Numerical simulation of wire-coating low-density polyethylene: Theory and experiments

The wire-coating process was analyzed numerically making use of a particular die design employed in highspeed industrial operations. Both the lubrication approximation theory and a fully two-dimensional finite element analysis were applied under isothermal and nonisothermal conditions, respectively. Particular emphasis has been given to the heat transfer effects between the melt arid the solid and free boundaries. A variety of thermal boundary conditions was studied, ranging from adiabatic to constant temperature walls. The influence of dimension less groups such as Peclet, Nahme, and Biot numbers is examined. Oscillation-free solutions are obtained for the temperature field by using a standard finite element Streamline-Upwind/Petrov-Galerkin technique. Rheological data for a wire-coating low-density polyethylene (LDPE) resin (Alathon-3535) were used in the analysis. The predictions include pressure and temperature distributions, shear stresses and shear rates both at the die wall and the wire, and wire tension for different wire speeds. The numerical results are compared with a set of experimental data for LDPE in a typical die used by Du Pont Co. It is found that the isothermal lubrication approximation for power-law fluids overestimates pressure distributions when applied at die operating temperature. The nonisothermal finite element analysis gives better predictions, especially when realistic thermal boundary conditions are imposed, with the experimental results lying between those found from simulations assuming isothermal walls (upper limit) and adiabatic walls (lower limit).     

抗氧剂1010对3D打印用聚乳酸氧化降解性能的影响

为研究抗氧剂1010(KY1010)对3D打印用聚乳酸(PLA)氧化降解性能的影响,以PLA和KY1010为原料,通过挤出成型工艺制得3D打印用PLA丝材,并采用FDM工艺制备复合材料,研究KY1010添加量对PLA丝材拉伸性能、动态热机械性能、氧化诱导期以及复合材料力学性能的影响.结果表明,KY1010可有效改善PL...     

Effect of metallic wire inserted in nozzle in high-speed melt spinning of poly(ethylene terephthalate)

High-speed melt spinning of poly(ethylene terephthalate) was performed using a spinning nozzle with an inserted metallic wire of various lengths (0, 8, 30, and 45 mm). The molecular orientation of as-spun fibers increased with the increase in the wire length at all the take-up velocities examined. Along with the enhanced molecular orientation, the longer wire length led to the starting of orientation-induced crystallization at lower take-up velocities. The structure of crystallized fibers obtained at low speeds can be characterized by high crystallinity and relatively low molecular orientation. From the on-line measurement of the diameter and temperature profiles of the spin line with the 30-mm metallic wire, it was revealed that the spin-line had a maximum diameter of about 6 mm at the wire end. The spin-line temperature at this position was about 190°C. The solidification of the spin-line occurred at positions much closer to the spinneret in comparison with ordinary high-speed spinning. These results show that high-speed spinning with a wire inserted in the nozzle corresponds to a spinning process operated at extremely low extrusion temperature using a nozzle with an extremely large diameter. From the starting of orientation-induced crystallization at lower levels of birefringence in comparison with ordinary high-speed spinning, the alteration of the inherent fiber structure that cannot be represented by birefringence was also suggested. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 665–674, 1998     

热线外低Rayleigh数自然对流换热的机理

采用铂丝自测流体温度的实验方法,利用50×10^-6 m²·s^-1硅油对低Rayleigh数下水平与竖直热线外自然对流传热的机理进行了研究,对比实验测得的实验数据和Tsubouchi、Fand的实验数据发现,实验结果与Tsubouchi的拟合曲线吻合度较高,低Ra下水平热线外的Nu高于竖直热线,但均远高于数值模拟的预测值。为了解释该现象,进行了低振动Re下的自然对流数值模拟,发现在低于某一振动Re下,Nu将与Re无关,但此时Nu与实验测的Nu基本一致,与Tsubouchi的数据偏差也在5%以内,说明微尺度铂丝外自然对流可能存在振动的作用机理。     

