.0m/s,Re为4.08×103～2.04×104时,局部阻力的理论计算值与实测值非常接近,该理论计算式可用于计算局部阻力系数.     

Displacement Ventilation - the Influence of the Characteristics of the Supply Air Terminal Device on the Airflow Pattern

Displacement ventilation is acknowledged to be an efficient system for the removal of contaminants and excess heat from occupied zones of rooms. However, airflow rates, temperature and the design of the air supply device strongly influence the parameters which determine thermal comfort. This paper reviews experiments and theoretical models which show the connection between these parameters. The width and shape of the air supply device have been varied, and a porous media has been used on the inlet area of the air supply device. The velocity and temperature profiles have been measured. The results presented show also that the flow can be described with respect to width and form of the profiles for temperature and velocity. The flow does not operate like a turbulent jet due to thermal stratification. It is shown that the Archimedes number of the supply air is the parameter which determines the air velocity in the area close to the floor. (The Archimedes number is here defined as the ratio between buoyancy and inertia forces.) The results show that it is possible to remove considerable amounts of excess heat from a room, typically 40-50 W/m², without exceeding the limits for thermal comfort. However, this requires relatively high airflow rates and supply air terminal units at least along one of the walls.     

动态送风装置的试验研究

该装置用步进电动机带动分流板产生动态风。热工性能试验显示,与稳态送风相比,风速动态化后对风量和换热量影响很小。以大学生为试验样本进行了人体舒适性研究,显著性分析表明,受试者对动态风接受程度较稳态风有显著提高。     

湿热地区建筑被动式防热设计与节能的探讨——以广州为例

探讨了湿热地区城市热环境现状、建筑防热设计措施,以及改善居住区热环境的策略,以期满足人们对城市环境热安全性和热舒适性的要求,在创造美好的城市居住环境同时考虑建筑节能和经济性。     

Characterizing airflow through fabric air dispersion system using a porous media model

No existing diffuser models may be used to effectively describe the fabir air dispersion system (FADS), a new ventilation terminal made of ploymer. A porous media model was proposed to describe FADS in present work. And the corresonpongding mathematical model was developed for the airflow through FADS. The characteristics of airflow through FADS was predicted using the commercial software FLUENT with the standard k ? ? turbulent model. The simulation results were well matched with the corresponding experimental value suggesting that it is feasible to describe FADS using the porous media model. Results showed that the air in the central zone flows forward with a decreasing velocity along the flow direction, and the air in the porous fibre eventually creeps out through its tiny-size holes at very low speed in the direction perpendicular to the porous fibre. The airflow close to the FADS is evenly distributed along the flow direction with a very low velocity. It is also concluded that the internal total pressure and dynamic pressure decrease slightly, while the internal static pressure increases slightly with a decaying increment along the flow direction of the FADS.     

两种高效空气过滤器送风口特性分析比较

为了研究高效空气过滤器送风口对非单向流洁净室气流组织的影响及其特性,本文用模型试验的方法,对两种高效空气过滤器送风口性能进行了研究.获得了工作区的悬浮粒子浓度数据,将实验数据进行了分析对比.结果表明:带扩散孔板的高效空气过滤器送风口性能比带新型扩散孔板的高效空气过滤器送风口性能好得多,并对此结果进行了分析.最后给出这两种高效空气过滤器送风口的适用条件,并提出其选型的建议.     

