Wire Spacing Research Articles

Exchange bias of ordered α-Fe2O3 nanowires: A first-order reversal curve analysis

Ordered α-Fe2O3 nanowires with different gap sizes and diameters were fabricated using SBA-15 as template through varying calcination temperature. The composition, microstructure and morphology of the samples were characterized by XRD, TEM and N2 adsorption–desorption isotherms. The results showed that the α-Fe2O3 replicated the pore channels of SBA-15. The nanowire diameter and wire spacing were controllably changed at different calcination temperatures. ZFC-FC, hysteresis lines and First-order reversal curve (FORC) of the samples were tested at 10 K, 50 K, 100 K, 200 K and 300 K. Exchange bias (EB) was observed under low-temperature field cooling conditions due to the increase of spin disorder on the surface of small size α-Fe2O3 which was freezen into a spin-glass-like phase at low temperature. The influence of the domain states and interactions on EB of α-Fe2O3 were investigated using FORC. The mixed domain states were observed for small size samples at low temperatures. The excitation of EB at low temperatures was proven to be influenced by magnetic interactions.

Analysis of the turbulent flow in a partially blocked wire-wrapped rod bundle using LES with wall functions

One of the most promising nuclear reactor designs is the Liquid-Metal Fast Reactor (LMFR). Its fuel assembly consists of rods containing the fuel material, arranged in a triangular lattice and covered by a hexagonal duct. The rods are separated with wire spacers that are helically wrapped around each fuel pin. Because this geometry is tight and compact, accumulation of debris, cladding deformation or detachment of the wires may generate a partial or total flow blockage of coolant subchannels at different locations. The understanding of the coolant behavior in LMFR fuels under the influence of a partially blocked flow area is required for a thorough safety assessment. A Large Eddy Simulation (LES) with wall functions was executed to simulate the flow on a 61-pin wire-wrapped rod bundle under the presence of a blockage located on the bundle periphery to simulate an abnormal operation condition. The Reynolds number was Re=17000, which is in the turbulent regime. Results of mean velocity and root mean square (rms) fluctuating velocity profiles were compared with PIV experimental data from the Texas A&M Thermal-Hydraulic Research Lab. Both mean and rms velocities were found in reasonable agreement with the experimental data among different locations because the simulation results were within 2σ from the PIV measurements. A pressure form loss coefficient due to the blockage was calculated and found to be Kloss=1.0455. The fluctuating velocities revealed a pair of shear layers that formed on each side of the blockage carrying the highest turbulent intensities. A spectral analysis was conducted to visualize the dominant frequencies on the turbulent flow in the recirculation region. The spatial–temporal two-point cross-correlations based on the fluctuating velocities were calculated at different points along the shear layer and were used to estimate integral lengths scales and convection velocities. The cross-correlations showed larger structures at higher axial elevations from the blockage rear wall. The length scales were found in the range of 3 to 21 mm while the magnitudes of the convection velocities presented values between 0.69U¯in to 1.39U¯in, where U¯in is the inlet velocity. Proper orthogonal decomposition (POD) analysis was utilized to extract the dominant modes in the fluctuating flow. Large flow structures and low frequency time signals were observed for the lowest order modes.

Thermal-hydraulic study in a wire-wrapped 19-rod bundle based on an isotropic four-equation model

The thermal–hydraulic performance of rod bundles with wire spacers is significant for studying Lead–Bismuth Eutectic (LBE) cooled fast reactor. The problem is that using the traditional constant turbulent Prandtl number of 0.85 ∼ 0.9, which is generally derived from the Reynolds analogy hypothesis suitable for conventional fluids, will greatly affect the numerical heat transfer accuracy of LBE having low Prandtl number properties. Thus, a great quantity of development work of four-equation models, which may improve the calculation accuracy of turbulent heat transfer in LBE flows, has been made by researchers, while no commercial code is available. The present work addresses an effort to study the thermal–hydraulic phenomenon in an LBE-cooled 19-rod bundle with wire spacers geometry on a self-compiled CFD solver (iso4eqnFoam), which is implemented by a standard finite volume method and C++ program and developed on OpenFOAM. In particular, the simulation aims to perform fully-developed turbulent stresses and turbulent heat fluxes by solving an isotropic four-equation model, which allows simple zero-fixed-value boundary conditions for turbulent variables and considers the difference between viscous and thermal boundary layer of LBE. The simulation results on a bare 19-rod bundle are first compared with heat transfer experimental data and other simulations to validate the effectiveness of the solver. Then, an LBE-cooled 19-rod bundle with wire spacers is presented with thermal–hydraulic simulations. The result shows that iso4eqnFoam can simulate the turbulent heat transfer of LBE under complex geometry. Finally, the distributions of temperature, temperature fluctuation, and turbulent Prandtl number in the channel of the wire-wrapped rod bundle are reported based on the isotropic four-equation model.

