Air Gap Width Research Articles

The design of negative stiffness spring for precision vibration isolation using axially magnetized permanent magnet rings

A negative stiffness element is always employed to generate high-static–low-dynamic stiffness characteristic of the vibration isolator, reduce the resonance frequency of the isolator, and improve the vibration isolation performance under low and ultra-low frequency excitation. In this paper, a new compact negative stiffness permanent magnetic spring (NSPMS) that is composed of two axial-magnetized permanent magnetic rings is proposed. An analytical expression of magnetic negative stiffness of the NSPMS is deduced by using the Coulombian model. After analyzing the effect of air-gap width, air-gap position, height difference between the inner ring and outer ring on the negative stiffness characteristic, a design procedure is proposed to realize the negative stiffness characteristic with a global minimum linear component and uniformity stiffness near the equilibrium position. Finally, an experimental prototype is developed to validate the effectiveness of the NSPMS. The experimental results show that combining a vibration isolator with the NSPMS in parallel can lower the natural frequency and improve the isolation performance of the isolator.

Design and Analysis of a Novel Air Gap–Based Semi-elliptical Nanoplasmonic Coupler

Efficient coupling of light between the dielectric waveguide and plasmonic waveguide has been investigated theoretically in three dimensions. An air gap-based novel nanoplasmonic semi-elliptical structure of silicon (Si) is used as a coupler, which connects these waveguides. Finite integration technique (FIT) has been deployed for the investigation. Theoretical coupling efficiency of ∼85% at optical communication wavelength (1.55 μm) has been achieved through numerical simulations. The dependency of coupling efficiency has been investigated by varying the curvature of the semi-elliptical coupler, the air gap width between the two waveguides and the width of the air gap of silver-air-silver waveguide, and an optimal dimension of the proposed structure has been determined. A number of performance parameters like coupling efficiency, reflection coefficient, return loss, and voltage standing wave ratio (VSWR) have been analyzed with the obtained optimal dimensions. Broad range of operating frequency, tolerance to coupler thickness, angular, and air gap misalignment, and excellent agreement to a demonstrated experimental coupler has made the proposed coupler distinctive.

Determination of Dependence of Equivalence Ratio on the Air Gap of the Medium Pressure Injection Gas Burner

In this work, a series of calculations of a complete premixing injection gas burner with various air gap widths with ANSYS Fluent software was performed. A natural gas fired injection gas burner is used as a heat source as a part of a thermoelectric generator. Assuming that the gas-air mixture flow is one-dimensional and axisymmetric, the issues were solved in axisymmetric setting, taking into account the gas compressibility. In the performance of a task, a set of assumptions was made: k-epsilon realizable model was picked as turbulence model with scalable wall functions; the flow in the ejector, mixing chamber and diffuser is subsonic; the pressure of the injected air was set to atmospheric pressure; pressure at the inlet to the gas burner is subcritical (≤ 86 kPa for methane). Based on the calculations represented above, the dependence of the equivalence ratio on the air gap width was determined.

Investigation of Modelling Depths for an Electromechanical Simulation of a Direct-Drive Generator Considering Parasitic Airgap Forces and External Loads

This paper shows a multiphysical simulation approach for direct - drive generators, including electromagnetic force calculations and multibody simulation. The objective of this method is to determine the airgap width distribution of the generator during operation.In this investigation different modelling depths of the electromechanical model are discussed. Especially the modelling of the electromagnetic force application and integration of flexible structural elements is discussed.

Development of heat and mass transfer correlations and recovery calculation for HCl–water azeotropic separation using air gap membrane distillation

In the present work, the air gap membrane distillation (AGMD) process has been experimentally studied for the separation of aqueous HCl azeotropic (20.2 wt% HCl) mixture. A test cell AGMD module equipped with polytetrafluoroethylene flat sheet membrane of 0.22 µm pore size was used to perform different experiments. The effect of operating parameters, mainly feed bulk temperature and air gap widths on the total permeate flux, selectivity and HCl concentration on permeate and retentate, was analyzed. Heat transfer correlation was developed from experimental data of heat transfer coefficient. Also, the effect of operating time on membrane morphology was investigated by FESEM (field emission scanning electron microscopy) and AFM (atomic force microscopy) analysis. The SEM image was further studied to determine the pore size distribution. A recovery model was developed to assess HCl recovery at several temperatures in the range of 40–50 °C. At 45 °C of feed temperature, 42% recovery was achieved by recycling the retentate to the feed tank resulting in 31 wt% of HCl in the feed tank for 80 h of continuous operation. The experimental results show that total permeate flux increases from 12.35 to 25.89 kg/m2 h on decreasing air gap thickness from 11 to 3 mm at 1 lpm of feed flow rate. Also, it increases from 7.35 to 35 kg/m2 h on increasing temperature from 30 to 50 °C at 3 mm air gap thickness. The maximum concentration of HCl in the permeate and retentate was found to be 16.09 wt% and 31 wt%, respectively. The HCl selectivity in the permeate was found to be lower than one, which reflects the high HCl concentration in the retentate as compared to the permeate.

