Air Coil Research Articles

Experimental Characterization of Hydronic Air Coil Performance with Aluminum Oxide Nanofluids of Three Concentrations

This paper presents the continuation of experimental investigations conducted by the present authors to measure and compare the thermal and fluid dynamic performance of a residential hydronic air coil using nanofluids. The prior experiments were limited to testing only one volumetric concentration (1%) of aluminum oxide (Al2O3) nanofluid. They compared it with the base fluid, a 60% ethylene glycol/40% water mixture by mass (60% EG). The original tests revealed some deficiencies in the experimental setup, which was subsequently revised and improved. This paper summarizes the results of experiments from the improved test bed using three concentrations of Al2O3 nanofluids: 1, 2, and 3% volumetric concentrations prepared with an average particle size of 45 nm in a 60% EG dispersion. The test bed in these experiments simulates a small air handling system typical of heating, ventilation, and air conditioning (HVAC) applications in cold regions. Entering conditions for the air and liquid were selected to emulate typical commercial air handling systems operating in cold climates. Contrary to previous findings, our test results revealed that nanofluids did not perform as well as expected. Prior predictions from many analytical and numerical studies had promised significant performance gain. The performance of the 1% nanofluid was generally equal to that of the base fluid under identical inlet conditions. However, the performance of the 2% and 3% nanofluids was considerably lower than that of the base fluid. The higher concentration nanofluids exhibited heat rates up to 14.6% lower than the 60% EG and up to 44.3% lower heat transfer coefficient. The 1% Al2O3/60% EG exhibited a 100% higher pressure drop across the coil than the base fluid, considering equal heat output. This performance degradation was attributed to the inability to maintain nanofluid dispersion stability, agglomeration, and subsequent decline in the thermophysical properties.

A cryogenic tune and match circuit for magnetic resonance microscopy at 15.2T

Background and SignificanceAchievable signal to noise ratios (SNR) in magnetic resonance microscopy images are limited by acquisition times and the decreasing number of spins in smaller voxels. A common method of enhancing SNR is to cool the RF receiver coil. Significant SNR gains are realized only when the Johnson noise generated within the RF hardware is large compared to the electromagnetic noise produced by the sample. Cryogenic cooling of imaging probes is in common use in high field systems, but it is difficult to insulate a sample from the extreme temperatures involved and in practice imaging cryoprobes have been limited to surface or partial volume designs only. In order to use a solenoid in which the windings were not directly cooled and in close proximity to the sample, we designed a chamber to cool only the tune and match circuitry and show experimentally it is possible to achieve much of the theoretically available SNR gain. MethodsA microcoil circuit consisting of two tuning capacitors, one fixed capacitor, and SMB coaxial cable was designed to resonate at 650 MHz for imaging on a Bruker 15.2 T scanner. Sample noise increases with the sample diameter, so surface loops and solenoids of varying diameters were tested on the bench to determine the largest diameter coil that demonstrated significant SNR gains from cooling. A liquid N2 cryochamber was designed to cool the tune and match circuit, coaxial cable, and connectors, while leaving the RF coil in ambient air. As the cryochamber was filled with liquid N2, quality factors were measured on the bench while monitoring the coil's surface temperature. Improvements of SNR on images of ionic solutions were demonstrated via cooling the tune and match circuit in the magnet bore. ResultsAt 650 MHz, loops and solenoids < 3 mm in diameter showed significant improvements in quality factor on the bench. The resistance of the variable capacitors and the coaxial cable were measured to be 45% and 32% of room temperature values near the Larmor frequency. Images obtained with a 2 turn, 3 mm diameter loop with the matching circuit at room temperature and then cooled with liquid nitrogen demonstrated SNR improvements of a factor of 2. ConclusionsBy cooling the tune and match circuit and leaving the surface loop in ambient air, SNR was improved by a factor of 2. The results are significant because it allows for more space to insulate the sample from the extreme temperatures used in imaging cryoprobes.