Transparent, High‐Charge Capacity Metal Mesh Electrode for Reversible Metal Electrodeposition Dynamic Windows with Dark‐State Transmission <0.1%

AbstractDynamic windows allow user control over light and heat flow to save energy and maximize comfort. Reversible metal electrodeposition (RME) dynamic windows can uniquely tint to a color‐neutral privacy state (0.1% visible light transmission). The design parameters of transparent metal mesh counter electrodes for high‐contrast RME dynamic windows: high transparency, charge capacity and surface area with low haze, sheet resistance and cost are discussed, concluding that woven metal meshes meet these design parameters. Electroplated current is measured on an indium tin oxide electrode and two meshes with different wire spacings, showing the meshes’ cylindrical geometry enable them to draw more current per square area. The mesh material composition is analyzed to ensure cycling durability in a CuBi electrolyte by developing a transparent mesh with an inert core (stainless steel, SS), a thin Au coating, and a high charge‐capacity (1.5 C cm−2) CuBi outer coating. The study demonstrates that the films maintain a consistent Cu:Bi ratio and optical properties after 250 privacy cycles or 1500 cycles to 10% transmission, showing that the Cu and Bi coating is effective in keeping the films from becoming Cu rich with cycling. Finally, a 100 cm2 device with excellent uniformity and color neutrality is demonstrated.

On the Vertically Stacked Gate-All-Around Nanosheet and Nanowire Transistor Scaling beyond the 5 nm Technology Node.

This work performs a detailed comparison of the channel width folding effectiveness of the FinFET, vertically stacked nanosheet transistor (VNSFET), and vertically stacked nanowire transistor (VNWFET) under the constraints of the same vertical (fin) height and layout footprint size (fin width) defined by the same lithography and dry etching capabilities of a foundry. The results show that the nanosheet structure has advantages only when the intersheet spacing or vertical sheet pitch is less than the sheet width. Additionally, for the nanowire transistors, the wire spacing should be less than 57% of the wire diameter in order to have a folding ratio better than a FinFET with the same total height and footprint. Considering the technological constraints for the gate oxide and metal gate thicknesses, the minimum intersheet/interwire spacing should be in the range of 7 to 8 nm. Then, the VNSFET structure has the advantage of boosting the chip density over the FinFET ones only when the sheet width is wider than 8 nm. On the other hand, the VNWFET structure may have a better footprint sizing than the FinFET ones only when the nanowire diameter is larger than 14 nm. In addition, considering the different channel mobilities along the different surface directions of the silicon channel and also some other unfavorable natures such as more complicated processes, more significant surface roughness scattering, and parasitic capacitance effects, the nanosheet transistor does not show superior scaling capability than the FinFET counterpart when approaching the ultimate technology node.

Turbulent convective heat transfer behavior of supercritical water flowing upward in 2 × 2 rod bundle channels with various spacers

