Helical Coil Research Papers - Academia.edu (original) (raw)

Resumen: En este artículo se modela el flujo y la trasferencia de calor de un fluido al interior de un serpentín helicoidal cuando este es sometido a un flux de calor constante, usando el software de CFD ANSYS® Fluent 12.1. Además, se analizan las principales variables que intervienen en el fenómeno del aumento del coeficiente convectivo respecto a los tubos rectos, incluidos el flujo secundario y la caída de presión. Los resultados obtenidos fueron validados a partir de un prototipo para el estudio del intercambio de calor en tubos curvos en el Laboratorio de Ciencias Térmicas de la Universidad Nacional de Colombia -Medellín. Los resultados obtenidos presentan diferencias de hasta el 50% con los predichos por la correlación propuesta por Seban y Mclaughlin.

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- Computational Fluid Dynamics, Fluid Mechanics, Aerodynamics, Biofluids

Traditional electrospun nanofibers have a myriad of applications ranging from scaffolds for tissue engineering to components of biosensors and energy harvesting devices. The generally smooth one-dimensional structure of the fibers has stood as a limitation to several interesting novel applications. Control of fiber diameter, porosity and collector geometry will be briefly discussed, as will more traditional methods for controlling fiber morphology and fiber mat architecture. The remainder of the review will focus on new techniques to prepare hierarchically structured fibers. Fibers with hierarchical primary structures-including helical, buckled, and beads-on-a-string fibers, as well as fibers with secondary structures, such as nanopores, nanopillars, nanorods, and internally structured fibers and their applications-will be discussed. These new materials with helical/buckled morphology are expected to possess unique optical and mechanical properties with possible applications for negative refractive index materials, highly stretchable/high-tensile-strength materials, and components in microelectromechanical devices. Core-shell type fibers enable a much wider variety of materials to be electrospun and are expected to be widely applied in the sensing, drug delivery/controlled release fields, and in the encapsulation of live cells for biological applications. Materials with a hierarchical secondary structure are expected to provide new superhydrophobic and self-cleaning materials.

- by Nicole Zander
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- Energy, Biology, Morphology, Electrospinning

An objective of the present dissertation work is to design and develop a CAD model of Tube in tube type counter flow Heat
exchanger.The Dissertation is about preparing the CAD model as well modifying an experimental setup of tube in tube heat
exchanger and use of different type of inner tube configuration for the estimation of heat transfer, pressure drop and change invelocity gradient. The experimental results are compared withthe CFD results using CFD package, ANSYS CFX 14.0 .A designhas been made taking into consideration all the above mentioned Parameters and otherReal life circumstances which is also apart of this report

Despite much optimistic language on commercial websites, little data is available on actual performance of hydrokinetic turbines. This paper summarises the findings of a series of tests on several Darrieus type cross flow hydrokinetic turbines (HKTs). Although this type of hydrokinetic turbine (HKT) has some advantages over axial flow turbines, fixed pitch Darrieus HKTs also have some drawbacks, including inability to self-start under load, low efficiency and shaking. Variable pitch has been suggested to increase starting torque and efficiency, ducts to increase power output and helical blades to produce smooth torque. To assess each of these modifications, tests were conducted in Australia and Canada on HKTs with fixed and variable pitch straight blades, fixed helical blades, with and without a slatted diffuser, by mounting each turbine in front of a barge and motoring through still water at speeds ranging from less than 1 m/s up to 5 m/s. The diffuser increased the power output by a factor of 3 in one configuration but considerably less in others. A reason for this finding is suggested. The maximum coefficient of performance Cp of the fixed pitch straight blade and helical turbines without a diffuser ranged from about 0.25 at 1.5 m/s down to less than 0.1 at 5 m/s, while Cp for those with a diffuser ranged from about 0.45 down to about 0.3. Fixed blade turbines, both straight and helical, exhibited low starting torque, while variable pitch turbines started easily. Considerable differences in Cp were observed for the same turbine configuration at different speeds. The turbine with fixed pitch, straight blades was found to shake violently due to cyclical hydrodynamic forces on blades, while the helical and variable pitch turbines did not shake excessively. These findings suggest that variable pitch cross flow HKTs should be further investigated.

