A multi-layer zone model for predicting fire behavior in a fire room

A multi-layer zone fire growth model is developed to predict the fire behavior in a single room. The fire room volume is divided into an arbitrary number of horizontal layers, in which the temperature and other physical properties are assumed to be uniform. The principal equations for each laminated horizontal layer are derived from the conservation equations of mass and energy. The implemented fire sub-models are introduced, including combustion, fluid flow and heat transfer models. Combined with these sub-models, the zone equations can be integrated with Runge–Kutta method for the gas temperature and species fractions of each layer for each time step. The results of the sample calculations are compared with the experiments conducted by Steckler and the University of Canterbury. In general, a good agreement between experimental and theoretical results is obtained.     

VOCs and PAHs emissions from creosote-treated wood in a field storage area

In this study, the emissions of volatile organic compounds (VOCs, in this case aromatic hydrocarbons containing one benzene ring and furans) and polycyclic aromatic hydrocarbons (PAHs) from wood recently treated with creosote are examined. The VOCs and PAHs were identified and quantified in the gas phase. Additionally, the PAHs were quantified in the particulate phase. Glass multi-sorbent tubes (Carbotrap, Carbopack X, Carboxen-569) were used to hold the VOCs. The analysis was performed using automatic thermal desorption (ATD) coupled with capillary gas chromatography/mass spectrometry (GC/MS). PAHs vapours were collected on XAD-2 resin, and particulate matter was collected on glass fibre filters. The PAHs were analysed using GC/MS. The main components of the vapours released from the creosote-treated wood were naphthalene, toluene, m+p-xylene, ethylbenzene, o-xylene, isopropylbenzene, benzene and 2-methylnaphthalene. VOCs emission concentrations ranged from 35 mg m(-3) of air on the day of treatment to 5 mg m(-3) eight days later. PAHs emission concentrations ranged from 28 microg m(-3) of air on the day of treatment to 4 microg m(-3) eight days later. The air concentrations of PAHs in particulate matter were composed predominantly of benzo[b+j]fluoranthene, benzo[a]anthracene, chrysene, fluoranthene, benzo[e]pyrene and 1-methylnaphthalene. The emission concentrations of particulate polycyclic aromatic hydrocarbons varied between 0.2 and 43.5 ng m(-3). Finally, the emission factors of VOCs and PAHs were determined.     

用示踪气体方法研究通风房间的空气龄

应用示踪气体测量得到了8种强制通风工况下实验小室各各测点处的浓度衰减曲线,并计算出各测点的空气龄,实验结果表明,示踪气体用于强制通风研究时实验可重复性较好,实验结果正确合理,测得的空气龄反映了房间各点空气的新鲜程度,也揭示了室内空气的流动形态。     

示踪气体浓度衰减法在民用建筑自然通风研究中的应用

用示踪气体浓度衰减法对某会议室的自然通风作了实测研究，分析了影响换气次数的各种因素、示踪气体浓度衰法的有效性及其正确应用。揭示出不同的房间布置及不同的门窗开启民政部对换气次数有很大影响，而示踪气体浓度衰减法是对此进行实验研究的有效手段。     

Modeling of cooking-emitted particle dispersion and deposition in a residential flat: A real room application

Maintenance of good indoor air quality for residences could be very challenging. Episodic event such as cooking emits a large amount of ultrafine and supermicron particles. A numerical model is used to simulate a 10-min cooking process in a real room, followed by a few more minutes to allow the decay and removal of particles. Particle dispersion and deposition in the kitchen and the living room are simulated by a new drift-flux model. Strong buoyancy flow is observed and particle concentration is significantly affected by the thermal plume. Results show that for supermicron particles strong non-uniformity of concentration is observed in the kitchen but the non-uniformity is less obvious in the living room. Exposure analysis must take into account the influence of the particle sizes.     

复合墙体室内温度响应研究

针对建筑物内人体的热舒适性与内墙壁面温度的相关性,建立了具有复合材料墙体的房间内温度响应的数学模型.结果显示,在相同的加热(制冷)条件下,由相同材质、相同尺寸组合构成的复合材料墙体,在不同的材料排列方式情况下,室内的温度响应有很大的不同,这对间歇性供热(冷)房间内人体的热舒适性有较大的影响.     

