Air Gap Research Articles

Direct torque control of a dual star induction generator based on a modified space vector PWM under fault conditions

Recent studies have shown that electrical systems in wind power conversion are subject to a 67 % failure rate, and conventional three-phase generators are considered to be the most sensitive to these faults. Induction generator current harmonics are a major source of torque ripples causing acoustic noise and vibrations. These ripples can progressively increase under faulty operating conditions. In six-phase machines, there is appearance of high harmonic currents in the air gap as space harmonics. Power electronic converters are also subject to faults, the most common being Short-Circuit (SC) and Open-Circuit (OC) faults. SC faults cause large peaks in the line currents, which trigger the protection devices, resulting in a complete shutdown of the production system. OC faults, on the other hand, cause imbalances in the phases, but the system remains in operation.Direct Torque Control (DTC) based on Space Vector Modulation (SVM) at constant switching frequency is an effective solution to tackle induction generator current harmonics. This paper proposes a DTC combined with a Proportional Integral Fuzzy Logic Controller (PIFLC) optimized by Particle Swarm Optimization (PSO) in order to overcome the problems of torque ripples. Furthermore, using Vector Space Decomposition (VSD) and the Modified Space Vector Pulse Width Modulation (MSVPWM) strategy, a significant reduction of harmonics in the air-gap can be achieved.Simulations were carried out under MATLAB/Simulink, and the results obtained demonstrate the superiority of the proposed DTC-PIFLC-PSO controller in terms of robustness against wind speed variations and under faulty switch conditions in the power converter of the Dual Star Induction Generator (DSIG) generator. In addition, a comparative study with the classical PI controller is presented to show the effectiveness of the DTC-PIFLC-PSO controller against faults with a significant reduction in the Total Harmonic Distortion (THD) during both faulty and non-faulty conditions.

Siphon-based scalable and salt-resistant multistage thermal desalination system

Recent advances in thermal localization-based passive solar desalination provide a great opportunity for the economical generation of freshwater, particularly in regions with insufficient energy and water infrastructure. Yet, the capillary-assisted passive desalination systems with a high-water productivity flux (measured in Lm−2 h−1) suffer from the issue of performance degradation due to salt accumulation and the inability to be scaled up. In this work, we propose siphon-based supply of saline water over the evaporator that enables scale up of the desalination system to a size significantly higher than the capillary rise height of the hydrophilic evaporator while preventing salt accumulation on the evaporator. The composite siphon comprises insulating fabric wick and a metallic grooved surface for localizing heat to evaporate a thin layer of saline liquid over the evaporator. We perform heat and mass transfer analysis to show that the thermal-to-vapor efficiency depends on the inlet mass flow rate and air gap between the evaporator and the condenser. We propose a methodology to passively control the mass flow rate to maximize the thermal to vapor efficiency at different input heat flux and initial concentration of the brine. A grooved condenser avoids mixing of brine and the freshwater, even at air gaps as low as 2 mm. A siphon-assisted 10-stage desalination system with a footprint area 15 cm × 15 cm and an air gap of 2 mm is shown to have a high water productivity flux of ~5.73 Lm−2 h−1 from 3.5 wt% saline water at an applied heat flux 1000 W/m2, which increases to a record high distillate flux of ~6.23 Lm−2 h−1 and thermal to water collection efficiency of ~423 % for a 15-stage system. The ability of the desalination system to maintain a high-water productivity flux even when the evaporator area is increased by 4 times demonstrates its scalability to achieve higher desalinated water productivity rate.

Integrated LCC-LCC Topology for WPT System With CC Output Regarding Air Gap and Load Variations

Integrated LCC-LCC Topology for WPT System With CC Output Regarding Air Gap and Load Variations

Analysis and research on the hydrodynamic performance of offshore floating photovoltaic systems under large tidal variations

Abstract This paper focuses on the multi-module connected offshore floating photovoltaic system, designing a mooring system with buoys, considering the effects of buoy size, position on the motion response of the photovoltaic system, mooring cable tension, and photovoltaic air gap. Based on the three-dimensional potential flow theory, optimal parameters for buoys were selected using regular waves at an average depth of 10 meters. Subsequently, factors such as tidal differences, randomness of waves, wind, and currents were taken into account, and the motion response, mooring tension, and photovoltaic air gap were calculated separately at water depths of 8 m, 10 m, and 12 m. The analysis results indicate that the offshore floating photovoltaic system with a buoy mooring system, under the influence of tidal differences, does not show significant differences in the minimum air-gap height of the photovoltaic system, ensuring safe and stable operation.