Fast Analytic–Numerical Algorithms for Calculating Mutual and Self-Inductances of Air Coils

This paper deals with a method of calculating the mutual and self-inductances of various air coils located arbitrarily in space. Known elementary solutions (the Biot–Savart formulas) were used to determine the magnetic field of infinitely thin current loops and infinitely thin wires of finite length magnetically linking other coils. Unlike commonly used algorithms, these elementary solutions were not extensively transformed analytically but were used to perform calculations via direct numerical integration. This enabled the very quick and accurate obtaining of the self-inductance values, as well as determining the dependence of mutual inductances on the positions of both coils. This method allows for the analysis of different coil configurations (misaligned coils, inclined to each other, etc.) that other methods do not cover. It also enables the determination of the forces acting on the coils, as well as the calculation of the magnetic field distribution from any coil configuration. The obtained results were compared with those presented by other authors (both computational and measurement results).

Ferrite shielding thickness and its effect on electromagnetic parameters in wireless power transfer for electric vehicles (EVs)

Wireless power transfer (WPT) has become an increasingly popular technology for charging electronic devices wirelessly. One of the key challenges in WPT is increasing efficiency and reducing different losses in coils caused by the higher air gap and coil coupling between the primary and secondary coils. Ferrite shielding is a common technique used to reduce losses and increase the coupling in WPT systems. In this paper, we present an analysis and comparison study of the effect of ferrite shielding thickness (F_T) on the electromagnetic parameters of WPT systems. We investigate the impact of varying the ferrite shielding thickness on parameters such as power transfer efficiency, coupling coefficient (k), and magnetic field strength (B). Our results show that increasing the ferrite shielding thickness can significantly reduce losses and improve the performance of WPT systems. Also, analyze the trade-off between ferrite shielding thickness and power transfer efficiency and provide guidelines for selecting an optimal thickness for a given application. This study provides valuable insights into the design and optimization with weight vs. coupling comparison for WPT systems using ferrite shielding. It can help inform the development of future WPT technologies. The result obtained through simulation, i.e., coil-to-coil efficiency, is 98.88 to 99.7360% at 6.78MHz frequency for a 5-mm- to 50-mm-thick ferrite rectangular coupler using ANSYS Maxwell and ANSYS simplorer software.

A CFD investigation of the design variables affecting the performance of finned-tube heat exchangers

A wide variety of heating and cooling applications use heat exchangers. The increase in energy prices, the requirement for size reduction, and restriction on greenhouse gas emissions has led to the need for finding ways to develop efficient heat exchangers. A cost-efficient way to enhance the model of a heat exchanger by visualizing the effects of the design parameters is using Computational Fluid Dynamics (CFD). The reason for this exploration was to lead an examination of the varieties/changes in the general intensity move process for a Finned-Tube Heat Exchanger (FTHE), also known as Air Coil Heat Exchanger (ACHE) with a variety of plan boundaries like the quantity of tubes, course of action of tubes, and the material utilized for the intensity exchanger. The widely used heat exchanger that uses refrigerant R314a and air as the working fluids was simulated with different design modifications. The simulated results exhibited as to how the number of tubes, arrangement of coils/tubes, material of tubes, and density / spacing of fins, effects the pressure drop, temperature and velocities profiles, and heat exchangers’ transfer of a heat. The use of copper coils improved the heat transfer by approximately 61% as compared to aluminium coils.

