Permeability measurements and flow simulation for polyaniline carbon nanofibers modified nanopaper on glass fiber preform

Carbon nanofibers (CNFs) nanopapers have shown great potential to improve the surface of fiber‐reinforced polymeric composites, including providing electromagnetic interference shielding and erosion resistance. During typical resin transfer molding (RTM) process, the CNF nanopaper is incorporated into the fiber preform as a surface layer. To learn how resin flows through the fiber preform and nanopaper layer, permeabilities of the fiber preform and nanopaper need to be measured. As is well known, measuring the permeability of fiber preforms is experimentally challenging. Results usually exhibit large experimental variability. Measuring permeability of nanopapers is even more complicated. To improve the accuracy of results, permeability of CNF‐based nanopapers was measured using different experimental setups. In‐plane permeability of nanopaper was measured by both unidirectional microslit flow and radial flow approaches. Trans‐plane permeability was measured as well, using a trans‐plane flow cell and a flow visualization mold. In this article, we discuss the methods used and provide experimental results. We also conducted computational fluid dynamics simulations to study the detailed flow patterns of the nanopaper/RTM process and compared the simulated effect of the nanopaper on retarding the flow (length of the lag) with respect to the glass preform with flow visualization results. POLYM. COMPOS., 37:435–445, 2016. © 2014 Society of Plastics Engineers     

随机分布纤维束间纵向层流流动数值模拟

按层流流动理论,采用数值方法模拟了随机分布纤维束间纵向流动时的量纲1速度分布,讨论了中空膜组件中纤维的装填率对流动阻力系数fRe和纤维束间流量分布的影响,并得到了0.1≤≤0.7范围内的fRe与的关系式。模拟结果表明,对于随机分布的纤维束,纵向流动速度分布不均匀,存在明显的偏流现象;由Voronoi划分所得的子单元通道面积分布与流量分布存在一定的关系,装填率对此关系影响较小。流动阻力系数fRe明显小于相同装填率下纤维按正三角形排列时的数值,它的模拟值与Sullivant和Costello等的实验值基本一致,随装填率增大而增大。     

Experimental analysis and simulation of flow through multi-layer fiber reinforcements in liquid composite molding

Liquid composite molding (LCM) is a process in which a reactive fluid is injected into a closed mold cavity with preplaced reinforcement. Combined layers of different permeabilities are often used in LCM, which creates through thickness and inplane porosity and permeability variations. These inhomogeneities may influence the flow front profile in the thickness direction. To investigate the effect of the through thickness inhomogeneities, mold filling experiments were performed using preforms containing layers of two different fiber architectures. Aqueous corn syrup solutions were injected into a tempered glass mold containing the reinforcement stack. The progress of the flow front at various locations within the reinforcement was measured by an electrical conductivity technique based on the insertion of small wires between the reinforcement layers. Experimental data reveal the details of the flow front shape as the fluid penetrates the preform. Using these data, a model is proposed to calculate the overall in-plane permeability of the preform. Numerical simulations of the flow front progression performed with the computer software RTMFLOT developed in our laboratory are compared to the experimental flow front for various stacking arrangements. Results show good agreement between simulations and experiments and demonstrate the capability of the software to simulate multi-layer flow process.     

随机分布纤维束间纵向层流时传质的数值模拟

按层流流动理论模型,对纤维为随机分布的中空纤维膜组件的壳程,在恒定壁面传质量和恒定壁面浓度边界条件下的传质现象进行了数值模拟,并得到了不同装填率下传质Sherwood数关联式。结果表明,纵向层流时,随机分布纤维间的传质仍可分进口段和充分发展段。对于某一给定的纤维束,在传质的充分发展段,传质Sherwood数为一个定值,且较纤维束规则排列时小得多,纤维分布不均一性将导致膜组件的传质能力下降。在传质进口段,传质Sherwood数也较纤维束规则排列时要小,装填率不但对传质系数的关联式Sh=BReaScbf(de/L)的系数B值有影响,且对该式中的Reynolds数的指数a和Schmidt数的指数b值也均有影响。     

Liquid flow through aligned fiber beds

The influence of surface properties on the flow of fluids, including epoxy resin, through aligned glass and other fiber beds has been examined. The observed flow rates were higher than those predicted from the Kozeny-Carman equation, and were influenced by the surface properties of the fluid used. This is attributed to variations in the distribution of porosities and to the presence of air bubbles trapped during the initial wetting of the bed. The implications of these findings to the preparation of composites are discussed.     