Design of an Objective Magnetic Lens and Study of its Magnetic and Optical Properties in the Scanning Electron Microscope

The study's objective is to investigate the optical properties of the objective magnetic lens, which is considered as the most crucial part of the electron microscope. Three models of objective lenses (Snorkel, Pinhole, Gemini), equal in geometric dimensions were taken, and their optical properties, as well as their magnetic properties. It was found that the lens (P) achieved the best results, which were studied at a continuous excitation (NI=2000 A-t) and different acceleration voltages ranging from (8-16 kV), in addition to different values for the aperture angle (α). Then, we conducted an improvement on the selected lens by changing the width of the air gap between the poles (S) and studying the properties of the lens. We obtained better results for spherical (Cs=1.62 mm) and chromatic (Cc=1.84 mm) aberrations, focal length (fₒ=2.92 mm), as well as the highest value of the magnetic field (Bz=0.38 T) at an acceleration voltage (Vr=10000 V), excitation (NI=2000 A-t), and air gap width (S=5 mm), and the diameter of the electron probe (dp=11.25 nm) at an aperture angle (α=2 mrad).

CFD analysis of the impact of air gap width on Trombe wall performance

AbstractIn recent years, there has been a lot of research and debate on how solar energy can be used instead of conventional sources of heating to power residential heating. In this study, the Trombe wall (TW) technique, based on natural convection and energy storage, was examined to predict mass flow rate, temperature field, and velocity field for the TW system under steady conditions. A numerical simulation model was investigated for further validation using k‐ε turbulence and discrete ordinates (DO) radiation models. Independent grid studies were conducted to ensure that there were no changes after varying the grid numbers. The effect of the air gap was carried out to enhance TW thermal performance. CFD simulation shows good agreement with published data in the literature, and the optimum air gap was set at 0.1 m. The results pave the way for future studies to improve passive solar heating systems, which will eventually help move towards more sustainable residential heating solutions.

Local and nonlocal conditions for electron runaway in a gas gap with a conical cathode with a variable opening angle

The conditions for the generation of runaway electrons in an air gap are compared at different degrees of inhomogeneity of the electric field distribution provided by varying the opening angle of the conical cathode: in the range 40°–120° in experiments and 0°–180° in calculations. It is demonstrated that, in a weakly inhomogeneous electric field (according to the proposed classification, this corresponds to cones with angles greater than the Taylor angle of 98.6°), the runaway condition has a local character. The transition of free electrons into the runaway mode is determined by the local distribution of the electric field near their starting point—the tip of the cone. The local electric field strength must exceed a threshold value comparable to the strength critical for the runaway of electrons in a uniform field. In a strongly inhomogeneous field (cones with angles less than 98.6°), this condition is not sufficient for electrons to run away throughout the gap. Electrons accelerating in the near-cathode region may begin to slow down in a weak field at a distance from the cathode. In this case, the runaway condition becomes nonlocal. It is determined by the dynamics of electrons in the entire gap, primarily in the near-anode region, and reduces to the requirement that the potential difference applied to the gap exceeds a certain threshold value.

A low voltage semiconductor arc discharge plasma actuator with long discharge gap distance

Long-gap spark discharge is beneficial for plasma-assisted combustion. However, the longer the discharge gap, the higher the breakdown voltage required, which is not feasible in practical applications. In the present study, based on a custom-built semiconductor, a long gap discharge plasma actuator is designed, and the breakdown voltage is relatively low compared with the normal spark discharge method. The breakdown discharge voltage for 25mm gap at atmospheric pressure is only 3.24kV. The discharge characteristics were investigated in detail. The influence of voltage, capacitance, and the semiconductor geometric parameters on the discharge characteristics is investigated. Based on a high-speed camera, the temporal and spatial long gap discharge process was captured firstly. Combined the discharge waveforms and images, the discharge process of the semiconductor arc discharge plasma actuator is divided into four stages: applying high voltage, surface discharge, air breakdown, and conduction discharge. Using digital image processing techniques, the influence of voltage, capacitance and air gap on surface discharge evolution velocity was studied.

