Search

In the existing investigation, the influence of wire-cut electrical discharge machining (WEDM) input factors such as pulse-on time, pulse-off time, wire tension, and taper angle on the material removal rate (MRR) on Inconel 825 was investigated. Experimental trials were performed according to the central composite design (CCD). An ANOVA test was conducted to evaluate the influence of the most significant WEDM process input parameter. The optimization of the response was achieved using the desirability approach to attain the maximum MRR. The optimum setting conditions were obtained as Ton of 0.8 µs, Toff of 38 µs, wire tension of 14 N, and taper angle of 2° for the MRR value of 2.98 g/min with a desirability of 1. Finally, the 3D surface plots were used to illustrate the variations of the output response with respect to input parameters. [ABSTRACT FROM AUTHOR]

This paper describes a crystal growth system employing novel concepts in fabrication of a high temperature furnace, thermocouples and a novel crystal pulling mechanism. This has reduced the costs substantially, without compromising the quality of grown crystals. The core of the furnace, a wooden cylindrical dummy had been prepared with equi-spaced helical groves with widths equaling the diameter of the heating wire on its outer surface machined by a lathe machine. The Kanthal heating wire was wound in the groves. It was covered with a thick layer of natural clay available locally. After the clay had dried up, an electric current was passed through the heating wire and the wooden frame was burnt out. A thick layer of the clay was applied on the inner and the outer surfaces. The furnace can operate at temperatures up to about 1000 °C. The temperature was measured with a chromel-alumel thermocouple prepared by an ingenious spot-welding technique established in the laboratory. The seed holder was hanged above the melt kept in the crucible with help of a float kept in a water container, which has a small tap at the bottom. When the tap is opened the float goes down and the seed assembly goes up. In this manner a quality pulling system, without any motor has been developed and reported here. It has been possible to grow good quality crystals of potassium chloride with excellent diameter control. [ABSTRACT FROM AUTHOR]

We discuss the effect on the transient dynamics of the Richtmyer–Meshkov instability due to small-scale perturbations introduced by a set of solid circular cylinders located along the material interface. The arrangement of the cylinders mimics (in a two-dimensional domain) the presence of the solid supporting grid wires used in the formation of the material interface in an experimental setup. The numerical experiments are performed by utilizing an embedded boundary adaptive mesh refinement method. We quantify the effect of introducing the cylinders on the mixing layer growth and the mixedness level and qualitatively demonstrate the effect of the perturbation introduced by the cylinders on the mixing layer structure. We empirically model the effect of the solid cylinders based on their diameter and find that the effect of the cylinders on the mixing layer growth is a linear function of the cylinder diameter. The linear model allows us to predict the change in the mixing layer growth within a ± 10 % range, except for very small ratios of the initial perturbation amplitude of the density interface to the cylinder diameter. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan University of Science & Technology, Natural Science is the property of Editorial Office of Journal of Henan University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Distributions of temperature and residual stress of the deposition bead and the substrate during a wire feeding type direct energy deposition (DED) process are crucial to avoid undesired thermal effects and premature failure of the fabricated part due to repeated heating and cooling cycles during successive deposition. The goal of the paper is to investigate the influence of process parameters on distributions of temperature and residual stress of the deposited bead and the substrate for a single layer deposition through thermo-mechanical finite element analyses (FEAs). Ti-6Al-4V is chosen as the material of the wire. The effects of the power of the laser, the travel speed of the table and the length of the bead on the formation of the heat affected zone (HAZ) and the stress influenced region (SIR) are quantitatively examined using the results of FEAs. From the results of the examination, an appropriate gap between adjacent beads for successive deposition is proposed to reduce undesirable thermal effects and residual stress of the part fabricated by the Ti-6Al-4V wire feeding type DED process. [ABSTRACT FROM AUTHOR]