- by Brian Kirke
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- Mechanical Engineering, Renewable Energy, Efficiency, Coefficient of Performance

This study presents a brief review of forced heat transfer through helical coil heat exchangers The helical coil heat exchangers can be made in the form of a shell and tube heat exchangers and can be used for industrial applications such as power generation, nuclear industry, process plants, heat recovery systems, refrigeration, food industry etc. Helical coils of circular cross section have been used in wide variety of applications due to simplicity in manufacturing. Forced Convection is a mechanism, or type of transport in which fluid motion is generated by an external source. The helical coil heat exchanger showed increase in the heat transfer rate, effectiveness and overall heat transfer coefficient over the straight tube heat exchanger on all mass flow rates and operating conditions. In forced convection it is clear that the forced convection through helical coil heat exchanger is best.

The aim of this study is to investigate the enhancement of thermal performance factor and characteristics in tube fitted with helical screw louvered rod inserts using water and carbon nanotubes (CNT)/Water nanofluids with constant heat flux under turbulent flow condition. Nanofluids of 0.1%, 0.2% and 0.5% volume fraction were prepared by a two step method. In the experiments, the swirling flow was introduced by using helical screw louvered rod inserts arrangements (forward and backward) inside the inner test tube with different twist ratios, Y = 1.78, 2.44 and 3.0. The Reynolds number varied from 10,000 to 27,500. The experimental results revealed that the increase in heat transfer rate of the helical screw louvered rod inserts was found to be strongly influenced by tape-induced swirl or vortex motion. The heat transfer increased with an increase in the volume concentration. Thermal performance analysis based on the constant pumping power criteria showed that helical louvered rod tape inserts with forward arrangement led to better thermal performance than that with backward arrangement. A Cross sectional area (m 2) S Surface area (m 2) D Test section diameter (m) L Test section length (m) V Voltage (V) I Current (A) m Mass flow rate (kg/s) Re Reynolds number, 4m/πμD Pr Prandtl number, μcp/k cp Specific heat (J/kg K) f Friction factor h Convective heat transfer coefficient (W/m 2 K) k Thermal conductivity (W/m K) Nu Nusselt number, hD/k T Temperature (o C) v Fluid velocity (m/s) Q Heat input (W) q Actual heat flux (W/m 2) P pitch Y Twist ratio FWD forward BWD backward Greek Symbols Δp Pressure drop (Pa) μ Dynamic viscosity (kg/m 2 s) ρ Density (kg./m 3) φ Volume concentration (%)

In this paper, flow and heat transfer around a compact coil condenser of a built-in refrigerator was studied numerically for various pitch values between the coils. Condenser in a housing was assumed to be cooled by an exhaust fan. This configuration is in accordance with a number of practical applications. Flow inside the housing was assumed turbulent. The fluid was assumed to be incompressible and Newtonian. The governing equations were solved by a computational fluid mechanics simulation software. The results show that when the pitch between the coils is increased, the heat transfer performance increases significantly. An increase of 27% in heat transfer rate is seen when the pitch value is increased from 6mm to 10mm. Further increase in the pitch value from 10mm to 12mm provides an extra 9% increase in heat transfer rate. As the increase in pitch value also increases condenser length, the pitch value of 10mm can be considered an optimum value when there is a strong restriction on space in chassis region.

- by Kamil Kahveci and +2
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- Helical Coil, Air Cooled Condensers

In the present paper, the effect of bubbles on the pressure drop and drag reduction of air-water two phase flows in vertical helical coils was experimentally investigated. The curvature ratio of the studied coils was 0.06 and 0.095. The ranges of the investigated Reynolds numbers and void fractions were 8000-50,000 and 0-0.09, respectively. The effect of the drag reduction will decrease with the increase of Reynolds number and the amount of drag reduction increases with increasing void fraction. It was found that for helical coil, the drag reduction increases with the decrease of curvature because of the secondary flow increases with the increase of curvature. The average diameter of injected bubbles was 270 lm; and as the Reynolds number increased, the diameters of injected bubbles diminished. The experimental results indicate that in this range of void fraction, the maximum reduction of friction drag is 25%, which occurs at low Reynolds numbers. Also, in void fraction 0.01 the drag reduction was 9% which was observed in Reynolds of 11,000.

