Theoretical prediction on double-layer coating in wet-on-wet optical fiber coating process

A theoretical investigation is conducted on the wet-on-wet (WOW) process for double-layer resin coating of optical glass fiber. The coating process in the secondary coating die is modeled as a simple two-layer Couette flow of two immiscible fluids in an annulus with an assigned pressure gradient. The assumption of fully developed flow permits an exact solution to the Navier–Stokes equations. The solution discloses the relevant parameters in design and operation of a WOW coating applicator of optical fiber. For a given diameter of glass fiber and primary coating thickness, the secondary coating thickness is a function of the applied pressure gradient, the diameter of coating die, the viscosity ratio, and the fiber drawing speed. The influences of each of these control parameters on double-layer coating are scrutinized. A practical concept of thermal control of the coating process utilizing temperature-dependent viscosity of coating resins is explored.     

Optical fiber coatings: High modulus coatings for fibers with a low microbending sensitivity

An important function of an optical fiber coating is to prevent optical losses due to microbending induced by lateral forces on the fiber. To protect the fiber over a wide temperature range the modulus of the primary and the secondary coating should be low and high, respectively, and temperature independent. However, selecting the most appropriate organic coating materials introduces a new source of optical losses. Since the linear thermal expansion coefficients of silica and the organic coatings differ by about two orders of magnitude, thermal, fluctuations will cause axial stresses. Cooling may then induce bending or buckling of the glass fiber in the soft primary coating, resulting in increased transmission losses. This effect is especially pronounced when a high-modulus secondary coating is selected with a glass transition temperature above 80°C. For this type of coating the difference in radial shrinkage between the buffer and the top coating during cooling from the curing temperature becomes important. The influence of primary coating thickness is discussed.     

Theoretical analysis of the thermally induced delamination of polymeric coatings in double-coated optical fibers

To maintain its mechanical strength, the glass fiber of optical fibers is coated by polymeric materials during the fabrication process, However, when the thermally induced shear stress at the interface of the glass fiber and primary coating is larger that its adhesive stress, the adhesive bond between the glass fiber and primary coating will be broken. When the polymeric coatings are delaminated from the glass fiber, the optical fiber will lose its mechanical strength. In this article, the thermally induced delamination of polymeric coatings in double-coated optical fibers is investigated. To minimize the coating's delamination, the thermally induced shear stress at the interface of the glass fiber and primary coating should be reduced. The method to minimize such a shear stress is to select suitable polymeric coatings as follows: The thickness and Poissòn's ratio of the primary coating should be increased, but the Young's modulus of the primary coating and the thickness, Young's modulus, and thermal expansion coefficient of the secondary coating should be decreased. Finally, the optimal design of commercialized double-coated optical fibers to minimize the thermally induced coating's delamination is also discussed.     

Measurement of cure in optical fiber coatings by infrared microspectroscopy

A method suitable for measuring the state of cure in acrylate optical fiber coating is described. Both the outermost (secondary) and the innermost (primary) coatings cure states can be determined. The method is reproducible and suitable for manufacturing process control and quality control in produced fiber. © 1995 John Wiley & Sons, Inc.     

非牛顿流体研究进展及发展趋势

鉴于非牛顿流体在工业生产和日常生活中占有重要地位,详细总结了近两年来国内外非牛顿流体在各个研究领域内的研究近况,对非牛顿流体今后的研究趋势作了预测。最近,国内外对非牛顿流体的研究主要集中在非牛顿流体流变特性、非牛顿流体气液两相流流动、非牛顿流体的传质和传热以及非牛顿流体数值模拟方法等8个方面。今后,在对非牛顿流体研究的众多内容中,其首要解决的问题是非牛顿流体微观结构和流变特性的相互关系,流动规律准确的数值模拟以及非牛顿流体的新机能及相关设备的开发。     