We determine possible causes of premature failures of typical reinforcing ropes of the protective shells of nuclear power plants with regard for the mechanical parameters of wires, the character of damages to their surfaces, and the fractal dimensions of the fracture surfaces. It is shown that brittle fracture is realized for lower levels of plasticity of the metal of wires and lower degrees of its damage. This type of fracture is characterized by a higher fractal dimension of the fracture surfaces. [ABSTRACT FROM AUTHOR]

The formation of a fluoropolymer coating by chemical deposition has been studied experimentally. It has been found that increasing the flow rate of the precursor gas leads to a decrease in the growth rate of the coating. Deposition conditions were analyzed, and the gas-dynamic parameters of the process were estimated. The estimates are consistent with experimental data. [ABSTRACT FROM AUTHOR]

The direct simulation Monte Carlo method was used to study plane-parallel flow of hydrogen through an obstacle formed by a series of parallel infinite wires. Particular attention was paid to the influence of the geometric parameters of the wire obstacle, the degree of rarefaction, and the flow velocity on the degree of hydrogen dissociation due to heterogeneous reactions on the wire surface. [ABSTRACT FROM AUTHOR]

Helical wire spacers are widely used in sodium cooled fast reactors. One of the main effects of wire spacers is enhancing the inter-channel cross flow in triangular arrayed rod bundles. To study the characteristic of sweeping flow rate across the gaps between the sub-channels, the computational fluid dynamics (CFD) method is used in the present study to analyze the flow field in a 19-rod bundle with wire wraps. This CFD work only considers the fluid zone of one section of the rod bundle. The height of the CFD model with periodic inlet and outlet boundary conditions is one wire pitch. The k - ω SST model is used as the turbulent model. The wire effect on the velocity distribution of the flow across the interface between two sub-channels is investigated in the CFD study. Based on the force balance equation between the wire wake force and the surface friction force of rods in the circumferential direction, a theoretical model for estimating the average swirling flow rate driven by one single wire is proposed. The simulation shows that the ratio of rod pitch ( P ) to rod diameter ( D ) has a strong effect on the velocity of the sweeping flow. The flow rate increases with the P / D ratio. The simulation agrees well with the proposed model. In addition, the effect of the ratio of wire pitch ( H ) to rod diameter has also an influence on the cross flow rate: A small H / D ratio leads to higher cross flow rate. A correlation as a function of both P / D ratio and H / D ratio is proposed to predict the sweeping flow velocity by the present study. [ABSTRACT FROM AUTHOR]

The physical process of electrical explosion of wires in vacuum is featured with the surface discharge along the wire, which generates the corona plasma layer and terminates the Joule heating of the wire core. In this paper, a fiber-array probe was designed to directly measure the radiation of surface arc with spatial and temporal resolution. The radiation of the exploding wire was casted to the section of an optical-fiber-array by a lens and transmitted to PIN diodes and finally collected with an oscilloscope. This probe enables direct diagnostics of the evolution of surface discharge with high temporal resolution and certain spatial resolution. The radiation of a tungsten wire driven by a positive current pulse was measured, and results showed that surface discharge initiates near the cathode and propagates toward the anode with a speed of 7.7 ± 1.6 mm/ns; further estimations showed that this process is responsible for the "conical" structure of the exploding wire. [ABSTRACT FROM AUTHOR]

Transverse flow induced by helical spacer wires has important effects on the flow and heat transfer behavior of reactor core. In this paper, transverse flow in a wire-wrapped hexagonal seven-pin bundle was simulated by the open source code, OpenFOAM, based on computational fluid dynamic (CFD) method. The Shear Stress Transport (SST) k-ω model and Spalding wall function were used to resolve the momentum field. Hexahedral dominated meshes were generated to achieve high grid quality. Periodic boundary condition and parallel processing were adopted to save the computational cost. Transverse velocity distributions in four different kinds of subchannel gaps were analyzed. The results show that the influence of wire number and position on the transverse velocity distribution is obvious. For an interior gap, transverse flow seems to be dominated by wires near the gap, and its direction changes periodically in one helical pitch. However, for a peripheral gap, transverse velocity is affected by more wires and its direction is decided by the direction of wire rotation. Parameter studies reveal that the Reynolds number ( Re , at the range of 6000–100,000) has little effect on the normalized transverse flow, while the pitch to pin diameter ratio ( P/D , at the range of 1.11–1.22) and the helical pitch to pin diameter ratio ( H/D , at the range of 12–24) have a great influence on it, especially the P/D . Large discrepancies between our simulation results and some existing correlations were observed. This indicates that new correlations comprehensively considering both P/D and H/D effects need to be developed in future. [ABSTRACT FROM AUTHOR]

