Improvement Of Uniformity Research Articles

Numerical study on variable aperture extraction grids of a titanium hydride cathodic vacuum arc ion source

Titanium hydride cathodic vacuum arc ion sources are widely used in particle accelerators, neutron sources, etc. For the application in neutron sources, higher H+/D+ fraction and higher beam uniformity are preferred. In this work, to improve the beam uniformity of a miniature titanium hydride cathodic vacuum arc ion source, a new scheme of variable aperture extraction grids is proposed. A 2D numerical model is developed for the investigation of the variable aperture extraction grids. Numerical results indicate that the extraction grid plays important roles in the titanium hydride cathodic vacuum arc ion source that can improve the stability of ion source. Moreover, simulated results show that the designed variable aperture extraction grids can reduce the beam nonuniformity to less than ±10%, while the beam nonuniformity of the fixed aperture extraction grids are between ±22% and ±37%. Thus, the presented work can provide a potential reference for the improvement of beam uniformity of the vacuum arc ion sources.

Uniformity improvement of a reconstructed-holographic image in a near-eye display system using off-axis HOE.

When a near-eye display (NED) device reproduces an image at a location close to the eye, the virtual image is implemented at a large angle. The uniformity of the image is unbalanced due to the change in diffraction efficiency by the hologram recording angle and angular selectivity. This study proposes a method for implementing an optimal uniform image by analyzing the diffraction efficiency and the reconstructed image was analyzed using angular selectivity generated while reproducing the source point of the diffused image as an intermediate element by holographic optical element (HOE). This research provides practical results for displaying high diffraction efficiency and immersive holographic images in the NED system with HOE as uniformed intermediate elements.

Thermal uniformity enhancement of the motorcycle exhaust thermoelectric generator—Part 2: Muffler outlet optimization

AbstractFollowing the development of the muffler with the optimal guide fins (MOGF) in the companion paper (Part 1), this study optimizes the muffler outlet in terms of structure and geometry to further improve the thermal uniformity of the hot‐side heat exchanger (HHE). Two outlet structures and two outlet geometry parameters (i.e., outlet angle φ and outlet position y) are proposed. The exhaust flow uniformity of HHE serves as an assessment criterion in numerous computational fluid dynamics simulations to determine the optimal outlet structure and optimal values of φ and y. The outlet of the MOGF is then modified based on the simulation results to create the muffler with the optimal guide fins and outlet (MOGFO). Various experiments on the MOGFO are conducted to verify the simulation results and evaluate the improvement of the HHE's thermal uniformity. The simulation results prove that the optimal outlet improves the exhaust flow uniformity by 1.78% on average compared with the original outlet. In experiments, the combination of optimal muffler's outlet and optimal muffler's guide fins on the MOGFO raises the thermal uniformity of HHE by an average of 22.71% and 50% compared with the MOGF and the muffler model with nonoptimal guide fins and outlet in Part 1, respectively. The remarkable outcomes of this paper, together with Part 1, are expected to enhance the efficiency and lifespan of the thermoelectric generator unit.

Influence of different etching methods on the structural properties of porous silicon

PurposePorous silicon (Si) was fabricated by using three different wet etching methods, namely, direct current photo-assisted electrochemical (DCPEC), alternating CPEC (ACPEC) and two-step ACPEC etching. This study aims to investigate the structural properties of porous structures formed by using these etching methods and to identify which etching method works best.Design/methodology/approachSi n(100) was used to fabricate porous Si using three different etching methods (DCPEC, ACPEC and two-step ACPEC). All the samples were etched with the same current density and etching duration. The samples were etched by using hydrofluoric acid-based electrolytes under the illumination of an incandescent lamp.FindingsField emission scanning electron microscopy (FESEM) images showed that porous Si etched using the two-step ACPEC method has a higher porosity and density than porous Si etched using DCPEC and ACPEC. The atomic force microscopy results supported the FESEM results showing that porous Si etched using the two-step ACPEC method has the highest surface roughness relative to the samples produced using the other two methods. High resolution X-ray diffraction revealed that porous Si produced through two-step ACPEC has the highest peak intensity out of the three porous Si samples suggesting an improvement in pore uniformity with a better crystalline quality.Originality/valueTwo-step ACPEC method is a fairly new etching method and many of its fundamental properties are yet to be established. This work presents a comparison of the effect of these three different etching methods on the structural properties of Si. The results obtained indicated that the two-step ACPEC method produced an etched sample with a higher porosity, pore density, surface roughness, improvement in uniformity of pores and better crystalline quality than the other etching methods.

