Frequency response analysis of nonisothermal film blowing process using transient simulations

Frequency response of the nonisothermal viscoelastic film blowing process to the ongoing sinusoidal disturbances has been investigated using transient simulation techniques. Of the many state variables exhibiting resonant peaks with the input frequency, amplitude ratio of the film cross‐sectional area at the freezeline height has been used as an indicator of the process sensitivity. The effects of operating conditions and viscoelasticity on the sensitivity have been scrutinized around the middle point of three multiple steady states under the given conditions. The sensitivity results have been interpreted through their correlation with results from linear stability analysis. Increasing draw ratio generally makes the system more sensitive to sinusoidal disturbances, whereas the cooling induces more sensitive or less sensitive system, according to the location of a steady state. Also, the viscoelasticity makes the system of extensional thickening fluids more sensitive at low Deborah number and less sensitive at high Deborah number. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The sensitivity and stability of spinning process using frequency response method

The sensitivity and stability by frequency response of the final filament to several sinusoidal disturbances have been investigated in viscoelastic spinning by using various novel numerical algorithms. Amplitudes, or gains of the spinline cross-sectional area at the take-up, show resonant peaks, which are frequently encountered in hyperbolic systems. To effectively solve the complex system of the frequency response equation, alternative ways have been performed and compared. Interestingly, in the one-dimensional systems considered, integrating the linearized equations over the spinline length to shoot at the take-up boundary condition using two initial guesses (“two-shot” method) proved far more efficient than modal analysis using eigenfunction data or solving the matrix problem from the entire length by a direct method or an iterative one (GMRES). Also, the methodology to determine the stability of the system by using frequency response data, as suggested in Kase and Araki [1982], has been revamped to viscoelastic spinning system.     

Enhanced frequency response estimator to guarantee pre-specified phase angle and static disturbance rejection with all harmonics removed

We propose a new frequency response estimation method in order to guarantee a pre-specified phase angle of the estimated model under static disturbance circumstances with rejecting harmonics completely. The proposed method uses one cycle of the conventional relay feedback signal followed by a sinusoidal signal. The sinusoidal signal in a cyclic steady state has no harmonics, resulting in exact frequency response estimates. Also, it guarantees the pre-specified phase angle and removes the effects of static disturbances by adjusting the reference value of the sinusoidal signal.     

Sensitivity of spinning process with flow-induced crystallization kinetics using frequency response method

The sensitivity of the low- and high-speed spinning processes incorporated with flow-induced crystallization has been investigated using frequency response method, based on process conditions employed in Lee et al. [1] and Shin et al. [2,3]. Crystallinity occurring in the spinline makes the spinning system less sensitive to any disturbances when it has not reached its maximum onto the spinline in comparison with the spinning case without crystallization. Whereas, the maximum crystallinity increases the system sensitivity to disturbances, interestingly exhibiting high amplitude value of the spinline area at the take-up in low frequency regime. It also turns out that neck-like deformation in the spinline under the high-speed spinning conditions plays a key role in determining the sensitivity of the spinning system.     

Contents Lists and Abstracts from the Journal of the Adhesion Society of Japan

This paper discusses a new method of evaluating thin film adhesion both qualitatively and quantitatively via a combination of peeling and image processing techniques. The adhesion of thin film on the entire substrate can be quickly evaluated and quantified to a continuous response variable which is superior to a discrete response variable as described in the ASTM D3359-78 publication. Feasibility of this technique has been demonstrated through a gauge capability study which resulted in 2.7% P/T (precision to tolerance) ratio at six sigma standard deviation for a tolerance of 100. Experimental results using the proposed method to evaluate the process/property relationship of aluminum films as deposited onto various dielectric substrates such as polyimide, silicon dioxide, and silicon nitride have been obtained and have been shown to agree with conventional stud pull test results. The estimated cycle time to evaluate thin film adhesion is five minutes per 4-inch size wafer once the sample is prepared. This short process cycle time and proven reliability show that there is merit in implementing this technique both in the laboratory for process development and in the factory for statistical process control of products.     

Fabrication and structural control of anodic alumina films with inverted cone porous structure using multi-step anodizing

Porous anodic alumina (PAA) film has recently attracted much attention as a key material for the fabrication of various nanostructures. In this study, a multi-step anodization and leaching process was employed to produce three-dimensional nanometer scale structured film. During the leaching process, the porous alumina film was dipped in phosphoric acid solution for pore widening. Each anodization process was followed by this leaching process. This method produced alumina film with multi-step structure. Meanwhile, with five-step film production, the structure showed inverted cone structure. We produced the low aspect ratio pores of this structure, which would be applicable for fabrications of nanomaterials. In addition, the aspect ratio was controlled by changing the anodization duration.     