In this contribution, a thermodynamically consistent and mathematically canonical modelling framework for the investigation of the cyclic thermomechanical behaviour of Nickel-Titanium shape memory alloy wires is developed. Particular focus is placed on the self-heating of the material subjected to multiple load cycles. The relatively high load rates necessitates the consideration of inertia terms, the applied load amplitudes of six percent strain motivates the use of a non-linear, Hencky-type strain measure. Comparisons of the results with experimental data on the one hand reveal reasonable results and on the other hand underline the necessity of further model enhancements. [ABSTRACT FROM AUTHOR]

We report on the construction and performance of a scanner using a collimated x-ray beam to find the positions of wires, straws, slots and spheres. The technique is based on measuring the transmission rate of the beam, and their positions can be determined ~25 μm accuracy. The spheres or slots attached to the detector can also be optically surveyed externally to transfer the coordinates of wires and straws to other detector systems. The scanner was developed for the Mu2e straw tracker but may have a wide range of applications. [ABSTRACT FROM AUTHOR]

A typical emitter contact of an IGBT consists of a front metallization and bond wires. In this study, the power cycling performance of a special emitter contact design is experimentally verified. The emitter contact includes a metal plate, which is Ag-sintered to the metallization and wire bonded on the top surface. Either Cu or Al bond wires were implemented. Power cycling tests were performed to investigate the performance of such IGBT modules. The results were very promising and a cycling lifetime was achieved, which is about 20 times higher than the lifetime of typical IGBT modules. For a better understanding of the experimental results, the electrical and thermal response of the IGBT modules were simulated by FEM. The results of this study, provide a key for high-reliability designs of the emitter contact of IGBT modules with superior power cycling capability. [ABSTRACT FROM AUTHOR]

Abstract: Simultaneous development of flow and temperature fields in the entrance region of fast breeder reactor (FBR) fuel pin bundles with helical spacer wires has been investigated by three-dimensional computational simulations. The Reynolds number, pitch of helical spacer wire and number of pins in the bundle are systematically varied. It is found that the magnitude of mean cross-stream velocity in the fully developed region is inversely proportional to the helical pitch length and it is nearly independent of the number of pins. But, there is a strong correlation between the locations of spacer wire and the peak cross-stream velocity. Flow attains full development at an axial length of 70 times hydraulic diameter in all the cases and this length is found to be unaffected by the helical pitch length. Friction factor is seen to fluctuate periodically over a mean value and the fluctuation over each helical pitch corresponds to a specific position of helical wire. The mean value of the friction factor in the entrance region reduces below the mean value in the fully developed region contrary to that seen in ducted flows. The mean fully developed friction factor is inversely proportional to the helical pitch. But, it is independent of the number of pins in the bundle. The Nusselt number passes through multiple minima before attaining fully developed periodic fluctuations and its development is slower than that of friction factor. For larger number of pins thermal development length is larger. Traditionally, the correlations reported for fully developed flow are considered for core design. But, the present study indicates that this approach is not conservative. Further, the entrance region effects and the oscillations in the fully developed region have to be properly accounted in the core design. Nusselt number exhibits a strong dependence on helical pitch similar to that of friction factor. A correlation for Nusselt number is proposed as a function of helical pitch and other influencing parameters. The hotspot factor in the pin bundle is found to vary from 3 to 4. Further, it increases, when either Reynolds number is low or the number of pins is more. [Copyright &y& Elsevier]