Autoinjector optimization through cavitation response and severity minimization

Abrupt acceleration of the syringe of an autoinjector (AI) upon rod-plunger impact may induce undesired severe cavitation events and impose extraneous stresses upon the device, leading to device failure. Cavitation results from a rapid and significant pressure drop in a liquid, leading to the formation and growth of small vapor-filled cavities. Upon collapse, these cavities generate an intense shock wave that may lead to protein aggregation and device container damage and shatter. Since the maximum acceleration of the syringe depends upon the operating conditions of the AI, the severity of cavitation will likewise depend on the operating conditions of the AI. Likewise, injection time and ensuring proper needle displacement before drug release also depend on operating conditions, making optimization of the autoinjector a multiobjective optimization problem.Therefore, in this study, optimization of an autoinjector to limit cavitation severity is pursued via an experimentally validated computational model for cavitation in spring-driven autoinjectors. Our goal is to locate AI design configurations that balance maximizing device performance and patient comfort and minimizing the risks of device damage and severe cavitation upon actuation.Relevant parameters of interest are the drive spring force, air gap height, solution viscosity, friction between the rod and spring, frictional force on the plunger, rates of change of frictional force on the plunger, elasticity of plunger, viscosity of the plunger, and initial displacement between the plunger and the driving rod. The kinematics of the syringe barrel, needle displacement (travel distance) at the start of drug delivery, and injection time are gathered using an experimentally validated autoinjector kinematics model. At the same time, cavitation bubble dynamics are resolved using an experimentally validated cavitation model that takes the temporal displacement of the syringe and temporal air gap pressure as inputs.We use our experimentally validated models to explore the parameter space and understand the driving factors of our desired outcomes. Subsequently, we pose the design problem as a multi-objective optimization problem and develop a deep neural network surrogate model supplemented with iterative learning to speed up optimization. A variance-based sensitivity analysis was performed to determine the sensitivity and influence of design parameters on the outcomes, and the main contributors to the outcomes of interest were isolated. Using a multi-objective optimization framework, we located 300 + successful candidates and evaluated them through uncertainty analysis to identify three promising candidates that meet all criteria for drug viscosities of interest. Finally, we show that this methodology can be used to conduct hypothesis testing, leading to novel design configurations.

Enhancing building energy efficiency: Innovations in glazing systems utilizing solid-solid phase change materials

This study investigates the energy efficiency of a double-glazing window (DGW) integrating a solid–solid phase change material (SSPCM) with limited thickness, applied to the inner glass pane within the air gap. Numerical model, validated against experimental data, is developed using a finite volume method in ANSYS Fluent. In this model, the Discrete Ordinates (DO) model is applied to simulate radiation, while the enthalpy-porosity approach is used to capture the solidification and melting processes in the phase change material. With this model, the energy performance of the system is analyzed under various transient temperature values (10 to 30 °C) and ranges (1 to 5 °C) during the coldest and hottest days of the year, as well as during cloudy and sunny days in Montreal (Dfb), Vancouver (Cfb), and Miami (Aw). According to the obtained results in Montreal, the DGW-SSPCM system consistently saves energy under summer sunny conditions, with optimal performance when the SSPCM remains transparent. However, it incurs energy losses in cloudy days, where the energy lost is 2.3 times greater than the energy saved in sunny days. In Vancouver, the system shows consistent energy savings, particularly at Tc = 30 °C, with average savings of 20.5 kJ (23 %) under summer sunny conditions. The system is most beneficial in Vancouver, where winter energy savings in cloudy days (50.6 kJ) are 7.1 times greater than the losses in sunny days (7.1 kJ). In Miami, the system results in energy losses by 60 % and 5 % (at Tc = 30 °C) under both summer sunny and cloudy conditions, respectively, indicating unsuitability for its climate. During winter sunny conditions, all three cities experience energy losses, with Vancouver showing the lowest of 7.1 kJ (3 %) and Montreal the highest of 64.4 kJ (19 %) at Tc = 30 °C. In winter cloudy conditions, the system saves energy in all cities, with the highest savings in Miami of 54.5 kJ (26 %) at Tc = 30 °C. Overall, the SSPCM-DGW system has proven to be beneficial in Vancouver across various conditions in terms of energy and visual performance. These findings highlight the necessity of considering localized climate factors when designing and implementing energy-efficient glazing systems. Finally, the SSPCM-DGW system has provided complete visual clarity during office hours, making it more suitable for commercial buildings.

