Height Of Sheets Research Articles

Investigation of temperature distribution and heat transportation involving flame spread over liquid fuel in a tube

Flame spread over liquid fuel possibly occurs in a long and narrow confined space, i.e., tunnel, pipeline or corridor. The spread of liquid fire in a tube belongs to the ventilation-controlled combustion. The 100 cm-long cylindrical quartz glass tube was built to examine flame spreading behavior on butanol surface in the tube. The inner diameters of the tube were 10 and 20 cm, respectively. The sealing ratio and sealing end position were controlled by the height and position of glass sheets at both ends. Three blocking methods were conducted: ignition-end blocking, non-ignition-end blocking and two-ends blocking. The effects of sealing ratio and sealing end position on flame spreading characteristics such as gas-liquid temperature distribution, oxygen concentration, preheating time and heat transportation of surface flow were revealed. The flame separation behavior was observed due to the insufficient oxygen supply. The non-ignition end blocking could effectively reduce the surface flow velocity and restrain the flame spread. The gas- and liquid-phase transfer involving surface flow of flame spread were revealed. For ignition-end blocking at D = 200 mm, when the blocking ratio increases from 10 % to 40 %, the radiant heat flow from front flame to surface flow area decreases by 17.6 %.

Weld pool dynamics and joining mechanism in pulse wave laser beam welding of Ti-6Al-4V titanium alloy sheets assembled in butt joint with an air gap

A validated CFD model coupling the multiple phases and multiple physics was developed for the dynamic simulation of pulse wave laser welding (PWLBW) process of 1.2 mm-thick Ti-6Al-4V alloy sheets assembled in butt joint with a reserved air gap. A laser spot diameter of 700 μm was used to compensate for the energy loss with the clearance applied at 0.2 mm and therefore improve the gap bridging ability. The distributions and evolutions of temperature, velocity, phase interface and weld pool dimensions were characterized and discussed to reveal the joining mechanism and the heat and flow behaviors during welding. The results show that the liquid bridges firstly occur in the middle height of sheets as the welding begins, and rapidly extend to the whole thickness with the increasing heat input. The reduction on laser power causes the rebounding of keyhole surface and the backfilling of molten metal. The keyhole closes at root surface and rebounds completely in 2 microseconds, leading to the merging of liquid bridges, bottom-up moving of high temperature area, and temporarily enlargement on weld pool size at root surface. During the pulse interval, the weld pool volume shrinks significantly and the molten metal slows down from Marangoni vortexes to thermal buoyance flows. The proposed process parameters allow an air gap accounting for 16.67% of specimen thickness and result in a well-formed and defect-free weld bead.

Pulsed Magnet Design and Fabrication for Generating Background Magnetic Field in Discharge Current-Based Forming

Discharge current-based forming (DCF) is a forming method that directly loads a pulse current into two parallel placed metal sheets connected in series, and the mutually exclusive electromagnetic force between them causes the sheets to be deformed. Compared with the electromagnetic forming (EMF), this method can improve the current density for the low-conductivity sheets. However, the forming height of the sheets is extremely poor due to the weak magnetic field generated by the pulsed current. In order to solve this problem, a new DCF approach adopted a pulsed magnet for wide sheets forming is proposed, which can provide a background magnetic field (BMF) with high uniformity and strength during the forming process. The influence of magnet parameters (shape, size, wire size, number of turns, etc.) on the magnetic field uniformity and strength at the forming region is analyzed by the finite element method, and the design scheme is listed. After that, the magnet is fabricated based upon the manufacturing technique of pulsed magnets, and the DCF and EMF experiments of AA1060 and SS304 sheets with 100 mm widths are carried out. The testing results show that the magnet can provide a 2.8 T BMF with more than 93% uniformity for the forming region. The forming results show that the forming height of sheets in DCF under BMF can be increased by 300% compared with that without BMF, and DCF has a huge advantage in comparison with EMF in forming low conductivity materials.