Using Gas Counter Pressure and Combined Technologies for Microcellular Injection Molding of Thermoplastic Polyurethane to Achieve High Foaming Qualities and Weight Reduction.

Microcellular injection molding technology (MuCell®) using supercritical fluid (SCF) as a foaming agent offers many advantages, such as material and energy savings, low cycle time, cost-effectiveness, and the dimensional stability of products. MuCell® has attracted great attention for applications in the automotive, packaging, sporting goods, and electrical parts industries. In view of the environmental issues, the shoe industry, particularly for midsole parts, is also seriously considering using physical foaming to replace the chemical foaming process. MuCell® is thus becoming one potential processing candidate. Thermoplastic polyurethane (TPU) is a common material for molding the outsole of shoes because of its outstanding properties such as hardness, abrasion resistance, and elasticity. Although many shoe manufacturers have tried applying Mucell® processes to TPU midsoles, the main problem remaining to be overcome is the non-uniformity of the foaming cell size in the molded midsole. In this study, the MuCell® process combined with gas counter pressure (GCP) technology and dynamic mold temperature control (DMTC) were carried out for TPU molding. The influence of various molding parameters including SCF dosage, injection speed, mold temperature, gas counter pressure, and gas holding time on the foaming cell size and the associated size distribution under a target weight reduction of 60% were investigated in detail. Compared with the conventional MuCell® process, the implementation of GCP technology or DMTC led to significant improvement in foaming cell size reduction and size uniformity. Further improvement could be achieved by the simultaneous combination of GCP with DMT, and the resulting cell density was about fifty times higher. The successful possibility for the microcellular injection molding of TPU shoe midsoles is greatly enhanced.

Influence of drying process on the aluminosilicate fiber hot gases filter element properties

The influence of drying process on the properties of ceramic filter elements for industrial high-temperature gases purification was studied. Filter elements were based on aluminosilicate fiber manufactured via vacuum filtration with the following molding and machining of the workpiece, it's treatment with a colloidal silicon oxide sol binder, and drying with the employment of various processes. Convective drying (CD), microwave drying (MWD) and filter element freezing followed by convective drying (FCD) processes were employed to study the related binder migration and its effect on filter properties. Diffusional redistribution of the binder through the thickness of the filter element's wall decreases in the series CD→FCD→MWD with the accordingly observed improvement of the structural uniformity and mechanical strength of the filters. The tensile strength of samples dehydrated via convective drying, freezing followed by convective drying and microwave drying, all of which then heat-treated at 1000 °C (the assumed maximum operating temperature), is 0.35 MPa, 0.57 MPa and 0.48 MPa, respectively. The pressure drop measured at the specific air flow of 100 m3/m2 is respectively 700Pa, 490Pa and 410Pa.

Thermal uniformity enhancement of the motorcycle exhaust thermoelectric generator—Part 1: Guide fins optimization

AbstractIn this study, the hot‐side heat exchanger (HHE) thermal uniformity in the thermoelectric generator unit (TGU) is enhanced by optimizing the muffler's guide fins. Three parameters of the guide fins (i.e., fin gap δ, fin angle θ, and fin position x) are proposed. Various muffler models with different guide fins’ geometry are numerically investigated to achieve the optimal set of δ, θ, and x parameters by assessing the exhaust flow uniformity of the HHE. The optimal muffler model is then simulated to compare with the nonoptimal muffler model. The HHE's thermal uniformity of these two models is experimentally investigated under various testing conditions. The results show that the parameters of δ and θ significantly affect the exhaust flow uniformity of the HHE, whereas the variable of x only has a minor influence. Thanks to the optimal values of δ, θ, and x, the exhaust flow uniformity increases 11.23% on average compared to the nonoptimal model. Consequently, the thermal uniformity is improved, and the maximum temperature difference on the HHE of the optimal model is 35% lower on average than that of the nonoptimal model. The improvement in thermal uniformity resulting from this study is expected to increase the performance and lifespan of the TGU.

