固定床颗粒层除尘实验研究

针对高温除尘中细微粉尘的脱除难题,设计了固定床颗粒层除尘实验台,在常温下进行除尘实验.实验结果表明:颗粒层除尘效率与过滤介质粒径、过滤层厚度、过滤时间以及过滤速度有关;减小过滤介质粒径、降低过滤风速、增加床层高度都使细微粉尘的脱除率有一定提高.本实验条件下最佳过滤层厚度为100 mm,过滤风速0.4 m/s,介质颗粒粒径为0.9～1.2 mm.优化后的颗粒层除尘器除尘效率最高可达99.8%.     

一种改进型旋风除尘器

通过在旋风除尘器(刹克龙)的圆柱部分的内壁以及圆锥上端部分的内壁焊接若干数量的竖直筋条,使内壁的粗糙度和摩擦阻力增加,同时对快速气流中的粉尘颗粒起到正面直接阻击作用,增强沿程能量损失效应,消耗气流及粉尘颗粒动能,致使粉尘颗粒的速度迅速下降,除尘效率提高.     

干燥旋风分离器尾气粉尘去除方法初探

介绍了干燥旋风分离器尾气粉尘的布袋除尘法和沉降除尘法。由于湿热的尾气粉尘表面吸附了胶粒,使用常规的布袋除尘十分困难;在沉降除尘中,如果能把尾气风速降到远低于粉尘悬浮速度,让粉尘在重力作用下自然沉降,便可除去尾气中的大部分粉尘。     

湿式振弦除尘器除尘特性研究

根据影响除尘性能的因素,研究了风速、水量和振弦过滤板数量对湿式振弦除尘器的除尘效率和阻力的影响.结果表明:在喷水量一定的情况下,除尘效率和阻力随风速和振弦过滤板数量的增加而增加,但过高风速会造成风机带水,除尘效率下降;喷水量对除尘效率和阻力影响较小.     

木工机械吸尘罩之设计与应用

木工机械吸尘罩之设计与应用木工机械设置的除尘系统，除为保护操作者的健康外，其最主要功能还是为排除加工过程中产生的木屑及粉尘。吸尘罩虽可搜集细小的粉尘颗粒，但其重点在于清除大量的粗木屑，因此大多数木工机械吸尘罩的外型设计符合木屑射出的轨道，除尘系统性能...     

卷烟制丝生产线集中除尘系统的改进

为解决制丝生产线集中除尘系统管道中存在粉尘沉积及管道堵塞等问题,基于气-固两相流理论和风速计算方法对除尘系统进行了改进。简化管道结构,将两条并联连接的除尘支管改为串联连接,增大管道内风速;采用耐磨弯头,并将弯头的曲率半径由原来的管道直径1.5倍增加至2倍,减少气流动能的阻力损失。以南京卷烟厂的4条制丝生产线为对象进行测试,结果表明:改进后集中除尘系统管道内风速达到29.4 m/s,远大于粉尘输送所需的最小风速18 m/s;管道堵塞次数减少4.33次/月,停机时间减少344.2 min/月。该技术可为提高制丝线集中除尘系统的运行效率提供支持。     

包装容器内粉体的振动密实过程分析与数值模拟

研究振动对粉体包装容器内粉体密实的影响。基于离散单元的理论知识,对粉体在不同振幅和频率下的振动密实过程进行仿真。对不同振幅和频率影响下,颗粒X方向上的速度进行分析。在其他条件一定的情况下,随着振幅和频率的增加,颗粒X方向上的速度波动变大,且振幅对颗粒速度波动的影响不显著。这说明基于离散元法的数值模拟可使粉体的振动密实过程清晰可见,振动参数的分析对粉体包装工艺的改进提供了有意义的依据。     

