Modelling of emission of volatile organic compounds from building materials—estimation of gas-phase mass transfer coefficient

A mathematical model is developed to predict Volatile Organic Compound (VOC) emission rates from homogeneous materials. The model considers both mass diffusion and mass convection processes in the boundary layer between the material surface and the air flow. Establishing the relationship between the surface air flow and emission rate; the model, therefore can predict the material emission rate under different environmental conditions. The other feature of the model is that all the parameters have clear physical meaning and can be either found in literature or calculated using known theories and/or equations.The prediction of the mathematical model was validated at three different levels; with experimental results from the CBS specially designed test chamber, with experimental results from the EPA which were carried out in an ASTM chamber, and finally with the predictions made by other models. The results indicate that there is, in general, good agreement between the model predictions and the experimental results. The main advantage of this model is that the model does not require any experimental data as input.     

Experimental and numerical study on indoor temperature and humidity with free water surface

Free water surface may generate excessive moisture and heat and have adverse effects on indoor environment and energy loss. A series of experiments have been carried out to study the characteristics of indoor temperature and moisture distributions using a free water surface within a test chamber. Some parameters such as air change rates, surrounding air temperature and humidity, water temperature and water surface area, were chosen to find their influences on simultaneous moisture and heat transfer. In addition, a new method for determining the simultaneous heat and mass transfer rates from free water surface is developed. Using this method with connection of CFD simulations, the moisture-related problems due to free water surface can be predicted precisely.     

Sensory Characterization of Emissions from Materials

Abstract The exposure-response relationship between the concentration of air pollutants and perceived air quality was studied for eight materials often found indoors and for a mixture of three of the materials. Samples of the materials were placed in a ventilated test chamber. The exhaust air from the test chamber was diluted with different rates of unpolluted air to obtain five different concentrations of polluted air. A sensory panel assessed the perceived quality of the five concentrations of polluted air. The exposure-response relationship differed between the materials and also from the corresponding relationship for human bioeffluents. The exposure-response relationships can be described by straight lines in a log-probit plot and be defined by two constants characteristic for each material. Determination of the two constants characterizing each material requires sensory assessments at least at two pollution concentrations. The sensory pollution load for a material may change with the pollution concentration in the air. The use of a simple measurement method based on a dilution system connected to a ventilated small-scale test chamber is proposed to characterize the emissions from materials in sensory and chemical terms.     

The spatial distribution of carbon dioxide in an environmental test chamber

The spatial distribution of CO₂ level in a classroom carried out in previous field work research has demonstrated that there is some evidence of variations in CO₂ concentration in a classroom space. Significant fluctuations in CO₂ concentration were found at different sampling points depending on the ventilation strategies and environmental conditions prevailing in individual classrooms. However, how these variations are affected by the emitting sources and the room air movement remains unknown. Hence, it was concluded that detailed investigation of the CO₂ distribution need to be performed on a smaller scale. As a result, it was decided to use an environmental chamber with various methods and rates of ventilation, for the same internal temperature and heat loads, to study the effect of ventilation strategy and air movement on the distribution of CO₂ concentration in a room. The role of human exhalation and its interaction with the plume induced by the body's convective flow and room air movement due to different ventilation strategies were studied in a chamber at the University of Reading. These phenomena are considered to be important in understanding and predicting the flow patterns in a space and how these impact on the distribution of contaminants. This paper attempts to study the CO₂ dispersion and distribution at the exhalation zone of two people sitting in a chamber as well as throughout the occupied zone of the chamber. The horizontal and vertical distributions of CO₂ were sampled at locations with a probability that CO₂ variation is considered high. Although the room size, source location, ventilation rate and location of air supply and extract devices all can have influence on the CO₂ distribution, this article gives general guidelines on the optimum positioning of CO₂ sensor in a room.     

Influence of modified pent roof combustion cavity on diesel engine performance and emission characteristics

The utmost vital role of the IC engine burning chamber is to offer correct mixing of air and fuel in a little time to lessen the ignition lag phase, which determines the quality of the combustion, performance and the exhaust emission characteristics. To attain this, a systematised air movement termed ‘air swirl’ is offered to create high comparative velocity amongst fuel droplets and air. In this work, the engine piston head is modified to a 6° angle at the crown part, and the engine performance and emission analysis are carried out. The modified piston promotes speedier mingling between the inducted air and injected fuel, which speeds up the combustion process. By modifying the combustion chamber, we obtained a very less amount of NO_x Emissions and a moderate amount of hydrocarbon and carbon monoxide emissions.     

