Coil Surface Research Articles

Dehumidification effects in the superheated region (SPR) of a direct expansion (DX) air cooling coil

A DX air cooling coil may normally be assumed to have two regions in its refrigerant side, according to refrigerant status, a two-phase region (TPR) and a superheated region (SPR). Dry air side surface of the SPR in a DX air cooling coil has been normally assumed in lumped-parameter mathematical models previously developed without however being validated. Therefore, an experimental study has been carried out to examine such an assumption under different operating conditions. The experimental results suggested that the air side surface of the SPR in a DX air cooling coil was either fully or partially wet under all experimental conditions and assuming dry air side of the SPR could lead to an underestimated total amount of water vapor condensed on the entire DX coil surface. Therefore, it is recommended that the assumption of dry air side in a SPR be no longer used in future lumped-parameter models to be developed for improved modeling accuracy.

Needleless electrospinning of nanofibers with a conical wire coil

AbstractIn this article, we have demonstrated a novel needleless electrospinning of PVA nanofibers by using a conical metal wire‐coil as spinneret. Multiple polymer jets were observed to generate on the coil surface. Up to 70 kV electric voltage can be applied to this needleless electrospinning nozzle without causing “corona discharge.” Compared with conventional needle electrospinning, this needleless electrospinning system produced finer nanofibers on a much larger scale, and the fiber processing ability showed a much greater dependence on the applied voltage. Finite element calculation indicates that the electric field intensity profiles for the two systems are also quite different. This novel concept of using wire coil as the electrospinning nozzle will contribute to the further development of new large‐scale needleless electrospinning system for nanofiber production. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Delineation of frost characteristics on cold walls by using a new formula for psychrometrics demarcation boundary

In this study, a direct formula that predicts either the frost formation on cold walls is correspondence to psychrometric-subsaturated or supersaturated regions is presented. The developed formula uses the data of the entering air dry-bulb temperature and absolute humidity, and the absolute humidity of the air at saturation corresponding to the coil surface temperature. Cases studies of demarcation criteria for frost formation on evaporator coil using experimental measured data, and on walls of cold storage freezer using measured data from literature are used to validate the formula and it is found that results are completely matches to the graphic plot of the data on the psychrometric chart. In case of cold storage freezers, the result clearly shows that a greater demarcation criteria value indicates frost formation under sever condition that is characterized as snow-like with low density and thermal conductivity.

Finite element analysis for cooling effect of magnetic fluid with alternating magnetic field

We present a fully coupled finite element method (FEM) for analyzing a cooling effect of magnetic fluid with an alternating magnetic field driven with the power frequency, 60 Hz. There are two different heat sources with an alternating magnetic field such as the Joule’s loss in coils excited with electric input and the power dissipation corresponding to Neel and Brownian relaxation. Because the input frequency is relatively low, the Joule’s loss in coil is a dominant heat source. The heat, therefore, transfers from the coil to the magnetic fluid and the natural convection phenomena arise on the coil surfaces. To consider the natural convection phenomena, the buoyant force density was considered in a magnetic fluid. Additionally, the forced convection, magnetoconvection, results from the magnetic body force density with the magnetization as a function of magnetic field intensity and temperature. These two convection phenomena play a key role for cooling effect of magnetic fluid with an alternating magnetic field. To derive the magnetic body force density, we, here, numerically employed the continuous approach of Kelvin force density, which has been derived by introducing the virtual air-gap scheme incorporating with the FEM. The Langevin function was employed to consider the nonlinear magnetic susceptibility for evaluating the Kelvin force density and the power dissipations due to the Neel relaxation and Brownian relaxation.

Probing the Recognition Properties of the Antiparallel Coiled Coil Motif from PKN by Protein Grafting

Coiled coils have long been recognized as the major constituent of many fibrous proteins and also serve as oligomerization domains in a wide variety of proteins. More recently, it has become clear that the surfaces of two-stranded coiled coils are also involved in macromolecular recognition. Indeed, the helical hairpin or intramolecular antiparallel coiled coil (ACC) can serve as a protein or nucleic acid recognition motif. Protein kinase N (PKN) interacts with the small GTPase RhoA through ACC motifs. The crystal structure of RhoA with the N-terminal ACC motif (PKN-ACC1) is unusual in that these proteins interact through two distinct surfaces. Using the ACC domain of seryl tRNA synthetase (SRS-ACC) as a scaffold for protein grafting experiments, we show that RhoA interacts with only one face of PKN-ACC1. This result highlights the potential of the SRS-ACC scaffold for protein engineering applications and provides insight into the mechanism of RhoA-mediated signal transduction through PKN.