The turbulent flow and heat transfer characteristics of supercritical water, flowing in vertical 2 × 2 rod bundle channel, are numerically investigated to find useful methods to improve the cooling performance in the core of a supercritical water-cooled reactor. The heat transfer behavior as a function of mass flux and inlet temperature is analyzed and discussed. Standard grid and helical wire spacers are added to the channel, and overall heat transfer performance is evaluated and compared. The results indicate that the fuel rods can be cooled more effectively when the fluid temperature is near the pseudocritical point due to the high specific heat capacity at this temperature and pressure, and the local heat transfer coefficient can be improved greatly from the application of grid spacers; however, heat transfer enhancement only happens in limited regions downstream of the grid spacers. By contrast, strong swirl flow can be induced by a helical wire, thus the mixing of coolant is strengthened, and the convective heat transfer is enhanced. However, local hot spots also occur in the region near the wires. Both grid and helical wire spacers will lead to an increase in pressure loss, but the additional pressure drop induced by the helical wire is smaller, hence better comprehensive heat transfer performance is achieved for a wire-wrapped channel. Moreover, heat transfer performance can also be enhanced by reducing the pitch of the spacers. This suggests that applying spacers and optimizing their configurations and structures is helpful to achieving better cooling performance in rod bundle channels.

Experimental study on crushing of concrete columns by high voltage pulse discharge

High voltage pulse discharge (HVPD) crushing tests were carried out on 30 concrete columns with section sizes of 400 mm × 400 mm, 500 mm × 500 mm, 600 mm × 600 mm and 700 mm × 700 mm respectively. Based on the comparative analysis of the electrohydraulic effect and the copper wire explosion on the fracture test of a concrete beam, the latter is determined as the optimal method. The parameters in the test of crushing concrete columns by HVPD include strength grade of concrete, column borehole aperture, hole spacing, discharge voltage and number of copper wires. Columns with sectional dimensions of 400 mm × 400 mm and 500 mm × 500 mm are arranged in single row boreholes, and columns with sectional dimensions of 600 mm × 600 mm and 700 mm × 700 mm are arranged in double rows of boreholes. The results show that the crushing effect of concrete columns increases obviously with the increase of discharging voltage and the number of copper wires, and slightly increases with the decrease of concrete strength. When other parameters are the same, the crushing effect of the concrete columns with hole diameter of 40 mm is better than that of the ones with hole diameter of 50 mm. The crack connectivity of concrete columns with hole spacing of 300 mm is similar to that of the ones with hole spacing of 400 mm. According to the test results, the mathematical expressions of the damage degree of concrete columns with single and double rows of holes (i.e., the width of concrete cracks around boreholes) and the output voltage, the number of copper wires and the strength grade of concrete are established respectively. In order to meet the needs of the project, the suggestion of further crushing construction combined with mechanical method was put forward

Bond Behavior of Deformed Bamboo (Bambusa vulgaris) Embedded in Fly Ash Geopolymer Concrete

As the fastest growing plant with high tensile strength, bamboo provides an excellent alternative material to replace steel reinforcement in a concrete structure. However, the bond of bamboo embedded in concrete is very poor due to its surface properties and swell–shrink behaviors, especially when embedded in ordinary Portland cement concrete (OPCC). Thus, this paper presents the experimental investigation on the bond performance of deformed and undeformed bamboo species of Bambusa vulgaris strips embedded in fly ash geopolymer concrete (FAGC). Undeformed bamboo strips with and without nodes were compared to deformed bamboo strips in a corrugated and Galvanized Iron (G.I) rolled wired form in the pull-out test to study the mechanical interlocking effect on the bond performance of bamboo strips embedded in concrete. The groove on the corrugated bamboo strip was made using a router machine, while the wired bamboo was produced by wrapping the G.I wire along the bamboo strip. The difference in groove and wire spacing of the deformed bamboo strip on the bond strength was also observed. The result showed that the geometry of the bamboo strip had a significant effect on the bond performance, with the deformed bamboo strip outperforming the undeformed bamboo strip. In addition, the utilization of FAGC could also reduce the moisture absorption by the bamboo strip. Thus, these results showed that using bamboo strips in FAGC is feasible, contributing to a promising approach for full utilization of bamboo and industrial waste products such as fly ash as construction materials.