Numerical modeling of a complex diffuser in a room with displacement ventilation

A micro/macro-level approach (MMLA) has been proposed which makes it possible for HVAC engineers to easily study the effect of diffuser characteristics and diffuser placement on thermal comfort and indoor air quality. In this article the MMLA has been used to predict the flow and thermal behavior of the air in the near-zone of a complex low-velocity diffuser. A series of experiment has been carried out to validate the numerical predictions in order to ensure that simulations can be used with confidence to predict indoor airflow. The predictions have been performed by means of steady Reynolds Stress Model (RSM) and the results have good agreement both qualitatively and quantitatively with measurements. However, measurements indicated that the diffusion of the velocity and temperature was to some extent under-predicted by the RSM, which might be related to high instability of the airflow close to the diffuser. This effect might be captured by employing unsteady RSM. The present study also shows the importance of detailed inlet supply modeling in the accuracy of indoor air prediction.     

A multi-component numerical leach model coupled with a general chemical speciation code.

A multi-component numerical leach model (SBLEM) was developed by coupling a general chemical speciation code with a modified Crank-Nicolson algorithm to determine the leaching behavior of contaminants in stabillized/solidified (s/s) wastes. The thermodynamic database of the speciation code was modified using batch leaching data. SBLEM was evaluated by simulating a dynamic leaching test of cement-treated combined bottom and fly ash from a municipal solid waste (MSW) incinerator. Simulations used an input composition prepared from acid neutralization capacity (ANC) test data of the ash. The results show that SBLEM can reasonably predict the dynamic leaching behavior of metals from the cement-treated ash when the ANC of the ash and pH-solubility curves of metals are well described. This indicates SBLEM simulations may be able to augment or replace experimental leaching tests that can consume a substantial period of time (> 2 months) and in some cases, provide unreliable results.     

Mixing characteristics in a ventilated room with non-isothermal ceiling air supply

A two-dimensional turbulence k–ε model is used to predict distribution of air velocity, temperature and turbulence kinetic energy in an air-conditioned room using ceiling air supply. Mixing characteristics of the airflow are analyzed under different air supply velocities and temperatures. A modified Archimedes number is correlated with the parameters characterizing heat transfer, ventilation system, and turbulence kinetic energy of room air flow. Significant correlations have been shown. It is found that the linear ceiling air supply air-conditioning system with a high level return air provides excellent air mixing across a wide range of Archimedes numbers. The results are useful for air-conditioning design and thermal comfort study.     

Modeling of the HESCO nozzle diffuser used in IEA Annex-20 experiment test room

The modeling of air supply devices has been identified from the IEA (International Energy Agency) Annex-20 project as one of the most important problems in applying computational fluid dynamics to predict air flow pattern and air distribution in buildings. In this paper, a simplified model for the modeling of the HESCO nozzle diffuser used in the IEA Annex-20 test room is tested and evaluated against experimental data. It is found that with the ReNormalization Group k–ε turbulence model and local mesh refinement, this model can give very good prediction of the wall jet flow issued from the diffuser. The influences of different numerical discretization schemes and turbulence models for the prediction of the wall jet flow are also investigated. Flow asymmetry phenomena observed both in numerical simulations and in experiments are discussed.     

Simulation of mixed convection flow in a room with a two-layer turbulence model

Most indoor airflows are mixed convection. In order to simulate mixed convection accurately and efficiently, this paper uses a two-layer turbulence model. The two-layer model combines a one-equation model for near wall flow together with the standard k-epsilon model for outer-wall flow. The model has been used to predict the mixed convection by displacement ventilation in an office. The computed results agree well with the corresponding airflow pattern and the distributions of air temperature, air velocity, air velocity fluctuation, and tracer-gas concentration. The model can predict correctly heat transfer from a wall where the standard k-epsilon model and re-normalization group (RNG) k-epsilon model with wall functions often fails. The computing cost required by the two-layer model is comparable to that of the standard k-epsilon model and RNG k-epsilon model and is significantly less than that by a low-Reynolds number model.     

Airflow modelling in a computer room

This study concerns the numerical simulation of airflow and the prediction of comfort properties in a visualisation room of a research centre. Because simulation accuracy depends on the modelling level, special care has been given to fine details. Particular interest has been concentrated on the four-way ceiling air supply diffuser, on the furniture and on the thermal conditions given on computers and on mannequins.

The geometric model was created using the parametric features of the pre-processor Gambit, in combination with elements created with the Rhinoceros NURBS modelling tool.

Mass, momentum, energy, turbulence, species and radiation conservation equations were solved using Fluent commercial flow solver. Computed airflow and heat transfer parameters were used for numerical prediction of indoor air quality quantities based on ISO 7730. Basic parameters included air temperature, relative humidity and air velocity. These were combined with clothing insulation and metabolic activity measures to obtain standard IAQ indices such as the mean age of air, the predicted mean vote and the predicted percentage of dissatisfied room occupants.

Post-processing was carried out with standard Fluent elements and also using Vu, a multi-platform tool which also allows data to be displayed in the Cave immersive environment.     