Temperature fluctuations (flickering) of catalytic wires and gauzes — II experimental study of butane oxidation on platinum wires

An experimental study of butane oxidation on various platinum wires revealed the existence of local temperature fluctuations (flickering). These fluctuations were measured by an infrared detector and various statistics of this random process were determined. It was found that the amplitude and frequency of the temperature fluctuations increase with decreasing wire diameter. When the average temperature at a given point on the wire is close to the extinction temperature, a rapid decrease in the frequency of the local fluctuations is noted. The experiments indicate that a certain similarity exists between flickering and turbulent velocity fluctuations of the reacting stream.     

Heat transfer to wires and cylinders in high-temperature surroundings

This paper presents an extension to the case of wires and thin cylinders of a theoretical analysis previously reported by the authors to account for the effects of large temperature differences and large variations of the fluid property on the heat transfer process to a sphere exposed to a gas at very high temperatures. Two concepts were used in this theoretical derivation: (i) the use of a limiting Nusselt number at Re = 0, as derived from the energy equation, and (ii) the use of a reference film temperature for the evaluation of the Reynolds number different from that used for the Nusselt number. The predictions of this analysis are shown to be in excellent agreement with published experimental data in the Re range 0.01 to 40, when the ratio of the wire to the free stream temperature exceeds 0.4. This range of operating conditions is frequently encountered in industrial plasma processing and in certain high-temperature chemical engineering operations. Measurements in argon and chlorine plasma tailflames with temperature differences exceeding 2000 K are described.     

Finite element analysis of wire coating

A general-purpose finite element program has been used to simulate the flow of polymers through wire-coating dies. The analysis includes Newtonian and power-law fluids. The effect of normal stresses was examined through a simple viscoelastic constitutive equation, Nonisothermal wire coating was studied to obtain the temperature field within the melt. The effect of a slip condition at the solid boundaries was also examined. The determination of the coating melt free surface was carried out through an iterative procedure. The finite element solution provides details about the existence and extent of recirculation regions, about hot spots due to viscous dissipation, and also captures the stress singularities present at the impact of the melt with the wire and at the exit from the die. Pressure distribution, maximum temperature rise, haul-off wire tension, maximum wire tension, and stresses at the wire surface and die wall are also presented.     

Propagation of solid flame along a wire rolled in spiral

Propagation of solid flame along a wire rolled in spiral was explored theoretically. Besides conductive heat transfer along the wire, a contribution from relay-race heat exchange between neighboring spiral loops was taken into account. Combustion of spiral was found to occur in a mode of pseudo-conductive or pseudo-spinning combustion. In the former case, the temperature profile of combustion was close to that in a straight wire. A contribution from relay-race heat transfer between spiral loops can be taken into account as an elevated thermal diffusivity of wire. A specific feature of pseudo-spinning combustion is the formation of a hot spot with a temperature exceeding the thermodynamic combustion temperature. Variation in a pitch and length of spiral loop can be readily used to regulate the temperature and burning velocity of spiral combustion.     

子午线轮胎带束层、胎体及钢丝圈应力计算

推导了子午线轮胎胎体帘线应力计算公式,讨论并比较了不同理论带束层、帘线及钢丝圈应力的计算。结果表明,对于帘线张力计算,F.Frank公式和本文推导的公式较合理;对于带束层张力计算,萨尔特阔夫理论计算结果为上限,薄膜理论计算结果为下限,本文推导的公式计算结果介于二者之间;各理论的钢丝圈张力计算结果差别不大。     