Analytical Model and Concept Study of an Air Gap Fringing Shield to Reduce Losses in Gapped Inductors

Analytical Model and Concept Study of an Air Gap Fringing Shield to Reduce Losses in Gapped Inductors

Experimental investigation of material extrusion additive manufacturing of copper with high powder loading rate

Beam-based additive manufacturing has challenges in fabricating pure copper due to high reflectivity. Material extrusion additive manufacturing (MEAM) avoids these issues with low costs, making it suitable to fabricate complex structures in pure copper. In this work, the effects of several printing parameters on the geometry of the samples are studied from single line, thin wall to cube using homemade copper feedstocks with high powder loading rate (65 vol%). The results show that the single line is most affected by layer thickness, while the thin wall has stricter requirements for printing temperature and printing speed. The geometric accuracy of the cube demonstrates large parametric tolerance due to the overlap and support between the lines. Central composite face-centered (CCF) design and central composite design (CCD) are used to analyze and optimize process parameters for densification. The measured porosity at the optimized printing (printing temperature = 177 °C, air gap = −0.05 mm, layer thickness = 0.3 mm) and sintering parameters (sintering temperature = 1045 °C, holding time = 4 h) is in good agreement with the predicted values. Air gap and sintering temperature have the greatest influence on the porosity, and other parameters within a certain range of on-demand adjustments do not have a significant effect. The ultimate tensile strength and elongation of the sintered samples under the optimal parameters are 153.9 ± 6.1 MPa and 31.36 ± 3.24%, respectively. No printing defects are found at the fracture and the elongation is good, showing the effectiveness of the parameter optimization.

A Critical Review on Polymer Composites Reinforced with Artificial Fibers using Fused Deposition Modelling

The practical application of Additive Manufacturing (AM) technology expands constantly in the automotive, aerospace, and biomedical sectors, among others. Additive manufacturing technology has been categorized by ASTM into seven groups according to the type of material and process used to fabricate the parts. Intellectual property rights of manufacturer restrict the users to process few materials in a machine. Nevertheless, compared to extrusion or injection molding, the mechanical strength and robustness of three dimensional (3D) printed items are significantly lower. First, some researchers have looked into optimizing process factors such build orientation, layer height, infill density, and air gap with the purpose of enhancing the mechanical properties. Secondly, altering the material with reinforcement improves mechanical properties compared with un-reinforced material. Fusion Deposition Modelling (FDM) technology based on 3D printer retains a market share of 40% globally. This article reviews the mechanical performance of FDM feed stock filament of thermo-plastic polymers ABS/PLA/PP with a reinforcement of CF/CNF/CNT/JFRT/CPT. The researchers reported improvements in mechanical characteristics such as strength, strain failure rate, and Young's modulus.

Modification of poly (vinylidene fluoride-co-hexafluoropropylene) membranes by sulfonated poly (ether ether keton) coating for membrane distillation of textile wastewater

The textile and related industries can produce a large amount of wastewater with organic dyes pollutants which can cause uncertain environmental impacts. In this study, the improved poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were used in a continuous air gap membrane distillation (AGMD) operation for wastewater treatment of the Hamadan textile factory, Iran. The porous membranes were fabricated by a phase-inversion process and the inner surface was coated by a thin layer of sulfonated poly (ether ether keton) (SPEEK). After SPEEK coating, the water contact angle of the membrane decreased from about 93° to 57°. The SPEEK coated membrane presented mean pore size and overall porosity of 10 nm and 82.2%, respectively. For the wastewater treatment, the improved membrane presented the water flux and color rejection of 24.7 kg/m2 h and 99.8% during 72 h of the AGMD operation, respectively. Additionally, the treated wastewater reduced to the turbidity of ∼2 NTU, total dissolved solid (TDS) of 16 mg/L and chemical oxygen demand (COD) of 10 mg/L. The coated membrane presented a reasonable anti-fouling property with a flux recovery ratio (FRR) of 91.7% after 72 h of the operation. Hence, the improved PVDF-HFP membrane can be a potential alternative for the removal of organic dyes from wastewater via a membrane distillation process.