A New Method to Evaluate Thin Film Adhesion

This paper discusses a new method of evaluating thin film adhesion both qualitatively and quantitatively via a combination of peeling and image processing techniques. The adhesion of thin film on the entire substrate can be quickly evaluated and quantified to a continuous response variable which is superior to a discrete response variable as described in the ASTM D3359-78 publication. Feasibility of this technique has been demonstrated through a gauge capability study which resulted in 2.7% P/T (precision to tolerance) ratio at six sigma standard deviation for a tolerance of 100. Experimental results using the proposed method to evaluate the process/property relationship of aluminum films as deposited onto various dielectric substrates such as polyimide, silicon dioxide, and silicon nitride have been obtained and have been shown to agree with conventional stud pull test results. The estimated cycle time to evaluate thin film adhesion is five minutes per 4-inch size wafer once the sample is prepared. This short process cycle time and proven reliability show that there is merit in implementing this technique both in the laboratory for process development and in the factory for statistical process control of products.     

Operability coating windows and frequency response in slot coating flows from a viscocapillary model

Slot coating, indispensable to the manufacturer of flat panel displays and long-life secondary batteries, can be susceptible to unexpected disturbances at high speeds, leading to many kinds of undesirable defects. Operability coating windows for both Newtonian and non-Newtonian (shear-thinning) liquids have been investigated using a simplified viscocapillary model in a slot coating bead flow regime. Stable coating windows, free from leaking (or dripping) and bead break-up, have been determined by the position of upstream meniscus. They quantitatively coincided with those from two-dimensional calculations by a CFD Fluent solver. The pressure range that allowed a stable bead widened as the viscosity of the coating liquid or the capillary number in downstream die region increased. Also, the sensitivity of the slot coating flow through frequency response method was tested by measuring the amplitude of final wet coating thickness with respect to ongoing sinusoidal disturbances at different frequencies imposed to web speed, flow rate, bead pressure and coating gap. The viscocapillary model was compared with a 2D model and was found to be a fast and efficient tool that could enhance the productivity and processability of coating systems.     

Study of the stability of the film casting process

A theoretical study of the film casting process has been carried out. In this industrial process, a molten polymer is extruded through a flat die, then stretched in air and cooled on a chill roll. This involves mainly an extensional flow. Between the die and the chill roll, thick edges are formed and a neck-in phenomenon is observed. Above a critical take-up speed, a drawing instability, known as draw resonance, may occur. In this paper, a one-dimensional model adapted from the classical model of the fiber spinning is developed (for a Newtonian or a Maxwell fluid). The influence of the processing parameters (draw ratio, Deborah number, and aspect ratio) on geometry of the lateral free surface (the so-called neck-in phenomenon) is studied. An unattainable zone very similar to the one encountered in fiber spinning is predicted, which only slightly depends on the stretching geometry (initial film width and stretching distance). The onset of draw resonance is studied through the linear stability method. A stability zone, depending on the geometry of the process, the elasticity of the polymer, and the draw ratio, has been obtained. This instability is observed with simultaneous width and thickness film variations. It is proved that the aspect ratio (stretching distance divided by die width) has a strong influence on the onset of the draw resonance instability.     

RUPTURE OF THIN MICROPOLAR LIQUID FILM ON A CYLINDER

The dynamic rupture process of a thin liquid film on a cylinder has been analyzed by investigating the stability to finite amplitude disturbances. The dynamics of the liquid film is formulated using the balance equations including a body force term due to van der Waals attractions. The governing equation for the film thickness was solved by finite difference method as part of an initial value problem for spatial periodic boundary conditions. A decrease in the cylinder radius will induce a stronger lateral capillary force and thus will accelerate the rupture process. The rupture time increases with the material parameter, Δ.     

RUPTURE OF THIN MICROPOLAR LIQUID FILM ON A CYLINDER

The dynamic rupture process of a thin liquid film on a cylinder has been analyzed by investigating the stability to finite amplitude disturbances. The dynamics of the liquid film is formulated using the balance equations including a body force term due to van der Waals attractions. The governing equation for the film thickness was solved by finite difference method as part of an initial value problem for spatial periodic boundary conditions. A decrease in the cylinder radius will induce a stronger lateral capillary force and thus will accelerate the rupture process. The rupture time increases with the material parameter, Δ.     