Comparison of three small chamber test methods for the measurement of VOC emission rates from paint

The aim of this study was to demonstrate a correlation between the measurement of emission rates of volatile organic compounds (VOCs) in three different climate chambers. In order to achieve this aim, the early state of the emission process in the three chambers was investigated and the effects of some important factors on the emission rates from paint were determined. The paper presents results of measurements in three different climate chambers. For the study, a 1-m3 chamber, a field and laboratory emission cell (FLEC), and a chamber for laboratory investigation of materials pollution and air quality (CLIMPAQ) were used. The airflow and surface area were selected so that the area-specific ventilation rates were identical in the three chambers. Temperature and relative humidity were identical during all the measurements. The paint examined was a solvent-based alkyd paint intended for indoor, which use contained between 30 and 60% of white spirit in wet condition. The paint was applied to electropolished and cleaned stainless steel plates. After application, the test material was stored for 14 days for drying in a well-ventilated conditioning room before the measurements were made. After 2 weeks storage, the most pronounced emissions were pentanal, hexanal, octanal, and decanol. The period before the emission rate stabilized differed for the three chambers studied. However, all chambers gave similar emission rates within the overall uncertainty used in these experiments.     

Contaminant particles removal by negative air ionic cleaner in industrial minienvironment for IC manufacturing processes

This study was carried out in a closed test chamber under natural decay, negative ionic air cleaner application, as well as air mixing mechanism with negative ionic air cleaner. Among three operation modes, the air mixing mechanism with negative ionic air cleaner can reduce particles better under the flow field condition. In the air mixing, especially vigorous one (5 ACH (Air Changes per hour)), enhanced the air cleaning effect. The highest removal efficiency was measured at a height of 0.6 m from the floor and it was decreased substantially with an increase in height. The relative effectiveness of negative ionic air cleaners was predicted to decrease with an increasing particle size. We also found that there was a limited horizontal diffusion of ions. The empirical curves fit based for the concentration gradient of NAI (Negative air ionization) generated was developed for estimating the NAI concentration with different heights and distances from the source of negative ionic air cleaner discharge.     

基于ASA的节能建筑围护结构传热系数实测与分析

随着国家对节能减排及可持续发展战略的实施.一种基于ASA的新型建筑材料被引入国内市场.以北京昌平某一采用该技术的生态节能示范房为研究对象.分别采用热箱法和热流计法进行围护结构传热性能测试.测试结果表明,基于ASA的新型节能建筑具有较好的节能效果,其外墙传热系数平均测试结果为O.716 W/(m2·K),传热系数平均测试结果比理论计算值高19%.     

A study of the air quality in the breathing zone in a room with displacement ventilation

This paper is concerned with the difference in the air quality that is perceived by the occupants (breathing zone) and that existing in the occupied zone as a whole. An environmental chamber with displacement ventilation system has been used to carry out the measurements with the presence of a heated mannequin and other heat sources. Measurements of the age of air distribution, the air exchange index and the ventilation effectiveness were carried out at different points in the chamber for different room thermal loads. CFD simulations were also carried out for the purpose of flow visualisation as well as the calculation of air velocity, temperature and age of air distribution. In addition, CFD simulations were carried out to study the effect of changing the airflow rate to the chamber and the position of air inlet to extend the range of parameters. The results from the CFD simulations were compared with those from measurements and good agreement was obtained in most cases.     

Impact of varying area of polluting surface materials on perceived air quality

A laboratory study was performed to investigate the impact of the concentration of pollutants in the air on emissions from building materials. Building materials were placed in ventilated test chambers. The experimental set-up allowed the concentration of pollution in the exhaust air to be changed either by diluting exhaust air with clean air (changing the dilution factor) or by varying the area of the material inside the chamber when keeping the ventilation rate constant (changing the area factor). Four different building materials and three combinations of two or three building materials were studied in ventilated small-scale test chambers. Each individual material and three of their combinations were examined at four different dilution factors and four different area factors. An untrained panel of 23 subjects assessed the air quality from the chambers. The results show that a certain increase in dilution improves the perceived air quality more than a similar decrease in area. The reason for this may be that the emission rate of odorous pollutants increases when the concentration in the chamber decreases. The results demonstrate that, in some cases the effect of increased ventilation on the air quality may be less than expected from a simple dilution model.     