3D CFD modelling and experimental validation of conjugate heat transfer in wheel hub motors in micro-mobility vehicles

An experimental and 3D CFD (computational fluid dynamics) based numerical investigation of the in-wheel hub internal permanent magnet synchronous machine (IPMSM) has been carried out to understand the thermal dynamics associated with the power loss within the motor. This study can serve as a clear case baseline for the future development of thermal management systems in micro-powertrain systems. Experimental results show that the maximum winding temperature of 65.9 °C has been observed on the end-windings (EW) for an operating condition of 500 rpm (base speed), 4.5 Nm. Stretching beyond this operating point would increase the winding temperature beyond 65.9 °C, potentially damaging the winding insulation’s capabilities and magnetic properties of the permanent magnets (PMs) and adversely affecting the performance of the wheel motors. The hysteresis and eddy current loss coefficients for the stator core have been identified as 14.5×10-2 and 1.6×10-4 respectively. The experimentally identified losses have been distributed among the motor components for the development of the numerical thermal model in commercial CFD software Star-CCM+™. The CHT (conjugate heat transfer) thermal paths show that 68.4 % and 31.4 % of the total power loss from the stator components undergo convection and conduction, respectively. This indicates that convection heat transfer dominates on the in-wheel hub IPMSM motor topology. Almost 34.5 % of the heat loss is transferred radially through the air gap to the Permanent Magnets. When the air gap size decreased by 80 %, the amount of convection heat transfer through the air gap increased by a factor of 2 (69 %) and reduced the winding temperature by 13 % (57.3 °C).

A novel acoustic micro-perforated panel (MPP) based on sugarcane fibers and bagasse

Natural materials are becoming a reliable alternative to traditional artificial materials used in sound absorption insulation. The present study was conducted to investigate the acoustic insulation of micro-perforated panel (MPP) based on sugarcane fibers and bagasse as an available and environmentally friendly material. The absorption properties of single- and double-leaf natural micro-perforated panels (MPP) made of bagasse and also nonnatural MPPs made of Plexiglass were measured using an impedance tube based on ISO 10534–2. Then the effect of bagasse and sugarcane fibers composite on the air gap of MPP was investigated. The results showed the peak sound absorption of the bagasse composite is in the range of 1000 to 2000 Hz, and the sugarcane fiber composite has a higher sound absorption coefficient than the bagasse composite. Also, natural MPPs have a higher absorption coefficient than nonnatural MPPs at all frequencies, and as the panel thickness increases, the peak absorption coefficient shifts to lower frequencies. The peak sound absorption coefficient of double-leaf MPPs made of bagasse is 76%, in the range of 160 to 200 Hz. Using sugarcane fiber composite in the air gap of single- and double-leaf natural MPPs causes the absorption peak to shift to frequencies below 100 Hz. According to the results, natural MPPs have a high sound absorption coefficient at low frequencies. These panels can control sounds with much lower frequencies, especially in a double layer and along with cane fiber composite in their air gap.

Energy and exergy analysis of a novel solar-powered passive multi-stage osmosis desalination system for sustainable water production

Climate change and population growth constantly exacerbate global water scarcity, and seawater desalination technology is crucial to addressing this crisis. Conventional fossil-fuel desalination poses environmental and economic challenges, especially in remote, water-scarce regions. Renewable energy offers sustainable options for seawater desalination; however, most related technologies face challenges in flexible deployment. Among passive technologies, interfacial evaporation still confronts issues of salt accumulation impacting desalination efficiency. Therefore, this study investigates a novel solar-powered passive multi-stage osmosis device that emulates mangroves’ transpiration and natural osmosis processes. Harnessing solar energy, it employs hydrophilic nanoporous membranes for water movement and evaporation and an osmosis membrane for solute retention, aiming for efficient seawater desalination without external power and pressure. Energy and exergy analyses reveal key efficiency factors. Results reveal significant pressure gradients across the osmosis membrane as a challenge. Optimizing salinity and adjusting the area ratio of the nanoporous membrane to the osmosis membrane is vital for stability and performance. Moreover, potential increases in water production from 0.97 kg/m2/h to 3.53 kg/m2/h with a five-stage setup, though benefits diminish with additional stages due to heat/exergy losses. The exergy efficiency increases from 0.14 % for a five-stage device to 0.18 % for a ten-stage system. This study demonstrates the solar-powered passive multi-stage osmosis device’s dependence on solar flux and highlights the importance of optimizing the air gap thickness and insulation to boost efficiency.