- by edris gholami
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- Chemical Engineering, Heat Transfer, Helical Coil

- by Brian Kirke
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- Mechanical Engineering, Renewable Energy, Efficiency, Coefficient of Performance

Total scalp irradiation is a treatment technique used for a variety of superficial malignancies. Helical tomotherapy is an effective technique used for total scalp irradiation. Recent published work has shown the TomoTherapy planning system to overestimate the superficial dose. In this study, the superficial doses for a helical tomotherapy total scalp irradiation have been measured on an anthropomorphic phantom using radiochromic and radiographic film as well as a new skin dosimeter, the MOSkin. The superficial dose was found to be accurately calculated by the Tomo-Therapy planning system. This is in contrast to recent reports, probably due to a combination of the smaller dose grid resolution used in planning and this particular treatment primarily consisting of beamlets tangential to the scalp. The superficial dose was found to increase from 33.6 to 41.2 Gy and 36.0 to 42.0 Gy over the first 2 mm depth in the phantom in selected regions of the PTV, measured with radiochromic film. The prescription dose was 40 Gy. The superficial dose was at the prescription dose or higher in some regions due to the bolus effect of the thermoplastic head mask and the head rest used to aid treatment setup. It is suggested that to achieve the prescription dose at the surface ͑ഛ2 mm depth͒ bolus or a custom thermoplastic helmet is used.

- by Wolfgang A Tomé
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- Biomedical Engineering, Medical Physics, Verification, Total
- by Bih-Yaw Jin
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- Nanotechnology, Fullerenes, Computer Software, Computer Simulation

The aim of this work was to determine the accuracy and precision of stereotactic localization and treatment delivery using a helical tomotherapy based stereotactic radiosurgery (SRS) system. A tomotherapy specific radiosurgery workflow was designed that exploits the system's on board megavotage CT (MVCT) imaging system so that it not only provides a pre-treatment volumetric verification image that can be used for stereotactic localization, eliminating the need for a patient-frame based coordinate system, but also supplies the treatment planning image. Using an imaging guidance based intracranial stereotactic positioning system, a head ring and tabletop docking device are used only for fixation, while image guidance is used for localization. Due to the unconventional workflow, a methodology for determining the localization accuracy was developed and results were compared to other linear accelerator based radiosurgery systems. In this work, the localization error using volumetric localization was found to be 0.45 mm ± 0.17 mm, indicating a localization precision of 0.3 mm within a 95% confidence interval. In addition, procedures for testing the delivery accuracy of the Tomotherapy system are described. Results show that the accuracy of the delivery can be verified to within ±1 voxel dimension. These results are well within conventional SRS tolerances and compare favorably to other linear accelerator based techniques.

- by Geoff Sobering and +1
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- Radiosurgery, Treatment, Quality Control, Image

This study investigates the dose from the 1 mm collimator width megavoltage fan-beam CT (fine, normal and coarse pitch) available on tomotherapy as well as for whole-breast tomotherapy treatments. The BEIR VII lifetime attributable risk... more

- by Nicholas Hardcastle
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- Cancer, Risk, Risk assessment, Image guided radiotherapy

Biodegradable stent prototypes were produced from poly l-lactic acid polymers with different molecular weights. The effects of molecular weight, drug incorporation and stent design on the collapse pressure of the stents were evaluated. While molecular weights did not show a significant effect on the collapse pressure of the stents, drug incorporation at high percentage decreased the collapse pressure of the stents substantially. Cryogenic fracture surfaces showed significant drug agglomeration as the concentration increased. The design of the stent was also found to a have significant effect on the collapse pressure. The stent produced from the same material has a higher collapse pressure when the load bearing surface area is increased. r

- by Tan Poh
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- Cardiology, Biomaterials, Scanning Electron Microscopy, Polymers

The heat transfer enhancement techniques can be mainly grouped as active and passive techniques which improve the performance of a heat exchanger for a specific heat transfer duty. The external forces, like acoustic / surface vibration, electric field etc are required in active heat transfer enhancement techniques. The special surface geometries or certain fluid additives are required in passive heat transfer enhancement techniques. Helical tubes (Curved tubes) have been used as passive heat transfer enhancement technique in wide variety of heat transfer applications. This paper reviews heat transfer characteristics in helically coiled tubes. A review of published relevant correlations of single phase heat transfer coefficients is presented.

