Contact Diameter Research Articles

Glycerol dry reforming over Ni supported on fibrous ZSM5 and ZY: Correlation of structural properties on H2 production

This study investigates fibrous ZSM5 (FZSM5) and Zeolite Y (FZY) as supports for producing hydrogen via glycerol dry reforming. The fibrous ZSM5 and ZY were synthesized hydrothermally with microemulsion and impregnated with 10 wt% Ni via a sonication method. The catalytic test was conducted via a vertical stainless steel fixed-bed rig, at 800°C with a glycerol/CO2 ratio of 1. XRD and N2 sorption revealed the reduced surface area and crystallinity in Ni/FZSM5 compared to Ni/FZY. Ni/FZY catalyst displayed a larger surface area (264 m2/g) and aperture width (6.70 nm) in comparison to Ni/FZSM5, which had a surface area of 238 m2/g and an aperture width of 3.90 nm. Ni/FZY also had a smaller NiO crystallite size (8.73 nm) than Ni/FZSM5 (9.79 nm), suggesting well-dispersed Ni species on the wrinkle fiber of FZY’s surface. Ni/FZY outperformed Ni/FZSM5 with 52.49 % glycerol conversion, 44.87 % H2 yield, 71.31 % CO yield, and only 14.4 % carbon formation, attributed to robust Ni-O-Si contact and larger pore diameter. The discovery highlights the catalytic efficiency of the Ni-loaded fibrous zeolite in GDR, offering versatility for application in energy storage and catalysis.

Experimental study of the vacuum arc motion-diffuse transition in cup-shaped transverse magnetic field contacts

The arc in transverse magnetic field (TMF) contacts transitions to diffusion mode before current zero, affecting arc morphology and motion. TMF-generated force competes with local overheating's stagnation effect, impacting contact surface ablation. Cup-shaped TMF contacts exhibit slow, fast, and unstable transitions. Arc voltage declines gently, rapidly, or in repeated steps. Peak current, contact diameter, contact piece structure, and iron core influence transition characteristics. Transition energy increases linearly with peak current. Larger contact diameter and iron cores make transition constant earlier and transition current higher. Compared to circular contacts, annular contacts delay transition constant and widen transition current range. Scanning electron microscope (SEM) images showed that the ablation cathode surfaces exhibited five morphologies: melting pit, periphery, lamellar, particle, and pore. Energy dispersive spectrum (EDS) analyses show that the periphery has a higher Cu content than the interior, suggesting less Cu loss during fracture and less droplet splashing. The peripheral Cu content is comparable between the two contacts, 62.94 % vs. 62.37 %. However, the interior Cu content of contact NO.4 is higher than NO.6 at 60.54 % vs. 56.26 %. This indicates that the difference in the effect of fast and slow transitions on the cathode surface activity is mainly in the interior region.

A New Methodology for Evaluation of Large Vestibular Aqueduct in CT and MRI Images.

Development of a new method for large vestibular aqueduct (LVA)/large endolymphatic sac anomaly (LESA) assessment using magnetic resonance imaging (MRI) and computed tomography (CT)/cone beam CT (CBCT) images. The secondary objective was to compare both modalities. The gold standard for LVA diagnosis is the analysis of CT images using Valvassori and Clemis or Cincinnati criteria. The previous studies showed inconclusive results regarding the correlation between audiological and radiological data. Retrospective analysis of radiological images from 173 patients (315 ears), who were diagnosed with LVA/LESA based on CT/CBCT and/or MRI images of the temporal bone. The images obtained using both techniques were used to measure the following dimensions of vestibular aqueduct (VA)/endolymphatic duct (ED)/intraosseous endolymphatic sac (ES): width of the opening, length, and width at external aperture. In MRI images, the maximal contact diameters of the extraosseous or intraosseous ES and dura mater were measured as well. LVA has been reported to be bilateral in 82% (142 patients) and unilateral in 18% (31 patients) of cases. Comparison of MRI and CT/CBCT measurements showed a moderate correlation (0.64) in external aperture, a moderate correlation (0.57) in the width of the VA opening, and a weak correlation (0.34) in length measurements (p < 0.05). We developed a new method to identify the heterogeneous pathology of LVA/LESA using reconstruction along the VA/ED/intraosseous ES axis, three measurements on two planes, and focus on the maximal contact diameter between the extraosseous or intraosseous ES and dura mater.

Laser-Assisted Structures for Efficient Fluid Management on Stainless Steel Surfaces.