Relaxation of the axial strain induced stresses in double–coated optical fibers

The axial strain induced stresses in double‐coated optical fibers are analyzed by the viscoelastic theory. A closed form solution of the axial strain induced viscoelastic stresses is obtained. The viscoelastic stresses are a function of the radii, Young's moduli, relaxation times and Poisson's ratios of the polymeric coatings. If the applied axial strain linearly increases, the induced stresses increase with the time. On the other hand, if the axial strain is fixed, besides the axial stress in the glass fiber, the stresses exponentially decrease with the time. The relaxation of stresses is strongly dependent on the relaxation times of the polymeric coatings. If the relaxation time of the polymeric coating is very long, the viscous behavior of the polymeric coatings will not appear, and the axial strain induced stresses solved by the viscoelastic theory are the same as those solved by the elastic theory. On the other hand, if the relaxation time of the polymeric coating is very short, the relaxation of stresses is very apparent. A compressive radial stress at the interface of the glass fiber and primary coating will result in an increase of the transmission losses, and a tensile interfacial radial stress will possibly produce debonding at the interface of the glass fiber and primary coating. To minimize this interfacial radial stress, the radius, Young's modulus and Poisson's ratio of the polymeric coatings should be appropriately selected, and the relaxation time of the primary coating should be shortened. Finally, the stresses in single‐coated and double‐coated optical fibers are discussed.     

Free coating of non-newtonian liquids onto a vertical surface

The coating of non-Newtonian liquids onto a vertical surface continuously withdrawn from the liquid bath is considered. An analytic treatment is presented for purely viscous non-Newtonial liquids using the Ellis and generalised Bingham models both of which may be reduced to a new theory for power-law fluids. The theories give a relationship between the dimensionless film thickness, T₁, and the Capillary number, C₁, as a function of the fluid physical properties and the parameters of the viscous model. The dimensionless groups have been generalised to allow for non-Newtonian behaviour. The power-law and Ellis model predictions are compared with previous theoretical studies and shown to be consistent with known limits. Experimental data are also presented for a wide range of non-Newtonian fluids and compared with the new theories.     

Free coating of viscous and viscoelastic liquids onto a partially submerged rotating roll

Experiments are performed on the dynamics of formation of a liquid coating picked up by a cylindrical roll rotating partially submerged in a free bath. Data on coating thickness for Newtonian fluids are found to correlate according to T = H(ρg/μU)^1/2 = 0.56 for fluids whose viscosities range from 0.11 to 33 poise. Data for strongly non-Newtonian and Viscoelastic fluids (polyacrylamide solutions) can be forced to fit this correlation by defining an “equivalent coating viscosity.” It is clear that this defines a pseudo viscosity, because the “equivalent coating viscosity” is observed to increase with increasing roll speed. This suggests that strongly Viscoelastic fluids respond to the rapid deformation suddenly imposed in the dynamic meniscus near the pickup point in a distinctly elastic manner that alters the flow through the meniscus.     

Finite element analysis of calendering

The general equations describing the flow of Newtonian and non-Newtonian fluids in the gap of two calender rolls were simplified by making use of the lubrication approximation. The resulting equations were solved by the finite element method. The results are in excellent agreement with existing analytical solutions for Newtonian fluids. New results were obtained for pressure, velocity profiles and sheet thickness of non-Newtonian fluids for symmetric and asymmetric calendering (different roll diameters, different roll speeds). The solution of this problem demonstrated the great possibilities offered by the finite element method in solving Theological problems of practical significance, particularly whenever complicated wall boundaries or free surfaces are involved.     

Blade-coating of a viscoelastic fluid

A theory is presented which describes the dynamics of blade-coating of a viscoelstic fluid onto a moving sheet. The method begins with the usual “lubrication” approximation, and develops the solution as a perturbation about the Newtonian case. Viscoelasticity is described by an empirical constitutive equation which shows non-Newtonian viscosity and finite normal stress behavior consistent with typical observations of polymeric fluids. Theoretical results indicate a small increase in coating thickness due to departure from Newtonian behavior, and a significant decrease in the magnitude of the pressure developed under the blade. Consequently, the blade loading can be reduced significantly by viscoelastic effects. The results for the loading may be an artifact of the specific constitutive model, since it can be shown that some viscoelastic fluids, specifically an “elastic Newtonian” fluid, would exhibit increased loading relative to the inelastic Newtonian case.     