钢丝缠绕液压胶管设计优化有限元分析

钢丝缠绕胶管的爆破压力、轴向变形和径向变形与钢丝缠绕角度密切相关,目前的研究和工程实践中主要是基于压力容器薄膜应力理论和经验公式对四层排布角度相同或者相近的软管进行分析和设计。但是由于薄膜理论的假设建立在胶管小变形和材料各向同性的假设条件下,而由于各层钢丝在受力后,会发生耦合作用,工程上已发现四层角度相同的设计,无论在受力,还是轴向位移都不是最佳方案,不能满足优化的目的。因此,本文使用有限元的分析方法,对四层缠绕胶管的排布角度进行独立优化,发现四层钢丝缠绕胶管每层角度的变化对其本层和其他三层的应力分布均有影响,并且有一定的规律性。利用这一规律,可以实现对钢丝缠绕胶管排布角度的优化,使爆破压力和变形都达到符合使用要求的结果。本文分析的结果被证明和工程试验结果有很好的相关性。     

Dynamic modelling of a heterogeneously catalysed system with stiff Hopf bifurcations

We report the results of a detailed dynamic modelling of CO oxidation on a platinum catalytic wire, carried out via an iterative parameter estimation scheme which employs both experimental bifurcation-to-oscillation data as well as the actual oscillatory data. By exploiting the stiffness of the system's model equations, some algebraic equations that describe the oscillatory boundaries in the feed temperature/partial pressure parameter space are extracted. The resulting model is shown to fit quantitatively these boundaries and the dynamic oscillographs of the wire temperature and simulate, with satisfactory accuracy, the unfitted dynamic data. Following an extension of the independent parameters space of the model beyond the reported experimental one, interesting bifurcation sequences (including multiple steady states) obtained via a computational study are predicted. The utility of both the resulting model in catalytic reactor design and the novel iteration scheme in general parameter estimation work on catalytic models is discussed.     

Heat capacity of polypropylene composite at high pressure and temperature

The heat capacities of isotactic polypropylene and its composite with glass fiber have been measured at high pressure, up to 7 MPa, in the melt state by high pressure differential scanning calorimetry (HPDSC). The values also have been calculated from the data of specific volume (V) measured by dilatometry and thermal conductivity (κ) and thermal diffusivity (α) measured by a compensating hot wire method. The values of the heat capacity measured from HPDSC are consistent with those from the calculation method. The heat capacities of molten polypropylene and its composite increase linearly with temperature at a constant pressure and decrease with pressure at a constant temperature. It was found that the heat capacity of polypropylene is insensitive to molecular weight. The heat capacities of molten polypropylene composites are found to be predicted by an additive rule from the weight fractions of heat capacities of polypropylene and glass fiber.     

CD MOISTURE PROFILE CONTROL RESULTS WITH THE CORRECTA HOOD IN TISSUE PRODUCTION

In order to reduce cross machine (CD) moisture deviations and their detrimental effects in tissue production, control components are more frequently used today. The CORRECTA hood, a high temperature/high velocity hood with an integrated correction system, is described. It controls both wet and dry streaks by re-distributing the drying capacity of the hood. Test results from a commercial installation in a twin wire tissue machine are reported. The experimental data agree to a great extent with theoretical calculations undertaken beforehand to predict the correction potential of the CORRECTA hood. Economic evaluation shows a high return on investment for such a CD moisture profile control unit.     

Optimization of the Cementation Process for the Removal of Copper in Process Effluent Discharges

Cementation is an effective process that meets the requirements of process cleanliness. The performance of the cementation reaction is dictated by a number of variables. In this study, the effects of various parameters on the yields of copper‐iron cementation (wire and powder) were investigated. Statistical full factorial designs were used to produce appropriate mixture models for the yields. The experimental designs were done at three different levels of three operating variables, namely initial concentration, temperature, and pH. The optimization studies were carried out with MATLAB 7.0 software. The optimum yields obtained from the predicted models were found to be 0.9916 and 0.9088 for iron wire and powder, respectively, under optimized conditions, and these were in accordance with the experimental observations.     

