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1.
Abstract Analysis of the impact of sources on indoor pollutant concentrations and occupant exposure to indoor pollutants requires knowledge of the emission rates from the sources. Emission rates are often determined by chamber testing and the data from the chamber test are fitted to an empirical model. While the empirical models are useful, they do not provide information necessary to scale the chamber data to buildings nor do they provide information necessary to understand the processes controlling emissions. A mass transfer model for gas-phase-limited mass transfer is developed and described in this paper. Examples of sources with gas-phase-limited emissions are moth cakes, floor wax, stain, and varnish. The mass transfer model expresses the emission rate in terms of a mass transfer coefficient and a driving force. The mass transfer coefficient can be predicted from correlations of the Nusselt number and the Reynolds number. The experiments and data analysis used to develop the correlation are described in the paper. Experiments to verify the assumptions used to describe the driving force are also described. Suggestions for using data from existing empirical emission models to determine parameters for the mass transfer model are provided. The mass transfer model provides a significantly better fit to data from an indoor air quality test house than does the empirical first order decay model.  相似文献   

2.
室内空气污染源散发量的确定是建立室内空气质量(IAQ)模型的重要步骤之一。目前研究建筑装饰材料和建筑涂料散发污染物的模型主要有经验模型和理论模型两类。经验模型简洁,但应用受到测试条件的限制,不具有普适性。基于传质理论而提出的理论模型目前研究较多,本文对研究建筑材料散发有害物的三个传质模型进行了评述。VB模型是一个简单的溶剂基室内涂料散发的总挥发性有机物(TVOC)的传质模型,低估了污染物的长期散发量。对流传质模型是基于界面平衡所导出的稳态模型,适用于固体和液体等材料的散发过程。Yang等提出的四层传质模型通常需与数值求解结合,计算较麻烦,但能较好地确定建筑材料散发挥发性有机物的散发量。  相似文献   

3.
The main parameters which control the emission of volatile organic compounds between wall materials and indoor air were examined. A physically based model considers that the global emission phenomenon results from three elementary physical phenomena: diffusion through the boundary layer separating the wall from environment, diffusion within the porous network of the materials, and sorption of the gas molecules on the active sites of the materials. The pollutant transfer between porous material and air is therefore subjected to two complementary resistances and we identify first the resistance which controls the transfer. Then, we predict the global emission time constant from the mass transfer coefficient of convection and the thickness of the material. Experimental results from a small scale chamber are compared to predicted values in the case of acetone emission from chipboard in humid air and for high initial acetone concentration. Good agreement is obtained at the beginning of emission but an acetone retention effect by chipboard is observed, showing that it will be necessary to take into account the interactions of water vapor with materials and the pollutants to achieve accurate modeling of the material VOC emission process.  相似文献   

4.
The purpose of this paper is to study how and to what extent effluent BOD5 is related to influent BOD5 and flow in an activated sludge process. The analysis is based on data collected hourly over a 2-week period at a Wisconsin sewage treatment plant. The methodology applied to establish a dynamic model for the system is that of Box & Jenkins (1970). With this approach, stochastic and transfer function components can be combined to form a model. The relative importance of these two components can be quantitatively assessed. A simple first-order model is able to explain the data very well. In this empirical model, which does not need flow as a predictor variable, the stochastic component is much more important than the transfer function component. Frequent return sludge control is not needed for the plant studied because it possesses remarkable inherent stability.  相似文献   