- by IAEME Publication
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- Heat Transfer, Turbulent Flows, Research, Laminar Flow

Recent discoveries on the improved versatility of helical polycarbodiimides capable of undergoing low energy reversible conformational changes from realignment of their restricted polyarene pendant groups has led to seven new polycarbodiimides that each present unique information in regards to how the electronics and connectivity of the arene p-system play a crucial role in the behavior of these polymers. In addition to their individual anomalous behavior, this series of functional polymers unlock new answers toward the global understanding of the governing forces behind this complex switching process. Through the incorporation of functional groups covalently attached to the naphthalene pendant, dramatic changes and new application of these systems are realized. Variable temperature polarimetry is used to observe the reversible conformational changes of these chiral polymers.

- by Bruce Novak
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- Materials Engineering, Optical switching, Molecular Machine, Polarization

Helical structures are designed to support heavy loads, which can significantly affect the dynamic behaviour. This paper proposes a physical analysis of the effect of axial load on the propagation of elastic waves in helical beams. The model is based on the equations of motion of loaded helical Timoshenko beams. An eigensystem is obtained through a Fourier transform along the axis. The equations are made dimensionless for beams of circular cross-section and the number of parameters governing the problem is reduced to four (helix angle, helix index, Poisson coefficient, and axial strain). A parametric study is conducted. The effect of loading is quantified in high, medium and low frequency ranges. Noting that the effect is significant in low frequencies, dispersion curves of stretched and compressed helical beams are presented for different helix angles and radii. This effect is greater as the helix angle increases. Both the effects of stress and geometry deformation are shown to be non-negligible on elastic wave propagation.

- by Patrice Cartraud
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- Applied Mathematics, Modeling, Low Frequency, High Frequency

- by Subbu Venkatraman
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- Cardiology, Biomaterials, Scanning Electron Microscopy, Polymers

This paper presents a highly efficient power transfer system based on a co-design of a class-E power amplifier (PA) and a pair of inductively coupled Helical coils for through-metal-wall power transfer. Power is transferred wirelessly through a 3.1-mm thick aluminum barrier without any physical penetration and contact. Measurement results show that the class-E PA achieves a peak power gain of 25.2 dB and a maximum collector efficiency of 57.3%, all at 200 Hz. The proposed system obtains a maximum power transfer efficiency of 9% and it can deliver 5 W power to the receiver side through the aluminum barrier.

- by ahmed frikha and +1
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- Applied Mathematics, Modeling, Low Frequency, High Frequency

Nowadays electrical power is one of the most vital requirements for daily life and industries. Since with the rise of the human population, providing electrical energy is an important challenge, some methods should be used to reduce the electrical demand or shift the demand from peak-hours to off-peak hours. Ice storage systems are one of the devices which can be used for this purpose. In this article, a transient 3D numerical simulation was carried out to investigate the effects of two geometrical parameters of double helical coil heat exchanger in the charging process of an ice storage system with the volume of 15 L. These parameters were helical coil pitch length and the distance between inner and outer coils. The results indicated that with higher values for pitch length and inner and outer coils distance, compared to smallest values for these parameters, the distribution of formed ice in the storage improves and the rate of ice formation increases by 22.81% and 13.99%, respectively. Increasing these values can also retard the ice block formation which is an undesirable phenomenon in the external discharge process of the ice storage systems.

- by Seyed Soheil Mousavi Ajarostaghi
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- Solidification, Helical Coil, Ice storage system, Ice formation

- by Daniel Lucas
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- Radiosurgery, Treatment, Quality Control, Image

- by Brian Kirke
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- Mechanical Engineering, Renewable Energy, Efficiency, Coefficient of Performance