3D-CFD analysis of diffusion and emission of VOCs in a FLEC cavity

This study is performed as a part of research that examines the emission and diffusion characteristics of volatile organic compounds (VOCs) from indoor building materials. In this paper, the flow field and the emission field of VOCs from the surface of building materials in a Field and Laboratory Emission Cell (FLEC) cavity are examined by 3D Computational Fluid Dynamics (CFD) analysis. The flow field within the FLEC cavity is laminar. With a total flow of 250 ml/min, the air velocity near the test material surface ranges from 0.1 to 4.5 cm/s. Three types of emission from building materials are studied here: (i) emission phenomena controlled by internal diffusion, (ii) emission phenomena controlled by external diffusion, and (iii) emission phenomena controlled by mixed diffusion (internal + external diffusion). In the case of internal diffusion material, with respect to the concentration distribution in the cavity, the local VOC emission rate becomes uniform and the FLEC works well. However, in the case of evaporation type (external diffusion) material, or mixed type materials (internal + external diffusion) when the resistance to transporting VOCs in the material is small, the FLEC is not suitable for emission testing because of the thin FLEC cavity. In this case, the mean emission rate is restricted to a small value, since the VOC concentration in the cavity rises to the same value as the surface concentration through molecular diffusion within the thin cavity, and the concentration gradient normal to the surface becomes small. The diffusion field and emission rate depend on the cavity concentration and on the Loading Factor. That is, when the testing material surface in the cavity is partially sealed to decrease the Loading Factor, the emission rate become higher with the decrease in the exposed area of the testing material. PRACTICAL IMPLICATIONS: The flow field and diffusion field within the FLEC cavity are investigated by CFD method. After presenting a summary of the velocity distributed over the surface of test material and the emission properties of different type materials in FLEC, the paper pointed out that there is a bias in the airflow inside the FLEC cavity but do not influence the result of test emission rate, and the FLEC method is unsuitable for evaporation type materials in which the mass transfer of the surface controls the emission rate.     

Influence of temperature on styrene emission from a vinyl ester resin thermoset composite material

Composite materials made with vinyl ester resins are lighter, stronger and corrosion resistant compared to most metals, and are increasingly being used as building materials and in public transportation. Styrene monomer is used as both a diluent and strengthener in the production of vinyl ester resin (VER) composites. Some researchers contend that free styrene in VER composites is available to diffuse out of the material into air, perhaps leading to adverse health effects via inhalation exposures in humans, yet there is no known data on styrene emissions from these materials in the literature. In this study, a typical VER composite made with resin containing 38% by weight styrene, reinforced with E-glass fiber and formed using a vacuum assisted resin transfer method was characterized for styrene emissions by environmental test chamber (ETC) methodology. Styrene concentrations in the ETC were measured over a temperature range of 10 to 50 °C. Initial evaporative styrene emissions increase with increasing temperature. There is a nearly linear relationship in the total mass of styrene emitted and emission factor as emissions increase with increasing temperature. Styrene emission factors appear to vary for different materials, which could indicate more complex processes or the influence of material physical properties on emission rates. These results can be used to validate and improve mass transfer emission models for the prediction of volatile organic compound concentrations in indoor environments.     

Emissions of volatile organic compounds from polymer-based consumer products: Comparison of three emission chamber sizes

The ISO 16000 standard series provide guidelines for emission measurements of volatile organic compounds (VOCs) from building materials. However, polymer-based consumer products such as toys may also release harmful substances into indoor air. In such cases, the existing standard procedures are unsuitable for official control laboratories due to high costs for large emission testing chambers. This paper aims at developing and comparing alternative and more competitive methods for the emission testing of consumer products. The influence of the emission chamber size was investigated as smaller chambers are more suited to the common size of consumer products and may help to reduce the costs of testing. Comparison of the performance of a 203 L emission test chamber with two smaller chambers with the capacity of 24 L and 44 mL, respectively, was carried out by using a polyurethane reference material spiked with 14 VOCs during the course of 28 days. The area-specific emission rates obtained in the small chambers were always similar to those of the 203 L reference chamber after a few hours. This implies that smaller chambers can provide at least useful numbers on the extent of polymer-based consumer product emissions into indoor air, thereby supporting meaningful exposure assessments.     

Nonlinear properties analysis on rutting behaviour of bituminous materials with different air void contents

Rutting is one of the major distresses of flexible pavement. It is defined as the formation of longitudinal depressions along the wheel paths caused by the progressive movement of materials under traffic loading in the asphalt pavement layers or in the underlying base through consolidation or plastic flow. This structural damage has a negative financial impact to the economy. In this study, the rutting behaviour of bituminous materials with different air void contents was investigated. The dynamic cyclic compression testing was carried out to establish nonlinear material models with multiple regression technique. With the specified material models, finite element analysis was carried out to study the rutting behaviour of the wearing course materials with different air void contents in a flexible pavement structure. The simulation result shows that the rutting depth is small at the air void contents of 4.5–8% for wearing course materials. However, for the air void contents above or below this range, the rutting resistance reduces, and thus the rutting depth increases. To verify this simulation result, wheel tracking tests were performed to obtain laboratory data, and the test data was found to be very close to the simulated one. This proved that the developed nonlinear model is applicable to simulate the rutting performance of bituminous mixture and it is a convenient and economical method to be used for the design of bituminous mixtures for both new and rehabilitated pavements.     

Design and Characterization of the CLIMPAQ,Chamber for Laboratory Investigations of Materials,Pollution and Air Quality*

A test chamber has been developed in order to provide a small and simple emission testing facility capable of testing construction products in a climate where the important climatic parameters such as temperature, ventilation rate and air velocity can be varied independently around typical indoor values. The test chamber CLIMPAQ is made of panes of window glass. Other main surface materials are stainless steel and eloxated aluminium. The chamber has a volume of 50.9 litres and is designed to meet the requirements for quantifying air pollution. In this investigation human subjects acted as air pollution judges, and chemical characterization of the air pollution was carried out. Carpet, linoleum, wall paint and seal- ant were tested simultaneously in the CLIMPAQ and in four other chambers ranging from a full-scale chamber of 28 m³ to a field and laboratory emission cell of 3.5· 10^?5m³. Product ranking is the same in all chambers for the sensory measurements. Emission rates based on sensory measurements differ for all products less than 100 % except for tests in a 3-litre chamber where emission rates were higher. Chemical measurements differ up to approximately 10 times for the same product in different chambers. Deviations appear to be the result of different environmental parameters in the various chambers. Low air concentrations or high specific ventilation rates seem to increase emissions, while differences in air velocities and sink properties may also be the cause of differences in emission rates.     

活塞风作用下超长公路隧道火灾烟气蔓延特性研究

汽车在隧道中行驶时会产生活塞风,有效利用活塞风可降低机械排烟系统的成本和能耗。本文首先进行了理论分析,然后通过计算流体动力学软件对活塞风作用下公路隧道的火灾烟气蔓延特性进行研究。数值模拟探究了不同活塞风速对于隧道中不同火源功率（10、30、50 MW）情况下烟气层运动、温度场和流速场分布的影响。研究结果表明,近期、远期的活塞风速衰减模型在不同火源功率时,烟气层运动、温度场和流速场变化规律基本相同,随着火源功率增大,烟气回流到隧道入口的时间更短,隧道内流速场发生变化的时间越晚。     

板式叉-逆-叉流新风换气机换热性能仿真

本文根据厂家新风换气机实物原型,建立计算模型。通过FLUENT数值模拟软件,对板式叉流-逆流-叉流空气．空气换热器送风面和排风面的速度场、温度场和压力场进行仿真。根据仿真结果得出换热器的热交换效率及送风面与排风面阻力,为新风换气机的设计和生产应用提供参考。     

干燥滚筒内流场和传热过程的数值模拟

研究干燥滚筒的结构参数对其流场分布和传热过程的影响,建立干燥滚筒的三维仿真模型,运用流体动力学软件Fluent对干燥滚筒内的流场和传热过程进行数值模拟,并且通过现场试验数据对仿真结果进行验证,对深入研究干燥滚筒内部的热空气流动,指导其设计和参数的改进,提高干燥滚筒的热效率有一定的参考价值.     

Some local environmental effects on mercury emission and absorption at a soil surface

The purpose of this study was to quantify effects of some local environmental variables on the soil surface exchanges of total gaseous mercury (TGM), under controlled conditions. A dynamic flux chamber with a Tekran mercury analyzer was used to quantify TGM emissions from, and absorption by, a clean, fine sandy loam soil with very low mercury content inside of a building and in a low TGM environment, outside. Simultaneous measurements of mercury flux, air and soil temperatures, ozone concentration, humidity, soil moisture and solar radiation were made. Controlled applications of water were made to change soil H2O content and measure the response of mercury flux. Air-soil exchanges were highly dependent on soil temperature (r2 = 0.78) and the mercury concentration gradient between the TGM in the soil pores and the ambient TGM above the soil surface (r2 = 0.98 for absorption and r2 = 0.408 for emissions). Correlations with air temperature and ozone levels are explained by the relationships of these variables with soil temperature. No detectable correlation was found with solar radiation or humidity. Wet soil maintained higher rates of soil TGM emission and decreased soil absorption. Emissions increased with increasing soil H2O, peaked at approximately field capacity, and then decreased slightly until saturation.     

建筑门窗玻璃幕墙传热系数现场测试研究

建筑门窗玻璃幕墙是建筑围护结构节能最薄弱部位,其传热系数目前只能在实验室通过热箱法测定,在现场准确、快捷地测试该值对于建筑的节能评估改造具有重要意义。在现场测试门窗幕墙内外空气温度和表面温度的基础上,推导出了基于"准稳态"测试原理和"热阻法"、"表面温度法"、"传热系数法"3种传热系数现场测试方法,现场测试值与实验室检测值的较高一致性表明了该现场测试方法的准确性,连续测试数据与平均值的较小偏差表明了该测试方法的稳定性。研究结果表明,建筑门窗玻璃幕墙传热系数可通过该方法在现场准确、快捷地测试得到。