Impact of tension stiffening on the tensile and flexural behavior of ECC ferrocement

Ferrocement is a type of thin walls constructed of hydraulic cement mortar reinforced with closely spaced layers of wire mesh. Although the applications of ferrocement have been common, there has been a limited number of studies on the development of new ferrocement composites. Particularly, premature failure could occur to ferrocement due to the vulnerability of spalling and delamination. Engineered cementitious composite (ECC) is characterized by its ductile strain-hardening behavior and crack width control under direct tension. To enhance the mechanical properties and crack width control of ferrocement, the potential for using ECC to replace cement mortar in conventional ferrocement, termed ECC ferrocement, was explored. The influences of the volume fraction, wire size, and wire spacing of the steel mesh on the mechanical properties of ECC ferrocement under tension and flexure were studied. It was found that while ECC ferrocement had substantially enhanced strength and crack width control compared to pure ECC and conventional ferrocement, there was a relatively limited improvement in the deformation capacity. The test results also showed that the interaction between the embedded steel mesh and the surrounding ECC led to a pronounced tension stiffening effect, which significantly enhanced the uniaxial and flexural strengths of ECC ferrocement. In addition to the experimental study, three flexural models, including a rigorous implicit model and two simplified explicit models, were proposed to evaluate the flexural strength of ECC ferrocement. The comparisons between the experimental results and predicted strengths demonstrated that the proposed three models can reasonably predict the flexural strength of ECC ferrocement with an average error of less than 6% when the tension stiffening of ECC was accounted for. The results of parametric studies indicated that a variation in the ultimate ECC compressive strain ranging between 0.003 and 0.005 for the flexural models led to a negligible influence on the predicted flexural strength.

Investigation of interface profiles in meshed wicks and related evaporation characteristics

The porous wick in a heat pipe determines the working fluid capillary replenishment ability and heat transfer process. To study the evaporation characteristics of meshed wicks fabricated with wires of micron-scale, a mathematical model based on the augmented Young-Laplace equation and molecular kinetic theory to predict the evaporation interface profile is developed, and the Marangoni effect and slip velocity in the boundary are considered. The evaporation interface can be divided into the thin-film region and intrinsic meniscus region according to the ratio of capillary pressure and disjoining pressure. A new solution method considering the constraints at the intersection of the two regions to obtain the interface profile is proposed and validated. Based on the two-dimensional results, the area and heat transfer rates of the two regions formed in the meshed wicks are calculated by integrating along the four side wires. Then, the evaporation characteristics of the thin-film region, including the pressure and thermal resistance distribution, are studied. Finally, the influence of the Marangoni effect, superheat, wire spacing, interface pressure difference and slip velocity on the interface profile and heat transfer of these two regions are discussed.

The influence of four-wire structure on the flow and heat transfer process in supercritical water-cooled reactor fuel assembly

Based on the supercritical water-cooled reactor fuel assembly, a 19-rod bundle physical model with a hexagonal outer casing is established, and the four-wire structure is added to the bare bundle. To analyze the influence of wire spacers on the flow and heat transfer process, numerical investigations of supercritical water in the reactor under design conditions are performed by using the Reynolds stress model with enhanced wall treatment. The results show that the mass redistribution is the main factor affecting the distribution of thermal–hydraulic parameters regardless of the existence of wires. The wire plays a role in weakening the mass redistribution by reducing the cross-flow between the adjacent sub-channels. However, due to the large local hydraulic diameter of the side sub-channels and the sharp change of the supercritical water physical properties, the fluid gradually gathers in the external sub-channels. In addition, the four-wire structure drives the fluid to spiral upwards around the fuel rod, which significantly enhances the convective heat transfer between the fluid and the fuel rod. At the same time, the influence of the local hydraulic diameter on the circumferential non-uniformity is weakened by the wires, and the circumferential wall temperature gradient of the external fuel rod is significantly reduced.

Sub-channel analysis of lead–bismuth fast reactor fuel assembly with wire spacers for China initiative accelerator driven system

The lead bismuth eutectic (LBE) cooled fast reactor fuel assemblies in China Initiative Accelerator Driven subcritical System (CiADS) are supported by wire spacers, and the sub-channel code is a significant analysis method to evaluate the thermal–hydraulic behavior of fuel assemblies. In this study, a sub-channel analysis code for LBE coolant is developed, in which the pressure drop model, turbulent mixing model, and heat transfer model based on LBE are added and applied. Besides, the heat transfer experience of the 61-pin fuel assembly and other sub-channel codes are chosen to verify. Finally, the full-scale simulation of CiADS fuel assembly is calculated. The results show that the thermal–hydraulic parameters of CiADS meet the design criterion. The optimized range of pitch to diameter ratio is 1.133–1.145 according to the thermal–hydraulic analysis. It is recommended to use 37-pin bundle for the numerical simulation simplification of full-scale rod bundles.