排尘罩设计及管道节点压力平衡计算

轧花厂的粉尘是棉花在机械加工过程中产生的粉粒状和纤维状的固体颗粒，其粒径大都在10微米以上，用眼睛可以看得见。这些粉尘可以在空气中浮游很长时间，它扩散后不仅危害人体健康，而且还会对机器设备造成的影响。因此大多数轧花厂都安装了管道除尘系统，在粉尘产生的地点直接地把粉尘捕集起来，排到一定地方，既净化了工作环境，又可回收粉尘中的有效纤维，收到了较发的经济效果，但是有的轧花厂虽也没有管道除尘系统，但是运行效果却达不到设计要求，这是为什么呢？我认为除了风机和除尘器选择是否合适外主要有两个问题，一是排尘罩的设计，一是管道系统中节点压力平衡计算。     

基于DEM-CFD的粮堆气流阻力与传热特性模拟研究

谷物固定床干燥是测定通风过程中谷物温湿度变化、气流阻力规律的常用方法,在固定颗粒床中孔隙分布对粮堆气流阻力与传热特性影响明显。本文采用离散单元法(DEM)模拟了大豆颗粒随机堆积的孔隙结构,并对堆积颗粒间的接触进行处理,利用DEM-CFD方法模拟了大豆固定床中的气流阻力与传热特性。结果表明：粮堆压力降与入口速度近似呈二次函数关系,与考虑壁面效应的Reichelt方程计算结果一致。固定床层内部速度与温度场分布不均匀,受床层孔隙率分布、入口风速影响较大,近壁面区域气流速度与降温速度均高于床层中心区域。     

隧道式叶丝回潮机排气罩结构的优化设计

为解决隧道式叶丝回潮机在生产过程中存在的因排气罩吸风速度过快、风量过大等原因导致大量叶丝颗粒进入后续生产工序等问题,对排气罩进行了两次优化设计。第一次优化,将罩体底部由敞开式改为封闭式,并将罩体高度增加1 m;第二次优化,在罩体内部增加两块空气挡板,并在罩体壁上开设一条空气条缝。利用流体力学理论和数值模拟方法,建立了罩体内部流场和叶丝颗粒运动数学模型,通过对两次优化方案进行数值模拟,研究了叶丝颗粒运动轨迹与罩体形状、尺寸及内部结构之间的关系。结果表明:1一次优化后进入排气罩内的空气量减少23.5%,在罩体内停留时间大于10 s的叶丝颗粒占68.4%,悬浮的叶丝颗粒容易粘附在罩体内壁上,并发生颗粒沉积和脱落现象。2二次优化后停留时间大于10 s的叶丝颗粒仅占22.8%,粘附内壁现象明显减少;实现了叶丝颗粒的回收利用,回收率达80.67%;出口处颗粒浓度为37.5 mg/m~3,达到工艺排放允许浓度要求。两次优化后减少了排气罩内叶丝沉积现象,提高了叶丝利用率和产品质量。     

Normal use levels of respirable cosmetic talc: preliminary study

This preliminary study was undertaken to provide data from which a more comprehensive investigation to establish the safety in-use of cosmetic talcs could be designed. Methods for collecting and analysing respirable talc generated during the use of loose face powder and adult and baby dusting powders were established. Respirable particles in the air were separated from larger size particles by means of a cyclone and were collected on membrane filters. The collected dust was dissolved in acid and the solution was analysed for magnesium by atomic absorption spectroscopy. From the results the concentrations of talc in the air samples were calculated. The method was used to monitor the in-use levels of a range of cosmetic talcs. Mean concentrations in air sampled for 5 min from the start of use of Chinese grades and Italian 00000 grades of talc formulated for use as loose face powder, adult dusting powder and baby dusting powder were 0.48, 1.13 and 0.21 mg m^?3, respectively. Higher levels were found with micronised adult dusting powder (mean concentration 1.9 mg m^?3). There was no evidence that the presence of perfume in the talc or the ambient relative humidity in the range 54–74% during use affected the levels of respirable talc, but high relative humidity <90% reduced the amount of respirable talc. Utilisation des talcs cosmetiques: étude préliminaire des teneurs en talc respirable     

浅谈打包车间粉尘环境的处理

阐述了打包车间粉尘的安全隐患,并对粉尘的控制方法,如除尘器的选择、吸尘罩的安装、排风扇的安装、设备补缺补漏、风管的清理、滤袋的更换以及粉尘的监测展开了分析,以期为打包车间粉尘的治理提供参考。     