Automatic variable rate fertilisation system for improved fertilisation uniformity in paddy fields

China currently relies on manual labour to fertilise paddy fields, hindering the improvement of fertilisation uniformity, management efficiency, and fertiliser use efficiency. Following a drastic decrease in the availability of agricultural labour, fertilisation operations are facing increasing labour costs and low reliability rates and this is threatening food security. This study developed an automatic fertilisation system suitable for pipe and canal irrigation systems in paddy fields, which measures the irrigation flowrate every second and adjusts the variation of the fertiliser flowrate to maintain a steady water-fertiliser ratio ( WFR ). An inexpensive single-chip microcomputer was used as the core of the system for precise control and tests were conducted to check its performance in concentration control. Results show that the fertilisation system developed in this study steadily controlled fertiliser concentration with a normalised mean absolute error ( NMAE ) ranging from 0.15% to 0.58% and from 0.22% to 0.63% for the tested pipe and canal irrigation systems, respectively. The fertiliser flowrate was adjusted to the irrigation flowrate instantly and accurately, with a maximum deviation of 0.56% in the WFR . This system drastically improved fertilisation uniformity compared to manual fertilisation, and had a Christiansen uniformity coefficient of 96.30%; a distribution uniformity of 0.93, and a coefficient of variation of 0.05. It also decreases labour costs, reduces potential pollutions and increases management efficiency. Thus, it can improve fertiliser use efficiency and contribute to the development of precision agriculture. • Automatic fertilisation system for paddy fields developed based on an SCM. • System is suitable for both pipe and canal irrigation systems. • Fertilisation is controlled by irrigation flowrate and responds to its change. • Fertiliser was applied with great precision and distributed uniformly in the field. • Proposed system can improve fertiliser use efficiency and reduce manual labour.

Improvement of uniformity of biocemented sand column using CH3COOH-buffered one-phase-low-pH injection method

Improvement of uniformity of biocemented sand column using CH3COOH-buffered one-phase-low-pH injection method

Effect of fluid distribution along the channel length on the cooling performance of microchannel heat sink

Purpose The purpose of this study is to conduct research on a new kind of division microchannel heat sink (D-MCHS), which can distribute cooling water along the channel-length direction. First, the pressure drops in the D-MCHS with different division region numbers were compared. Then, the cooling performance of the D-MCHS with different division region numbers was also comparatively investigated. Finally, the temperature distribution on the bottom surface of the D-MCHS was analyzed. Design/methodology/approach First, experiments were conducted to investigate the numerical calculation method. Then, a three-dimensional steady, single-phase, laminar flow and solid-fluid conjugate heat transfer numerical model was used to research the flow and heat transfer characteristics in microchannels. Findings The pressure drop in the D-MCHS could be reduced by increasing the number of divided flow regions along the channel-length direction. The bottom average temperature of the D-MCHS could be simultaneously affected by the number of divided flow regions and the water flow rate. The thermal uniformity performance of the D-MCHS could be improved by increasing the number of division flow regions. The number of low-temperature and high-temperature areas on the bottom surface of the D-MCHS is corresponding to the division flow region number. Originality/value The D-MCHS exhibited a positive effect on the pressure drop decrease and thermal uniformity improvement. It not only keeps the electronic module working in a secure temperature environment but also consumes less pump power for a lower pressure drop.