The article presents a high-productivity laser-structuring method combined with a hydrophobic post-treatment to create zone-structured surfaces with a decreasing wetting angle on AISI 304 stainless steel surfaces. We have investigated the impact of laser processing modes and hydrophobic substances on wetting and hysteresis angles and successfully demonstrated autonomous droplet movement over this zone-structured surface. A critical condition for autonomous fluid flow is the need for the drop to touch the boundary between the two zones. This can be achieved by settling the droplet directly on the boundary of the two zones or by using droplets whose surface contact diameter is on the order of magnitude or higher than the zone size. The zone-structured surface showed reusability, maintaining its properties even after 30 droplet passages. The zone-structured surfaces with a decreasing wetting angle can be used for moving a droplet along a complex trajectory as well as for mixing various liquids.

Investigation on contact surfaces damage of copper contacts by an electric arc

Electrical contacts are used in general electrical applications such as circuit breakers, switches, relays, connectors, etc. Repeated separations of the parts (anode and cathode) of these contacts under input power can damage their contact materials. The objective of this work is to study the influence of the input electric power (100 W and 256W) and the contact sizes (hemispherical contacts with diameters D=5mm and D=8mm) on the variation of the arc energy and the damage of the contact surfaces by oxidization or by erosion. These parameters are decisive for selecting the best arc-resistant contact sample. Experimental results, SEM, and EDX analysis show that high input power leads to more degradation of contact surfaces. Also, the smaller and the larger contact diameters generate similar arcing energies with similar erosion sizes and oxidation rates, but contact with a small diameter has a higher lifetime (1215 operations) and oxidizes less quickly than the one with a large diameter that has a lower lifetime (374 operations). Experimental and numerical analyses demonstrate that arc mobility is one of several factors influencing the change in contact lifetime.

A Visualization Experiment on Icing Characteristics of a Saline Water Droplet on the Surface of an Aluminum Plate

When the offshore device, such as an offshore wind turbine, works in winter, ice accretion often occurs on the blade surface, which affects the working performance. To explore the icing characteristics on a microscale, the freezing characteristics of a water droplet with salinity were tested in the present study. A self-developed icing device was used to record the icing process of a water droplet, and a water droplet with a volume of 5 μL was tested under different salinities and temperatures. The effects of salinity and temperature on the profile of the iced water droplet, such as the height and contact diameter, were analyzed. As the temperature was constant, along with the increase in salinity, the height of the iced water droplet first increased and then decreased, and the contact diameter decreased. The maximum height of the iced water droplet was 1.21 mm, and the minimum contact diameter was 3.67 mm. With the increase in salinity, the icing time of the water droplet increased, yet a minor effect occurred under low temperatures such as −18 °C. Based on the experimental results, the profile of the iced water droplet was fitted using the polynomial method, with a coefficient of determination (R2) higher than 0.99. Then the mathematical model of the volume of the iced water droplet was established. The volume of the iced water droplet decreased along with temperature and increased along with salinity. The largest volume was 4.1 mm3. The research findings provide a foundation for exploring the offshore device icing characteristics in depth.

Determination and Analysis of Working Diameters and Working Angle of the Torus Cutter Blade in Multi-axis Machining in the Aspect of Tool Wear

The aim of this study is to provide a theoretical and experimental analysis of the multi-axis milling process by the torus milling cutter of nickel-based superalloy parts in terms of surface quality and tool wear. In the analytical part, using, among other things, matrix calculus and trigonometric relationships, mathematical models were developed to describe the relationships between the tool axis orientation and the geometric parameters of the cutting layer at the contact point. On this basis, mathematical relationships for contact diameter and effective diameter were derived. The basis for these considerations is the very rarely considered working angle of the cutter blade. In part of the experimental study, machining tests were carried out for selected kinematic variants of multi-axis cutting. Based on the results obtained, it was found that as the tool axis inclination angle increases, the contact diameter increases. The effective diameter at the upper characteristic point of the cutting layer increases up to a certain angle of inclination, after which it begins to decrease. The rotational angle of the tool axis does not affect any of the diameters, but it does affect the displacement of the contact point, the values of the working angle of the tool blade and the feed-related component decrease. The result of this displacement is a change from climb milling to conventional milling, which has significantly degraded surface quality and tool life. The best results of the machining test were obtained when only the angle of inclination of the tool axis was used. It was concluded that the parameter tool blade working angle can be a control variable in a multi-axis milling process and has a major impact on the physical aspects of the cutting process.