CHARACTERIZATION OF RECONSTITUTED MILK POWDER BY ULTRASOUND SPECTROSCOPY

When instant milk powder (IMP) is reconstituted with water, the product should resemble fresh milk. However, undissolved particles were found at the surface and in the bulk of the product. A visual reconstitution test (RT) is made on IMP to determine the reconstituted quality of the product. This test is directly linked to the presence of the undissolved particles. The particles found at the surface are formed by clustered liquid‐fat aggregates, which rise to the top of the milk and may give an impression of spoiled milk. The particles found in the bulk are small particles in the solution mostly composed of a protein gel. Because the repeatability and precision of the RT are very poor, a quantitative analytical technique is desirable. In this study we investigated five different quality milk powders by an ultrasound spectroscopy technique. The ultrasonic velocity and attenuation parameters were measured with a frequency scanning pulse echo reflectometer. We found that the ultrasonic velocity cannot be correlated to RT because the predominant phenomenon that affects the ultrasonic velocity is the physical state of the different components of the milk matrix (liquid fat, crystalline fat and lactose crystals), and this physical state is not a significant factor in powder quality. However, the ultrasonic attenuation coefficient is well correlated with RT. This is because, between two different quality powders, the most important factor that causes variation in the attenuation is scattering, correlated to particle size and to volume fraction rather than by the composition or physical state of the matrix and the same particle size factor, and volume fraction factor characterizes the powder reconstitution's quality.     

Characterization of airborne particles during production of carbonaceous nanomaterials

Despite the rapid growth in nanotechnology, very little is known about the unintended health or environmental effects of manufactured nanomaterials. The development of nanotechnology risk assessments and regulations requires quantitative information on the potential for exposure to nanomaterials. The objective of this research isto characterize airborne particle concentrations during the production of carbonaceous nanomaterials, such as fullerenes and carbon nanotubes, in a commercial nanotechnology facility. We measured fine particle mass concentrations (PM2.5), submicrometer size distributions, and photoionization potential, an indicator of the particles' carbonaceous content, at three locations inside the facility: inside the fume hood where nanomaterials were produced, just outside the fume hood, and in the background. The measurements were not selective for engineered nanomaterials and may have included both engineered nanomaterials and naturally occurring or incidental particles. Average PM2.5 and particle number concentrations were not significantly different inside the facility versus outdoors. However, large, short-term increases in PM2.5 and particle number concentrations were associated with physical handling of nanomaterials and other production activities. In many cases, an increase in the number of sub-100 nm particles accounted for the majority of the increase in total number concentrations. Photoionization results indicate that the particles suspended during nanomaterial handling inside the fume hood were carbonaceous and therefore likely to include engineered nanoparticles, whereas those suspended by other production activities taking place outside the fume hood were not. Based on the measurements in this study, the engineering controls at the facility appear to be effective at limiting exposure to nanomaterials.     

Modeling of fugitive dust emission for construction sand and gravel processing plant

Due to rapid economic development in Taiwan, a large quantity of construction sand and gravel is needed to support domestic civil construction projects. However, a construction sand and gravel processing plant is often a major source of air pollution, due to its associated fugitive dust emission. To predict the amount of fugitive dust emitted from this kind of processing plant, a semiempirical model was developed in this study. This model was developed on the basis of the actual dust emission data (i.e., total suspended particulate, TSP) and four on-site operating parameters (i.e., wind speed (u), soil moisture (M), soil silt content (s), and number (N) of trucks) measured at a construction sand and gravel processing plant. On the basis of the on-site measured data and an SAS nonlinear regression program, the expression of this model is E = 0.011.u2.653.M-1.875.s0.060.N0.896, where E is the amount (kg/ton) of dust emitted during the production of each ton of gravel and sand. This model can serve as a facile tool for predicting the fugitive dust emission from a construction sand and gravel processing plant.     