A multi-mode packaged dedicated outdoor air system embedded with a four-coil heat pump

Dedicated outdoor air system (DOAS) plays a critical role in building ventilation. In recent years, much attention has been paid to the DOAS with heat-pump heat recovery. It is expected to have better dehumidifying performance and more operating modes to efficiently cooperate with the parallel cooling system. This work proposes a novel packaged DOAS embedded with a four-coil heat pump. Of the four coils, supply air coil and exhaust air coil are basic components of vapor compression heat pump that facilitates heat recovery from exhaust air. Return air coil is added to reduce heat loss in the mixing of return air and additional outdoor air. Supply air coil is introduced to reheat fresh air and avoid moisture condensation on air ducts. Meanwhile, refrigerant subcooling is increased in heat pump cycle for better efficiency. With simple switch the DOAS can also operate in four modes, i.e., outdoor air dehumidification, outdoor air low-load dehumidification, outdoor air heating and return air dehumidification. A functional prototype of 300 m3/h supply air is made and tested. Dehumidification capacity of 101.4 L/day and specific moisture extraction rate (SMER) of 3.22 kg/kWh are reached under the design condition of 30 °C/27 °C. Compared to the system without supply air coil, the new DOAS can see an improvement of 46.3% in SMER at the same supply air humidity ratio of 8.5 g/kga. It also keeps the supply air temperature above indoor air dew point. At last, the system's multi-mode operation for varying outdoor conditions is discussed.

A Differential Compensated Air Coil Current Sensor for Switching Current Measurement of Power Devices

Accurate current measurement is the basis for power devices to achieve switching characteristics evaluation, real-time control, reliability diagnosis, life prediction, etc. With the rapid development of power semiconductor device technology, requirements for current measurement are getting more and more stringent. The printed circuit board Rogowski coil current sensor (PCB RCCS) is a potential competitor, which has excellent bandwidth and integrability. However, the contradiction of the droop and drift phenomena as one of the main challenges restricts the employ of the RCCS in switching current measurements. In this paper, a differential compensation scheme that can solve these problems simultaneously with a lower error and cost is proposed. And the sensitivity and bandwidth of this sensor can be accurately obtained. Finally, a buck and single-phase full-bridge inverter experimental platform are built to verify the effectiveness of the PCB RCCS in the measurement of the switching current and inductor current, respectively.

Experimental Exergy Analysis of Air Flow Through Micro Helical Tubes with Novel Geometries under Adiabatic Conditions

Helical microtubes are commonly used in micro-electronic cooling techniques and micro-heat exchangers because of the creation of secondary flows, which leads to greater temperature and velocity gradients. It is of great significance to further improve the overall efficiency of the helical microtubes so as to diminish energy consumption. This experimental work mainly focuses on exergy analysis of air flow through adiabatic helical microtubes with circle, triangle, square, and pentagon geometries with circular cross section. The temperature rises due to viscose dispassion and pressure drops have been measured for all adiabatic helical coils in the laminar flow range. To identify irreversibility of flow, rate of air flow, coil diameter and Dean number are varied to investigate their influences on the entropy generation. Also, the second law of thermodynamics was applied to recognize exergy efficiencies and to determine true magnitudes of exergy losses. Results indicate that entropy generation increases by increasing the flow rate and the coil diameters in all geometries, however, the exergy efficiency decreases. By considering geometry, in constant flow rate and identical coil diameter, the highest entropy generation can be approximately observed in the triangles, squares, pentagons, and circles, respectively. Moreover, the proportions of theoretical exergy losses to actual exergy losses have been computed for all geometries in order to probe the viscous heating effects and it is found that the predicted exergy losses distinguish substantially from measured amounts due to viscose dispassion.

Optimized Weight Low-Frequency Search Coil Magnetometer for Ground-Airborne Frequency Domain Electromagnetic Method.

The vertical component magnetic field signal in the ground-airborne frequency domain electromagnetic (GAFDEM) method is detected by the air coil sensor, which is parallel to the ground. Unfortunately, the air coil sensor has low sensitivity in the low-frequency band, making it challenging to detect effective low-frequency signals and causing low accuracy and large error for interpreted deep apparent resistivity in actual detection. This work develops an optimized weight magnetic core coil sensor for GAFDEM. The cupped flux concentrator is used in the sensor to reduce the weight of the sensor while maintaining the magnetic gathering capacity of the core coil. The winding of the core coil is optimized to resemble the shape of a rugby ball, taking full advantage of the magnetic gathering capacity at the core center. Laboratory and field experiment results show that the developed optimized weight magnetic core coil sensor for the GAFDEM method is highly sensitive in the low-frequency band. Therefore, the detection results at depth are more accurate compared with those obtained using existing air coil sensors.