Study on the Effects from Spacer Wires on Coolant Flow within a Ciads Fuel Assembly

Study on the Effects from Spacer Wires on Coolant Flow within a Ciads Fuel Assembly

Study on the Effects from Spacer Wires on Coolant Flow within a Ciads Fuel Assembly

Study on the Effects from Spacer Wires on Coolant Flow within a Ciads Fuel Assembly

ОСОБЕННОСТИ ТЕПЛОГИДРАВЛИКИ АКТИВНЫХ ЗОН БЫСТРЫХ НАТРИЕВЫХ РЕАКТОРОВ - НАРАБОТЧИКОВ МАЛОЙ И БОЛЬШОЙ МОЩНОСТИ ДЛЯ СИСТЕМЫ ЗАМКНУТОГО ТОПЛИВНОГО ЦИКЛА

The paper considered the features of heat transfer of two fast sodium reactors of large and low power (1000 and 190 MW(e.)), which are developed for use in the production of secondary nuclear fuel. The design of a case fuel assembly for a higher power reactor is a combination of thin fuel elements (6.1 mm) with U-Pu fuel and a wide grating (relative pitch 1.39) with spacing of the gratings. For a low-power reactor, in this paper, three fuel assemblies (diameter of fuel rod 8.1 mm, relative pitch 1.16) were considered: without a cover, with a cover 1 mm apart from the peripheral row of fuel rods and with a cover spaced 0,5 mm from the peripheral row of fuel rods. Calculations were carried out using the COBRA-IV-I code. Data were obtained on the azimuthal temperature distributions on the claddings of the corner, peripheral and central fuel rods, temperatures on the surfaces of the covers, and calculations were performed to optimize the designs of fuel assemblies in order to reduce the temperature difference on the claddings of the peripheral fuel rods. For a large-power reactor, optimization of the configuration of the corner cell was proposed in order to reduce the azimuthal temperature difference at the corner and peripheral fuel rods. For a low-power reactor, optimization of the fuel assembly design is recommended by replacing the spacer grids with wire spacing and equalizing the temperature field by mixing the coolant, as well as increasing the relative pitch of the fuel element grid from 1.16 to 1.19.

Action mechanism of liquid bridge between electroplated diamond wires for ultrathin wafer slicing

Ultrathin wafer slicing with low kerf loss for electroplated diamond wire sawing is the primary means to improve the productivity in wafering and reduce the manufacturing costs in the photovoltaic industry. Nevertheless, the reduction of the diameter and spacing of the diamond wires makes the liquid bridge action between them significant, which will affect the slicing process. Therefore, based on the principle of minimum potential energy, an analytic model of adhesion caused by the liquid bridge between the diamond wires with protruding abrasives is established in this paper. The variation of the adhesion length with initial wire web gap, wire span, and wire tension as well as wire diameter is analyzed. The results show that the adhesion length was increased with the increase of the wire diameter. The reduction of the initial wire web gap would increase the adhesion length, that was, the limitation of the liquid bridge on the thinner wafers sawing was more obvious. The adhesion length was decreased with the decrease of the wire span or the increase of the wire tension. So it is effective to weaken the limitation of the liquid bridge on the wafers slicing by reducing the wire span or enhancing the wire strength. Then, an experiment on the action of the liquid bridge between the diamond wires was carried out. The theoretical results were in accord with the experimental ones well, and the maximum error was 8.27%. The research work is of great significance to further reduce kerf loss and wafer slicing thickness.