Design of Optimal Slit Steel Damper Under Cyclic Loading for Special Moment Frame by Cuckoo Search

After the Northridge and Kobe earthquakes, several destruction of the structural beams were occurred. The difficulty and cost-effectiveness of beam replacement after earthquakes is a major problem on steel structures. For this purpose, the idea of using replaceable connection is suggested. A slit steel damper (SSD) is introduced that leads to the further energy damping and the ability to move the plastic joint outside of structural elements. The stiffness and damping characteristics of SSD is related to the thickness, height and number of sheets of the damper. The usage of SSD is more progressive and at the same time, the optimal design of SSDs should be proposed to meet the economical criterion and the reduction of the stress and deflection. In this study, an optimal SSD connection is proposed to enhance the performance of the classical SSD connection to meet the criterion of AISC to utilize in special moment frames. The results demonstrated that increasing the thickness and reduction of the steel sheets in the damper had a greater effect on the performance of the SSD connection, in comparison with the increase in the number of sheets. Therefore, the Cuckoo Search (CS) was utilized to optimize the several SSD parameters. Furthermore, a comparison between the CS-SSD and Reduced Beam Section (RBS) which is known as a common moment steel fixed-connection was accomplished. Results indicate that CS-SSD connection can reach the same function as the RBS connections under cycling loadings, in addition to the easy replacement capability after seismic excitations. The performance of the proposed CS optimization algorithm in designing of the optimal SSD was compared with the traditional Genetic Algorithm and the particle swarm optimization (PSO) with considering several designing constraints. High capabilities of the proposed CS optimization algorithm in terms of weight, energy absorption, stiffness and bearing capacity of SSD connections are simultaneously clarified by the results.

Numerical and experimental study of oscillatory behavior of liquid surface agitated by high-speed gas jet

This study examines high-speed air jet impingement on water surface in the penetration mode using CFD simulation and experimental observation. An axisymmetric approach was taken along with the volume of fluid (VOF) method and the k−ω SST turbulence model for simulations. Moreover, a test rig was designed and fabricated to diagnose the phenomenon by tracking the interface motion using a high-speed camera in conjunction with an image processing procedure, and to evaluate the validity of the numerical simulations. Important aspects of the oscillatory behavior of the interface, cavity depth oscillation and rising ligaments and sheets, are addressed in detail. The simulation results offer a very close prediction of the peak frequencies of the cavity oscillation, and the number of ejected liquid sheets and ligaments despite some discrepancies in the range of the cavity motion and the height of ligament and sheets. Induced waves on the interface, and bubbles escaping from the cavity, which are the main source of instability of this two-phase system, are reproduced successfully.

Vertically Oriented MoS2 with Spatially Controlled Geometry on Nitrogenous Graphene Sheets for High-Performance Sodium-Ion Batteries

Lithium-ion battery (LIB) has been a tremendous success for decades. As the demand for rechargeable batteries surges, a need has arisen for low-cost secondary batteries. Among various studies, sodium-ion battery (SIB) is the most promising secondary batteries due to its similar working principles and the abundance of sodium in the natural world. Among many anode materials for SIB, MoS­­2 has attracted attention because it can intercalate sodium ions in its layered structure. However, in the repeated intercalation of Na+ , MoS2 suffers from collapse of its layered structure. Herein, we present vertically grown MoS2 on nitrogenous reduced graphene oxides (N-RGO) with controlled sheet density and height of MoS2 sheets as SIB anode active material. The MoS2 materials are synthesized by gel-precursor based method. By adjusting the nucleation and growth processes, we controlled the height and density of MoS2 sheets to find optimal condition that show great performance and high stability. Control of the partial geometry can achieve these improved property because the high sheet density can prevent additional SEI layer and the shortened sheet length reduces the resistance of Na+ diffusion. It shows remarkably high reversible discharging capacity of 255mAh/g at 1C and 245mAh/g at 5C discharging with a capacity reduction of 5.35% after 1300 cycles. And closely packed MoS2 sheets shows specific capacity of 254, 243, 153, 86 mAh/g at 0.2, 2, 10, 50A/g current density, respectively. Furthermore, vertically grown MoS2 is paired with Na3V2(PO4)3 to fabricate SIB full cell, and the full cell shows a specific capacity of 262mAh/g (based on the mass of anode material) during 50 cycles. Figure 1

CFD Simulation and Optimization of Winpak-based Modular Catalytic Structured Packing

A recently designed packing sheet Winpak was assembled with catalysts in a modular catalytic structured packing (MCSP) column. A combined mesoscale–microscale methodology was used to analyze and determine the pressure drop mechanism in the MCSP. The proposed methodology differentiates the pressure drop into six different principles, which was determined and compared using computational fluid dynamics (CFD). The three major causes are gas flow confluence and diffluence through the packing windows, the sudden change in the effective gas channel area and the wall effect. Inspired by constructal theory, the height of packing sheets loaded with catalysts was reduced, which resulted in a less abrupt gas channel contraction and expansion at the packing layer junction and more favorable for the undisturbed gas flow. The optimized overall pressure drop was reconstructed in Fluent and was validated by both dry and irrigated packing experiments. Furthermore, irrigated packing experiments were also conducted. Result ...