Fabrication of high aspect ratio nanostructures using capillary force lithography

A new ultraviolet (UV) curable mold consisting of functionalized polyurethane with acrylate group (MINS101m, Minuta Tech.) has recently been introduced as an alternative to replace polydimethylsiloxane (PDMS) mold for sub-100-nm lithography. Here, we demonstrate that this mold allows for fabrication of various high aspect ratio nanostructures with an aspect ratio as high as 4.4 for 80 nm nanopillars. For the patterning method, we used capillary force lithography (CFL) involving direct placement of a polyurethane acrylate mold onto a spin-coated polymer film followed by raising the temperature above the glass transition temperature of the polymer (T_g). For the patterning materials, thermoplastic resins such as polystyrene (PS) and poly(methyl methacrylate) (PMMA) and a zinc oxide (ZnO) precursor were used. For the polymer, micro/nanoscale hierarchical structures were fabricated by using sequential application of the same method, which is potentially useful for mimicking functional surfaces such as lotus leaf.     

不对称正负脉冲电流铝阳极氧化研究

将不对称正负脉冲电流应用于铝的普通阳极氧化，研究了不对称脉冲电流氧化参数(正脉冲电流、负脉冲电流、周期比和频率)对铝阳极氧化过程和氧化膜性能的影响。结果表明，在合适的电解参数下采用不对称脉冲电流对铝进行阳极氧化，具有成膜速度快、膜层硬度高等特点。     

On the drying kinetics of non-spherical particle-filled polymer films: A numerical study

During the coating and drying of thin polymer-particle composites, the particle geometry has a big impact on the prediction of concentration profiles in the dry film. In this work, a plate-like geometry is used to evaluate the mass transport of the particles with the aspect ratio as a variable. The experimental determination of the viscosity and sedimentation rates allows to simulate concentration profiles in the wet film while drying. A previous simulation model was automated to describe the drying of the plate-like particles—polyvinyl alcohol-water material system using COMSOL with the initial concentration, aspect ratio, Péclet number, and sedimentation number as input parameters. The results are summarized in drying regime maps, which show an increase in the evaporation regime when the aspect ratio decreases due to lower particle mobility. This shows the importance of the geometry while predicting the particle distribution in the dry film and designing coating and drying processes.     

Effect of wall temperature modulation on the heat transfer characteristics of droplet-train flow inside a rectangular microchannel

The numerical studies of water–oil two-phase slug flow inside a two-dimensional vertical microchannel subjected to modulated wall temperature boundary conditions have been discussed in the present paper. Many researchers have contributed their efforts in exploring the characteristics of Taylor flows inside microchannel under constant wall heat flux or isothermal wall conditions. However, there is no study available in the literature which discusses the impact of modulated thermal wall boundary conditions on the heat transfer behavior of slug flows inside microchannels. Hence, to bridge this gap, an effort has been made to understand the heat transfer characteristics of the flow under sinusoidal wall temperature conditions. Initially, a single phase flow and heat transfer study was performed in microchannels, and the results of the fully developed velocity profile and heat transfer rate were validated with benchmark analytical results. Then an optimal selection of the combination of sinusoidal thermal wall boundary conditions has been made for the two-phase slug flow study. Later, the effects of amplitude(0 b ε b 0.03) and frequency(0 b ω b 750π rad·s~(-1)) of the sinusoidal wall temperature profile on the heat transfer have been studied using the optimal combination of the wall boundary conditions. The results of the numerical study using modulated temperature conditions on channel walls showed a significant improvement in the heat transfer over liquid-only flow by approximately 50% as well as over two-phase flow without wall temperature modulation. The non-dimensional temperature contours obtained for different cases of temperature modulation clearly explain the root cause of such improvement in the heat transfer. Besides,the results based on the hydrodynamics of the flow have also been reported in terms of variation of droplet shapes and film thickness. The influence of Capillary number on the film thickness as well as heat transfer rates has also been discussed. In addition, the measured film thickness has also been compared with that calculated using standard empirical and analytical models available in the literature. The heat transfer rate obtained from the numerical study for the case of unmodulated wall temperature was found to be in a close match with a phenomenological model to evaluate slug flow heat transfer having a mean absolute deviation of 7.56%.     

