The collection efficiency of a particle-loaded single filter fiber

The collection efficiency η(M) of single fibers, both isolated and within a parallel array, was determined as a function of accumulated particle mass for Stokes numbers St=0.3–3 and interception parameters In=0.04–0.32. This regime is dominated by inertia, interception and particle bounce. Measurements were made with an optical in-situ particle counting technique. Monodisperse polystyrene aerosols (1.3, 2.6, 3.6 and 5.2 μm) were deposited onto steel wires of 8 and 30 μm, respectively. Particle accumulation reached values on the order of M=0.5–1 μg/mm fiber, corresponding to 10⁴–10⁶ particles per mm, depending on size.η(M) was found to increase for all operating conditions between about 2 and nearly 50 fold, most strongly however for those conditions were the bare fiber is ineffective as a particle collector, i.e. for very low or very high values of St number, corresponding to low collision or low adhesion probabilities, respectively. The absolute efficiency increased to values approaching or exceeding unity, i.e. the effective fiber collision cross-section exceeded the diameter of the bare fiber. For fibers within an array of parallel fibers (equivalent packing density ∼0.004), the initial efficiency η₀ was higher than for an isolated fiber by almost an order of magnitude. However the increase with loading was substantially smaller, typically by an order of magnitude.The efficiency increase can be described by a power law of the type where b and c are empirical fit coefficients. Within an array, the exponent c is on the order of 0.7±0.05, but lower than reported in earlier work on fiber arrays which suggest a value near unity. For isolated fibers, c→1 as interception becomes dominant (at very low flow velocities) while at high impact velocities and significant particle bounce c≈0.5. The coefficient c correlates with fiber Reynolds number, but not with other parameters. The coefficient b is inversely proportional to η₀ (consistent with earlier work, however with significantly lower values than previously published) and a function of (St/R)².The experimental section of the paper is preceded by a literature review on single-fiber efficiency data and models for the inertia-interception regime, including both information on bare fibers and dust loaded fibers. An improved, general fit function with physically meaningful limits for St→0 and St→∞ is proposed for the efficiency of bare fibers.     

Random discontinuous carbon fiber preforms: Experimental permeability characterization and local modeling

Injection experiments indicate that for random discontinuous carbon fiber preforms, increasingly uneven flow fronts develop with increasing fiber bundle length and filament count. While at high propensity for fiber bundle splitting, the preform permeability increases continuously with increasing fiber length, no trend can be identified at low propensity. No clear influence of the virgin bundle filament count on the preform permeability was observed. Types of sizing used on the fibers and bundle cross‐sectional shapes may vary and affect the intrinsic filamentization behavior, thus dominating the preform permeability. In a model for local preform permeability, interbundle voids, distributed randomly across the preform thickness, are approximated via a regular void structure. Simulated filling patterns are qualitatively similar to those observed experimentally, showing more pronounced features than those derived from a model based on local through‐thickness homogenization of the filament distribution. A model based on an alternating arrangement of fiber bundles and voids allows prediction of global preform permeability values from series of injection simulations, showing quantitatively better agreement with corresponding experimental results than the homogenization model. For global permeability, agreement between simulated and experimental mean values improves with increasing fiber volume fraction, whereas calculated coefficients of variation show no strong dependence on the fiber volume fraction. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

纤维束滤料在给水滤池中的建模与实验研究

重力式纤维束滤池与均粒滤池的对比性平行生产试验表明,纤维束滤池处理效果理想,其滤料使用周期长、截污能力强、滤速高,生产效益显著。同时通过大量实验,对重力式纤维束滤池的除浊结果进行了公式拟合,并通过测试证明其误差0.5%。利用该数学模型可以对除浊结果进行很好的预测与分析。     

基于纤维取向的纳米纤维滤料设计及其性能

通过基于霍夫变换的图像分析法获取静电纺纳米纤维取向分布信息,分析纤维取向对纳米纤维滤料性能的影响,并据此设计制备了中间为杂乱纤维层、两侧为相互垂直的取向纤维层构成的复合纳米纤维膜滤料。采用扫描电镜对纳米纤维膜形貌进行观察并获取SEM图像,进行了透气性、拉伸性能、孔径尺寸和过滤性能测试。结果表明,纳米纤维膜纤维分布方向拉伸断裂强度高,纤维取向各向异性比例理论值和实验值相吻合,纤维取向是影响纳米纤维膜力学各向异性的主要参数;取向纳米纤维膜滤料孔径较大且有许多微粒可逃逸的通道,其过滤效率和过滤阻力均较低,与文献中报道的数值模拟结果相一致;所设计制备的复合纳米纤维膜滤料结合了取向纳米纤维膜滤料力学性能优良和杂乱纳米纤维膜滤料过滤效率高的优点,其纵向和横向断裂强度分别为8.85MPa和8.71MPa,气流流速为25L/min时过滤效率高达99.691%。     