A review of underwater inductive wireless power transfer system

AbstractThe IPT system has been studied for underwater applications such as autonomous underwater vehicles (AUVs) and subsea sensors. However, it rarely comparatively shows the performance of the IPT system in air, freshwater, and seawater. Based on the fore‐mentioned research background, this paper presents a survey of the properties of the IPT system in different mediums. Here, a 100 W power‐level experimental IPT prototype is built and tested. The resonant frequency is set at 300 kHz with a gap range from 10 to 190 mm. The comparison is focused on the efficiency, mutual inductance, coupling coefficient, coil resistance, and quality factor of the IPT system. The IPT system is placed in air, freshwater, and seawater with the same settings. What's more, the magnetic fields of coupling coils in air, freshwater, and seawater are presented in this paper. This paper could be acted as a reference to optimize the IPT system and facilitate future IPT research for underwater applications by analysing the performance of the IPT system in different mediums. The 3D Ansys Maxwell simulation of the IPT system is also given here to study the magnetic fields.

Detection and Characterization of Fatigue Cracks in Butt Welds of Offshore Structures Using the Eddy Current Method

Abstract A reliable assessment of the actual condition of wind turbines is essential for their continuous operation, or if an extension of their service life is considered. To be able to make valid statements about the condition of the welded structure, an inspection concept for the reliable detection of fatigue cracks and damage on welds of the offshore tower and foundation structures is essential. In the present study, five different eddy current differential sensors were evaluated on cyclically fatigued DY butt welds under tensile load with a focus on the signal-to-noise ratio (SNR). Based on previous evaluations, two sensors were selected for semi-automatic weld testing. It is shown that due to the weld crossing necessary for the detection of fatigue cracks, air coils arranged parallel to the test surface have the highest SNR. This must be contrasted with the potential for crack depth determination. In this context, coils with different arrangements with respect to the test surface were analyzed. It is shown that groove depths can be differentiated based on the imaginary part of the measurement signal for groove depths of up to 8 mm, and actual fatigue cracks in welds with a crack depth of 0.5 mm were detected.

Influence of structural parameters on the static performance of self-inductive radial displacement sensor

The self-inductive displacement sensor has been widely used in active magnetic bearing systems for its excellent performance. However, there is a lack of studies on this sensor’s output characteristics according to the voltages directly from the coils, not from the processing circuit. Therefore, it needs to be further studied to improve the sensor theory and provide technical guidance for the sensor design. This paper analyzed the sensor’s working principle and designed some radial sensors with different nominal air gaps and coil turns. Then the effects of the nominal air gap and coil turns on the sensor coil’s output voltage and sensitivity were studied through the finite element simulation and experiments. According to the results, the number of coil turns could hardly affect the sensor’s static output voltage and sensitivity. The sensor sensitivity in the linear measurement range is proportional to the reciprocal of the nominal air gap length, but it is much less than the theoretical value. The results of this paper provide a valuable reference for the theoretical analysis and structural design of the self-inductive displacement sensor.

A review of superconducting fault current limiters compared with other proven technologies

