Air Gap Size Research Articles

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).

Potential of wood fiber/polylactic acid composite microperforated panel for sound absorption application in indoor environment

This study introduces a novel approach using wood fiber/PLA composite microperforated panel (WFCMPP) for indoor sound absorption purposes. WFCMPP, comprising rubber tree chip-derived fibers and a polylactic acid (PLA) matrix, with the dimensions of the rubber tree chip-derived fibers ranging from 0.5 to 1 mm, demonstrated promising sound absorption coefficients comparable to other natural fiber composite microperforated panels. The maximum sound absorption coefficient was recorded at 0.989 with a resonance frequency of 1416 Hz when the wood fiber composition was 30 %. The study also investigates the impact of wood fiber composition on sound absorption, revealing a linear relationship between fiber content and both porosity and sound absorption. The peak sound absorption coefficient of WFCMPP remained almost identical at different air gap thicknesses, showcasing the versatility and effectiveness of the samples. Additionally, the performance remained robust even with variations in air gap size. Scanning electron microscope analysis confirms the irregular porous structure and complexity contributing to enhanced sound absorption. WFCMPP presents a sustainable and effective alternative for acoustic applications, combining sound absorption performance with environmental considerations.

An air gap correction method for permittivity extraction of high-loss materials

This paper developed a method for more accurate permittivity extraction of high-loss materials using the waveguide method to reduce the effect of the air gap. This method improves the Baker-Jarvis algorithm. It makes the errors of S-parameters caused by the air gap compensated by a correction factor β of the form: (S21 + S12) + β(S11 + S22). In our study, the correction results of β for materials on different frequencies and air gap sizes are quantitatively investigated. Furthermore, we propose a method to obtain an optimal frequency-independent β for different materials. A typical high-loss BeO-SiC ceramic commonly used in vacuum electron tubes is analyzed and discussed in detail. It shows that compared to traditionally utilizing only S21 (β = 0), adopting an optimal β can reduce the average errors of the complex permittivity from 17.7% to 7.9% with a 0.10 mm air gap. The proposed method is verified by measurements of unshaved and shaved samples.

Numerical-experimental study of the thermal behavior of a green facade in a warm climate in Mexico

Demographic growth entails an increase in the construction of buildings and streets, whose materials significantly absorb heat and, upon release, create discomfort for the inhabitants of large urban areas. Vegetation emerges as a crucial element to enhance both the indoor environment of buildings and the outdoor surroundings. Green facades present themselves as a highly efficient alternative to integrate vegetation in densely urbanized areas. This study focuses on evaluating the thermal performance of an indirect-type green facade system in a warm climate in Mexico. The research encompasses experimental measurements and numerical simulations of the thermal effect of the green facade and also a parametric study of the vertical leaf area index (LAIV) and air gap size. In the experimental test, temperatures were recorded in two identical test cells, one of which was equipped with a green facade with Pyrostegia Venusta plants on one of its surfaces. The numerical study validated the results obtained through experimental tests, using simulations of Computational Fluid Dynamics (CFD) considering a typical day for each season throughout the year. Validation results revealed Mean Percentage Errors (MPE) of −2.86 % and 0.25 %, Mean Bias Errors (MBE) of −0.49 °C and 0.08 °C, and Root Mean Square Errors (RMSE) of 1.34 °C and 1.29 °C for the bare facade and the green facade, respectively. In the numerical analysis, it was observed that the green facade succeeded in reducing the indoor air temperature in a range of 4.57 to 5.64 °C, while decreasing the heat flux in an interval of 7.84 to 16.79 W/m2. Moreover, a parametric study revealed that the LAIV ceases to be a significant parameter beyond 2.5, while the air gap size proves to be a considerably less influential factor compared to the LAIV. These results confirm the relevance of using vegetation in buildings to mitigate the effects of heat and improve the thermal comfort of inhabitants.