Numerical investigation and optimization of flat plate transpiration-film combined cooling structure

To improve the limited overall cooling effectiveness of laminated structure with the increase of coolant under larger Bi-number, a new optimized structure named transpiration-film combined cooling structure is proposed for the thermal protection of aero-engine combustion chamber. By replacing the lower impingement plate of the laminated structure with a porous layer, a desirable outside film coverage are achieved and the internal heat transfer is enhanced owing to the blocking effect and the large specific surface area of the porous layer. Accurate mathematical modeling and fully-coupled numerical approach are adopted to investigate and compare the cooling effectiveness, cooling uniformity, and the effect of skin friction reduction of the combined cooling structure and the laminated cooling structure under practical combustor conditions with larger Bi-number. The results show that the combined structure brings about a 30% increment in overall cooling effectiveness and a considerable improvement in temperature uniformity of the whole structure, and moreover, the frictional resistance on the structure surface is greatly reduced. Furthermore, an automatic single-objective optimized method is adopted to obtain optimal schemes of the combined cooling structure under a practical combustion chamber working condition, powerfully promoting the cooling effectiveness by 8.5%–8.7%. This work aims to provide the designers of aero-engine with a valuable reference for searching the thermal management approach with high efficiency and low frictional resistance.

Improvement of plasma uniformity and mechanical properties of Cr films deposited on the inner surface of a tube by an auxiliary anode near the tube tail

In order to improve the length of plasma in a whole tube and mechanical properties of Cr films deposited on the inner surface of the tube, a high-power impulse magnetron sputtering coating method with a planar cathode target and auxiliary anode was proposed. The auxiliary anode was placed near the tube tail to attract plasma into the inner part of the tube. Cr films were deposited on the inner wall of a 20# carbon steel tube with a diameter of 40 mm and length of 120 mm. The influence of auxiliary anode voltage on the discharge characteristics of the Cr target, and the structure and mechanical properties of Cr films deposited on the inner surface of the tube were explored. With higher auxiliary anode voltage, an increase in substrate current was observed, especially in the tube tail. The thickness uniformity, compactness, hardness and H/E ratios of the Cr films deposited on the inner surface of the tube increased with the increase in auxiliary anode voltage. The Cr films deposited with auxiliary anode voltage of 60 V exhibited the highest hardness of 9.6 GPa and the lowest friction coefficient of 0.68.

Combining Functional Prototyping of 3D Printed Reactors with a Modular Reactor Setup for Continuous Emulsion Polymerization

AbstractThe potential for fast and specific process optimization by functional prototyping with 3D printed reactors was shown for a known continuous emulsion polymerization in a modular setup. Three tubular reactors, two with static mixing elements and a continuously stirred tank reactor (CSTR) were printed from polylactic acid. Thermal imaging of the reactors allows to map the basically adiabatic progress of the redox‐started radical polymerization in a space‐resolved way. The application of static mixing elements led to a higher conversion stability and a more uniform product, as expected for a better mass transfer. Polymerization in combinations of CSTR and a tubular reactor showed further improvements of process stability and product uniformity in terms of particle size and mol masses.

Study on dispersion uniformity and performance improvement of steel fibre reinforced lightweight aggregate concrete by vibrational mixing

Steel fibres (SFs) easily cluster at high dosages during mixing, which directly limits the performance of concrete. Recently, vibrational mixing has provided a novel perspective to overcome the defects of ordinary mixing. However, the influence of vibration effects on steel fibre reinforced lightweight aggregate concrete (SFRLAC) has not been investigated. In this paper, SFRLAC was prepared based on ordinary mixing and vibrational mixing, respectively. Different volume dosages of SFs (0%, 0.5%, 1.0%, 1.5% and 2.0%) were selected as variables. The flowability test, the dry density test and the mechanical properties test were used to characterise the macroscopic performance of the concrete. After the macroscopic test of SFRLAC, the distribution and orientation of SFs were quantified by integrated digital image processing (DIP) technology. The interfaces of the SFs and the cement matrix were characterised by environmental scanning electron microscopy (ESEM). The obtained results revealed that vibrational mixing could improve flowability. Meanwhile, it can increase the compressive strength and flexural toughness of SFRLAC continuously after SFs volume exceeds 1.0%. Moreover, the technology was conducive to dispersing SFs at high dosages and made the orientation more consistent than the ordinary mixing. Notably, a dense paste film appeared on the fibre surface, suggesting a significant improvement in the load capacity. Thus, vibrational mixing can be used to prepare the reinforced concrete with high SFs contents.