• Fault Current Limiters Technologies. • Advantages and disadvantages of FCL technologies. • Commercial FCL Devices review. Several substations in operation were commissioned decades ago. These substations are overstressed, then their protection equipment cannot provide an effective safety condition to the system. In the worst cases, short-circuits can cause permanent damage to the system if the overcurrent is higher than the capacity of the installed equipment. There are some possible solutions for those cases: replace all the equipment in the overstressed substation, build a new one in parallel or install a fault current limiter (FCL) device. From an economic point of view, introducing FCLs in the power system is the best way to solve the described problem. The commercial solutions available are the pyrotechnic FCL, air coil reactor, neutral earthing resistor, and high impedance transformer. However, these devices are limited and present several drawbacks. Since the ’70s, there has been a search for reliable FCL devices that do not interfere in the regular operation of substations and could limit the fault currents to the protection system rated level. There were so many FCL technologies proposed in the last decades. These proposed new devices may use superconducting technologies, power electronics, or both. This paper reviews proven FCL technologies, focusing on full-scale devices demonstrated in field and lab tests. The goal is to introduce the main FCL technologies in development and discuss didactically their operation principle, the built prototypes, the commercial units, whether they exist, and the main drawbacks for each technology presented. A final analysis of the level of maturity for each FCL technology is discussed using the TRL (Technology readiness level) scale in order to find technologies with more potential for mass production. The three technologies closer to the full commercial application are: the Resistive Superconducting FCL, the Saturated Iron Core FCL, and the Series Reactor FCL.

Analytical Model of Electromagnetic Performance for Permanent-Magnet Vernier Machines Using Nonlinear Exact Conformal Model

This paper investigates the air-gap field distribution of the permanent-magnet vernier machine (PMVM) using nonlinear exact conformal model (NECM) to account for slotting effect, flux modulation effect and iron nonlinearity. The exact conformal model based on the region of one-slot and one-flux-modulation-pole (OSECM) are introduced to show the effectiveness of linear analytical model for PMVM. It can keep high calculation accuracy and significantly reduce the computational burden. Then, the NECM is developed from OSECM by introducing the equivalent saturation current into the air region and coil region. The lumped parameter magnetic circuit model (LPMCM) model is used to obtain the magnetic potential of iron region and therefore calculate the equivalent saturation current. The NECM which combines LPMCM and OSECM can essentially improve the accuracy of linear analytical model. The harmonic analysis of air-gap field is performed to theoretically explain the component of electromagnetic torque. Both finite element model (FEM) simulation and test results are presented to validate the NECM.

MO-0212 Dosimetric and geometric impact of on-patient placement of air coils in a clinical MRI-only workflow

MO-0212 Dosimetric and geometric impact of on-patient placement of air coils in a clinical MRI-only workflow

A Z-gradient coil on spheroidal geometry

A well-defined analytical magnetic field pattern is of merit in various fields of technological applications, especially in magnetic resonance imaging (MRI). Since the field inherently depends on the geometrical form of its generator, it is essential to put forth a convenient current coil structure to obtain a specific field pattern. This article is about the mathematical formulation, design, and production of a special spheroidal coil generating a magnetic field that linearly changes along its solenoidal axis. We proved that a specifically designed air coil helically wound on a spheroid, induces a perfectly linear field gradient. We also showed that the characteristic field pattern does not suffer from any changes in the geometrical size of the coil.

PERANCANGAN SISTEM AIR SUSPENSION PADA SEPEDA MOTOR HONDA VARIO 110

This study discusses the suspension on motorcycles by changing the standard suspension system, namely spring suspension / Coil Spring by designing an air suspension system to be applied to the Honda Vario 110 motorcycle. There are several problems with the suspension of spring-type motorcycles, namely when adjusting the suspension and the level of comfort. The purpose of this study is toknow the construction design, design and know the ratio of damping values pthere is an air suspension system and coil spring applied to the initial design of the motorcycle. The design and simulation method carried out is using Autodesk Inventor 2020 Software. In this design process, there are additions to the construction, namely the holder for the suspension as an air suspension support and changes to the size of the engine mounting which is extended to increase the suspension water storage space. As a result of the Autodesk Inventor 2020 simulation, the Air Suspension made of rubber with a load of 300 kg with a damping value of 7,744 N/m is greater than the initial suspension made of steel wire spring (SW) with a value of 7,500 N/m.