The impact of different air gap defects in polypropylene coaxial cables on electric field distortion

The internal cable will have different air gaps due to various physical influences, and partial discharge caused by air gap defects is the main cause of cable insulation aging. To avoid serious consequences caused by air gap defects, it is crucial to analyze the extent of the impact of early-stage air gaps on the electric field in the cable. In this paper, COMSOL Multiphysics software is used to build a three-dimensional model of the cable, and the insulation material is polypropylene. Different positions and sizes of air gap defects are designed in the model. The electric field distribution inside the cable is obtained through the finite element algorithm, and the degrees of distortion of the electric field under different air gap sizes, positions, and shapes are compared. The results show that the size of the air gap affects the change in the electric field. Air gaps closer to the copper core position produce greater electric field distortion. Additionally, air gaps with larger curvature also result in greater electric field distortion. Based on the conclusion of this study, the influence degree caused by different air gap defects can be determined and provide a basis for the analysis of such faults.

Wide-bandwidth mode converter based on a dual-hollow-core anti-resonant fiber

This paper proposes a broadband mode converter utilizing a dual-hollow-core anti-resonant fiber (DHC-ARF) for the first time, in which the mode index matching between LP01 and LP11 modes is achieved by adjusting the core diameter size of the hollow-core anti-resonant fiber (HC-ARF). Notably, the air gap can become the main channel for the energy exchange between the two cores by adjusting the air gap size between the two cores of the DHC-ARF. The coupling length of the mode converter is greatly reduced, and a compact and broadband mode converter is realized. Simulation results demonstrate that the proposed mode converter achieves a coupling efficiency (CE) of 92.79 % at a wavelength of 1.55 μm at a length of 10.7 mm. The bandwidth of 330 nm at a CE greater than 90 % covers the E + S + C + L + U bands. The proposed mode converter exhibits a large core diameter compatible with hollow-core fiber communication and is expected to be applied for high-speed and high-capacity hollow-core mode-division-multiplexing fiber-optic communication. The device design methodology presented in this paper can also provide technical references for developing higher-order mode converters, such as LP01 mode to LP02 mode and LP01 mode to LP21 mode, based on DHC-ARF.

Evaluation of wind-induced turbulence around offshore platforms in different wind speeds and directions, along with safety assessment of helicopter operation and helideck’s air-gap optimization

The demand for helicopter transportation has increased as offshore activity has expanded into more remote waters. In this situation, safe takeoffs, approaches, and landings on the platform's helidecks require understanding wind behavior. This study simulates the effect of a helideck air gap on wind turbulence around an offshore platform. The simulations are carried out using a validated computational fluid dynamics model based on the Reynolds-averaged Navier-Stokes k-equations. Five wind directions (with intervals of 45°), two wind speeds (5, 15, and 35 m/s, respectively, for winds with 7-days, 1-year, and 100-year return periods), and six air gap sizes (0–6 m) were assumed to calculate the induced turbulence. The Norsok C-004 standard, two speed-base, and one energy-based criterion were used to identify the turbulence conditions that allow helicopter operations. Wind-induced turbulence was significantly generated by the interaction of the wind with the crane and equipment placed on the highest level, limiting helicopter operation, particularly in most cases where the wind blows from the southwest. According to the findings, a minimum 4-m air gap is nedded to reduce turbulence caused by wind contact with equipment. Although no upward or downward flows (with ±2 m/s) have formed on the helipad, they have formed strongly around the helipad structure and in the direction of the helicopter approach.