Drying microcharacteristics of volatile and non-volatile droplets on smooth and structured surfaces

In order to analyze the dynamics of droplet evaporation from solid surfaces and to study the liquid-solid interactions, liquid droplets were deposited on substrates and examined under a microscope. Due to the variation of interfacial tensions at liquid-gas and at liquid-solid the contact line changes depending on the type of solid surface and liquid. In this study, two liquids with different surface tensions (water and ethanol) are employed to examine the effects of evaporation time and to elucidate the underlying mechanisms of solid-liquid interactions. In the case of rapidly evaporating ethanol droplets, the formation of residual droplets and internal currents was observed. In contrast, the evaporation of water droplets resulted in only a change in the shape of the contact line. The paper presents a dependence of the Ohnesorge number on the dimensionless diameter, which characterizes all the considered types of interaction. Additionally, an analysis of the contact angle and contact diameter is presented.

Исследование влияния конструкции антипараллельной пары диодов с барьером Шоттки на потери преобразования гармонического смесителя 3-мм диапазона

This paper presents the design and principle of operation of a passive harmonic mixer in the 3-mm range (75-110 GHz), the active element of which is an antiparallel pair of Schottky barrier diodes (SBD). A theoretical analysis of the mixer operation was carried out. A technique for measuring conversion losses using a vector network analyzer is presented. The experimental results of a study of the dependence of the conversion losses of a harmonic mixer on the design of an antiparallel pair of DBSs are presented. The variable parameters of the antiparallel pair of diodes were the distance between the anode leads, the length of the anode lead and the diameter of the Schottky barrier contact. The dynamic range of the mixer is investigated.

Regulating droplet impact dynamics of nanoparticle suspension: Phenomena, mechanisms, and implications

Droplet impact on solid substrates is a ubiquitous phenomenon in nature, agriculture, and industrial processes, playing a crucial role in numerous applications including self-cleaning, pesticide utilization, and inkjet printing. As a promising technique, adding nanoparticles into simple fluids to form nanofluids can effectively manipulate droplet impact behaviors. However, a comprehensive understanding of how nanoparticles modify the droplet impact dynamics, especially on the nanoscale, is still far from being fully explored. Hence, in this work, through the combined effort of molecular dynamics simulations and theoretical analysis, we elaborate on the influences of nanoparticles on droplet impact process. Using simple droplets as a control, we summarize four typical droplet impact modes and reveal how nanoparticles alter the impact behaviors of droplets, taking into account the key parameters including substrate wettability, impact velocity, volume fraction, and mass fraction of nanoparticles. We also demonstrate that with appropriate modifications, the theoretical/empirical models to predict the maximum contact diameter and the occurrence of breakup for simple droplets still hold to predict those of nanofluid droplets. Our findings and results enhance the understanding of the impact of nanoparticles on the droplet impact dynamics, with promising possibilities for various applications where regulating droplet impact behaviors is desired.

Numerical Study of Large Contact Diameter and Gap High Current Vacuum Arc

Numerical Study of Large Contact Diameter and Gap High Current Vacuum Arc

Microgel particle deposition patterns after impinging on nanofiber-based coatings

The study focuses on predicting the hydrodynamics of sodium alginate-based microgel “liquid core–gel shell” particles for droplet-based bioprinting. Hydrophobic polytetrafluoroethylene nanofiber-based coating (NBC #1) and hydrophilic polycaprolactone–polyvinylpyrrolidone NBC #2 are manufactured to serve as the basis for microgel deposition. An approach is proposed to model the flow of a Maxwell gel-like liquid with different fluidity, surface tension, and initial velocity along an inhomogeneous interface after microgel particle–NBC collision. Wetting and anti-wetting pressure differences allow estimating liquid impalement into NBCs at We = 10–50. For NBC #2, the initial particle velocity plays mainly a decisive role in predicting the contact diameter and height at maximum spreading and receding. For NBC #1, the pinning is considered by introducing the complex parameter resolving particle inertia, microgel rheology and surface tension, and NBC characteristics. The flow along the porous interface physically correlates with the extended Freundlich model, explaining the surface inhomogeneity caused by multilayer adsorption.