5.
In this paper, a three-dimensional non-isothermal computational model for predicting indoor SVOC distribution is proposed, considering the effects of turbulence diffusion and suspended particles. The realizable k-ε model is introduced for turbulent flow simulation in a room. The Euler-Euler method is adopted to deal with the gas-particle two-phase flow coupled problem. Inertia slip velocity and irreversible first-order absorption boundary are employed for more accurate prediction of particle motion. The simulated curve of outlet gas-phase di-2-ethylhexyl phthalate (DEHP) concentration with emission time is verified by available experimental data. The emission process of DEHP in a 15 m2 room in Beijing during 100 days with or without air cleaner is simulated by the developed model considering air leak through window and door gaps. It is found that if the air cleaner keeps on all the time during 100 days the gas-phase DEHP concentration in the room will tend to be uniform, while the emission process is far from equilibrium without an air cleaner even the emission lasts 100 days. Results also suggest that floor heating, decrease of particle concentration, weaken of heat transfer, enhancement of mass transfer, and air infiltration in window gap contribute to decrease DEHP concentration.  相似文献   

6.
Abstract Small environmental chamber tests were conducted to characterize the emissions of a toxic chemical compound – methyl ethyl ketoxime (MEKO) – from three different alkyd paints. It was found that MEKO emissions occurred almost immediately after each alkyd paint was applied to a pine board. Due to the fast emission pattern, more than 90% of the MEKO emitted was released within 10 hours after painting. The peak concentrations of MEKO in chamber air correlated well with the MEKO content in the paint. Material balance showed that good recovery (more than 68%) was achieved between the MEKO applied with the paint and the MEKO emitted. The chamber data were simulated by a first order decay emission model assuming the MEKO emissions were mostly gas-phase mass transfer controlled. The model was used to predict indoor MEKO concentrations during and after painting in a test house. It was found that the predicted test house MEKO concentrations during and after the painting exceeded a suggested indoor exposure limit of 0.1 mg/m3 for all three paints. The predicted MEKO concentrations exceeded even the lower limit of a suggested sensory irritation range of 4 to 18 mg/m3 with two of the three paints tested. The model was also used to evaluate and demonstrate the effectiveness of risk reduction options including selection of lower MEKO paints and higher ventilation during painting.  相似文献   

7.
X. Yang  Q. Chen  J. S. Zhang 《Indoor air》1998,8(3):180-189
Abstract Most of the existing emission models developed from small-scale chamber tests assume complete mixing in the chamber throughout the test period. This paper examined this assumption using a Computational Fluid Dynamics (CFD) model. The model simulated the three-dimensional air velocity profiles and Volatile Organic Compound (VOC) concentration distributions from wood stain in a well-designed mixing chamber of 1.0X0.8X0.5 m3. The model used measured data to determine the time-dependent VOC surface concentrations of wood stain. The CFD results show that the VOC concentrations in the test chamber were not uniform in the early stage (about 18 minutes). The first-order decay model using the complete mixing assumption will underestimate the Total VOC (TVOC) emission rates by 65% and 59% in the first 3 minutes and next 15 minutes, respectively. Since wood stain emitted about one third of the VOCs in the first 18 minutes, the impact of incomplete mixing in the early period is significant for calculating the material emissions. Furthermore, the mass transfer coefficient of TVOC calculated by CFD is also compared with that calculated by analogue theory and that calculated by experimental correlation.  相似文献   

8.
基于所建的污染物散发模型,分析了室内温度、传质系数、换气次数对多孔材料污染物散发的影响。结果显示,室内温度对材料内污染物散发的影响非常明显,温度越高,污染物散发时间越短;提高传质系数不能显著加速污染物散发,而降低该值却可以抑制污染物的释放;换气次数对污染物散发影响很小,但可以通过改变换气次数来控制室内污染物浓度。  相似文献   

9.
A numerical and an analytical model were developed to predict the volatile organic compound (VOC) emission rate from dry building materials. Both models consider the mass diffusion process within the material and the mass convection and diffusion processes in the boundary layer. All the parameters, the mass diffusion coefficient of the material, the material/air partition coefficient, and the mass transfer coefficient of the air can be either found in the literature or calculated using known principles.