Enhancing specific strength and stiffness of phenolic microsphere syntactic foams through carbon fiber reinforcement

Composite syntactic foams with different densities were fabricated with hollow phenolic microspheres, a phenolic resin binder, and a small addition of chopped carbon fibers. Compressive, shear, and tensile properties were studied for the syntactic foams with and without carbon fibers. Two fiber layer orientations, either parallel (P‐type) or perpendicular (N‐type) to the loading direction, were considered in the mechanical testing. For N‐type foams, mechanical properties were weakly dependent on foam density. For P‐type foams, the mechanical properties of the foams were strongly dependent on the strength of the supporting matrix. The specific strength and specific stiffness of the P‐type foams were significantly enhanced compared with the neat foams. These findings indicate that fiber reinforcement is an effective way to enhance the mechanical performance of syntactic foams, and the enhanced performance should lead to applications as a foam core material for sandwich structures. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Preparation and application of high sound insulation polyurethane composite film through glass fiber reinforcement

Laminated glasses have been widely used in buildings, physical protections, and vehicles because of their safety, sound insulation, thermal insulation, and other performance. In recent years, the high sound insulation performance of laminated glass intermediate films in the frequency range of low or high frequencies has attracted more and more attentions. In this work, a glass fiber/polyurethane elastomer composite (PU-MGF) film with high transparency and impact resistance has been successfully synthesized, 5 dB of the transmission loss increased at 1600–6000 Hz, and 3.6 dB increased at 63–1600 Hz compared with the control polyurethane film. This is a significant progress in the laminated glass industry. In addition, the transmittance of the composite reaches over 75%. The excellent impact resistance of the laminated glass, based on PU-MGF film, has been confirmed through falling ball impact test, demonstrating its ability to withstand multiple impacts without spattering. The PU-MGF film prepared in this work exhibits great potential for applications in building windows, transportation, and soundproof devices.     

旋转弯曲管内流动的数值模拟

为了分析弯曲管内流动的稳定性、解的分支产生以及流动类型的变化,对正方形断面弯曲管内的流动进行了数值模拟计算。这个流动除了外墙以外的其他墙壁随着弯曲管中心轴旋转,沿着管的轴向具有压力梯度。使用波谱分析法对内圆筒旋转和由压力综合作用下所产生的流动进行了计算。流动是以螺旋泵为模型的。获得了断面二次流动的变化规律,相对于断面中心线得到了2涡流,4涡流,8涡流以及非对称的流动类型,并获得了多重解。对得到的解,进行了线性稳定性分析,并且求解了流量的变化特性。     

中空纤维膜组件壳程流动的数值模拟

利用随机顺序添加算法(RSA)建立了中空纤维膜组件壳程三维几何模型,研究了膜组件壳程复杂结构条件下的流体力学特征,进行了组件壳程流动的数值模拟。通过与实验数据及现有经验关联式的比较表明,在低Reynolds数下,基于上述几何模型的数值模拟可较好地预测膜组件的传质特性,能够替代经验关联式,为具有特定几何结构的膜组件和膜过程设计提供依据。模拟结果表明,膜丝轴向的非平行分布导致的径向流动能够消除局部沟流和死区带来的影响,合理地安排膜丝沿组件轴向的排布方式是提高组件分离性能的潜在手段之一。     

纤维增强聚合物熔体的非等温流动数值模拟

建立了基于聚合物Carreau 4参数模型和纤维取向模型相耦合的数学模型,采用有限体积法和有限差分法相结合的方法对模型控制方程组进行了数值离散。通过对4∶1平板收缩腔内的纤维悬浮非等温聚合物流动的数值模拟,得到了流场的温度和黏度分布规律,并分析了不同温度对纤维取向和流场应力的影响。结果表明:较低的温度不仅有助于纤维的旋转取向,还有助于熔体黏弹性能的提高。该数学模型能够用于纤维增强聚合物复合材料加工过程的性能分析。     

锦纶纤维特性及纤维骨架材料的发展

一、锦纶骨架材料世界应用概况 锦纶66的合成及纺丝技术于1935～1937年由美国杜邦公司的Carothers发明，并于1938年实现了中试规模，第二次世界大战期间美国开始使用锦纶66帘布制造军用飞机轮胎，1947年后用于载重胎，到50年代后期，美国的载重胎用骨架材料几乎完全由锦纶66取代了人造丝。德国于1941年实现锦纶66工业化生产。日本1958年发明用锦纶6做轮胎骨架材料制造轮胎。     

Large eddy simulation of flow through a streamwise-periodic structure

We present a dynamic large eddy simulation of flow in a periodic open-cell structure in the turbulent regime. The flow domain is represented by a tube with inner diameter of 7 mm with integrated highly porous media. Simulations were performed for three different Reynolds numbers ranging from 1200 to 4500 based on the empty tube diameter. The obtained results were compared to experimental data for which measurements were performed downstream of the same periodic geometry manufactured from a transparent material by stereolithography. The measured pressure drop and turbulence statistics compare well to the results of the large eddy simulations. The numerical results give an insight into the forced convection mechanism within the porous media and enhance the understanding of flow through foamlike structures. Furthermore specific geometric details like the influence of the ligament shape of the porous material can be investigated applying this technique.     