A novel variable-height-pinfin isothermal heat sink for densely-packed concentrated photovoltaic systems

A major limitation of liquid cooling is that the temperature of the coolant rises down the stream, which gradually reduces the heat transfer from the heat source to the coolant causing a large temperature gradient (or temperature non-uniformity) along the flow direction. In this study, a technique has been presented to efficiently minimize the temperature non-uniformity of liquid-cooled heat sinks by incorporating simple geometrical modifications. The technique is demonstrated for a densely-packed concentrated photovoltaic module (CPV) by using a heat sink with cylindrical pinfin microstructures. Several cases of the proposed variable height pinfin (VHP) heat sink were investigated by systematically varying the height of pinfin rows to gradually reduce the heat transfer near the inlet zone while keeping the heat transfer near the outlet zone as close as possible to the conventional uniform height pinfin (UHP) heat sink. The heat sinks were designed for a CPV module consisting of an array of 5 × 5 multi-junction photovoltaic cells illuminated under a solar concentration of 1000 suns. The results showed that the best case of the VHP heat sink achieved a variation of merely 1.56 K in the maximum temperature among the cells, which is 84.1% lower than the UHP heat sink (9.82 K). Moreover, the same case exhibited a 33.1% reduction in the pumping power. However, there is a 2.4% increase in the maximum temperature rise among the cells which is an acceptable tradeoff considering the substantial improvement in the temperature uniformity and pumping power.

Multicore Cladding-Pumped Fiber Amplifier With Annular Erbium Doping for Low Gain Compression

We report the characterization of a cladding-pumped multicore fiber with annular erbium doping for low gain compression over the C-band (1528.8 nm to 1563.9 nm). The fiber aims to minimize saturation effects by placing the erbium doping in the cladding where the signal intensity is lower. The challenge of ensuring adequate erbium ion solubility in the cladding, without unduly raising its refractive index, was answered by using aluminophosphosilicate for the doped region. Before assembling the eight-core amplifier with fan-in and fan-out, we needed to determine the optimum fiber length to meet the gain compression target when the eight cores are loaded, for a given pump power injected in the cladding. We thus performed a thorough experimental characterization of a single core. This allowed the determination of all the relevant fiber parameters needed to do numerical simulations and predict the multicore fiber amplifier performance under the fully loaded scenario. For the first time, these numerical results are compared to the experimental results of a fully loaded multicore amplifier with cladding pumping and erbium doping in the cladding. We discuss the amplifier performance in terms of gain compression when the input power signal is varied, as would be the case in dynamic optical networks. We also examine the core-to-core gain variations and the sensitivity of the design to fabrication variations. Results show that significant reduction in gain compression of multicore cladding-pump amplifiers can be achieved with the proposed annular doping design in the cladding, although improvement in the fabrication uniformity of the core will be required for practical applications. Lastly, we discuss how this erbium doped fiber design can also lead to improved power conversion efficiency (PCE) in cladding-pumped amplifiers.

Evaluation and Improvement of Circumferential Uniformity for Blast Furnace Raceway

The bustle pipe model of a running 2500 m3 blast furnace was established. The local and overall uniformity indexes of the raceway were defined and constructed. And then the effects of blast flow rate, the diameter and length of all tuyeres or No. 2 tuyere on the circumferential uniformity of raceway were quantitatively evaluated. It was shown that the circumferential uniformity of raceway decreased with the increasing blast flow rate, and when the blast flow rate increased from 4300 m3/min to 4700 m3/min, the circumferential uniformity index of raceway decreased from 0.1715 to 0.0760. The diameter of tuyere had a significant effect on the circumferential uniformity, while the length of tuyere showed little influence. The circumferential uniformity of raceway could be improved by increasing the diameter of all tuyeres or No. 2 tuyere with the minimum blast kinetic energy. When the diameter of all tuyeres increased to 140 mm, the overall uniformity index of raceway increased to 0.207, but the blast kinetic energy was only about 64 kJ/s which couldn’t meet the smelting. requirement. While the diameter of No. 2 tuyere near the hot blast main increased to 126 mm, the overall uniformity of the raceway increased to 0.124, and the blast kinetic energy was 120.11 kJ/s which was still within the reasonable range. it was feasible to improve the circumferential uniformity of raceway by adjusting the diameter of one or some off-average tuyeres but not all.