CD MOISTURE PROFILE CONTROL RESULTS WITH THE CORRECTA HOOD IN TISSUE PRODUCTION

In order to reduce cross machine (CD) moisture deviations and their detrimental effects in tissue production, control components are more frequently used today. The CORRECTA hood, a high temperature/high velocity hood with an integrated correction system, is described. It controls both wet and dry streaks by re-distributing the drying capacity of the hood. Test results from a commercial installation in a twin wire tissue machine are reported. The experimental data agree to a great extent with theoretical calculations undertaken beforehand to predict the correction potential of the CORRECTA hood. Economic evaluation shows a high return on investment for such a CD moisture profile control unit.     

Comparison of Data for Thermal Diffusivity Obtained by Laser-Flash Method Using Thermocouple and Photodetector

Thermal diffusivities of cordierite glass and glass-ceramics measured by the laser-flash method using remote optical sensing to monitor the transient temperature of the specimen were higher than those obtained with a thermocouple. The latter data were thought to be lower because of thermal contact resistance, the heat capacity of the cement used to adhere the thermocouple, and heat loss along the thermocouple wire. It is concluded that remote optical sensing yields more reliable data.     

Sound emission from boiling on a submerged wire

The sound accompanying nucleate and film boiling on a platinum wire immersed in a water pool at atmosphere pressure is related to the rate of heat transfer from the wire surface. In particular the total sound intensity is shown to be a function of the heat transfer resulting from bubble evolution. Analysis of the acoustic spectra for saturated and sub-cooled boiling shows how the level of selected components varies with changes in the heat flux and liquid temperature. The possibility of using an acoustic detection device to detect boiling caused by channel blockage in a liquid cooled system is discussed.     

复合盐酸酸洗液在钢丝热镀锌生产中的应用

常温盐酸酸洗能耗小,对钢丝基体腐蚀性小,酸雾少,但去除铁锈和氧化皮速度较慢。盐酸酸洗液浓度较高时,酸雾逸出多,给生产环境造成了污染;同时对钢丝基体造成过腐蚀,易形成钢丝氢脆现象。在试验的基础上,优选出一种常温复合盐酸除锈酸洗液配方及浓度控制范围。生产使用结果表明,添加TX-10、SLS活性剂,含羧酸有机添加剂和磷酸都有利于提高酸洗速度,同时起到了抑制酸雾的逸出及其对钢丝的过腐蚀作用。     

EHD-Enhanced Drying with Multiple-Wire Electrode

The enhancement of drying rate by corona discharge from multiple wire electrodes has been experimentally evaluated in this study. The corona wind produced by an array of three wire electrodes, which resembles a series of slot jets, impinges, and removes moisture from the surface of 6 mm glass beads saturated with water. Corona discharges with positive and negative polarities have been considered. Two sets of experiments have been conducted (one with the cross-flow of air and the other without), at 1 kV increment from the corona threshold voltage to a maximum voltage of 25 kV. To evaluate the drying enhancement, a companion experiment was carried out simultaneously for each case under the same ambient conditions but without the application of electric field. Each experiment lasted for at least 5 h. The weight loss of water as well as the ambient temperature and humidity were measured. The results are compared with those obtained with a single wire electrode to evaluate the effectiveness of a multiple-wire system.     

Numerical analysis of sample dimensions in hot wire thermal conductivity measurements

The parallel hot wire technique has been widely used for experimental measurements of thermal conductivity of ceramic materials. The theoretical model that is used in the fitting procedure assumes that the sample behaves as an infinite medium. The finite dimensions of the actual samples are a source of potential errors. In this work temperature transients in finite samples are numerically simulated and the ones at the measuring point (Mp) are used to calculate thermal conductivities which are compared to the exact values. Consequently, the errors involved, due to the sample finite dimensions can be estimated. Since moving the measuring point further away from the external boundaries of the sample diminishes those errors, the positioning of the temperature sensor is numerically investigated. It is shown that for (r/w)(r=distance from wire to Mp; w=sample width) in the range of 0.2–0.3, the differences in the thermal conductivity values are less than 10%.