涡流空气分级机内三维流场的数值模拟与测量

为了清楚地认识涡流空气分级机内部流场分布,文中利用Fluent软件建立分级机的三维模型,对其内部三维旋转流场进行了数值模拟计算,得出不同工况下分级机内部流场分布。采用激光多普勒测速仪(LDV)对转笼叶片间流场进行测量,应用测量结果来验证模拟计算结果,模拟结果与测量结果吻合。研究表明,在一定的进口风速下,当环形区靠近叶片处气流切向速度与转笼外缘切向速度相近时,存在一个临界转速使得叶片间流场最稳定,分级机分级效果最好。这为改进涡流空气分级机操作提供了理论指导。     

Nylon fiber reinforcement for polyurethane composites

The potential of a nylon 6 fiber was evaluated for composite applications involving rigid polyurethane systems. A study showed that the use of COMPET N, a nylon 6 based fiber surface treated to enhance wetout and adhesion, in an ISP polyurethane system results in composites with higher impact values and lower weight than those reinforced with glass fiber. A 2 percent loading of COMPET N matt increased impact values by more than 300 percent over an unreinforced control while a 3 percent loading of glass matt resulted in increases of less than 100 percent. A drop impact test showed COMPET N fabric reinforced composites to absorb twice as much energy as an unreinforced and glass reinforced composite without major damage. These advantages have also been observed in COMPET N/Glass hybrids, in which layer orientation can be used to produce composites with specific properties. Cut fiber reinforced composites were found to exhibit similar properties as fabric reinforced ones resulting in the commercialization of a canoe end cap containing cut nylon fiber. Additional property benefits such as improved impact fatigue and decreased stress cracking have also been observed in nylon 6 reinforced composites resulting in the consideration of these materials for a wide range of applications.     

固定床流体流动特征数值模拟

为了研究固定床边壁效应、固定床床层数的变化以及颗粒的填充倾斜角度等参数对床内流体流动状况的影响,基于Ergun方程建立了轴对称多孔介质数学模型。同时对床内流体流动状况进行了研究:在床高确定的情况下,随着床层数的增加,压强降减少;随着颗粒填充倾斜角度的增加,压强降也减少,速度径向分布不均;在固定床边壁附近,气体速度明显增大。计算结果与实验值的比较表明模型能有效地描述固定床压强降和床内流体流动状况。     

Latex–fiber interaction and paper reinforcement

A model system for studying the reinforcement of paper is provided by the use of cationic latexes. The control of pH during addition of the latex to the pulp determines the uniformity of the latex deposition on the fibers. It is demonstrated, using scanning electron microscopy and mechanical testing of the sheet, that the dry and wet strength properties are improved by the more uniform distribution of a film-forming latex. Conversely, a nonfilming latex impedes bonding to the extent that the fiber surface is covered.     

旋转盘反应器流场特性的PIV测试和CFD模拟

通过PIV实验和CFD数值模拟研究了旋转盘表面的流动特性和变化规律。基于VOF多相流模型和Realizablek-ε湍流模型,CFD模拟结果与实验结果形成对比,考察了不同转速和流量条件下旋转盘表面的液膜厚度分布、停留时间和分布情况。结果表明:盘的中心区域受流速控制,流动方向更接近径向流动,边缘区域受转速控制,流动方向更接近圆周流动。液膜厚度随径向半径的增大先增大后减小,转速的增加导致边缘区膜厚减小。流速的增加导致中心区域的膜厚度减小和边缘区域的膜厚度增加。平均停留时间随转速和流速的增加而降低。停留时间分布表明,在实验条件下,液体流动更接近活塞流动。     

Numerical simulation of gas flow through porous sandstone and its experimental validation

Due to post-lithogenetic fracturing or weathering, sandstone can contain complex dual porosity structure, which makes it difficult to identify the fluid flow behaviour through it. The main objective of this study is to develop a three dimensional numerical model to simulate the flow of gas through porous sandstone under triaxial test condition. For the purpose of the modelling study, laboratory data which have been obtained from triaxial experiments conducted on porous sandstone samples [1] were used. In this study, a commercial reservoir simulator, COMET 3 was used to model the gas flow in the test samples. The COMET 3 model closely predicts the gas flow through the porous sandstone sample for the range of confining and gas injection pressures studied in the laboratory and for low gas flow rates (laminar flow). However the model fails at high flow rates (turbulent flows), due to the fact that the COMET 3 simulator uses Darcy’s law for flow simulations. Therefore, caution is required when interpreting the model results if the assumption of laminar flow does not apply to the flow conditions. An empirical relationship has been developed in this study which can be used to obtain an estimation of the flowrate when the flow has become non-Darcian. It is however important to be able to identify the transition point from Darcy to non-Darcy flow when the assumption of Darcian flow in COMET 3 no longer applies. Experiments conducted by Yi et al. [1] show very clearly the transition points, which are dependent on the injection and confining pressures. The model developed using COMET 3 appeared to give better prediction of the gas flow rate in sandstone sample, under triaxial test condition, than the COMSOL Multiphysics model given in the study in Yi et al. [1].