Computational design strategy to improve RF heating uniformity

PurposeRecent work has demonstrated the possibility of selectively sintering polymer powders with radio frequency (RF) radiation as a means of rapid, volumetric additive manufacturing. Although RF radiation can be used as a volumetric energy source, non-uniform heating resulting from the sample geometry and electrode configuration can lead to adverse effects in RF-treated samples. This paper aims to address these heating uniformity issues by implementing a computational design strategy for doped polymer powder beds to improve the RF heating uniformity.Design/methodology/approachTwo approaches for improving the RF heating uniformity are presented with the goal of developing an RF-assisted additive manufacturing process. Both techniques use COMSOL Multiphysics® to predict the temperature rise during simulated RF exposure for different geometries. The effectiveness of each approach is evaluated by calculating the uniformity index, which provides an objective metric for comparing the heating uniformity between simulations. The first method implements an iterative heuristic tuning strategy to functionally grade the electrical conductivity within the sample. The second method involves reorienting the electrodes during the heating stage such that the electric field is applied in two directions.FindingsBoth approaches are shown to improve the heating uniformity and predicted part geometry for several test cases when applied independently. However, the greatest improvement in heating uniformity is demonstrated by combining the approaches and using multiple electrode orientations while functionally grading the samples.Originality/valueThis work presents an innovative approach for overcoming RF heating uniformity issues to improve the resulting part geometry in an RF-assisted, volumetric additive manufacturing method.

SmartScan: An intelligent scanning approach for uniform thermal distribution, reduced residual stresses and deformations in PBF additive manufacturing

Parts produced by laser or electron-beam powder bed fusion (PBF) additive manufacturing are prone to residual stresses, deformations, and other defects linked to non-uniform temperature distribution during the manufacturing process. Several researchers have highlighted the important role scan sequence plays in achieving uniform temperature distribution in PBF. However, scan sequence continues to be determined offline based on trial-and-error or heuristics, which are neither optimal nor generalizable. To address these weaknesses, we have articulated a vision for an intelligent scan sequence optimization approach to achieve uniform temperature distribution, hence reduced residual stresses and deformations, in PBF using physics-based and data-driven thermal models. This paper proposes SmartScan, our first attempt towards achieving our vision using a simplified physics-based thermal model. The conduction and convection dynamics of a single layer of the PBF process are modeled using the finite difference method and radial basis functions. Using the model, the next best feature (e.g., stripe or island) that minimizes a thermal uniformity metric is found using control theory. Simulations and experiments involving laser marking of a stainless steel plate are used to demonstrate the effectiveness of SmartScan in comparison to existing heuristic scan sequences for stripe and island scan patterns. In experiments, SmartScan yields up to 41% improvement in average thermal uniformity and 47% reduction in deformations (i.e., warpage) compared to existing heuristic approaches. It is also shown to be robust, and computationally efficient enough for online implementation in the future.

Mechanical hardening of electrochemically deposited aluminum from chloroaluminate ionic liquid

In establishing electrochemically deposited Al as a structural microdevice, its surface uniformity and mechanical properties such as the hardness are of great importance. In this study, an improvement of surface uniformity and mechanical hardening of the film by factors of about 100 and 4, respectively, are reported. Both were associated to the grain size effect, which is attributed to the inclusion of 2-chloronicotinyl chloride additive acting as a grain growth inhibitor in the electrochemical bath. Other important properties, such as the elastic modulus, residual stress and electrical resistivity of the deposit are also studied. This study holds a great potential to pave the way for the utilization of the electrochemically deposited Al in microsystems and related technologies.