Correlation of low density polyethylene rheological measurements,with optical and processing properties

The processing properties of low density polyethylene melts, such as drawdown and neck-in, and the final product properties, such as film haze and gloss, have been successfully correlated with rheological functions and the level of longchain branching. The rheological functions employed are the entrance pressure drop ΔP_o and the swell ratio S_o, determined at a specified shear stress using aft-orifice with a length/ diameter (L/D) ratio of zero. The calculation of shear stress requires additional measurements using adie with a finite L/D e.g. 20. The rheological functions ΔP_o, and S_o are governed by the level of high molecular weight species and/or the level of long-chain branching(LCB). If determined at a constant shear stress, in order to eliminate the effect of viscosity, they are a relative measure of elasticity. Higher ΔP₀ and S_o indicate a higher level of LCB and correlate with poorer optical properties and drawdown in films.     

Biaxial elastic modulus of very thin diamond-like carbon (DLC) films

The biaxial elastic modulus of very thin diamond-like carbon (DLC) films was measured by the recently suggested free overhang method. The DLC films of thickness ranging from 33 to 1100 nm were deposited on Si wafers by radio frequency plasma-assisted chemical vapor deposition (r.f.-PACVD) or by the filtered vacuum arc (FVA) process. Because the substrate was partially removed to obtain sinusoidal free overhang of the DLC film, this method has an advantage over other methods in that the measured value is not affected by the mechanical properties of the substrate. This advantage is more significant for a very thin film deposited on a substrate with a large difference in mechanical properties. The measured biaxial elastic moduli were reasonable values as can be judged from the plane strain modulus of thick films measured by nanoindentation. The biaxial elastic modulus of the film deposited by r.f.-PACVD was 90±3 GPa and that of the film deposited by FVA process was 600±50 GPa. While the biaxial elastic modulus of the film deposited by FVA is independent of the film thickness, the film deposited by r.f.-PACVD exhibited decreased elastic modulus with decreasing film thickness when the film is thinner than 500 nm. Although the reason for the different behavior could not be clarified at the present state, differences in structural evolution during the initial stage of film growth seem to be the reason.     

Diffusion pathways of benzene, toluene and p-xylene in MFI

The diffusion of alkyl-substituted aromatic molecules in H-ZSM-5 was investigated by means of the frequency response method decoupling particle size effects and intracrystalline diffusion. For zeolite crystals above 5 μm average diameter, the transport in the zeolite pores exerts a significant effect on the overall transport causing anisotropic diffusion as the aspect ratio of the aromatic molecules increases. Diffusion of benzene is nearly isotropic, while p-xylene shows marked differences between the diffusive processes in the straight and sinusoidal channel system of ZSM-5. The isotropic diffusion of benzene is rationalized on the basis of its ability to reorient between the two channel systems without major hindrances. For p-xylene, switching between the channels is only possible by energetically unfavorable rotational motions leading to a low probability for changing between both channel systems.     

高纯度精馏过程的集成控制与在线优化策略

For high-purity distillation processes, it is difficult to achieve a good direct product quality control using traditional pro-portional-integral-differential (PID) control or multivariable predictive control technique due to some difficulties, such as long re-sponse time, many un-measurable disturbances, and the reliability and precision issues of product quality soft-sensors. In this paper, based on the first principle analysis and dynamic simulation of a distillation process, a new predictive control scheme is proposed by using the split ratio of distillate flow rate to that of bottoms as an essential controlled variable. Correspondingly, a new strategy with integrated control and on-line optimization is developed, which consists of model predictive control of the split ratio, surrogate model based on radial basis function neural network for optimization, and modified differential evolution optimization algorithm. With the strategy, the process achieves its steady state quickly, so more profit can be obtained. The proposed strategy has been successfully applied to a gas separation plant for more than three years, which shows that the strategy is feasible and effective.     

Stability of isothermal spinning of viscoelastic fluids

The stability of isothermal spinning of viscoelastic fluids which have strain-rate dependent relaxation time has been investigated using the linear stability analysis method. The instability known as draw resonance of the system was found to be dependent upon the material functions of the fluids like fluid relaxation time and the strain-rate dependency of the relaxation time as well as upon the draw-down ratio of the process. Utilizing the fundamental physics of the system characterized by the traveling kinematic waves, we also have developed a simple, approximate method for determining this draw resonance instability; it requires only the steady state velocity solutions of the system, in contrast to the exact stability analysis method which requires solving the transient equations. The stability curves produced by this simple, fast method agree well with those by the exact stability method, proving the utility of the method. The stability of other extensional deformation processes such as film casting and film blowing can also be analyzed using the method developed in this study.