Experimental and analytical modeling of the filtration mechanisms of a paper stack candle filter

A candle filter consisting of a paper stack is an adequate device to clarify the grinding oil employed in the industrial post-processing of hard metal because of its cleaning efficiency and its regenerative capability by means of backwashing. The complex particle deposition mechanisms occurring in this device have not yet been investigated. Filtration experiments with a suitable particle-oil suspension were performed in a pilot filter and in a laboratory filter in order to investigate and model the mechanisms taking place in the process. The effect of operating parameters such as particle concentration and pressure difference on filter performance was evaluated. The results show that more than one filtration mechanism takes place simultaneously. While some depth filtration occurs at the beginning of the lifetime of a candle filter, blocking and cake filtration are the major mechanisms responsible for the filter clogging. Although blocking and cake filtration occur, to some extent, simultaneously, the cake filtration is the mechanism relevant for the modeling and scale-up of the long term filtration process.     

Penetration and pressure drop of a HEPA filter during loading with submicron liquid particles

Experiments and a model have been made of the effects of mass loading of a HEPA fiber filter during filtration of submicron liquid aerosol particles. The measurements reveal that penetration of the test medium increased during clogging by a liquid aerosol, irrespective of particle size within the chosen range (0.02–0.5 μm). The physicochemical properties of the test aerosol did not seem to affect this phenomenon. Application of a non-stationary filtration model by Payet [1991, Thèse, Université Paris, 150 p] (based on the correlation of Liu and Rubow [1990, 5th World Filt. Congress, Nice 3, 112] showed that the increase in penetration can be explained in part by an increase in interstitial velocity and in part by a decrease in the number of fibers available for capture of particles.     

Mathematical modeling of fluid energy milling based on a stochastic approach

In this study, the stochastic method is used to simulate the grinding process in a fluid energy mill: the product particle size distribution is regarded as the result of repeating elementary breakage events, i.e. M_p=M₀[T_m]^m, where M₀ is the row vector of the size distribution of feed particles, M_p is the row vector of the size distribution of product particles, m is the number of elementary steps, and T_m is the matrix of transition probabilities representing the elementary breakage event. The matrix of transition probabilities can be related to the breakage rate function and the breakage distribution function of the elementary breakage event. A specially designed apparatus, named single-event fluid mill, was employed to experimentally estimate those two breakage functions of the elementary breakage event with a breakage rate correction factor θ. The classification effect is taken into consideration by defining a cutting size under which the particle will not break any more. Using this strategy, the product particle size distribution is calculated. The good consistency between the simulation and the experimental results indicates that this model is valid to quantitatively estimate the grinding performance of the fluid energy mill.     

Experimental and numerical study on creep behaviors of 2D twill woven quartz fiber/silica matrix composites

This study investigates the creep deformation, damage, and rupture behaviors of 2D woven SiO₂/SiO₂ composites via experimental and numerical methods. In situ monotonic tensile tests and creep tests were conducted at 900 °C using a self-designed experimental system and digital image correlation. The tested specimens were characterized by X-ray computed tomography and scanning electron microscopy to conduct quantitative analyses and fracture observations. The obtained creep strain–time curves consist of primary and secondary stages, similar to the creep strain–time curves of most ceramic matrix composites. The matrix at the intersection of fiber bundles cracked under tensile loading. During subsequent creep loading, the propagation of matrix cracks, interfacial debonding, and fiber breakage in longitudinal fiber bundles were observed. At the mesoscale, the creep rupture entails a mechanism analogous to that observed in the monotonic tensile tests. Overall, the SiO₂/SiO₂ composites employed in this study exhibit excellent potential for long-term operation under mechanical loads at high temperatures. Next, a micromechanics-based creep model was proposed to simulate the creep behavior of the composites. In this model, the primary creep law and rule of mixtures were combined to describe the stress redistribution of various constituents and predict the deformation of the composites. In addition, the rupture life was predicted based on the global load-sharing model, two-parameter Weibull model, and shear lag model. The degradation of the matrix modulus and fiber strength was also considered to improve the accuracy of the simulation. The predicted results were in good agreement with the experimental data.     