Electrohydrodynamic processing of natural polymers for active food packaging: A comprehensive review

The active packaging materials fabricated using natural polymers is increasing in recent years. Electrohydrodynamic processing has drawn attention in active food packaging due to its potential in fabricating materials with advanced structural and functional properties. These materials have the significant capability in enhancing food's quality, safety, and shelf-life. Through electrospinning and electrospray, fibers and particles are encapsulated with bioactive compounds for active packaging applications. Understanding the principle behind electrohydrodynamics provides fundamentals in modulating the material's physicochemical properties based on the operating parameters. This review provides a deep understanding of electrospray and electrospinning, along with their advantages and recent innovations, from food packaging perspectives. The natural polymers suitable for developing active packaging films and coatings through electrohydrodynamics are intensely focused. The critical properties of the packaging system are discussed with characterization techniques. Furthermore, the limitations and prospects for natural polymers and electrohydrodynamic processing in active packaging are summarized.     

Influence of woodworking machine cutting parameters on the surrounding air dustiness

From epidemiological studies experts conclude that wood workers are subjected to an increased health risk of nose and nasal cavity cancer under the influence of oak- and beech-wood dust. That is why, pursuant to Croatian regulations, the limit mass concentration for oak- and beech-wood respirable dust is 1 mg/m³ and for total dust 3 mg/m³. In this study the dustiness of the air surrounding woodworking machines has been researched in two woodworking companies, furniture factory and carpentry. Sampling of respirable and total wood dust from the surrounding air was carried out during workday by the method of personal samplers fixed on workers suit and then the daily dose of workers exposure was determined. Measured mass concentrations exceeded the Croatian limit values: in the furniture factory 16% of samples for respirable dust and 18% for total dust and in the carpentry 38% for respirable dust and 65% of all samples for total dust. In the furniture factory, mass concentration of respirable particles was higher near the belt sander than near the circular saws. At the workplaces of these woodworking machines higher mass concentration of respirable and total wood dust was measured than in the air around other machines, such as spindle moulder, band saw and jointer. In the carpentry mass concentration of respirable particles near the circular saws was significantly higher than near the jointer or lamello router. The highest share of respirable particles in total wood dust are recorded at the workplaces with low concentration of total wood dust and around machines with cutting parameters achieve the lowest value of chip thickness.     

Organic contamination of settled house dust, a review for exposure assessment purposes

People spend a considerable amount of time indoors. As a result, exposure to indoor contaminants is of great concern, notably via settled dust ingestion in particular for infants and toddlers. This paper proposes a critical review on the organic contamination of settled house dust and human exposure over the past 10 years and focused on sources, contaminations and measurement methods (sampling, pretreatment, storage and analysis). As many compounds were identified, arises the question of which ones to consider. Sensitive and selective analytical methods for simultaneous determination of targeted substances should be developed and evaluated. Various methods were described for sampling and sample preparation. Harmonization and standardization are needed to enable comparison of results from similar studies. Finally, an integrated multipollutant and multicompartment (settled dust, suspended particles and air) approach appears essential in order to determine the extent of the threat to public health posed by indoor contaminants.     

Nanocellulose in green food packaging

The development of packaging materials with new functionalities and lower environmental impact is now an urgent need of our society. On one hand, the shelf-life extension of packaged products can be an answer to the exponential increase of worldwide demand for food. On the other hand, uncertainty of crude oil prices and reserves has imposed the necessity to find raw materials to replace oil-derived polymers. Additionally, consumers' awareness toward environmental issues increasingly pushes industries to look with renewed interest to “green” solutions. In response to these issues, numerous polymers have been exploited to develop biodegradable food packaging materials. Although the use of biopolymers has been limited due to their poor mechanical and barrier properties, these can be enhanced by adding reinforcing nanosized components to form nanocomposites. Cellulose is probably the most used and well-known renewable and sustainable raw material. The mechanical properties, reinforcing capabilities, abundance, low density, and biodegradability of nanosized cellulose make it an ideal candidate for polymer nanocomposites processing. Here we review the potential applications of cellulose based nanocomposites in food packaging materials, highlighting the several types of biopolymers with nanocellulose fillers that have been used to form bio-nanocomposite materials. The trends in nanocellulose packaging applications are also addressed.