The predictions of the models were validated at two levels: with experimental results from the specially designed test and with predictions made by a CFD model. The results indicated that there was generally good agreement between the model predictions, the experimental results, and the CFD results. The analytical and numerical models then were used to investigate the impact of air velocity on emission rates from dry building materials. Results showed that the impact of air velocity on the VOC emission rate increased as the VOC diffusion coefficient of the material increased. For the material with a diffusion coefficient >10−10 m2/s, the VOC emission rate increased as the velocity increased; air velocity had significant effect on the VOC emission. For the material with a VOC diffusion coefficient <10−10 m2/s, the VOC emission rate increased as the velocity increased only in the short-term; <24 h. In the medium to long-term time range, the VOC emission rate decreased slightly as the air velocity increased; velocity did not have much impact on these materials. Furthermore, the study also found that the VOC concentration distribution within the material; the VOC emission rate and the VOC concentration in the air were linearly proportional to the initial concentration. However, the normalized emitted mass was not a function of the initial concentration: it was a function of the properties of the VOC and the material.  相似文献   


10.
为获取沥青路面结构层沥青材料模量参数,合理评价沥青路面结构性能,开展沥青路面反算模量与同温度下室内沥青混合料动态模量的关系研究。采用落锤式弯沉仪(FWD)对4个不同结构的沥青路面试验路进行测试,并通过路面结构埋设的温度传感器同步采集温度,对试验结果进行沥青层模量反算;采用沥青混合料性能试验机(AMPT)对试验路沥青材料进行动态模量试验,根据时温等效原理获取FWD测试的同温度下的沥青混合料模量值,结合沥青路面结构层厚度计算沥青混合料动态模量的当量模量;对沥青层同一温度下的FWD反算模量与动态模量的当量模量进行分析比较,建立回归模型。结果表明,不同路面结构的FWD反算模量与室内动态模量的关系基本一致,其变化趋势不依赖于沥青层厚度的变化;沥青路面FWD的反算模量和室内AMPT的模量呈非线性关系,当模量较小时,FWD反算模量要低于室内模量,随着模量的增加,在10000MPa附近时,二者的模量值是接近的,模量值再继续增大时,FWD反算模量的增加较快,明显大于室内动态模量,室内动态模量的增长趋于平缓。  相似文献   

11.
随着人们生活水平以及节能意识的提高,对建筑热工性能评价和建筑节能越来越重视。将建筑房间简化为含有多孔介质的双区域模型,因此,此类模型被应用到更多的领域。通过数值模拟展现了实际建筑环境中各物理条件对室内通风与热环境的影响,为室内舒适度的建设提供了依据。基于有限元法对含有多孔介质复合腔体这一类双区域模型的壁面热辐射与自然对流耦合换热问题在建筑房间内的应用进行了数值模拟分析。模拟了不同工况下多孔介质复合腔体内的流场和温度场随时间的变化情况。结果表明,表面热辐射对建筑房间内的自然对流换热有明显的增强作用;冬季与夏季,中间层与顶层不同的边界条件影响着室内的对流换热即方腔热环境的改变;多孔介质厚度d较大时能减弱传热,当到达一定值时影响不明显。  相似文献   

12.
Only recently, the radioactive gas thoron ((220)Rn) and its decay products have been regarded as significant health risk in the indoor environment. This is because of new findings of increased thoron concentrations in traditional mud dwellings and considerations leading toward reduced action levels for natural airborne radionuclides. A model which describes the sources and sinks of thoron and its decay products should help to assess the indoor exposure. This work presents an extensive depiction of the influences of indoor conditions on the occurrence of these radionuclides. Measurements were performed in an experiment room and in mud dwellings in China and India. Mud even with an average (232)Th concentration was identified as a significant thoron source. The spatial distribution of the decay products proved to be homogeneous, which is in contrast to thoron gas. The prominent contribution of the unattached and attached decay product (212)Pb to the exposure was elaborated. The theoretically derived impact of air exchange and aerosol concentration, which determines the proportion of unattached decay products, could be confirmed. Transfer coefficients of the model were determined. The thoron model with these transfer coefficients predicts annual doses of almost 2 mSv for dwellers of traditional Chinese and Indian mud buildings, confirming the potential health impact of thoron. PRACTICAL IMPLICATIONS: The radioactive noble gas radon with its decay products is well known as a health risk. After increased concentrations of the isotope (220)Rn (thoron) have been found in traditional Chinese mud-walled cave dwellings, the need for a model that describes the occurrence of thoron and its decay products indoors has arisen. This work presents such a model from the emergence of thoron in the building material until the decay to the stable (208)Pb and discusses the various influences on the occurrence of these nuclides. The model makes possible to predict the exposure of people staying in a room to thoron and its decay products and--combined with a dose model--to calculate their inhalation doses from easily measurable data.  相似文献   