Highlights: [•] A CFD model is benchmarked against the ORNL 19-pin Sodium Test assembly. [•] Sensitivity was tested for cell size, turbulence model, and wire contact model. [•] The CFD model was found to be appropriately representing the experiment. [•] CFD was then used as a predictive tool to help understand experimental uncertainty. [•] Comparison to subchannel results were carried out as well. [ABSTRACT FROM AUTHOR]

Highlights: [•] A 3D momentum source model is developed for the wire-wrapped bundles. [•] The concept is examined in 7 pin and 37 pin bundles steady state simulations. [•] The validity of the model is confirmed by mesh and parameter sensitivity studies. [•] The model is applied to transient simulations of a 61-pin EBR-II subassembly. [•] Significant computing resources are saved with the developed MSM. [ABSTRACT FROM AUTHOR]

Abstract: Friction pressure drop correlation equations are derived from a numerical study by characterizing the pressure drop phenomena through porous medium of both types namely stacked and wound woven wire matrices of a Stirling engine regenerator over a specified range of Reynolds number, diameter and porosity. First, a finite volume method (FVM) based numerical approach is used and validated against well known experimentally obtained empirical correlations for a misaligned stacked woven wire matrix, the most widely used due to fabrication issues, for Reynolds number up to 400. The friction pressure drop correlation equation derived from the numerical results corresponds well with the experimentally obtained correlations with less than 5% deviation. Once the numerical approach is validated, the study is further extended to characterize the pressure drop phenomena in a wound woven wire matrix model of a Stirling engine regenerator for a diameter range from 0.080 to 0.110mm and a porosity range from 0.472 to 0.638 within the same Reynolds number range. Thus, the new correlation equations are derived from this numerical study for different flow configurations of the Stirling engine regenerator. The results indicate flow nature and complex geometry dependent friction pressure drop characteristics within the present Stirling engine regenerator system. It is believed that the developed correlations can be applied with confidence as a cost effective solution to characterize and hence to optimize stacked and woven Stirling engine efficiency in the above specified ranges. [Copyright &y& Elsevier]

CdTe wires have been fabricated via a catalyst free method using the industrially scalable physical vapor deposition technique close space sublimation. Wire growth was shown to be highly dependent on surface roughness and deposition pressure, with only low roughness surfaces being capable of producing wires. Growth of wires is highly (111) oriented and is inferred to occur via a vapor-solid-solid growth mechanism, wherein a CdTe seed particle acts to template the growth. Such seed particles are visible as wire caps and have been characterized via energy dispersive X-ray analysis to establish they are single phase CdTe, hence validating the self-catalysation route. Cathodoluminescence analysis demonstrates that CdTe wires exhibited a much lower level of recombination when compared to a planar CdTe film, which is highly beneficial for semiconductor applications. [ABSTRACT FROM AUTHOR]

The article lists the members of the editorial board for the journal "Wires Computational Molecular Science" including editor-in-chief Peter R. Schreiner, associate editors Wesley D. Allen and Modesto Orozco.

Robustness of edge states and non-Abelian excitations of topological states of matter promises quantum memory and quantum processing, which are naturally immune to microscopic imperfections such as static disorder. However, topological properties will not in general protect quantum systems from time-dependent disorder or noise. Here we take the example of a network of Kitaev wires with Majorana edge modes storing qubits to investigate the effects of classical noise in the crossover from the quasistatic to the fast fluctuation regime. We present detailed results for the Majorana edge correlations, and fidelity of braiding operations for both global and local noise sources preserving parity symmetry, such as random chemical potentials and phase fluctuations. While in general noise will induce heating and dephasing, we identify examples of long-lived quantum correlations in the presence of fast noise due to motional narrowing, where external noise drives the system rapidly between the topological and nontopological phases. [ABSTRACT FROM AUTHOR]