鼓泡反应器中幂律型流体流动与传质特性

很多废水处理装置涉及非牛顿型流体中的多相流动和传质问题,研究其中的气液传质过程有助于实现装置的优化设计和高效节能运行。以鼓泡反应器内清水和不同质量分数的羧甲基纤维素钠（CMC）水溶液为实验对象,分别研究气相表观气速和液相流变特性对气泡尺寸分布、全局气含率和体积氧传质系数的影响。实验结果表明,液相的流变特性对其传质特性参数均有较大影响。与清水相比,CMC水溶液中气泡平均直径和分布范围更大;清水和CMC水溶液的全局气含率均随表观气速的增加而增大;CMC水溶液的体积氧传质系数随CMC水溶液质量分数的增加而减小。基于实验研究,得出修正的体积氧传质系数公式和适用于幂律型非牛顿流体流动体系氧传递过程的无量纲关联式,可很好地实现非牛顿流体流动的废水处理装置中气液传质参数的计算。     

Concentration by Membrane Ultrafiltration of a Shear-Thinning Fluid

Abstract

Many commercial membrane processes involve fluids whose rheological properties are non-Newtonian. However, very little has been published on ultrafiltration of non-Newtonian fluids. The aim of this work is to show some experimental results concerning the concentration by membrane ultrafiltration of fluids whose viscosity is high and shear-thinning. Experiments were performed with xanthan solutions as model shear-thinning fluids. The variations of permeate flux with respect to the operating parameters show the unusual effects of some of these parameters. It is shown that when the feed solution in an ultrafiltration process has shear-thinning properties, those properties have an enormous influence in determining the operation efficiency.     

Bubble drag and mass transfer in non-newtonian fluids: Creeping flow with power-law fluids

The drag and mass-transfer characteristics of a gas bubble moving in power-law non-Newtonian fluids are examined analytically in terms of the rheological properties of the system. An approximate solution for the case of creeping flow around circulating bubbles shows that the mass-transfer coefficient is enhanced for pseudoplastics and depressed for dilatants compared to the situation for Newtonian fluids. Some preliminary experimental results in support of the analysis are presented.     

Fire resistant optical cables with special plastic coated fibers

It is important to prevent transmission loss increase of optical fiber cables during a fire and fire fighting. One of the main reasons for the loss increase in a fire is the expansion and shrinkage of polymers used in optical fiber cables. The authors have developed a fire resistant optical fiber cable by studying the behavior of coating materials and coated fibers at high temperature. Polymer types investigated are thermoplastics, engineering plastics, and UV cured plastics. The fire resistant optical fibers are coated with a polymer which rapidly produces a carbonized layer by exposure to heat. The rapid carbonizing has the effect of reducing expansion and shrinkage. Besides the coating, the coated fiber is surrounded by carbon yarn to prevent breakage of the fiber. The fire resistant optical fiber cable passed the fire test at 840°C for 30 minutes and VTFT specified IEEE 383, without any breakage of the fibers. The optical loss of the fibers scarcely changed during the tests and after the tests. This paper presents the studies of coating materials and coated fibers at high temperature, the structure and properties of the coated fiber and characteristics of the fire resistant optical fiber cable.     

非牛顿流体薄膜流中质量传递的实验研究

本文通过实验,研究非牛顿流体层流降膜流中质量传递过程.实验系采用温壁塔测定二氧化碳在高分子水溶液中吸收速率.这些溶液符合幂律模型.实验证明非牛顿幂律流体降膜流中考虑速度分布的微分方程精确解是正确的;对拟塑性流体,用无因次长度Z<0.1作为渗透论适用范围的判据是合适的,而精确解则不受此范围的限制.     

Hybrid coatings as transducers in optical biosensors

Sensitive coatings are described for a novel enzyme-based optical sensor for in-situ continuous monitoring of reactants, such as glucose, in biotechnological production processes. Glucose oxidase, incorporated into suitable coating materials that are applied on lenses or optical fibers, is used to catalyze oxidization of glucose to gluconic acid in the presence of oxygen. The presence and consumption of oxygen is determined by measuring the fluorescence signal of incorporated metal organic ruthenium complexes, which is quenched by oxygen. Inorganic–organic hybrid polymers, synthesized via sol-gel processing, were used as coating material. Due to the hybrid character of the coating, good adhesion is achieved on both glass and polymer surfaces. Good compatibility is also given with enzymes and ruthenium complexes. The sensitive optical coating was built up as double-layer and single-layer structures. The double layer comprised a primary coating containing the oxygen-sensitive ruthenium complex, and a secondary coating containing the enzyme. The single layer comprised a single coating containing both the ruthenium complex and the enzyme.     