Induction shimming: A new shimming concept for superconductive undulators

Undulators are the most advanced sources for the generation of synchrotron radiation. The photons generated by a single electron add up coherently along the electron trajectory. In order to do so, the oscillatory motion of the electron has to be in phase with the emitted photons along the whole undulator. Small magnetic errors can cause unwanted destructive interferences. In standard permanent magnet undulators, the magnetic errors are reduced by applying shimming techniques. Superconductive undulators have higher magnetic fields than permanent magnet undulators but shimming is more complex. In this paper it is shown that coupled superconductive loops installed along the surface of the superconductive undulator coil can significantly reduce the destructive effect of the field errors. This new idea might allow the building of undulators with a superior field quality.

Heat transfer model of slurry ice melting on external surface of helical coil

This research studies the heat transfer phenomenon of melting slurry ice on external surface of a copper helical coil. There is water flowing inside the tube coil and exchanging heat with the slurry ice. In this experiment, the coil diameters are 6.35 mm and 9.53 mm each of 4.2 m coil length. The mass flow rate of water in the helical coil is between 0.0149–0.0562 kg/s, while the inlet temperature of water is varied in the range of 23–27 °C. The slurry ice has 60% ice and 40% water by mass at the starting. The experimental results show that, with small coil diameter, high mass flow rate of circulating water and low ice fraction, high heat transfer coefficient of the slurry ice at the warm helical coil surface is obtained. The heat transfer models of slurry ice during melting and post-melting in terms of Nusselt number with the pertinent parameters are also developed. The results agree very well with the experimental data.

The dependence of the chain branching degree on molecular weight: Fractal analysis

The fractal analysis methodology allows the clear structural identification of both chemical and physical factors controlling a chain branching degree. The effective number of branching centers per one macromolecule m is controlled by four factors: polymer molecular weight, MW, maximal 'chemical' density of reactive centers, cch, dimension of non-screening surface of macromolecular coil, du, and its fractal dimension, D. The presented research allows the determination of the critical value, Dcr = 1.10, the lower of which branching degree is equal to zero (i.e., branching does not occur).

Simulation-based prediction of hot-rolled coil forced cooling

Hot-rolled coils take a long time to cool under normal storehouse conditions due to their high mass. Hotter seasons will lead to even longer storage times and, thus, to shortage of space. Forced cooling methods such as water-immersion and water-spray can be employed to reduce hot-rolled coil cooling time. In this paper, a mathematical model of the thermal behavior of coils is developed to predict and to evaluate the results expected from employing these methods before any real changes can be made on the ground. The results obtained from the model were compared with those from various experiments to verify the model’s accuracy. The cooling time was then computed based on changes effected in the boundary conditions appropriate to each of the forced cooling methods employed. Moreover, the savings in storage times were compared to identify the best cooling method. Predictions showed that water immersion at the beginning of cooling cycle was more effective and that the cycle should not exceed 1 h for cost efficiency considerations. When using nozzles to spray it was found that spraying water on end surfaces of coils would be the optimum option resulting in savings in time, water and energy, and with restricted temperature gradient.

Evaluation of tungsten coil electrothermal vaporization-Ar/H 2 flame atomic fluorescence spectrometry for determination of eight traditional hydride-forming elements and cadmium without chemical vapor generation

A tungsten coil electrothermal vaporizer (W-coil ETV) was coupled to an Ar/H 2 flame atomic fluorescence spectrometer for the determination of eight traditional hydride-forming elements (i.e., As, Bi, Ge, Pb, Sb, Se, Sn, and Te) as well as cadmium without chemical vapor generation. A small sample volume, typically 20 μL, was manually pipetted onto the W-coil and followed by a fixed electric heating program. During the vaporization step, analyte was vaporized off the coil surface and swept into the quartz tube atomizer of AFS for further atomization and excitation of atomic fluorescence by a flow of Ar/H 2 gas, which was ignited to produce the Ar/H 2 flame. The tungsten coil electrothermal vaporizer and Ar/H 2 flame formed a tandem atomizer to produce reliable atomic fluorescence signals. Under the optimal instrumental conditions, limits of detection (LODs) were found to be better than those by flame atomic absorption spectrometry (FAAS) or inductively coupled plasma optical emission spectrometry (ICP-OES) for all the nine elements investigated. The absolute LODs are better or equivalent to those by hydride generation atomic fluorescence spectrometry (HG-AFS). Possible scattering interferences were studied and preliminary application of the proposed method was also reported.

Study of Cryogenic Conduction Cooling Systems for an HTS SMES

Superconducting magnetic energy storage (SMES) is more fast response, economical, and environment-friendly than uninterruptible power supply (UPS) using the battery. And the SMES not only has the ability to control active and reactive power simultaneously, but also has a long life time because the superconducting magnet does not have degradation problem which the battery has. Therefore, the SMES is a candidate for instead of the UPS using the battery. The SMES needs cryogenic system without exception. A conduction cooling system that has a simple, light and small structure is well adapted to high temperature superconducting (HTS) SMES. The cryogenic conduction cooling system is needed some technologies such as insulation, vacuum, and thermal analysis. Conduction heat is mainly transferred by cooler port, access port, support bar, etc., and radiation heat is transferred by vacuum chamber, thermal shield and HTS coil surface. The heat loads through the conduction and radiation of cryostat are calculated. Radiation shield heat load, temperature of HTS coil and conduction copper plate are estimated and measured. A cryopumping effect of cooled radiation shield was observed. A current lead and HTS coil heat load was evaluated to maintain HTS coil temperature was under 20 K.

Distance-adjusted motor threshold for transcranial magnetic stimulation

Objective To examine the relationship between coil–cortex distance and effective cortical stimulation using transcranial magnetic stimulation (TMS) in the left and right motor cortex. We also compare the effect of coil–cortex distance using 50 and 70 mm figure-eight stimulating coils. Methods Coil–cortex distance was manipulated within each participant using 5 and 10 mm acrylic separators placed between the coil and scalp surface. The effect of cortical stimulation was indexed by resting motor threshold (MT). Results Increasing distance between the coil and underlying cortex was associated with a steep linear increase in MT. For each additional millimetre separating the stimulating coil from the scalp surface, an additional ∼2.8% of absolute stimulator output (∼0.062 T) was required to reach MT. The gradient of the observed distance effect did not differ between hemispheres, and no differences were observed between the 50 and 70 mm TMS coils. Conclusions Coil–cortex distance directly influences the magnitude of cortical stimulation in TMS. The relationship between TMS efficacy and coil–cortex distance is well characterised by a linear function, providing a simple and effective method for scaling stimulator output to a distance adjusted MT. Significance MT measured at the scalp-surface is dependent on the underlying scalp–cortex distance, and therefore does not provide an accurate index of cortical excitability. Distance-adjusted MT provides a more accurate index of cortical excitability, and improves the safety and efficacy of MT-calibrated TMS.

PARÂMETROS QUE AFETAM O DESGASTE DAS CHAPAS METÁLICAS DURANTE A LAMINAÇÃO A FRIO

The Acesita’s cold rolling mill number 4, LB4, has a oil filter system that left to lose working time when stopped, because the excess of dirty. In this work, we developed a method to evaluate the generation of wear debris on sheet surface during cold rolling, intending to approximate to the real process condition. In this way, some analysis of material used, like samples and filter system residues were done. This work shows detachment of particles of metal during the cold rolling as a normal process condition. This phenomena increases with the increase of oil temperature, total cold reduction, surface and edge of coil. The process wasn’t with a problem and we needed to change the filter elements of the system.

Calculating Efficient Noise Resistance of RF Coils in Low Field MRI Systems

An analytical method to calculate efficient noise resistance of RF coils in low field MRI systems is presented. Coil self-resistance and sample resistance are evaluated respectively. Using this method, efficient noise at 12.72 MHz of solenoid coil and square-shaped surface coil are calculated. The results show that the coil self-resistance and sample resistance of surface coils are comparable. Thus, both parts of efficient resistance should be calculated when optimizing signal-to-noise ratio to design geometries of RF coils. DOI: 10.2529/PIERS061007080309

Migration of slab defects during hot rolling

Blisters and slivers are serious defects that can lead to downgrading and rejection of interstitial free (IF) steels used for automotive applications as they affect the painted appearance, structural integrity, durability and performance. It is therefore important to understand the origin of these defects and to follow their morphological changes during all stages of manufacturing. This paper presents a novel method to study continuously cast slab defects (inclusions, pores, gas entrapments) in terms of their migration towards the surface during hot rolling. The method adopted is a combination of experimental and numerical techniques. The experimental method involves a 'step machining' process where the slab surface is machined gradually to find out the nature and location of defects. These defects are then correlated in terms of their ability to cause blisters or slivers on the final hot rolled coil surface. The numerical method involves finite element simulation of multipass hot rolling with defects embedded at different depths from the slab surface. The experimental findings with respect to the migration of defects are in general agreement with the numerical predictions. This analysis provides a guidance and direction towards producing defect free IF coils as well as improvements in productivity and yield.