Deformation and flying height orbit of glass sheets on aerostatic porous bearing guides

Handling devices have been developed for liquid crystal display fabrication that are equipped with aerostatic porous bearing pads to feed large glass sheets while supporting them with compressed air in a non-contact state. The deformation behavior and the orbit of the flying height of glass sheets on porous bearing pads during the feeding process were investigated using the compressible Reynolds equation and Timoshenko's thin film theory. Theoretical and experimental results showed that glass sheets are easily deformed by the pressure distribution in the air film and that they tilt easily on the bearing pad during the feeding. The results also showed that the hole pitch for air suction and the interval between bearing pads arranged next to each other should be shorter to achieve more stable feeding of the glass sheets with a constant flying height.

Sputtering Fabrication of Large Scale ZnO Nanobowl Arrays Using Colloidal Crystal Templates

Ordered ZnO nanobowl arrays over cm2 areas were prepared by magnetron sputtering using the self-assembled polystyrene spheres arrays as templates. The process started with self-assembled sedimentation of there-dimensional (3D) hexagonal polystyrene sphere arrays. By depositing ZnO within the interstitials of 3D polystyrene colloidal crystal templates using magnetron sputtering, large-area ordered ZnO nanobowl sheets were prepared after removing the spheres by annealing. The whole nanobowl sheet could be lifted off, leaving accidentally observed inverse opal structures. The sizes of the nanobowls could be controlled by the size of the polystyrene spheres, the height of nanobowl sheets could be altered by changing sputtering parameters.

Effects of process parameters on warm and electromagnetic hybrid forming of magnesium alloy sheets

As the lightest structural metal, magnesium (Mg) is attracting increasing interest from both the industrial and academic fields. Magnesium alloy parts are mainly processed by die casting due to their poor sheet formability at room temperature. Warm forming is a popular method of forming; Mg alloy sheets produced in this manner show excellent formability around 200–400 °C. Electromagnetic forming (EMF) can improve the formability of metal sheets without the need for lubricants. In this paper, a new approach, called warm and electromagnetic hybrid forming (WEMF), is presented. The effects of voltage, capacity, and temperature on the bulging height of Mg alloy sheets are investigated. Results show that the bulging height of Mg sheets increases with moderate discharging energies. Enhancing the discharging voltage is also a more efficient method for increasing bulging height compared to simply increasing the capacity. When the discharging energy is kept constant, the bulging height first decreases (<150 °C) and then increases (>150 °C) from room temperature to 230 °C. The formability of Mg alloy sheets improves with increasing temperature, while the forming efficiency of WEMF decreases under similar conditions.

Mechanical, electrical, thermal performances and structure characteristics of flexible graphite sheets

The mechanical, electrical, and thermal performances of flexible graphite sheets (FGS) derived from HClO4-graphite intercalation compounds were characterized by measuring their tensile strength, electrical resistivity, and thermal conductivity. Results show that these performances are closely related to the density of sheets and exfoliated volume (EV) of exfoliated graphite. Enhancing density of sheets tends to improve their in-plane tensile strength, electrical, or thermal performance while using the exfoliated graphite of low EV to prepare sheets is prone to resulting in low in-plane tensile strength but high electrical or thermal performance. The structure characteristics of FGS were characterized by using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The X-ray diffraction results show that the average interlayer spacing of graphite microcrystals for sheets, d 002, is 3.357 A which is the same as that of natural graphite flake, but the stacking height of sheets, Lc, is lower than that of natural graphite. The Raman spectra indicate that sheets has both disorder peak and graphite one and the intensity ratio of them is ca. 0.06, which is almost the same as that of natural graphite, but higher than that of exfoliated graphite.

Some Problems in Printing Standardization

Abstract The lack of standardization of certain factors which enter into the design and use of cylinder printing presses is discussed in a general manner, particularly relative to the standardization of plates and bases, diameters of cylinders, depth of impression surface below cylinder bearers, height of bed bearers, sheets, forms, and names of parts.