EFFECT OF USING GEOPOLYMER MORTAR IN FERROCEMENT BY VARYING THE COMBINATION, NUMBER AND SIZES OF MESHES

Globally, Cement production contributes about 1.6 billion tons of CO2 or about 7% of global loading of CO2 into the atmosphere. The manufacture of Cement Releases Carbon dioxide that is significant contributor of Green house gas emissions to the atmosphere. So there was a need to develope and use eco-friendly material having similar properties as like of cement mortar. Geopolymer is produced without the presence of cement as a binder; instead, the base material such as fly ash, that is rich in Silicon (Si) and Aluminium (Al), is activated by alkaline solution to produce the binder. Hence Geopolymer mortar can be used instead of cement mortar which will have no adverse effect on our environment. Ferrocement is a composite material formed by closely spaced wire mesh which uses wire meshes as reinforcement and filled with rich cement mortar. Experimental investigation was carried out to study the effect of Geopolymer mortar in Ferrocement for variation in mesh size and number of layers. For this, tensile testing was done on Geo-ferrocement specimens of size 750 x 60 x 30 mm reinforced with single, double, triple layer using variation in meshes of different sizes. Similarly, compression testing of cubical specimens of side 70 mm reinforced with single, double, triple layer of meshes sizes was done. Results indicated an significant increase in tensile strength and compressive strength of specimens with increase in number of layer of meshes. Test results also provided the most suitable combination and size of mesh to be used for obtaining the maximum strength of different sizes was done.

Optimal Determination Method of the Transposition Steps of An Extra-High Voltage Power Transmission Line

During the design of extra-high-voltage transmission lines, studies of the influence of asymmetry due to the phase difference of the parameters on its processes and the electrical network were performed. To compensate for this source of asymmetry for transmission lines longer than 100 km, a relatively simple technical means was proposed and implemented—phase transposition (change of the mutual location of phase wires in space). However, at the same time transposition causes additional capital costs in construction and reduces reliability during operation, so when designing a specific transmission line, extra-high-voltage is desirable to evaluate the effectiveness of the use of this measure in the real electricity network. Thus, under certain conditions, even for a transmission line 600 km in length, it was possible to perform either an incomplete transposition cycle, or abandon this measure altogether.

Optimization design and prediction of the snow-melting pavement based on electrical-thermal system

Electrically heated roads are used as a substitute for chemicals and mechanical devices to ensure mobility and traffic safety in winter weather. This paper aims to design an electrical-thermal system and recommends the best system parameters based on the melting efficiency, energy costs and mechanical durability of the pavement. In addition, the snow melting effect was verified experimentally according to the recommended parameters and the accuracy of the electrical-thermal system was predicted and evaluated by back-propagation neural network. Experiment results indicate that the 24 K Teflon‑carbon fiber heating wire is suitable for the road heating system. It can provide a stable heat source and has the characteristics of high temperature/pressure resistance during the asphalt mixture molding and rolling process. The system parameters were recommended based on snow melting efficiency and mechanical durability of the pavement such as temperature stress and temperature uniformity. The optimal heating wire spacing is 10 cm, set heating wire depth as 4 cm, besides, the heating wire power can be determined based on energy consumption, and actual environmental conditions. The recommended parameters were used for snow melting laboratory experiments to verify the validity of the electrical-thermal system. Finally, the temperature trend of this system can be predicted and evaluated well with high accuracy by the back-propagation neural network. The research enriches the theory of thermodynamic structural design for snow melting pavement systems.

Reliability of computer structures of integrated modular avionics for hardware configurations

The problem of designing advanced computing systems in the class of structures of integrated modular avionics is considered. The unified topology of the internal network of the computer on the basis of Space Wire exchange channels and variants of its execution for various onboard applications is offered. Equivalent reliability schemes of each of the specific structures are introduced and the probabilities of trouble-free operation of each structure are analyzed. Families of graphic dependencies are given. The analysis of the existing principles and algorithms for testing multiprocessor multimodal onboard digital computer systems is given; the new testing algorithm for the multiprocessor systems which follows the software design standards for products of integrated modular avionics is offered. The structure of the unified automated workplace for checking the functional modules of integrated modular avionics is considered. Specific requirements inherent in the workplaces for testing integrated avionics are identified: an increased level of control of the hardware component of products; the ability to simulate the failure state of individual components of avionics to check the mode of reconfiguration of the computer system; modular construction of software with the division of verification tests into components performed at the level of each CPM and the computer as a whole in single-task and multitasking modes; openness of architecture of a workplace, which provides an ability to change the level of control complexity of a product and control of one class of complexity; intra-project unification of both hardware and software of the workstation of the inspection.