Effects of air gap and compression on the dual performance of multilayer thermal protective clothing under low radiant heat

An air gap in thermal protective clothing (TPC) plays an important role in determining heat transfer, but it may also increase the amount of stored thermal energy that would discharge to the skin after exposure, especially when the TPC suffers compression. To investigate the effect of air gap and compression on the dual thermal protective performance (TPP), thermal hazardous performance (THP) and overall thermal protective performance (OTPP) of TPC, nine air gap configurations with different sizes and positions and five compression levels were designed in this study. Regression models were established to explore the relationships among air gap size, compression and THP for different air gap positions. The results demonstrate that increasing the air gap size without exceeding 12 mm not only significantly enhances the TPP by impeding heat transfer from the heat source to the fabric system during exposure but also decreases the THP by reducing heat discharge from the fabric system to the sensor even when compression is applied. Although an inner air gap contributes more to increasing the TPP during exposure than an outer air gap, it may also bring about severe stored energy discharge when compression is applied. It suggests that a larger air gap size should be divided into individually separate air gaps within different fabric layers to reduce the heat transfer during exposure as well as lower the stored thermal energy discharge after exposure.

An experimentally validated cavitation inception model for spring-driven autoinjectors

Cavitation, the formation and collapse of vapor-filled bubbles, poses a problem in spring-driven autoinjectors (AIs). It occurs when the syringe accelerates abruptly during activation, causing pressure fluctuations within the liquid. These bubbles expand and then collapse, generating shock waves that can harm both the device and the drug molecules. This issue stems from the syringe’s sudden acceleration when the driving rod hits the plunger. To better understand cavitation in AIs, we explore how design factors like drive spring force, air gap size, and fluid viscosity affect its likelihood and severity. We use a dynamic model for spring-driven autoinjectors to predict and analyze the factors contributing to cavitation initiation and severity. This model predicts the motion of AI components, such as the displacement and velocity of the syringe barrel, and allows us to investigate pressure wave propagation and the subsequent dynamics of cavitation under various operating conditions. We investigated different air gap heights (from 1 to 4 mm), drive spring forces (from 8 to 30 N), and drug solution viscosities (from 1 to 18 cp) to assess cavitation inception based on operational parameters. Results reveal that AI dynamics and cavitation onset and severity strongly depend upon AI operating parameters, namely drive spring force and air gap height. The maximum syringe acceleration increases with spring stiffness and decreases with air gap height; increases in air gap height prolong the time interval of syringe acceleration but diminish the maximum syringe acceleration. From actuation to injection, air gap pressure peaks twice, first due to impact with the rod/plunger and secondly due to the deacceleration event upon injection. The maximum air gap pressure increases with spring stiffness and decreases with air gap height. Results show that maximum cavitation bubble radii and collapse-driven extension rates occur with higher driver spring forces, smaller air gap heights, and less viscous solutions. A cavitation criterion is developed for cavitation in autoinjectors that concludes that cavitation in autoinjectors depends on the peak syringe acceleration.

Development of a Novel Radial-Flux Machine With Enhanced Torque Profile Employing Quasi-Cylindrical PM Pattern

This article presents a novel radial-flux surface-mounted PM (SPM) machine with quasi-cylindrical pole pattern (QCPP). With the proposed configuration, the cogging torque and torque ripple of surface-mounted machines could be greatly decreased due to the adoption of large eccentric distance and the reduction of high-order airgap flux density harmonics. Moreover, the increase of fundamental flux component helps to improve torque generation well. Additionally, the magnet poles are semi-embedded into the rotor, and thus the sleeve in conventional SPM machines is no longer necessary, which helps to reduce the airgap size and improve the torque output further. Besides, the quasi-cylindrical magnet could offer lower rotor eddy loss and higher anti-demagnetization capability than conventional radial and eccentric pole patterns. Studies have been conducted on the novel structure to validate its advantages. Firstly, the topological structure and working principle of the QCPP machine are presented. Then, the influence of the QCPP structural parameters on the torque performance is investigated. Next, an electrical machine with quasi-cylindrical pole pattern is designed. Subsequently, the electromagnetic characteristics, such as flux density distribution, back EMF, average torque, cogging torque, torque ripple, eddy loss in sleeve, rotor stress and anti-demagnetization capability, of the proposed machine are analyzed and compared with those of conventional SPM machine with eccentric magnetic poles and skewing slots. Finally, one research prototype is developed, and experiments are carried out to evaluate the design concept and performance of the proposed QCPP machine.