预测压气法隧道施工中的漏气量的模型研究

在阐述压气法隧道施工原理的基础上,建立了水–气二相流模型来模拟压气法隧道施工过程中超压空气驱替隧道周围土体的孔隙水的水–气二相流过程。该模型同时考虑了土体中气相和水相的流动以及水相和气相相互作用的影响,比较符合水–气二相渗流过程的物理意义。通过工程算例,计算出不同施工进度下开挖面和隧道混凝土衬砌上的空气损失速率以及空气入流对隧道周围土体渗流场的影响,结果表明:在均质的地质条件下,开挖面上的漏气速率一般为常数,而衬砌上的漏气速率将随着隧道长度的增加而线性增大。最后,提出了利用水–气二相流模型进一步提高压气法隧道施工的漏气量的数值模拟精度,需要深入研究的两点意见。     

地下水曝气修复一维土柱试验集总参数分析

目前挥发与半挥发性有机物(VOCs/SVOCs)地下水曝气修复机理描述主要包括集总参数模型和多相流模型两类,但这些模型相对复杂,不适于实用化设计与评价。基于曝气过程气液两相间污染物传质双区理论和试验条件,对已有一维集总参数模型进行简化,得到一个以液相表示的集总参数方程。然后通过不同粒径饱和砂土中甲基叔丁基醚(MTBE, methyl tert-butyl ether)地下水曝气修复一维土柱试验,确定了不同曝气流量条件下的液相集总参数。试验结果表明,液相集总参数与砂土的性质及曝气流量密切相关。最后,利用获得的集总参数对不同深度处曝气修复过程污染物浓度变化进行了预测。结果表明,简化处理后的模型可以预测及评价高进气流量条件下地下水曝气修复过程及效果,具有一定实用性。     

Small-Chamber and Research-House Testing of Tile Adhesive Emissions

The objective of this study was to compare measured indoor air concentrations of toluene, from an adhesive used in installing floor tiles, with concentrations estimated from a multi-chamber indoor air quality model. Measurements of toluene emissions from floor adhesive with and without tiles covering the adhesive were made using a small chamber. Emission data from the chamber measurements were used as input to the indoor air quality model. The modeling results were compared with concentrations of toluene measured in a research house when adhesive was applied in a bedroom of the house. Three zones of the house were defined for modeling purposes-the bedroom in which the adhesive was applied, the remainder of the upstairs area, and the downstairs area. Zone-specific volumes and infiltration/exfiltration and interzonal airflows measured during and after adhesive application were also used as model inputs. Relatively good correspondence between measured and model concentrations was obtained, particularly in the bedroom where the adhesive was applied. Modeled concentrations were fairly sensitive to the input matrix of airflow rates.     

Approaches for improving airflow uniformity in unidirectional flow cleanrooms

Airflow behavior inside a cleanroom with vertical unidirectional flow has been investigated. The design parameters, such as porosity and height of raised floor, width of cleanroom and inlet velocity profile, which affect the uniformity of air velocity distribution inside the cleanroom have been studied computationally. The Reynolds-averaged Navier–Stokes equations governing the flow are solved using a finite-volume code STAR-CD. The standard k-ε turbulence model has been used. Approaches for improving airflow uniformity have been proposed and quantitatively examined based on intensive case studies. The present results show that the uniformity increases along with the height of raised floor. Alternatively, better airflow uniformity can also be achieved through a proper allocation of floor porosity or by controlling the distribution of inlet velocity profile. Suggestions on how to design unidirectional cleanrooms with desired airflow uniformity under practical constraints have been given.     

某数据中心室内空调气流组织的模拟研究

以天津某数据中心工程实例为对象,通过CFD模拟软件6SigmaRoom建立了数学和物理模型,并对列间空调系统前送后回的气流组织形式以及室内热工环境进行模拟,对比分析了机房内不同高度平面的速度分布和温度分布,根据模拟得到的流线、速度分布、温度分布来检验室内是否存在局部热点问题。针对局部热点问题提出提高送风量方案、改变空调布置形式方案和封闭冷通道优化方案,并进行模拟结果对比分析,提出了针对该数据中心的气流组织优化建议。     

双层通风幕墙自然风与热气流混合有限分析计算的研究

研究双层幕墙在外界大气总风压及温差作用下引起热气流流动状态,简化计算模型,建立通道各截面气流的贝努里能量方程、质量连续方程及相关动量方程、温度场方程,并在一维流动下寻求方程组的解析解,同时设计有限分析计算程序和给出计算实例。