Monitoring the thermal state of an ingot with beveled and rounded corners in a slab crystallizer of a CCM

The organization of ingot cooling in the continuous caster mold affects the reliability, productivity and quality of the resulting ingots. Insufficient heat exchange between the solidifying metal and the wall of the mold leads to a decrease in the thickness of the solid shell of the ingot, which causes the formation of surface defects, and when the ingot is pulled out of the mold, emergency breakthroughs occur. Excessive heat transfer leads to an increase in the thickness of the solid shell, which entails excessive shrinkage of the ingot surface with the formation of a gap between the solid shell of the ingot and the walls of the mold. The appearance of an air gap leads to increased wear of the copper walls of the mold. There is a design of copper walls that makes it possible to reduce the normal component of forces that occurs during wear, reduce the temperature gradient and stress concentration in the corner of the ingot, and also bring the thickness of the hard crust stocking in the corner closer to the perimeter of the mold. However, the thermal state of the formed ingot with such a crystallizer design remains poorly understood. The goal of the work is to create a virtual tool for monitoring the operation of the mold of a slab continuous caster based on the development of a mathematical and computer model of the thermal state of an ingot with beveled and rounded corners. The temperature distribution in the ingot was calculated using the quasi-equilibrium theory of solidification. The numerical implementation of the mathematical model and obtaining an approximate solution using a computer were carried out using the finite dif-ference method and an implicit difference scheme. A computer program was developed in the Matlab development environment. Using computer modeling, the temperature distribution over the volume of the slab at the outlet of the mold with beveled and rounded corners was obtained. The program for the selected mold design allows you to analyze the solidification of the ingot skin and monitor this process for the selected steel grade and specified casting technological parameters

Development characteristics of rod-plate Gap streamer-leader system at high altitude areas

Abstract Air density is an important factors affecting the morphology characteristics of long air gap discharge channels. Analyzing characteristic parameters, such as the propagation velocity and angle of the streamer-leader system at high altitude areas is indispensable in studying the discharge mechanism of long gaps. In this paper, optical images and optical power of the discharge channel were captured. The propagation velocity of the streamer-leader system and angle distribution characteristics of the streamer region were obtained.In accordance with the findings, the downward velocity of the streamer-leader system at low pressure ranges from 1×104 to 5×104 m/s. Simultaneously, the velocity decreases slightly under the voltage with a low rise rate, and it is often accompanied by the phenomenon of leader re-luminescence. In addition, the optical images were processed by the pseudo-color algorithm, and the angle of the streamer region of the downward leader head was obtained between 50.3° and 71.6°. The angle of the streamer region is inversely correlated with the voltage rise rate but positively correlated with the gap distance. The results obtained in this paper have academic significance for improving the theoretical system of long gap discharge in high-altitude extreme environments.

Metal-only anisotropic impedance holographic metasurface

Abstract This paper presents a kind of metal-only anisotropic impedance holographic metasurfaces (MOAIHMs) made up of periodic wavelength size-variable meta-atoms. The proposed meta-atom has only two metal layers, i.e., a upper patterned layer carved with cylindrical hollows connecting by a narrow metal cuboid, and a lower grounded layer. The two metal layers are separated by an air gap. The anisotropy of this tensor impedance meta-atom can be skillfully realized by simultaneously controlling the radius of cylindrical hollows and the orientation angle of the narrow metal cuboid. The relationship between the geometrical parameters of the meta-atoms arranged in different positions and the impedance strips with alternating light and shade can be directly mapped based on the integration of the holographic theory and the leaky-wave principle. For proof of concept, two MOAIHMs are applied to design linearly polarized broadside pencil beam and dual linearly polarized pencil beams with different radiation angles in the C-band. There is good consistency between the measurements and the simulated results. The satisfactory performance and ultralow profile metal-only structure with reduced fabrication complexity/cost make this proposed design a competitive candidate for space applications.