TRANSMITTING TORQUE DETERMINATION OF AN END MAGNETIC COUPLING WITH THIN HIGHLY COERCIVE PERMANENT MAGNETS

The article considers the possibility of a standard method using for calculating the transmitted torque of an end magnetic coupling with thin highly coercive permanent magnets having a thickness of 4.5 mm and magnets with a thickness of 9 mm composed from two thin magnets with a thickness of 4.5 mm each. The range of variation of the air gap between the magnets in the half couplings of the end coupling is from 1 to 20 mm. The results of the study made it possible to introduce a correction coefficients into the methodology for calculating the transmitted torque of an end magnetic coupling with thin magnets. It is noted that the end magnetic couplings are used with an air gap size between the magnets of the coupling halves from 5 to 12 mm.

Analysis of the Vibration Characteristics and Vibration Reduction Methods of Iron Core Reactor

Series iron core reactors are one of the most commonly used electrical equipments in power systems, which can limit short-circuit currents and suppress harmonic waves from capacitor banks. However, the vibration of the reactor will not only generate noise pollution but also diminish the service life of the reactor and jeopardize power system safety. In order to reduce the vibration noise in the core disc region of the reactor, the vibration characteristics of a core reactor are calculated by modifying the anisotropy parameters of the Young’s modulus of the core disc lamellar structure and introducing the core magnetostriction effect based on the simulation analysis method of electromagnetic and mechanical coupling. A detachable single-phase series core reactor model is established, and the validity of the simulation calculation is measured and verified. At the same time, from the perspective of improving the air gap size of the series core reactor and the arrangement of electrical steel sheets, the corresponding iron core vibration reduction scheme is given. The average vibration reduction in the reactor is about 11.6% after comprehensive improvement according to the vibration reduction scheme, which provides an effective method for realizing the vibration and noise reduction in the reactor.

Evaluation of the Ethos synthetic computed tomography for bolus-covered surfaces

PurposeEthos allows online adaption of radiotherapy treatment plans. Dose is calculated on synthetic computed tomographies (sCT), CT-like images generated by deforming planning CTs (pCT) onto daily cone beam CTs (CBCT) acquired during treatment sessions. Errors in sCT density distribution may lead to dose calculation errors. sCT correctness was investigated for bolus-covered surfaces. MethodspCTs were recorded of a slab phantom covered with bolus of different thicknesses and with air gaps introduced by spacer rings of variable diameters and heights. Treatment plans were irradiated following the adaptive workflow with different bolus configurations present in the pCT and CBCT. sCT densities were compared to those of the pCT for the same air gap size. Additionally, the neck region of an anthropomorphic phantom was imaged using a plane standard bolus versus an individual bolus adapted to the phantom’s outer contour. ResultsVarying bolus thickness by 5 mm between pCT and CBCT was reproduced in the sCT within 2 mm accuracy. Different air gaps in pCT and CBCT resulted in highly variable bolus thickness in the sCT with a typical error of 5 mm or more. In extreme cases, air gaps were filled with bolus material density in the sCT or the phantom was unrealistically deformed near changed bolus geometries. Changes in bolus thickness and deformation also occurred in the anthropomorphic phantom. ConclusionsCTs must be critically examined and included in plan-specific quality assurance. The use of tight-fitting air gap-free bolus should be preferred to increase the similarity between sCT and CBCT.

Shape optimization of high-rise solar chimneys to improve the uniformity of flowrate distribution

Solar chimneys (SC) are passive ventilation devices which can induce natural ventilation by utilizing solar radiation. Many studies of SCs have focused on single-storey or low-rise buildings, but much less attention has been given to SCs for high-rise buildings. This paper investigates the airflow induced by 10- to 50-storey SCs using an experimentally validated computational fluid dynamics (CFD) model. The effects of the total number of storeys and the air gap size on the induced average flowrate were first studied, and their correlations were derived through linear regression. The flowrate induced by a conventional SC with a constant air gap size is highly non-uniform. To improve the uniformity of flowrate distributions among storeys, a taper structure with a narrowing air gap downwards was proposed for multi-storey SCs. Numerical simulations show that adopting the taper structure can significantly improve the uniformity of flowrate distributions. For example, in a 20-storey SC, the flowrate difference between the maximum and minimum among the middle 17 storeys, normalised by the average, decreases from 122.8% to only 15.8% when the taper structure is adopted. A parametric study of 441 numerical simulation cases was conducted to derive the optimum ratios of the bottom gap size to the top gap size for taper multi-storey SCs. The results of this paper can provide guidance on how to design multi-storey SCs for high-rise buildings to exploit the potential of natural ventilation and reduce energy demand for cooling and ventilation.

Results of a Study of Electromagnetic Forces and Heat Release Power in Induction Systems with a Traveling Electromagnetic Field

The results of studying the influence of various factors on the distribution patterns of electromagnetic forces and heat release power in three-phase induction systems with a traveling electromagnetic field of power frequency are presented. In the analysis, the following influencing factors were considered: phase sequence of inductors, distance between the inductor magnetic circuits end parts, and air gap size between the inductor magnetic circuit poles and the flat ferromagnetic load surface. The graphs of electromagnetic forces and heat release power in the load versus the above-mentioned factors, obtained by carrying out computational experiments in the Elcut software environment, are presented.

Performance Study of a Permanent-Magnet Eddy Current Damper for Guns Recoil Control

Eddy current damper (ECD) is a promising device for dissipating kinetic energy in dynamic systems, this study is conducted to analyze the dynamic characterization and structural optimization of linear ECD under guns launch load. The recoil resistance of ECD under guns launch load is highly nonlinear at high recoil velocity, and the recoil resistance curve shows an increase-decrease-increasing shape like a “saddle”, which is not conducive to the stability of ECD during operation. The effects of several structural parameters on the dynamic characterization of ECD were studied in details. Results show that the air-gap size, the thickness of the magnetic conduction tube and conductive tube all have a notable influence on the recoil resistance curve of ECD. Moreover, BP neural network and genetic algorithm were used for structural optimization and the optimal value was verified by FEM. The optimization results indicate that the “saddle” shape of optimized recoil resistance curve is basically invisible. The fullness of the recoil resistance curve is significantly improved from 84.93% to 92.1%, which guaranteeing a smooth recoil movement. Finally, an impact loading test system for eddy current damper was built and the experimental results were basically consistent with the simulation results.

Impact of Clothing Size on Thermal Insulation – A Pilot Study

Abstract Thermal insulation may be influenced by the size of clothing and thus the volume of air gaps. The aim of this study was to determine the relationship between the size of outer wear clothing, and thus the indirect fit (the volume and size of air gaps), and thermal insulation in static and dynamic conditions. A set of underwear and two types of outerwear for workers of the energy sector and the chemical industry were selected for the study. Results showed that the value of thermal insulation (regardless of the type of outerwear) first increased with increasing clothing size.

Performance, energy and economic investigation of airgap membrane distillation system: An experimental and numerical investigation

Airgap membrane distillation (AGMD) is an efficient configuration employed widely for the solar membrane distillation desalination process. In the present work, 1-D Knudsen and molecular transport (KMT) model has been developed to investigate the performance of the flat sheet PVDF membrane. A new solution algorithm for the co-current and counter-current flow regime has been designed to solve the heat and mass transfer equations iteratively for a single-stage AGMD module. The feed temperature, feed flow rate, airgap size, salinity, membrane porosity and module length were varied and compared with experimental results. The increase in feed temperature from 40 °C to 80 °C resulted in 10.38 times increase in flux for co-current flow and 11.05 times for counter-current flow. The maximum permeate flux at 80 °C was 8.668 kg/m2h and 8.871 kg/m2h for the co-current and counter-current processes, respectively. Optimizing the feed temperature, flow rate, and membrane length using RSM suggests 80 °C, 1.528 LPM and 10 m as the optimum operating condition. An AGMD module of size 0.8 m width and 10 m length under the optimum operating condition exhibited a freshwater yield of 8.73 kg/h by consuming 24.98 kWh/m3 of specific energy, and the water production cost would be around $2.25/m3.

On the rub-impact force, bifurcations analysis, and vibrations control of a nonlinear rotor system controlled by magnetic actuator integrated with PIRC-control algorithm

This article presents the Proportional Integral Resonant Controller (PIRC-controller) as a novel control strategy to suppress the lateral vibrations and eliminate nonlinear bifurcation characteristics of a vertically supported rotor system. The proposed control algorithm is incorporated into the rotor system via an eight-pole electromagnetic actuator. The control strategy is designed such that the control law (PIRC-controller) is employed to generate eight different control currents depending on the air-gap size between the rotor and the electromagnetic poles. Then, the generated electrical currents are utilized to energize the magnetic actuator to apply controllable electromagnetic attractive forces to suppress the undesired lateral vibrations of the considered rotor system. According to the suggested control strategy, the whole system can be represented as a mathematical model using classical mechanics' principle and electromagnetic theory, in which, the rub-impact force between the rotor and the stator is included in the derived model. Then, the obtained discrete dynamical model is analyzed using perturbation techniques and validated numerically through bifurcation diagrams, frequency spectrums, Poincare maps, time responses, and steady-state whirling orbit. The obtained results illustrate that the proposed control algorithm can mitigate the nonlinear vibration and eliminate the catastrophic bifurcations of the rotor system when the control gains are designed optimally. In addition, the system dynamics are analyzed when the rub-impact occurrence between the rotor and the pole housing is unavoidable. The acquired results revealed that the system may perform periodic-1, periodic-n, or quasiperiodic motion with one of two oscillation modes depending on both the impact stiffness coefficient and the dynamic friction coefficient.Article HighlightsNonlinearity dominates the uncontrolled rotor response, where it suffers from the jump phenomenon and multiple solutions.The proposed controller forces the Jeffcott rotor to respond as a linear system with small oscillation amplitudes.The rotor oscillates with full-annular-rub or partial-rub-impact mode when rub-impact occurs between the rotor and stator.

A new approach for measuring the air gap between diaper and baby skin

The air gap between baby skin and top sheet of disposable diapers is the main place where baby’s metabolic heat, perspiration, and moisture produced by evaporation of urine stay and transfer. Heat and moisture transfer underneath a diaper are greatly affected by the shape and size of the air gap, therefore, it is of significant importance to explore the air gap between diaper and baby skin for comfort and skin health of babies. Currently, it is still a big problem to accurately measure and characterize the air gap of diaper for scholars. In this article, a new approach to measure the air gap, combining three-dimensional scanning, liquid silicone rubber filling, and image processing methods, was proposed to obtain the shape and size of the air gap between diaper and baby skin by region, for quantitative research on heat and moisture transfer mechanism of diapers. In addition, several indicators, including air volume, air gap thickness, and contact area, as well as clothing area factor of the diaper, were chosen to quantify the air gap size and distributions. After verification of accuracy and repeatability, this new approach can effectively measure the size of the air gap underneath the diaper, and provide a feasible way for exploration on quantitative relationship between thermal and moisture comfort of diapers and their structural design, fit, and diapering habits. Furthermore, diaper designers and baby caregivers can obtain guidelines of diaper structural design, wearing and change to improve the microclimate in the diaper for baby comfort and skin health.