A simulation model to approximate penetration of a non-Newtonian fluid into a porous media during slot die coating

A computational fluid dynamics (CFD) model has been developed to predict the penetration depth of a non-Newtonian fluid as it is directly coated onto porous media by a slot die coating process. The model couples 1-D modified Blake–Kozeny equations and Navier–Stokes equations. Experiments of coating a non-Newtonian solution (black strap molasses) onto carbon paper (Toray 090) are conducted and the penetration depths are measured to validate the model. Preliminary results show that predicted and measured penetration depths follow the same trend; that is, as the coating speed increases the penetration depth decreases. However, the simulated penetration depths are found to be one to two times higher than measured values at low coating speeds. Even so, the results are considered reasonable, due to imposed simplifications and approximations of the CFD model and errors associated with the experiments and measurements.     

Filtration of non-Newtonian fluids

Equations of motion characterizing the flow of incompressible, time-independent non-Newtonian fluids, exhibiting the anomalous surface effect, through compressible porous media are developed. Approximations are made to arrive at workable filtration equations for slurries of non-Newtonian (power-law) fluids. The constant-pressure and constant-rate filtration relationships developed are verified experimentally using slurries of calcium carbonate in water and dilute CMC solutions. The anomalous surface effect is found to exist in the filtration of the non-Newtonian fluids. The specific cake resistance in the case of the non-Newtonian sludge and the ratio of the effective slip velocity to the pore velocity are found to be functions of both the CMC concentration and the pressure drop across the filter bed.     

RHEOLOGICAL CHARACTERIZATION OF NON-NEWTONIAN FLUIDS WITH A NOVEL VISCOMETER

A hydrostatic head viscometer and its novel viscosity equation were developed to determine flow characteristics of Newtonian and non-Newtonian fluids. The objective of this research is to test capabilities of the hydrostatic head viscometer and its novel non-Newtonian viscosity equation by characterizing rheological behaviors of well-known polyethylene oxide aqueous solutions as non-Newtonian fluids with 60 wt.% sucrose aqueous solution as a reference/calibration fluid. Non-Newtonian characteristics of 0.3–0.7 wt.% polyethylene oxide aqueous solutions were extensively investigated with the hydrostatic head viscometer and its non-Newtonian viscosity equation over a 294–306 K temperature range, a 0.14–40 Reynolds number range, and a 55–784 s^?1 shear rate range at atmospheric pressure. Dynamic viscosity values of 60 wt.% sucrose aqueous solution were determined with the calibrated hydrostatic head viscometer and its Newtonian viscosity equation over a 3–5 Reynolds number range at 299.15 K and atmospheric pressure and compared with the literature dynamic viscosity value.     

RHEOLOGICAL CHARACTERIZATION OF NON-NEWTONIAN FLUIDS WITH A NOVEL VISCOMETER

A hydrostatic head viscometer and its novel viscosity equation were developed to determine flow characteristics of Newtonian and non-Newtonian fluids. The objective of this research is to test capabilities of the hydrostatic head viscometer and its novel non-Newtonian viscosity equation by characterizing rheological behaviors of well-known polyethylene oxide aqueous solutions as non-Newtonian fluids with 60 wt.% sucrose aqueous solution as a reference/calibration fluid. Non-Newtonian characteristics of 0.3-0.7 wt.% polyethylene oxide aqueous solutions were extensively investigated with the hydrostatic head viscometer and its non-Newtonian viscosity equation over a 294-306 K temperature range, a 0.14-40 Reynolds number range, and a 55-784 s^-1 shear rate range at atmospheric pressure. Dynamic viscosity values of 60 wt.% sucrose aqueous solution were determined with the calibrated hydrostatic head viscometer and its Newtonian viscosity equation over a 3-5 Reynolds number range at 299.15 K and atmospheric pressure and compared with the literature dynamic viscosity value.