Dynamic wetting behavior of molten Al on α-Al2O3 substrate during heating in high magnetic field

The study observed the dynamic wetting behavior of molten Al on C-plane α-Al2O3 and R-plane α-Al2O3 substrates during heating under both 0 T and 6 T high magnetic fields (HMFs). Contact angles, contact (spreading) diameters, and heights were quantified using photographic data. The underlying mechanisms of dynamic wetting behavior under HMFs were analyzed, and dynamic wetting behavior models were developed. Under the 6 T HMF, the dynamic wetting behavior of molten Al on both oriented α-Al2O3 substrates underwent significant intensification, leading to distinctive changes in the molten Al's morphology. Upon reaching stability, molten Al exhibited significantly reduced contact angles and heights, along with a notable increase in spreading diameter under the 6 T HMF compared to the 0 T HMF. The dynamic wetting behavior was determined by the relative relationship between driving forces (resulting from changes in the three interfacial energies) and resistance (due to friction and hindrance caused by the surface oxide film of the molten Al during outward spreading). Consequently, two distinct dynamic wetting models were formulated for 0 T and 6 T HMFs. These findings open up novel possibilities for using HMFs to manipulate the wetting behavior of molten metals.

Study on arc characteristics and influencing factors of cup-shaped axial magnetic field contact at different gap distances

The cup-shaped axial magnetic field (AMF) contact, integral to high-voltage vacuum interrupters, undergoes innovation by enhancing the slotting rotation angle of the cup wall. This adjustment significantly amplifies the gap magnetic field, promising breakthroughs in handling long-gap arcs within high-voltage vacuum interrupters. Comprehensive vacuum arc experiments were conducted on cup-shaped AMF contacts with varying slotting rotation angles at different gap distances. The research meticulously analysed the evolution of vacuum arc characteristics under diverse breaking currents. Scanning electron microscope (SEM) images of the cathode surface unveiled three distinctive microscopic morphologies: particle gullies, pore platforms, and particle platforms. Notably, the chromium content corresponding to these morphologies exhibited a progressive increase. Integrating the surface distribution of copper and chromium, the study proposed a plausible cathodic erosion mechanism. Extending the investigation, the research delved into the influence of the iron core, contact diameter, and slot number on vacuum arc characteristics, which expected to provide reference for the application of the cup-shaped AMF contact in high voltage vacuum interrupters.

An analytical framework for predicting the total freezing delay time of water droplet impact on hydrophobic solid surfaces

An analytical framework is developed to investigate the impact and freezing delay of a water droplet on solid surfaces, particularly hydrophobic ones, at subfreezing temperatures. Submodules for droplet dynamics, supercooling, nucleation and recalescence, and equilibrium solidification are developed for different droplet impact and freezing stages. These submodules are then integrated to estimate the total freezing delay time per unit mass of the water droplet. It is found that the nucleation time depends on the impact height, surface temperature, droplet impact temperature, and the droplet-substrate contact angle, while the solidification time depends on the droplet size, the nucleation temperature, and the droplet final contact diameter, which is related to the initial droplet diameter, the Weber number, the Reynolds number, and contact angle. The analytical model is validated with results from droplet freezing experiments in a subfreezing environment. By simplifying the complex droplet dynamics, nucleation, and freezing processes, the new analytical framework provides a useful way to estimate the total freezing time of impacting water droplets on hydrophobic surfaces. Its accuracy needs to be improved for practical engineering applications.

Influence of microstructural refinement on cold deformation behavior of nanocrystalline Al–Zn–Mg alloy processed by solid-state mechanical milling and hot pressing

This research work was aimed at studying the workability behavior of Al–Zn–Mg alloys during a cold upsetting process. Nanocrystalline Al 7017 alloys were synthesized by mechanical milling (MM) at different milling times and consolidated by hot-pressing. The nanocrystalline Al 7017 alloy samples were incrementally deformed with a load step of 0.5 ton in a universal testing machine. Artificial image capturing and comparison techniques were introduced in this study and deformed images were captured using a high-resolution camera. For each incremental load (without removing the sample from the platens), different parameters such as the height of the deformed samples, and the corresponding contact diameters (top and bottom) were measured and analyzed using Matlab software (image processing). Cold upsetting was performed until the first crack formed. The influence of milling time on cold workability and strain hardening behavior was investigated under triaxial stress state conditions. The results revealed that the Al 7017-10 h nanocrystallite alloy exhibited improved deformation properties in terms of various tri-axial stress, strain hardening, formability stress index, and stress ratio parameters owing to the fine grain size, lower amount of dislocation pile-up, and fewer migrated atoms near the grain boundaries compared to other samples (after10 h). The microstructure and phase evolution were studied using an X-ray diffractometer and various electron microscopes. Several strengthening mechanisms are also discussed among which the dislocation strengthening mechanism plays a major role in the deformation behavior. Finite element analysis (FEA) was performed to examine the equivalent stress distribution during cold-upset forging.

