Coil Diameter Research Articles

Jet diameter of the first coil in the electrospinning whipping region: the role of fluid viscosity

In solution electrospinning, the ultrafine fiber is derived from the dramatic stretching of the whipping fluid jet. The first coil of the whipping fluid jet with the highest stretch rate plays a vital role in determining the microstructure and physical property of electrospun submicron/micron fibers. However, it still remains challenging to control precisely the stretching and jet diameter of the first coil of the whipping fluid jet. Herein, a comprehensive model for the jet diameter of the first coil of the whipping fluid jet is established, indicating that the jet diameter is a consequence of the balance between viscous and electrostatic forces, and is a function of the fluid viscosity, electric current, and flow rate. Furthermore, the stretch rate of the first coil of the whipping fluid jet is predicted, which decays as a scaling law with an exponent −1/2 along the axial direction. The theoretical predictions agree well with the experimental results. This work compensates for the deficiency of previous diameter models and enriches the mechanism of jet stretching, which can provide a valuable theoretical guide for the structural and functional design of submicron/micron fibers.

Research on the thermal performance of a heat exchanger with meso-scale twisted helical tube bundles

Heat exchangers with helical tubes are applied widely in various industrial fields and cryogenic applications. Currently, the most common ones are the spiral wound heat exchangers, which consists of many layers of spiral tubes with different coil diameters in a closed shell. Most of the fluid in the shell-side passes directly through the gap between two adjacent layers, which weakens the turbulence and the associated heat transfer coefficient. A novel twisted helical bundle geometry is proposed in this paper of which the thermal performance is explored using CFD simulation. The heat exchanger uses helium gas as the working fluid and operates between 300 K and 30 K. The curve of each tube in the bundle is generated by different 3D sinusoidal equations, and the tubes at adjacent layers are twisted together thereby producing the same end-to-end length for each tube. By simulating a spiral wound heat exchanger using different turbulent equations and comparing the results with experimental data from literature, the k-omega SST model is found to be the most suitable one to simulate this kind of geometry. Nusselt numbers and friction factors are obtained under different Re values and compared with those of standard spiral wound heat exchangers. The creative twisted geometry can improve the Nu number although also increasing the friction factor. Geometry parameters such as pitch length are being further explored to obtain an optimal thermal performance.

Liquid dripping dynamics and levitation stability control of molten Ti–Al–Nb alloy within electromagnetic fields

The dripping dynamics of the electromagnetically levitated (EML) liquid Ti–Al–Nb alloy under high temperatures was investigated by both numerical simulation based on the Arbitrary Lagrangian–Eulerian method and corresponding EML experiments. A dripping formation parameter εD was defined to describe the critical shape of alloy droplet. According to the simulated results, the high-temperature dripping phenomenon took place when εD < 0.68, which was in good agreement with experimental data. When dripping event occurred, the Lorentz force applied on alloy droplet decreased by approximately 11.7% within 0.07 s. Three typical methods were accordingly proposed to avoid the dripping failure of a bulk liquid Ti–Al–Nb alloy, which was implemented by enhancing electric current, adjusting levitation coil diameter, or increasing coil winding number. To control the droplet shape, the deformation pattern and the flow behavior of the liquid alloy were studied in a wide current range from 700 to 1400 A. With the increase in excitation current, the cone-shaped alloy melt transformed to a rhombus, and the flow behavior transformed from a typical four toroidal flow vortexes up to a complex eight toroidal flow vortexes. Moreover, the centroid position of liquid alloy rose up significantly at first and then slowly approached to levitation ceiling.

Antenna Characteristics of Helical Coil with 2.45 GHz Semiconductor Microwave for Microwave-Enhanced Laser-Induced Breakdown Spectroscopy (MW-LIBS).