CFD simulation of VOCs concentrations in a resident building with new carpet under different ventilation strategies

This paper investigates the effect of ventilation strategies on the concentrations of volatile organic compounds (VOCs) emitted from a new carpet in an apartment with the VOCs emission characteristics taken from chamber test data. The commercial software FLUENT 6 has been employed to solve the continuity, momentum, turbulence and concentration equations under five different ventilation strategies. Numerical results show that ventilation strategies have a small effect on VOCs emission from carpet. Continuous ventilation keeps a low level of VOCs concentration in the air. Flushing ventilation has a significant effect on the VOCs concentration in the air. During a period without ventilation, VOCs concentration in the air usually increases to a high level. Thus, the ventilation should be carried out before the arrival of residents to ensure a low level of VOCs concentration. At the startup of ventilation run, the sudden flow strongly promotes the mixing of VOCs, which may lead to local high concentration.     

Convective heat transfer coefficients in a full-scale room with and without furniture

The convective heat transfer coefficient at an outer ambient wall with a window exposed to natural climate was measured in a room with and without furniture. The method used was to estimate the heat flow from measured temperatures and solar radiation. The convective heat transfer was calculated as the difference between the heat flow through the building element and the calculated long-wave radiation. Even though the accuracy was at best ±15%, the effect of different heating and ventilation strategies could clearly be detected. Local coefficients may be more than 10 times the expected, due to ventilation or position of the radiator.     

Air flow characteristics of a room with square cone diffusers

A computational fluid dynamics model with radiant exchange between surfaces is developed to examine the air flow characteristics of a room with square cone diffusers. As an input to the full-scale 3-D room model, a 2-D diffuser model that supplies direction and magnitude of air flow into the room is developed and evaluated using infrared visualization. The room air flow model is assessed using several previously documented problems with various geometries and boundary conditions. Simulations are conducted for heating and cooling of the room with one or two supply air diffusers. The results show that the offset and lips of the diffuser work together to determine the discharge air angles, which play an important role in determining the room air flow patterns. For a certain discharge angle in the heating case, the air flows along the ceiling. The results indicate that, for the same supply air flow, operating only a single diffuser initiates more mixing of the room air flow, which results in enhanced temperature uniformity compared to that for two diffusers. Radiant exchange between the exterior window and interior surfaces causes a significant change in the window temperature.     

广州大学城医院直加机房大体积混凝土施工

结合工程实际情况，分析了大体积混凝土裂缝控制措施及温度的计算，从温度控制、配制、浇筑、运输等方面介绍了直加机房大体积混凝土施工技术，以减少混凝土裂缝的产生。     

下送风房间热分布系数影响因素的方差分析

提出了用热射流起始无因次高度Ｈ来反映热源起始高度对下送风空调房间热分布系数ａ的影响，利用回归原理得出了ａ随阿基米德数Ａｒｎ、热射流自由度Ｚｒ、机械射流自由度Ｚｊ及热射流起始无因次高度Ｈ变化的准则关系式。用连结向量图法和对实验数据回归公式的Ｆ检验，对影响室内热分布规律的各个因素进行了分析，发现这些因素均为主要影响因素，其影响的相对主次依次为Ａｒｎ，Ｚｒ，Ｈ和Ｚｊ，回归结果具有很强的显著性。     

Prediction of airflow and temperature field in a room with convective heat source

A CFD simulation of airflow and temperature field in a heated room has been described in the paper. The tracking of pollutant particle movement is also presented here. The comparisons between computation and experiment show good and acceptable agreement. It can be concluded that CFD prediction can capture the main features of convective flow and provide satisfactory results. It can be seen that the thermal wall jet created by a radiator greatly influences the airflow pattern, temperature and pollutant particle distribution in the heated room. It can also be seen that the area close to the heat source has a high risk of air-borne contamination and imposes a harmful effect on the occupant.     

Numerical study on temperature stratification in a room with underfloor air distribution system

In this study, numerical prediction using computational fluid dynamics (CFD) was utilized to investigate air temperature stratification in a room with an underfloor air distribution (UFAD) system. The numerical modeling using CFD computation was validated with physical test in a full size experimental room with an UFAD system. The different supply air conditions and heat loads were discussed. The results show that the effect of three parameters, heat load, supply volume flux and supply air velocity, on room air temperature would be expressed by the length scale of the floor supply jet. When the length scale increased from 0.8 to 1.56 m, the ratio of vertical temperature difference between 2.5 and 0.1 m at the occupied zone to the difference between return and supply air temperature decreased from 0.62 to 0.25. When there was only one local heat source in the room, there was a thermal stratified interface at the occupied zone. The interface height was about 1.42 times the length scale. The results may suggest ways to optimize UFAD design and operation.