Principles of energy conversion and noise characterization in air ventilation ducts exposed to solar radiation

The aim of this paper is to present a design tool with its guiding principles for energy conversion and noise characterization of an exterior rectangular duct often installed on building envelopes for pre-conditioning of fresh air. The energy conversion in an exterior rectangular duct is a function of solar irradiation, air gap width, mass flow rate and pressure, wall and air temperatures. A generalized two dimensional thermal analysis of an outdoor duct is presented by placement of surface and air nodes into two adjacent stacks of control volumes representing outer and inner walls of duct. A matrix solution procedure is adopted by constituting conjugate heat exchange of conduction, convection, radiation and ventilation heat transport. The rectangular duct model is built by a metallic exterior wall exposed to a steady heat flux generation due to solar heat gain and a well-insulated back panel as its counterpart wall. The model improves the results of traditional thermal models for the cases where: (i) there are sections of conjugate heat exchange; and (ii) stack effect due to thermal buoyancy necessitates 2-D nodal analysis for distant composite nodes. The design tool is supported with some numerical and experimental results of an airflow window with a photovoltaic (PV) solar wall installed in an outdoor test-room. Furthermore, some examples of noise characterization calculations are illustrated using devised noise measurement equations.

Surface patterns of reactive species on model tissue treated by a surface air discharge

Surface dielectric barrier discharge is capable of generating large-scale, flexible-shape and chemically active plasmas in open air, and hence has attracted much attention with relevance to clinical applications. An important application requirement is that the plasma treatment should have good homogeneity, which can be reflected by the surface distributions of reactive species on the treated sample. In this letter, a surface air discharge was used to treat a model tissue made of gelatin gel, and the surface distributions of H+, and O3 were detected. When the air gap width between the plasma and the model tissue is 3 mm, it is found that the distributions have mesh patterns similar to that of the ground electrode, but O3 concentrates on the edges of each mesh element, while and H+ concentrate in the center part. A wider air gap width benefits the mixing of reactive species but their surface distributions are more inhomogeneous, which should ascribe to a weak gas flow caused by the ionic wind and/or the gas heating effect. Gas flow can also be generated by rotating the plasma source, which is found to achieve a good homogeneity of treatment with a slow rotating speed of 1.2–2.4 rpm. This approach is easy to implement in clinical applications.

Modeling of Energy Conversion and Noise Characterization in Outdoor Ducts exposed to Solar Radiation

The energy conversion and noise characterization in an exterior rectangular duct is important, for example, in modeling PV solar wall and transpired unglazed structures. The energy conversion in an exterior rectangular duct is a function of solar irradiation, air gap width, mass flow rate and pressure, wall and air temperatures. A generalized two dimensional thermal analysis of an outdoor duct is presented by placement of surface and air nodes into two adjacent stacks of control volumes representing outer and inner walls of duct. A matrix solution procedure is adopted by constituting conjugate heat exchange of conduction, convection, radiation and ventilation heat transport. Noise characterization due to energy conversion in outdoor ducts is also presented. The energy conversion and noise characterization is supported with some experimental results of a photovoltaic (PV) solar wall installed in an outdoor test-room. Furthermore, some examples of noise characterization calculations are illustrated using devised noise measurement equations.

Theoretical modeling of combined solar chimney and water wall for buildings

In this paper, a combined solar chimney and water wall is proposed to provide ventilation as well as moderate heating to an attached room. A transient heat balance model (THBM) is established to predict the thermal performance of the combined system under mild winter conditions in Sydney, Australia. The effects of the glass panel thickness, air gap width, water column thickness, surface tinting and the relative position of solar chimney and water wall are studied respectively. The results show that the combined solar chimney and water wall is capable of providing ventilation throughout the day and night while maintaining the warmth level of the room even though it continuously draws fresh air from the ambient into the room. It is found that increasing the glass panel thickness or reducing the water column thickness enhances the thermal performance of the combined system by increasing both the room temperature and the ventilation rate. On the other hand, increasing the air gap width helps to increase the ventilation rate, but will cause the room temperature to decrease. In addition, between the two configurations, one with the water wall in front of the solar chimney (referred to as the WW-SC configuration) and the other with the solar chimney in front of the water wall (referred to as the SC-WW configuration), the ventilation rate and room temperature obtained with the SC-WW configuration are higher, and thus the latter configuration is more favorable. Furthermore, it is found that surface tinting generally degrades the thermal performance of the proposed system.

A high sensitivity D-type surface plasmon resonance optical fiber refractive index sensor with graphene coated silver nano-columns

A high sensitivity surface plasmon resonance (SPR) fiber sensor with graphene coated silver nano-columns on the surface of the D-type single mode fiber has been proposed and simulated in this paper. The sensor uses evanescent wave on the surface of the fiber to excite free electrons on the metal surface to generate surface plasmon waves (SPW), and the change of refractive index (RI) is measured by monitoring the variation of the resonance absorption peak. The COMSOL Multiphysics software is used to optimize the diameter of sliver nano-column, the width of air gap between sliver columns, and to study the effect of graphene sensing layer thickness on sensor sensitivity. The simulation results show that the sensitivity of the sensor can be greatly improved with graphene coated sliver nano-columns. The maximum external RI response sensitivity of the sensor proposed in this paper can reach 8860.93 nm/RIU in the RI range of 1.33–1.39 when the diameter of silver nano-column is 90 nm, the graphene is 23 layers and the width of air gap between columns is 53.82 nm. When the RI is 1.39, the sensitivity of the sensor with 23 layers of graphene can be increased by 28% compared with the sensor without the graphene layer. The simulation results will be helpful for design and fabrication of optical fiber SPR refractive index sensor.

Design and simulation of mems shunt capacitive switch for lower switching time

As Demand of High speed devices increasing for RF and satellite communications with better accuracy, MEMS technology is considerd to be emerging technology to fulfill that need. In this paper, A MEMS shunt capacitive switch with fixed- fixed beam have been designed and simulated for numerous parameters. The parameters for study are Selection of beam material for the switch, air gap distance between electrodes and importantly the actuation voltage. For studying the effect of air gap and beam width on switching time , the air gap was varied from 0.6 μm to 2.0 μm and beam width from 1 μm to 50 μm. For an actuatiuon voltage of 10.5 V and air gap distance of 0.6 μm, switching time result is 0.2 ns for spring constant equal to gold material.Study also considers the effect of increasing beam dimension in terms of width for a constant gap height. This syudy will be helpful for designing a MEMS capactitive switch for higher speed and for selection of proper dimension to get better performance.

The Impact of Air Gap Width on the Free Thermal Load in the Trombe Wall Contains a Phase Change Material

The objective of the present study is to investigate the effect of the air gap on the amount of mass flow rate and the ratio of energy storage in the thermal storage system containing a Trombe wall and that is through conducting experiments inside a room with dimensions of (1.5*1*1.5) m3, made of PVC sandwich insulation panel. The room contains a thermal wall of a dimension of (0.96*1.44*0.1) m3 made from a wood frame and contains 99 capsules of industrial wax of (6) cm diameter and (9.6) cm length, distributed by matrix form of (11*9). The wall is supported by four iron guides from both sides to move it easily in a distance of (10 to 35) cm from the glass cover in the south direction. The experiments have been conducted under real weather conditions of December 2016 for Kirkuk city, and this study included six widths of the air gap, arranged from (35 to 10) cm with steps of 5cm each. the results showed that the width of the air gap has a great effect on the mass flow rate through the air gap and energy incoming to the thermal system, where the best case for both factors was obtained at (b=35cm), and the max energy storage has been obtained at (b=15cm) and is about 45% of energy incoming to the system at the experiments of sunny days

Coil Inductance Model Based Solenoid on⁻off Valve Spool Displacement Sensing via Laser Calibration.

Direct acting solenoid on–off valves are key fluid power components whose efficiency is dependent upon the state of the spool’s axial motion. By sensing the trajectory of the valve spool, more efficient control schemes can be implemented. Therefore, the goal of this study is to derive an analytical model for spool displacement sensing based on coil inductance. First, a mathematical model of the coil inductance as a function of air gap width and lumped magnetic reluctance is derived. Second, to solve the inductance from coil current, an optimization to obtain an initial value based on physical constraints is proposed. Furthermore, an experiment using a laser triangulation sensor is designed to correlate the magnetic reluctance to the air gap. Lastly, using the obtained empirical reluctance model to eliminate unknowns from the proposed air gap-inductance model, the model in atmosphere or hydraulic oil environments was tested. Initial results showed that the proposed model is capable of calculating the spool displacement based on the coil current, and the estimation errors compared to the laser measurement are within ±7% in air environment.

Analysis of fluid flow and heat transfer characteristics in multiple glazing roofs with a special emphasis on the thermal performance

This study aims to investigate the effect of air layer thickness, glass coating emissivity and number of panes on the flow and heat transfer characteristics in glazing roof and evaluate thermal performance of glazing roof in terms of overall heat transfer coefficient and inner surface temperature. A conjugate heat transfer analysis including radiative heat transfer is conducted considering different emissivity values and air gap values available in the market for double, triple and quadruple pane windows. Computational results show that a progressive improvement is achieved by adding more panes or decreasing surface emissivity. However, increasing air layer thickness may promote heat transfer considerably which defeats the purpose. The-best thermal insulation performance is achieved with-the air gap width of 9 mm for all the cases considered while the poorest performance is obtained with the gap width of 6 mm or 15 mm depending on the number of panes. By using quadruple pane windows, coating the glass surfaces with low emissivity materials and optimizing air gap, the U-value can be reduced down to 0.77 W/(m2 K) providing a great amount of energy saving potential (up to 71%). Besides, the inner surface temperature of window approaches to the indoor temperature which enhances thermal comfort.

EXPERIMENTAL STUDY OF SOLAR CHIMNEY PERFORMANCE FOR PASSIVE HEATING

An experimental investigation on solar chimney used for heating under climate of Iraqis carried out. Experiments were conducted on the chimney installed on vertical wall withabsorber plate placed at the front side of the air gap. The solar chimney attached to room ofdimensions (2.5×1.29×1.07) m. The chimney is studied to measure the effect of the air gapwidth with constant height of (1.07 m). Three widths are tested, namely, 0.2 m, 0.3 m and0.4 m. The experimental results showed that the solar chimney can achieve about (13 °C)difference in temperature between indoor and outdoor as well as it gives acceptabledifference in partial cloudy days. The results also indicated that the best performance ofsolar chimney is with 0.3m air gap width.

Investigations on a Three-dimensional Model of the Moving-coil Linear Motor Applied in the Space-borne Micro Compressor

In order to optimize the magnetic circuits of the linear motor applied in the space-borne pulse tube cryocooler, a three-dimensional magnetostatic field model of the moving-coil linear motor in the micro compressor is established. The effects of several key dimensions on the distributions of the magnetic flux density inside the air gap are simulated and discussed by finite element method. The simulated results show that the magnetic flux density decreases with the increase of both width and thickness of air gap. According to the analysis, it will greatly facilitate the design, fabrication and future practical applications of the micro moving-coil linear compressor.

Experimental and mathematical study of air gap membrane distillation for aqueous HCl azeotropic separation

AbstractBACKGROUNDIn the present study, the feasibility of air gap membrane distillation (AGMD) process is investigated for breaking an azeotropic mixture. A test cell AGMD module with hydrophobic PTFE membrane was fabricated and HCl/H2O azeotrope (20.2 wt% HCl) was taken as feed. A mathematical model based on Stefan diffusion multicomponent molecular‐Knudsen mass transfer approach has been developed and validated with experimental data. The effects of different process parameters on total permeate flux, on selectivity and on breaking an HCl/H2O azeotrope mixture also have been studied. The feed side membrane surface temperature and membrane side condensing surface temperature were estimated by CFD modelling.RESULTSThe HCl selectivity obtained in the permeate was <1, which indicates that permeate flux is leveraged with water and a higher HCl concentration in the retentate was achieved relative to the permeate. The permeate flux decreased from 36 to 17 kg m−2 h−1 upon increasing the air gap from 3 mm to 11 mm at 50 °C feed temperature. The permeate flux increased from 4 to 28.5 kg m−2 h−1 upon increasing the feed temperature from 30 to 50 °C at 5 mm air gap.CONCLUSIONWith azeotropic feed, the maximum concentration of HCl achieved in the retentate was 30.8 wt% HCl (i.e. a hyperazeotropic solution) and in permeate was found to be 15.29 wt% HCl (i.e. hypoazeotropic solution). This indicates a strong possibility of using AGMD for azeotropic mixture separation. It also was observed that the permeate flux is affected mainly by feed temperature and air gap width. © 2018 Society of Chemical Industry

Flux measurement and conditioning system for heteropolar active magnetic bearing using Kapton-foil Hall sensors

Abstract This paper addresses the problem of measuring the electromagnetic flux in the air gap of the active magnetic bearing (AMB) without mechanical structure modifications. The designed and fabricated flux measurement and conditioning system based on the ultra-thin flexible Kapton-foil Hall sensors (developed by IFW Dresden Institute for Integrative Nanosciences) and signal amplifiers are presented. The flexible sensors are directly mounted on the curved surfaces of stator poles of the AMB and measure flux density in the AMB air gap. Then, the measurement itself and the conditioning system are verified in different measuring conditions of the heteropolar radial AMB with the air gap width of 0.4 mm. The measurement results were used in identifying crucial rotor flux-AMB system parameters. The proposed direct flux measurement system is successfully verified in the designed test rig in the presence of rotor position disturbances or coil current oscillation. The advantages and drawbacks of the presented measurement setup are discussed.

ANALISIS PENGARUH LEBAR CELAH UDARA PADA CHANNEL OUTLET TERHADAP KONDISI RUANGAN DAN DAYA LISTRIK DENGAN MEMANFAATKAN PANEL SURYA

Only a Part of the energy of sunlight is absorbed by solar panels during the day will be converted into electrical energy, the rest will be converted into thermal energy that conducted to the solar panel surface with high surface temperatures. High temperatures on the surface of solar panels can be combined as a trombe wall to produce a temperature gradient in the channel outlets or vents. The produced gradient temperature will create air flow velocity in the chamber and will increase due to the difference in density gradient. So heat in the room will be pushed out. This study will vary, the air gap width 3 cm, 4.5 cm and 6 cm by comparing the indoor temperature, humidity and electric power by using solar panels and without 450 tilted solar panel facing north. Room dimensions are 0.5x0.5x0.5 m, with solar panels 150x180x18 mm dimensions. Collecting data every 10 minutes from 07:00 until 19:00. The sensor used is LM35, DHT11, Voltage Sensor, and ACS712. Air condition obtained will be compared with the standard of comfort of air in the tropical building. Results obtained from the research is a widening gap Outlet Channel or ventilation in the room conditions will increase the temperature, the humidity, increase power and decrease the comfort in the room. Otherwise the narrow width of the gap or ventilation Outlet Channel it will lower the temperature, increase humidity, lower power and increased comfort in the room.

A high resolution 2D array detector system for small-field MRI-linac applications

A monolithic silicon small-field array detector is proposed for relative dosimetry applications in hybrid MRI-linac systems. The detector has high sampling resolution, with 512 active elements arranged with 2 mm pitch over a 46 mm × 46 mm detection area. Experimental measurements were performed in a custom-designed permanent magnet device that is compatible with a standard clinical linear accelerator. It can be configured in both inline and perpendicular magnetic-field-to-photon-beam orientations and produces magnetic field strengths 0.95 T and 1.20 T, respectively. Monte Carlo simulation data, obtained using the GEANT4 toolkit, are presented to supplement experimental data. Beam profiles show agreement to EBT3 film within 0.5 mm for FWHM and penumbral width measurement of small square fields (width ranging from 0.75 cm to 2.25 cm), in both inline and perpendicular magnetic field orientations. The detector can be used to accurately resolve normalised beam profiles in magnetic fields. The impact of electron return effects (ERE) in a small air gap surrounding the detector was also quantified. For the perpendicular orientation, a reduced profile intensity was observed for an increasing air gap width above the detector (10% at 2 mm) due to ERE. In the inline orientation, a very small increase in response relative to the zero field case was observed with an air gap above the detector (2% at 2 mm). Calibration of the device in a magnetic field will therefore be necessary; the zero field calibration is non-transferable. The MagicPlate-512 provides a high-resolution real time alternative to accurately measure normalised beam profiles in magnetic fields, and is expected to be a suitable array detector for use in magnetic field environments typical of MRI-linacs.