A copper helical coil antenna was developed, characterized, and optimized for 2.45 GHz operations supplied by a microwave semiconductor oscillator. The application field of interest is laser-induced breakdown spectroscopy enhanced by microwave. Simulations using the Ansys HFSS demonstrate the superior localized E-field strength of the helical coil antenna, compared with other antenna-type structures. Simulation results show that E-field strength at the tip of the antenna has a logarithmic trend for increasing the coil pitch. The optimum pitch is 5 mm for a coil diameter of 6.5 mm upon consideration of the system compactness. Despite the antenna’s open-circuit end, the presence of target samples does not interfere with the E-field and H-field distribution of the antenna and the surrounding environment. Applications in microwave-enhanced laser-induced breakdown spectroscopy (MWLIBS) confirm the importance of the antenna reflector. The electric field strength was over 100 times higher than the previous capacitor-like antenna. The antenna configuration angle was then experimentally optimized for maximum enhancement effects in the spectrochemical analysis of Al2O3. The antenna angle of 60° from the laser beam propagation achieved maximum enhancement in the emission signal of Al I.

Detection of magnetic force fields at macroscopic distances with a micromechanical cantilever oscillator

We report a procedure for measuring variations of the magnetic field gradients generated by a macroscopic coil. A micromechanical cantilever oscillator covered with a magnetic material is used to detect variations of the magnetic force field at distances exceeding several times the coil diameter (4 mm). The detection is based on the phase of the first eigenmode of the cantilever while modulating the magnetic field at low frequencies. The nanoscale oscillation of the cantilever along with the high-quality resonance factor are responsible for a coherent oscillation allowing high sensitivity. A detection sensitivity, under ambient conditions, of the order of 10−13 T/nm2 is estimated with the help of numerical calculations. The approach is useful for evaluating the spatial variation of the magnetic field gradients generated by any source of magnetic field when the magnetic field can be modified at rates below the resonant frequency of the cantilever. These results can be useful for gradient fields monitoring in macro- and micro-scale magnetic resonance imaging, non-contact electric currents identification from stray magnetic fields, electrical power monitoring, 3D-magnetic fields mapping, or miniature orientation devices.

Analysis of Symmetric Two and Four-coil Magnetic Resonant Coupling Wireless Power Transfer

This study examined the efficiency of power transfer for two-coil and four-coil spiral magnetic resonant coupling wireless power transfer (WPT) using distance to coil diameter (D/dm) ratio and reflection coefficient, S21 value. Adding resonators reduced the total resistance in the two-coil WPT system while increasing the S21 values of the whole system. A same-size spiral coil was proposed for the system and simulated using computer simulation technology (CST). A prototype with similar specifications for a four-coil design was implemented for verification. The proposed method yielded an optimal efficiency of 76.3% in the four-coil system, while the two-coil WPT yielded a 23.2% efficiency with a 1.33 D/dm ratio.

Two‐Photon Printing of Shape‐Memory Microstructures and Metasurfaces via Radical‐Mediated Thiol‐Vinyl Hydrothiolation

AbstractShape‐memory resists capable of high‐resolution curing into arbitrarily designed structures are increasingly demanded for soft robotics, optical sensors, microscale manufacturing, and biomedicine. Amorphous, shape‐memory thiol‐vinyl networks are printed using two‐photon polymerization (2PP) curing of a simple resin formulated with commercially available reagents. The ability to print high‐resolution feature sizes down to 200 nm is attributed to the use of radical‐mediated, thiol‐vinyl step‐growth polymerization that quickly cross‐links the resin, limiting diffusive transport. The thermomechanical behavior of the 2PP‐cured material analyzed in compression, tension, and three‐point bending is similar to the behavior of the UV‐polymerized samples. To demonstrate the ability to design, field, and test 4D responsive microstructures, an array of nine springs with coil diameters of 330 µm is printed. Following compressive shape‐fixing, printed arrays can release 11 µJ of stored elastic strain energy when reheated. Further, a new concept of dichroic‐memory of a metamaterial device is demonstrated by printing a twisted woodpile structure with circular dichroism as characterized by Mueller Matrix ellipsometry. The results of this study demonstrate how combining high‐resolution 2PP curing with stimuli‐responsive molecular architectures can further the engineering of responsive microstructures and metamaterials.

Combined Membrane Dehumidification with Heat Exchangers Optimized Using CFD for High Efficiency HVAC Systems.

Traditional air conditioning systems use a significant amount of energy on dehumidification by condensing water vapor out from the air. Membrane-based air conditioning systems help overcome this problem by avoiding condensation and treating the sensible and latent loads separately, using membranes that allow water vapor transport, but not air (nitrogen and oxygen). In this work, a computational fluid dynamics (CFD) model has been developed to predict the heat and mass transfer and concentration polarization performance of a novel active membrane-based energy exchanger (AMX). The novel design is the first of its kind to integrate both vapor removal via membranes and air cooling into one device. The heat transfer results from the CFD simulations are compared with common empirical correlations for similar geometries. The performance of the AMX is studied over a broad range of operating conditions using the compared CFD model. The results show that strong tradeoffs result in optimal values for the channel length (0.6–0.8 m) and the ratio of coil diameter to channel height (~0.5). Water vapor transport is best if the flow is just past the turbulence transition around 3000–5000 Reynolds number. These trends hold over a range of conditions and dimensions.

Performance analysis of shell and helical tube heat exchanger using CuO/water and Al2O3/water nanofluids

PurposeA computational fluid dynamics based parametric analysis for shell and helical tube heat exchanger (SHTHE) using CuO/water and Al2O3/water nanofluids is the main purpose of the present work. The parameters having impact on the performance of a heat exchanger have been studied in depth. As the solid nanoparticle shows higher thermal conductivity compared to liquid particles, inclusion of this nanoparticle into the base fluid significantly enhances the thermal conductivity of the liquid. Incorporation of nanofluid in the heat exchanger can increase its performance.Design/methodology/approachThe simulation is performed in Solid-Works flow simulation, and the performance of SHTHE is observed by varying the pitch of helical tube from 0.013 to 0.018 m and coil diameter from 0.0813 to 0.116 m, keeping the other parameters constant. The tube side and shell side flow rate is kept as 2 LPM.FindingsThe results indicate that the effectiveness of the heat exchanger increases with the increase of pitch and coil diameter. The maximum effectiveness of 0.5022 for CuO/water and 0.4928 for Al2O3/water nanofluid is observed at a pitch of 0.018 m and the coil diameter of 0.116 m.Originality/valueIt is observed that CuO/water nanofluid shows better performance compared with Al2O3/water nanofluid. For a coil diameter of 0.116 m and pitch of 0.018 m, the SHTHE with CuO/water nanofluid shows 1.82% greater effectiveness compared to the effectiveness with Al2O3/water nanofluid.

Water ice-cooled MgB2 coil made by wind and react process

A wind and react (W&R) coil of inner diameter 53 mm has been made from multi-core MgB2/Nb/CuNi wire manufactured by the internal magnesium diffusion (IMD) process. The W&R coil is wound from non-insulated rectangular wire of 1 mm2 with only 5 µm thick stainless steel foil used for interlayer insulation. The transport current performance of the coil and short wire samples was measured in a liquid He bath at external magnetic fields of 4.5–8.5 T and also in self-field conditions in sub-cooled water ice at temperatures between 33 K and 38 K. The presented MgB2 coil exhibits stable behavior at water ice cooling, and its high space factor allows a high current density of winding in comparison to the data from the already published MgB2 coils. The presented results demonstrate that MgB2 windings can be used safely in He-free conditions inside sub-cooled water ice, and this technique can be further optimized and used for future MgB2 coils.

Study on the radiofrequency transparency of electrically floating and ground PET inserts in a 3T clinical MRI system.

The positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system that implements the radiofrequency (RF) built-in body coil of the MRI system as a transmitter is designed to be RF-transparent, as the coil resides outside the RF-shielded PET ring. This approach reduces the design complexities (e.g., large PET ring diameter) related to implementing a transmit coil inside the PET ring. However, achieving the required field transmission into the imaging region of interest (ROI) becomes challenging because of the RF shield of the PET insert. In this study, a modularly RF-shielded PET insert is used to investigate the RF transparency considering two electrical configurations of the RF shield, namely the electrical floating and ground configurations. The purpose is to find the differences, advantages and disadvantages of these two configurations. Eight copper-shielded PET detector modules (intermodular gap: 3mm) were oriented cylindrically with an inner diameter of 234mm. Each PET module included four-layer Lutetium-yttrium oxyorthosilicate scintillation crystal blocks and front-end readout electronics. RF-shielded twisted-pair cables were used to connect the front-end electronics with the power sources and PET data acquisition systems located outside the MRI room. In the ground configuration, both the detector and cable shields were connected to the RF ground of the MRI system. In the floating configuration, only the RF shields of the PET modules were isolated from the RF ground. Experiments were conducted using two cylindrical homogeneous phantoms in a 3T clinical MRI system, in which the built-in body RF coil (a cylindrical volume coil of diameter 700mm and length 540mm) was implemented as a transceiver. For both PET configurations, the RF and MR imaging performances were lower than those for the MRI-only case, and the MRI system provided specific absorption ratio (SAR) values that were almost double. The RF homogeneity and field strength, and the signal-to-noise ratio (SNR) of the MR images were mostly higher for the floating PET configuration than they were for the ground PET configuration. However, for a shorter axial field-of-view (FOV) of 125mm, both configurations offered almost the same performance with high RF homogeneities (e.g., 76±10%). Moreover, for both PET configurations, 56±6% larger RF pulse amplitudes were required for MR imaging purposes. The increased power is mostly absorbed in the conductive shields in the form of shielding RF eddy currents; as a result, the SAR values only in the phantoms were estimated to be close to the MRI-only values. The floating PET configuration showed higher RF transparency under all experimental setups. For a relatively short axial FOV of 125mm, the ground configuration also performed well which indicated that an RF-penetrable PET insert with the conventional design (e.g., the ground configuration) might also become possible. However, some design modifications (e.g., a wider intermodular gap and using the RF receiver coil inside the PET insert) should improve the RF performance to the level of the MRI-only case.

Effect of geometrical and operational parameters on paraffin's melting performance in helical coiled latent heat storage for solar application: A numerical study

In latent heat storage (LHS), the melting of phase change material depends on the flow path of the heat transfer fluid (HTF). The helical path is one of the most effective arrangements for the intended heat exchange between PCM and HTF. The geometric parameters of the helical path such as the coil diameter, coil pitch, tube diameter influences heat transfer rate. In the presented study, the geometric parameters of the helical path and HTF flow parameters are varied to study the effect on the PCM (paraffin wax 56 °C - 58 °C) charging of the vertical helical coiled LHS system numerically. It is found that with an increase in the coil spacing, the charging process is improved, and approx. 20% of the melting time is saved if the 16 mm pitch is increased to 27 mm. The other parameters which affect the charging are the ratio of coil diameter to shell diameter, the optimal value of the ratio lies in the range of 0.65–0.75. In addition to the geometric parameters, different values of the operating parameters like inlet temperature and HTF flow rate are used to simulate the solar field application. When HTF's inlet temperature is increased from 70 °C to 75 °C and 75 °C to 80 °C, the required charging time is reduced by 28%, and by 22%, respectively. Moreover, when the HTF flow rate is varied from 1 LPM to 5 LPM, there is no significant difference in the charging rate of the PCM. The change in the geometric and operating parameters affects heat transfer and PCM motion thus melting rate varies.

Multiwire Parallel Fluxgate Sensors

Fluxgate sensors with straight wire or rod cores are used in nondestructive testing (NDT), portable gradiometers, and sensor arrays and for the detection of small objects. We show that their sensitivity at the voltage output mode depends on the excitation parameters, properties of the core material and geometry, pick-up coil length, but only slightly on the pick-up coil diameter. This finding allows one to design multiwire cores with large wire pitch, which decreases their magnetic interactions and thus reduces demagnetization and correlation of their noise. As a result, using <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> wires theoretically increases sensitivity <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula>-times, which is not achievable with dense cores. We have demonstrated this tendency for <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> up to 8 and one type of permalloy wire.

Nonlinear elastic plastic load deflection curves in NiTi shape memory alloy helical coils

Reversible deflection of coil spring due to shape memory effect was examined. Coil springs were prepared by winding the wire of Nickel -50.at.% Titanium alloy followed by the annealing at 800 C for 1h to set the coil shape. The Mf and Af temperatures were 30 C and 87 C and the spring was deformed in the fully martensite state at room temperature. A tough pitched spring with the coil diameter of 6.6 mm and the element diameter of 0.6 mm showed shape memory effect after extension larger than 1,000 %. The load-deflection curves measured showed nonlinear relationship with rapid increase of load at a certain extension. It was found that the shape memory strain of coil spring is not limited by that of element wire but by the geometry of coil spring against the extension. Noted that and the deflection was accompanied with the rotation around the coil axis. Elastic plastic deflection analysis was performed, and the prediction of the theory was compared with the experimental curves.

Numerical analysis of wire coil inserted corrugated tube for laminar flow

Laminar flow in which fluid particles flow in organised manner with definite path. The heat transfer performance of heat exchange device in case of laminar flow comparatively lower. There are different techniques described in the literature to augment heat transfer. Providing corrugation on heat exchange surface is one of the techniques. The current research focuses on numerical analysis of thermal hydraulic performance for pipes with coil-wire inserts when different coil-wire insert parameters are varied. Initially, wire coil diameters of 0.5, 1, and 1.5 mm with a pitch of 40 mm are considered for investigation in laminar flow at Reynolds numbers ranging from 437 to 2188. For laminar flow, a wire coil diameter of 0.5 mm provides the best thermo-hydraulic performance.

A study on transmission coil parameters of wireless power transfer for electric vehicles

Electric vehicles (EVs) are becoming more popular as people become more concerned about global issues, such as fossil fuel depletion and global warming, which cause severe climate change. Wired charging infrastructure is inefficient because it requires the construction of one charging station for each electric vehicle. As a result, wireless power transfer via magnetic coupling, which is small, compact, and may be placed underground, is a promising technology for the future of charging electric vehicles. One of the disadvantages of wireless power transfer is that efficiency drops rapidly as air gaps grow larger, and it is particularly sensitive to other electrical characteristics such receiver unit capacitance. The purpose of this paper is to investigate the coil parameter, more specifically the outer diameter of wireless power transfer coil effects on the wireless power transfer efficiency at various air gaps and receiver capacitance values for EV applications. The simulations show that a larger outer diameter coil has a better power transfer efficiency at larger air gaps and a more stable range.

Development of an analytical model for the dryout characteristic in helically coiled tubes

In helically coiled tubes, the geometry-induced centrifugal force exerts upon the fluid to make the dryout phenomenon complicated. Hence, it is essential to understand the dryout mechanism and develop a model to accurately predict the dryout quality and dryout pattern in helically coiled tubes that can cover a wide range of parameters. In this paper, 17 helically coiled tubes with different coil diameters (160 ∼1350 mm), inner diameters (9 ∼14 mm) and inclined angles (2.5 ∼ 10°) are used to conduct the experimental study of the dryout characteristic under different conditions, including pressure between 2 and 7 MPa, mass flow rate between 100 and 1000 kg/(m2·s), heat flux between 50 and 700 kW/m2. Three types of dryout patterns in helically coiled tubes were observed by analyzing the circumferential distribution of the wall temperature, including the gravity-dominated pattern, the secondary-flow-dominated pattern and the centrifugal-force-dominated pattern. Then the effects of the operational and geometric parameters of helically coiled tubes on the dryout characteristic have been studied, such as system pressure, mass flow rate, heat flux, tube diameter and coil diameter. Finally, a “dryout map” was developed based on the experimental data (297 data points), and an analytical model of dryout quality was proposed in terms of dimensionless groups for each zone. The correlations were verified by comparing with the experimental results in the open literature. The proposed correlations in this paper can give a better prediction for different experimental results.

HEAT TRANSFER CHARACTERISTICS OF THE HELICAL OSCILLATING HEAT PIPE WITH A CHECK VALVE

The performance of the helical oscillating heat pipe (HOHP) is remarkable. It was improved by the check valve (CV). The scarcity of helical oscillating heat pipe with a check valve (HOHP/CV) literature necessitates. The purpose of this research is to investigate the heat transfer characteristics of the HOHP/CV with various working fluids such as R11, ethanol, and DI water. The HOHP/CV was constructed from copper tubes with inner diameters of 1.8, 2.4, and 3.4 mm. The condenser and evaporator were of the same length, but the straight tube was divided into three lengths, 600, 800, and 1000 mm, before bending to a helical shape. The coil diameter was set to 50 mm, and the pitch to 10 mm. It was tested at three angles of inclination: 30, 60, and 90 degrees. The heat sources were 60, 75, and 90 oC. The condenser temperature was set to 25 oC, and the flow rate was set at 20 liters/hour. The adiabatic section was fixed at 100 mm and a check valve was installed per tube, but this condition was divided into two positions, namely up-flowing and down-flowing direction of a working fluid. The thermocouple Type-K and data logger were used to record the inlet and outlet water temperatures in the condenser section. The highest heat flux was 12.84 kW/m2, which occurred at the 1000 mm tube length, inclination angle 90 degrees, inner diameter 3.4 mm, R11 as working fluid, and check valve installed on the down-flowing side.

Experimental analysis to study the effect of perforated louvered strip‐coiled spring insert on heat transfer performance in a double pipe heat exchanger

AbstractExperiments have been conducted to study the effect of louvered strip‐coiled spring (PLSCS) turbulators having different pitches and the same angle of attack on thermal performance and pressure drop of a concentric tube heat exchanger. Two inserts in combined form were used for experimentation under turbulent flow at different Reynolds numbers (Re) ranging between 5000 and 20,000. Two pitches (40 mm and 50 mm) of elliptical‐shaped perforated louvered strips (PLS) having the same angles of attack have been taken that were welded on the central core rod. Spring inserts have the same coil diameter of 12 mm with two varying pitches to achieve pitch ratios of 0.5 and 1. Both heat transfer and pressure drop increase with a decrease in pitches of both LS and spring inserts. Nusselt number has the maximum value with spring of pitch 6 mm in combination with a PLS of 40 mm pitch at which is 130.75% higher than the plain tube at the lowest Re among the PLSCS inserts. With perforation, a slight increase in both Nusselt number and friction factor was observed. The maximum thermal performance efficiency value is 1.105 for the lowest Re value.

Highly stretchable-compressible coiled polymer sensor for soft continuum manipulator

In recent years, soft continuum robots have become emerging research hotspots, but sensing of the robot shape needs to be addressed for precise control. To solve this problem, we present an optical coiled polymer sensor that can measure strain based on macro bending power loss. Proposed sensor is fabricated by coiling and annealing a polymer optical fiber of diameter 0.25 mm. Under applied strain, the bending curvature of the coiled sensor changes which leads to light intensity change. Due to its coiled design, the proposed sensor is highly stretchable and can measure both tensile and compressive strain of the coiled sensor structure in a wide range (>250%). Static and dynamic responses of the proposed sensor were observed by controlling the design parameters, such as spring diameter and number of coils. Fabricated coiled polymer sensor with a light-weight (<0.5 g) and compact structure showed a high stretchability-compressibility, high stability, and low hysteresis error. By placing three fabricated sensors inside the soft continuum manipulator, a 3-degree-of-freedom (DOF) configuration including bending and torsion motions can be obtained. We used an artificial neural network to derive the relationship between the sensor outputs and the 3 DOFs configuration of the soft continuum manipulator. The results showed that the configuration of the soft continuum manipulator can be obtained in real-time with high accuracy (error < 2.17%).