13.
生土建筑围护结构表面吸放湿过程实验研究   总被引:1,自引:0,他引:1  
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  相似文献   

14.
Latex paints are widely used in residential and commercial indoor environments. The surface areas covered by the paints in these environments are relatively large. Thus, latex paints have the potential for having a major impact on indoor air quality (IAQ). A study was undertaken to develop methods for evaluating the impact of latex paint emission on IAQ. Small chamber experiments using stainless steel and painted and unpainted gypsum board substrates were conducted to determine the emission characteristics of latex paint. The emissions from the stainless steel were relatively short lived (3 to 4 days), whereas the emissions from gypsum board lasted for over 200 days. Because gypsum board is a common substrate for latex paint, all emission models were developed for the gypsum board substrates. The data from the small chamber tests led to the development of two empirical and two mass-transfer-based source emission models. Approximately 100 to 200 days of data were required to estimate the parameters required for the empirical models. Only 8 days of data were required to estimate the parameters for the mass-transfer-based models. The final models use paint formulation and mass transfer correlations to predict the emissions of the major individual volatile organic compounds emitted by latex paint.  相似文献   

15.
Lee CS  Haghighat F  Ghaly WS 《Indoor air》2005,15(3):183-196
Building materials can strongly affect indoor air quality. Porous building materials are not only sources of indoor air pollutants such as volatile organic compounds (VOC) but they are also strong sinks of these pollutants. The knowledge of VOC transfer mechanisms in these materials is an important step for controlling the indoor VOC concentration levels, and for determining the optimum ventilation requirements for acceptable IAQ. This study provides a theoretical investigation of primary and secondary VOC source and sink behavior of porous building materials. A new analytical model was developed based on the fundamental theories of mass transfer mechanisms in porous materials. The proposed model considers both primary and secondary source/sink behavior for the first time. The former refers to the transfer of gas-phase and/or physically adsorbed VOC, while the latter refers to the generation or elimination of VOC within the solid because of chemical reactions like oxidation, hydrolysis, chemical adsorption, etc. The proposed model was assessed with experimental data, namely emission tests of carpets and sorption tests of wood chipboard. It was demonstrated that, unlike the existing analytical models, the proposed analytical model could simultaneously account for the effect of air velocity on both VOC source as well as sink behavior. Case studies were then carried out for secondary VOC source behavior. Due to the lack of experimental studies on mechanisms of secondary behavior, hypothetical generation functions were implemented. It was demonstrated that the proposed analytical model is suitable for describing various mechanisms involved in the secondary behavior due to the little limitations imposed on the generation/elimination term. When VOC generation takes place at the material-air interface, the simulation shows that although the primary emission is not affected by air velocity, the secondary emission, however, is clearly affected. This behavior agrees with the available experimental findings on secondary emissions. PRACTICAL IMPLICATION: The analytical model presented in this paper can predict both primary and secondary VOC source (emission) or sink (sorption) behavior of porous building materials. Since the model considers diffusion and adsorption/desorption within the material, and convection over the material surface, the simulation using the model can readily provide the effects of material properties and airflow properties on the primary and/or the secondary behavior, hence, it can provide a better understanding on the mechanisms. This will enable us to keep the indoor VOC concentration within a desirable level.  相似文献   

16.
《Building and Environment》1999,34(4):377-389
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.  相似文献   

17.
Transmittance of external radiation from a CO2 laser through a boundary layer of decomposition products over a vertical sample surface is measured during the ignition period. The results indicate that there is significant absorption of the external radiation for PMMA, and a lesser but still not negligible amount, for red oak. An increase in gas phase temperature over surface temperature is observed over much of the ignition interval. Using the experimentally measured incident flux at the sample surface, surface temperature history was calculated from a model that included re-radiation and convection losses from the surface, endothermic decomposition and conduction into the material. The results confirm the significant effect of gas phase absorption on surface temperature. Steady-state-derived surface regression rate expression was used for PMMA in this model. The results raise questions about the validity of such data for the dynamic heating conditions during the ignition period. Further studies needed to understand the radiative ignition mechanism are identified.  相似文献   

18.
PM2.5 exposure is associated with significant health risk. Exposures in homes derive from both outdoor and indoor sources, with emissions occurring primarily in discrete events. Data on emission event magnitudes and schedules are needed to support simulation‐based studies of exposures and mitigations. This study applied an identification and characterization algorithm to quantify time‐resolved PM2.5 emission events from data collected during 224 days of monitoring in 18 California apartments with low‐income residents. We identified and characterized 836 distinct events with median and mean values of 12 and 30 mg emitted mass, 16 and 23 minutes emission duration, 37 and 103 mg/h emission rates, and pseudo‐first–order decay rates of 1.3 and 2.0/h. Mean event‐averaged concentrations calculated using the determined event characteristics agreed to within 6% of measured values for 14 of the apartments. There were variations in event schedules and emitted mass across homes, with few events overnight and most emissions occurring during late afternoons and evenings. Event characteristics were similar during weekdays and weekends. Emitted mass was positively correlated with number of residents (Spearman coefficient, ρ=.10), bedrooms (ρ=.08), house volume (ρ=.29), and indoor‐outdoor CO2 difference (ρ=.27). The event schedules can be used in probabilistic modeling of PM2.5 in low‐income apartments.  相似文献   

19.
Natural materials of biological origin degrade over time and may emit odorous chemical compounds that can influence the perceived indoor air quality. The objective of this study was to investigate how the perceived air quality is influenced by emissions from building products with linseed oil compared with similar conventional synthetic products without linseed oil. Two types of linoleum, two types of wall paint and two types of floor oil were selected as examples of natural products containing linseed oil. The selected synthetic products were PVC floor covering, a water-based paint, and a synthetic floor oil. The emissions from the products were monitored over a one-year period in small ventilated test chambers. The odorous emissions were evaluated by sensory panel assessments of odour intensity and acceptability and by chemical analysis of the odour-active volatile organic compounds (VOCs) and carbonyl compounds. Odour-active VOCs in the emissions from one floor oil with linseed oil and two pure linseed oils were detected by gas chromatography combined with olfactometry (GC-O) and attempted identified with mass spectrometry (MS). The products with linseed oil influenced the perceived air quality more negatively than the similar synthetic products and the odour was persistent over time. It was found that the products with linseed oil did not qualify for the Danish Indoor Climate Label, because of the persistency of the odour. The results of the GC-O/MS investigations and VOC measurements indicated that an almost constant emission of odour-active VOCs with low odour thresholds resulted in the persistency of the odour. The VOCs probably originated from oxidation products from the linseed oil used as raw material. The study indicates that the acceptability of the emissions from the floor oil was influenced by the linseed oil used as raw material. It is therefore suggested that systematic use of less odorous linseed oils may improve the acceptability of the emission from products with linseed oils. The applied combination of sensory assessment of perceived air quality and GC-O/MS seems to be a useful approach in the effort to eliminate unwanted odours from building products.  相似文献   

20.
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.  相似文献   

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