新型助滤剂的合成和对细粒煤助滤的应用研究

以实验室自制辛基酚聚氧乙烯醚丙烯酸酯(AOP)、丙烯酰胺(AM)、2-丙烯酰胺-2-甲基丙磺酸(AMPS)为原料,过硫酸盐氧化还原体系为引发剂,采用水溶液共聚法合成同时具有表面活性和絮凝作用的新型共聚物PAAA。研究了合成条件对产品助滤、脱水效果的影响。得到了合成助滤剂的最佳反应条件:单体质量分数10%,溶液pH值6.0,引发剂质量分数0.1%,温度60℃,所得助滤剂能有效地提高细煤的过滤速度和降低滤饼含水质量分数。助滤剂在真空度为0.05 MPa时可将细粒煤滤饼含水质量分数从35.51%降至21.7%,过滤速度从0.229 L/(m2.s)提高到0.474 L/(m2.s)。     

Experimental determination and mathematical modeling of the drying kinetics of a single droplet of colloidal silica

ABSTRACT

Colloidal silica has been used frequently as a model material of drying in the past two decades. Several models of single droplet drying have been validated against the sole experimental evidence by Ne?i? and Vodnik (Kinetics of droplet evaporation. Chemical Engineering Science 1991, 46(2), 527–537), in which relatively scattered experimental data on drying of single droplet of colloidal silica were provided. Due to the importance of this sort of data, the drying of single droplet of colloidal silica was determined more accurately under more extensive conditions in this work. The effect of air temperature on the drying of single droplet of colloidal silica was probed as well as the evolution of particle morphology. The droplet of colloidal silica was found to shrink irregularly during drying due to uneven exposure of droplet surface to air stream. The moisture within the droplet appears to transfer freely to the surface, keeping the surface highly moist. For a large part of drying process, drying of single droplet of colloidal silica is similar to the evaporation of water droplet, which can be predicted well using a simple mathematical model.     

The effect of the flow field recalculation on fibrous filter loading: a numerical simulation

We present a simple model for the loading process of aerosol particles on fibrous filters with the aim to show the influence that the flow recalculation around a single fibre has on the complete loading process, up to the final clogging of the filter. At each loading stage (i.e., at any given degree of particle deposition), the change of shape of the fibre is presented, and information on the flow field around a fibre and the filter efficiency are obtained. The effect of the flow recalculation on the filter efficiency is shown; the single fibre efficiency is proven to be overestimated when the effect of further deposition is neglected. To perform the study, we have developed a CFD code and we have combined it with particle trajectory simulations.     

基于鲁棒模型优化的工艺设计与控制系统集成

采用一种基于鲁棒模型优化方法求解工艺设计与控制集成问题,其核心思想是采用参数不确定状态空间模型描述闭环系统的非线性行为,基于该模型以及二次李雅普诺夫函数可估计系统在外部扰动作用下过程变量变化的最大边界,同时也可测试系统的鲁棒稳定性。该方法避免了求解集成优化问题常用的动态优化方法,可将其转化成一个非线性规划问题。该方法应用于CSTR反应过程的集成优化设计中,结果表明在存在外部扰动时,不仅可以保证过程的经济性能和动态性能,也可保证系统的鲁棒稳定性。     

Experimental and analytical approach for the size effect on the fiber strength of CFRP

In this article, experimental test and an analytical approach were conducted to verify the fiber tensile strength of filament wound pressure vessel. As a test method, improved hoop ring test method was considered. From a series of fully scaled hoop ring tests, the size effect showed the clearly observed tendency toward fiber strength degradation with increasing stressed volume. As an analytical method, Weibull weakest link model and the sequential multistep failure model (SMFM) were considered and compared with the test data from hoop ring test and unidirectional specimens test. It was found that the Weibull weakest link model and the SMFM significantly overestimate the size effect on fiber strength. Thus, the fiber strength showed much lower values than those of test data. In this study, an improved SMFM was proposed by considering a modification of the length size effect. Because this model enhances the accuracy of predicting the fiber strength, the fiber strengths from the improved SMFM showed good agreement with the test data.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Experimental characterization and modeling stiffness of polymer/clay nanocomposites within a hierarchical multiscale framework