Maximum spreading of an impacting drop

The maximum diameter of a drop impacting on a flat solid surface is studied theoretically assuming axi-symmetric spreading without splashing. The energy balance between the initial state of the drop (sphere diameter d0) and that a maximum spread (contact diameter dm) is closed by two novel concepts. For the gas-liquid surface area, an approximate spherical cap model is proposed. Energy loss by viscous dissipation is related to the total energy dissipation when the drop has come to rest. The fractional dissipation upon maximum spread is modelled as a function of an impact parameter (P) that combines the power laws of the capillary and viscous regimes depending on a regime discrimination parameter (A). Exponents of the Weber (We) and Reynolds (Re) numbers in P=WeRe−2/5 are determined by asymptotic analysis. The parameter A is determined from experimental data as a function of the advancing contact angle (θa). In this way, an explicit model for the maximum spread factor (βm=dm/d0) is proposed which includes the scaling laws βm∼We1/2, βm∼We1/4 and βm∼Re1/5 and is in good agreement with experimental data for wide ranges of We, Re and θa.

An experimental study on edge-affected frosting characteristics on a vertical cold plate at different surface temperatures

Frosting has received significant attention in various fields due to its potential threat. To accurately predict and control the frosting process on vertical cold plate surface considering the edge effect, the frosting characteristics with surface temperature between −15.0 °C and −5.0 °C are experimentally studied under forced convection. The results show that as the cold plate temperature decreases, the durations of droplet solidification stage in the edge-affected region decreases slowly. Meanwhile, the area-average equivalent contact diameter and the coverage area ratio of edge-affected droplets both increases. The density difference of droplet distribution between the edge-affected and unaffected regions increases from 1.02 × 107 to 3.58 × 108 per m2. The average frost layer thickness reaches 7.41 × 10−4 m for −7.5 °C at 2,400 s, and it increases by 21.20%, 38.40%, and 82.08% when the temperature decreases to −10.0 °C, −12.5 °C, and −15.0 °C, respectively. Results of this study are expected to be meaningful for the optimization of frost detection and defrosting technologies.

Experimental study of relative humidity effect on the edge effect of frosting characteristics on a vertical cold plate surface

As a common phenomenon, frosting often brings negative impacts in various fields. To gain more insight into the frosting process on a vertical cold plate considering the edge effect, a specific experimental system is designed and built to perform frosting experiments under forced convection conditions with relative humidity varying from 40% to 80%. The results show that as the relative humidity increases, the droplet solidification stage period in the unaffected region decreases, but the equivalent width of edge-affected region, area-average equivalent contact diameter of droplets, and coverage area ratio of droplets increases and then decreases. The area-average equivalent diameter of droplets in edge-affected region increases by 41.25%, 214.63%, 137.98%, 159.03%, and 30.30%, when compared to the unaffected region from Case 1 to Case 5, respectively. Besides, the difference between the droplet distribution density in the edge-affected and unaffected regions gradually decreases, but the average frost layer thickness in the edge-affected region increases significantly as the relative humidity increases. The frost layer growth rate decreases first and then increases as relative humidity increases. From Case 1 to Case 5, the frost growth rates at 1,800 s decrease by 90.05%, 70.19%, 56.08%, 62.28%, and 82.39%, respectively, compared to the initial ones. Results of this study can provide a reference for the anti-frosting and defrosting control technologies in the field such as refrigeration and air source heat pump units.

Liquid metal embrittlement in Zn-coated steel resistance spot welding: Critical electrode-contact and nugget growth for stress development and cracking

Liquid metal embrittlement (LME) crack is a severe defect which can affect the joint integrity of Zn-coated advanced high-strength steel resistance spot welds (RSW). The tensile stress that causes LME cracking is a consequence of thermal contact at the electrode-sheet interface during welding. Currently, there is no systematic study to identify the critical stages of LME occurrence during welding with understanding the tensile stress development. This research aims to address this gap by combining in-situ observation, ex-situ verification, and finite element modeling to identify the critical stages in LME cracking. The study reveals that the large LME cracks form only after a critical welding time (tcrit) of 250 ms, when the growth of the weld nugget exceeds that of the electrode-sheet contact and electrode tip-face diameter. As tcrit was attained, the LME responsible thermal gradient increased from 2000 °C/mm to 4000 °C/mm, consequently tensile stress increased from 200 MPa to 300 MPa, resulting in large LME crack. A mechanistic model explaining the effect of nugget growth rate and electrode-contact growth on thermal gradient, stress development and LME cracking was then proposed and verified through cross-comparison of crack observations. This research provides valuable insights into the critical stages of LME cracking during RSW of Zn-coated steel and suggests enhancing the growth rate of electrode-contact as a solution to mitigate this issue without altering the nugget growth rate.