Theoretical, numerical, and experimental modal analysis of a single-winding gradient coil insert cylinder

The objective of this paper is to find the relatively low-frequency (200-2,000 Hz) mode shapes of a single-winding gradient coil cylinder with intermediate wall thickness. The dynamic behavior of a gradient coil cylinder plays a crucial role in determining and controlling the vibroacoustic performance of magnetic resonance imaging (MRI) scanners. Modal analyses of the gradient coil cylinder were carried out under different boundary conditions to obtain the various mode shapes. Theoretical modes, predicted by using modified Love's governing equations, and numerical modes simulated using a finite element method show close agreement with experimental modal results and reveal the mode shapes for both free-end and fixed-end boundary conditions. These results were further compared to in situ measurements of the mode shapes of the gradient coil cylinder insert during scanning in a 4 Tesla MRI. The general agreement among the analytical, numerical, and experimental mode shapes indicates that a linear combination of basic beam vibration and ring vibration patterns occupy the dynamic vibration modes in the low frequency range. The in situ vibration measurements show that the forcing function developed by the distributed Lorentz forces on the surface of the single-winding gradient coil results in predominantly beam-type bending mode patterns in the low frequency range.

Prediction of the air temperature and humidity at the outlet of a cooling coil using neural networks

The main objective of this study is to predict air temperature and humidity at the outlet of a wire-on-tube type heat exchanger using neural networks. For this purpose, initially the heat exchanger was coupled to a refrigeration unit and placed in a wind tunnel. Afterwards, its performance was tested under various experimental conditions. We measured nine input parameters, namely, temperature and humidity of the air entering the coil, air velocity, frost weight, the temperature at the coil surface, mass flow rate of the heat transfer fluid and its temperatures at the inlet and outlet of the coil along with ambient temperature. Additionally, we measured temperature and humidity of the air leaving the coil as the output parameters. Then, a feed-forward neural network based on backpropagation algorithm was developed to model the thermal performance of the coil. The artificial neural network (ANN) was trained using the experimental data to predict the air conditions at the outlet of the coil. The predicted values are found to be in good agreement with the actual values from the experiments with mean relative errors less than 1% for outlet air temperature and 2% for outlet humidity. This demonstrates that the neural network presented can help the manufacturer predict the performance of cooling coils in air-conditioning systems under various operating conditions.

Stress relief effect on fatigue and relaxation of compression springs

In the manufacturing process of mechanical springs, high tensile residual stresses are generated which reduces considerably the spring strength and service life. These unfavorable residual stresses are partially eliminated by the heat treatment. In this process, the spring is heated uniformly below the material transformation temperature. An experimental investigation has been conducted to assess the stress relief influence on helical spring fatigue properties. First, S– N curves were determined for springs treated under different conditions (times and temperatures) on a testing machine specially designed to do this task. Next the stress relief effect on spring relaxation induced by cyclic loading was evaluated. Finally, residual stresses were measured on the inner and outer coil surfaces to analyze the effect of heat treatment. The most suitable heat treatment conditions (time range and temperature level) were obtained, these parameters give rise to the highest fatigue resistance with minimum spring relaxation.

Induced activity and damage of superconducting materials for a fusion reactor

The induced activity, radiation damage, and compositional change of several superconductor materials, such as Nb-based alloys, V-based alloys, and MgB 2, for the toroidal field (TF) and central solenoid (CS) magnets of a tokamak-type fusion reactor have been evaluated under the first wall neutron loading of 1 MW/m 2 with a numerical calculation. The damage rates of both Nb- and V-based alloys calculated are about (1–3) × 10 −4 dpa/y at the TF coils adjacent to the vacuum vessel and (2–6) × 10 −7 dpa/y at the surface of CS coil. The damage rate of MgB 2 is about 1 order magnitude higher than those of Nb- and V-based superconducting materials. Most of the induced activity of V-based alloys and MgB 2 after shutdown of the reactor is controlled by 60Co formed from Cu. Nb-based alloys are predicted to emit gamma rays for tens of thousands years due to 94Nb from Nb. In the case of the CS coils, the formation of 94Nb is minimal, and the gamma ray decay of Nb-based alloys is expected to be faster than that of V-based alloys.

The Compression Deformation Mechanism of a Metallic Rubber

In this paper, the microcompression deformation mechanisms of a porous wire-like metallic body, designated metallic rubber, in uniaxial compression loading along the direction of cold stamping, have been investigated by conducting the macroscopic compressing tests and microscopic observation of the deformed material. The stress/strain relation suggest that the stress/strain relation curve could be divided into three distinct stages depending upon the variation in the stiffness with the compression deformation. The results which reveal that there exist different microscopic compression deformation mechanisms in each distinct stage: In the first stage, referred to as stage I, the elastic deformation, owing to the elastic bending of each small segments of metallic wire, occurs in the body piece by piece. In the second stage, referred to as stage II, the elastic deformation of all small segments of the metallic wire and crossed sliding friction operating in the contacted surfaces of the wire represent the main deformation mode of this stage. The third stage is the re-strengthening stage, referred to as stage III. In this case, the deformation due to nonlinear elastic bending of a series of small segments of metallic wire coils and extruded sliding friction operating in the contacted surfaces of wire coils govern the behaviour of the metallic rubber.