To provide a better understanding of the relationship between nanostructure and overall material stiffness in the case of polymer/clay nanocomposites, both analytical and finite element modeling were considered. A micromechanical analytical approach based on a multiscale framework is presented in which special attention is devoted to the constrained region around reinforcements. The thickness of the constrained region is seen as a characteristic length scale and the effect of particle size is explicitly introduced in the model. Moreover, the constrained region presents graded properties. The hierarchical morphology of intercalated silicate stacks is also explicitly introduced in the micromechanical model from an equivalent stiffness method in which the silicate stacks are replaced by homogeneous particles with constructed equivalent anisotropic stiffness. The orientational averaging process is used to derive the overall stiffness tensor of nanocomposite materials containing randomly oriented reinforcements. The respective influence of volume fraction, aspect ratio, size and orientation of the reinforcements, matrix properties, number of silicate layers per stack, and interlayer spacing on the overall nanocomposite stiffness is analyzed. The overall stiffness of polymer/clay nanocomposite systems is also evaluated by means of finite element simulations and the results compare favorably with model predictions. From an experimental point of view, relevant morphological and mechanical data were obtained on polyamide‐6 nanocomposites prepared using a modified montmorillonite Cloisite 30B and an unmodified sodium montmorillonite Cloisite Na⁺. The amount of constrained region around reinforcements was estimated using results issued from dynamic mechanical analyses and differential scanning calorimetry. Comparison to the model clearly underlines the contribution of the constrained region to the stiffness improvement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Development of a modeling approach to predict ash formation during co-firing of coal and biomass

The scope of this paper includes the development of a modelling approach to predict the ash release behaviour and chemical composition of inorganics during co-firing of coal and biomass. In the present work, an advanced analytical method was developed and introduced to determine the speciation of biomass using pH extraction analysis. Biomass samples considered for the study include wood chips, wood bark and straw. The speciation data was used as an input to the chemical speciation model to predict the behaviour and release of ash. It was found that the main gaseous species formed during the combustion of biomass are KCl, NaCl, K₂SO₄ and Na₂SO₄. Calculations of gas-to-particle formation were also carried out to determine the chemical composition of coal and biomass during cooling which takes place in the boiler. It was found that the heterogeneous condensation occurring on heat exchange surfaces of boilers is much more than homogeneous condensation. Preliminary studies of interaction between coal and biomass during ash formation process showed that Al, Si and S elements in coal may have a ‘buffering’ effect on biomass alkali metals, thus reducing the release of alkali–gases which act as precursors to ash deposition and corrosion during co-firing. The results obtained in this work are considered to be valuable and form the basis for accurately determining the ash deposition during co-firing.     

Treatment of enzyme-initiated delignification reaction mixtures with ceramic ultrafiltration membranes: Experimental investigations and modeling approach

Membrane reactors offer a promising configuration for enzymatic delignification processes (lignin modification, removal and utilization). However, membrane fouling reduces the efficiency of filtration and of the entire bioprocess. The flux and retention characteristics of protein-ligninsulfonate model mixtures were investigated. A 5-kDa tubular ceramic membrane achieved a sufficient and constant ligninsulphonate retention of 80–90%. The retention of phenolic monomers (e.g. guaiacol) increased with the ligninsulphonate concentration. Mass transfer-controlled regions were observed in which permeate fluxes could be predicted by the limiting flux model. Finally, the underlying fouling mechanisms were evaluated, revealing a predominance of complete pore blocking and cake filtration.     

Study on the effect of woven sisal fiber mat on mechanical and viscoelastic properties of petroleum based epoxy and bioresin modified toughened epoxy network

Sisal fiber reinforced biocomposites are developed using both unmodified petrol based epoxy and bioresin modified epoxy as base matrix. Two bioresins, epoxidized soybean oil and epoxy methyl soyate (EMS) are used to modify the epoxy matrix for effective toughening and subsequently two layers of sisal fiber mat are incorporated to improve the mechanical and thermomechanical properties. Higher strength and modulus of the EMS modified epoxy composites reveals good interfacial bonding of matrix with the fibers. Fracture toughness parameters K_IC and G_IC are determined and found to be enhanced significantly. Notched impact strength is found to be higher for unmodified epoxy composite, whereas elongation at break is found to be much higher for modified epoxy blend. Dynamic mechanical analysis shows an improvement in the storage modulus for bioresin toughened composites on the account stiffness imparted by fibers. Loss modulus is found to be higher for EMS modified epoxy composite because of strong fiber–matrix interfacial bonding. Loss tangent curves show a strong influence of bioresin on damping behavior of epoxy composite. Strong fiber–matrix interface is found in modified epoxy composite by scanning electron microscopic analysis. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42699.