Measurement-Based Black-Box Harmonic Stability Assessment of Single-Phase Power Electronic Devices Based on Air Coils

The increasing share of power electronic (PE) devices in public electricity networks has increased the chance of harmonic instabilities, which are caused by the interaction of the device control with the network impedance. Usually, the detailed internal design of PE devices is not available and only measurement-based black-box approaches are feasible for the analysis of harmonic instabilities. A major drawback of such black-box approaches is the need for expensive programmable grid simulators. To overcome that issue, this article proposes a new approach to identify the sensitivity of a PE device for harmonic instabilities, which solely requires two air coils and which can simply be connected to any available power supply including the low voltage (LV) network. By systematically increasing the resulting inductance of air coils, the proposed method is able to identify the frequency regions that are critical with regard to the harmonic stability of the PE device. Critical frequency regions are determined by analyzing the measurement results in time-frequency domain using the estimation of signal parameters via rotational invariance techniques (ESPRITs). The proposed method is applied to a commercially available single-phase photovoltaic (PV) inverter. The critical frequency region has been determined at around 500 Hz, which is confirmed by formal stability analysis.

Experimental Assessment of a Magnetic Induction-Based Receiver for Magnetic Communication

This paper presents the topology of a novel approach to magnetic communication using a differential magnetic induction (MI)-based receiver and a differential MI receiving sensor. In this paper, a differential MI sensor based on two ferromagnetic cores is proposed as a receiving sensor, unlike the air coil-type MI sensor in the conventional search coil sensor concept. This differential MI sensor has the advantages of ultra-high sensitivity characteristics of the pT/√Hz level, which can detect weak magnetic fields in magnetic communication; moreover, the sensor is smaller than a conventional air coil MI sensor. The proposed differential MI sensor contributes to improving sensor performance by increasing its signal-to-noise ratio. The design and fabrication of the proposed MI sensor were based on a printed circuit board (PCB). The pickup coil of the PCB-based MI sensor directly wound the pickup coil onto a ferromagnetic core composed of Ni-Zn ferrite material. To analyze the key factors that affected the performance of the receiver, the magnetic field-to-voltage conversion ratio (MVCR) and equivalent magnetic spectral density measurements of the proposed PCB-based MI sensor were performed. Wireless digital communication using quadrature phase shift keying (QPSK), which is less sensitive to noise and has a high data rate, was used to evaluate the proposed MI-based receiver. The transmitted and received waveforms were compared to confirm that the transmitted digital data were accurately received as a result of the final demodulation of the receiver. Additionally, several performance metrics, such as constellation and error vector magnitude, were measured. The results of the comprehensive analysis confirmed the applicability of the proposed differential MI-based receiver to a magnetic field.

A Uniformed DC Magnetic Generator Using Ferromagnetic Slot Cage by Geomagnetism Distortion Cancellation

A widely uniform and highly ambient robust DC magnetic field generator for precise motion sensors using inertial measurement units (IMUs) is newly proposed in this paper. Chronic problems such as low uniformity of magnetic field and geomagnetic disturbance of conventional Helmholtz, Merritt, Rubens, Lee-Whiting, and Tetra coils can be significantly mitigated by the proposed uniform DC magnetic field generator (UFG). Different from the previous air coils, the proposed UFG adopts a core-cage so that a strong and uniform DC magnetic field distribution can be generated inside the cage and that the UFG may be quite magnetically robust to ambient changes such as geomagnetic field and ferromagnetic objects. A dedicated power supply was developed for providing not only a DC current to generate the required magnetic field but also an exponentially decaying AC current to demagnetize the residual magnetic field in the core-cage. Design procedures for the UFG are fully established, considering the manufacturing cost, performance, and mechanical robustness for commercialization. Detailed designs of the UFG for magnetic field generation, enhancing uniformity, geomagnetic cancellation, and demagnetizing of the UFG are provided. Experimental results verified by a 30 cm × 30 cm × 30 cm prototype UFG showed that the geomagnetic field inside the UFG was significantly attenuated by 22 dB while the DC magnetic field uniformity (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>t</i></sub> < 5.0°) was achieved over 85% of the total volume of 27,000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .