Search

Metal hydride offers an efficient and cost-effective method to store hydrogen. In this study, Taguchi method coupled with grey relational analysis was used to optimize the design parameters i.e., diameter of helical tube (dh), major diameter of helical tube (dm), number of turns of helical tube (N) and velocity of heat transfer fluid ( V f ) for the helical tube heat exchanger embedded inside metal hydride bed to achieve minimum desorption time (td) for 80% desorption and minimum outlet temperature (T0) of heat transfer fluid (HTF). The performance of all experiments in the orthogonal array used for Taguchi and Grey relational analysis was evaluated by 3-D numerical simulations performed in commercial software COMSOL 5.3a. This stepwise methodology is significantly computationally efficient as the number of required simulations reduced by 90% as compared to the traditional parametric study-based methodology. Further, this methodology enables to estimate an optimized level of the parameters by considering all the objective functions (td, T0) simultaneously. Later, the performance of the optimally designed systems was compared with the orthogonal array experiments and it was found out that the optimized system designs have better performance in terms of the objective parameters i.e., td and T0 when compared with the other experiments of orthogonal array. These optimized systems will then be used for refrigeration and cooling applications.

The saddle shaped secondary helical coil electromagnetic launcher, which has the advantage of long-distance propulsion is improved on the basis of helical coil electromagnetic launcher (HEML). However, the current fluctuation of the system is the same as that of the traditional helical coil electromagnetic launcher, and current fluctuation can cause thrust fluctuation and commutation arc problems. Therefore, it is particularly important to analyse the commutation current fluctuation of the saddle shaped secondary HEML. In this paper, the commutation process of HEML is analysed in detail by analogy with the commutation process of DC series excited rotating motor. Then the system model is built in ANSYS/Maxwell, and the excitation circuit is built with Simplorer to jointly simulate the system. The reason of commutation current fluctuation is analysed by using the principle of flux continuity, and the correctness of the principle of flux continuity is verified by analysing and calculating the simulation datas. It has a good guiding significance for the subsequent improvement of thrust fluctuation and commutation arc.

Helical coil heat exchanger is used in the food industries, air cooling industries etc.., due to its advantage of structural compact and high heat transfer coefficient. Many existing researches have been carried to improve the heat transfer efficiency and pressure drop. Mathematical model of the heat exchanger has been used to validate the performance of the heat exchanger. This paper involves in review the researches related to the optimization of helical coil tube heat exchanger. Some of the optimization methods such as Taguchi method, Genetic Algorithm (GA) and Multi-Objective Genetic Algorithm (MOGA) is used. From the analysis, Artificial Neural Network (ANN) and GA method has efficient performance in modelling and optimization of heat exchanger. Although, some methods involved in economic optimization of heat exchanger and these method has lower performance.

Heat exchangers has been widely used in power plants and industries for heating or cooling applications. Heat is transferred from one medium to another medium by using heat exchangers. Helical coil heat exchangers with two different shell configurations are designed. First shell configuration with a central core and second without a central core. Both the configurations has a copper helical coil. Designing of heat exchangers is done with counter flow arrangement by using CATIA V5 R2015. The performance of both the configurations are analysed and compared by using Fluid flow (Fluent) in ANSYS WORKBENCH 18.1 for CFD simulations. Further the helical tube materials Copper and Aluminium which are widely used in heat exchangers are also analysed in shell with core configuration and heat transfer rates are also compared using CFD (Fluent) analysis.

Heat transfer characteristics of a tube in tube helical heat exchanger in the laminar flow regime is analysed numerically. Numerical scheme is validated with the experimental results reported in literature. The effect of helix angle on the overall heat transfer coefficient is analysed. The overall heat transfer coefficient increases with Dean number and its rate of increase at higher Dean number is low. The rate of heat transfer is maximum at a helix angle of 27°. Simulation studies show that the secondary flows that originate in a coiled tube due to curvature and torsion produce an additional transport of the fluid over the cross section of the pipe. The overall heat transfer coefficient increases with increase in inner diameter.

Estimation of local heat flux is challenging in a helical coil tube heat exchanger due to the complex flow field developed by tube curvature. The heat flux has uneven distribution in the angular direction of the tube cross-section. The current research aims to estimate the local heat flux at the fluid-solid interface for the turbulent flow of water in a helical coil tube by solving the inverse heat conduction problem (IHCP). Conjugate gradient method (CGM) with an adjoint problem is used as an inverse algorithm. First, the commercial CFD software ANSYS FLUENT is used for solving the governing equations of continuity, momentum, and energy for turbulent flow to obtain the heat flux at the fluid-solid interface. This heat flux is used to determine the temperature distribution at the outer surface of the tube. The heat flux is then considered unknown and it is estimated by CGM algorithm with the developed in-house code in MATLAB. The result shows that the estimation of heat flux by CGM is very accurate.

Different from the classical coaxial coils, a new type of asynchronous linear motor with helical 3-phase helical coil been brought forward in this paper. It has simple structures and produces peculiar travelling magnetic waves along the axis, which lead to the metal projectile is subjected invariable axial driving forces and rotary torques at the same time. It has a very useful property of this kind of winding, which is applied as a linear asynchronous launcher’s primary section. The high speed rotating projectile has stable flying attitude in moving direction because of the gyroscopic effect. The basic electromagnetic problems of the motor were discussed in this paper. An experimental model was build and tested to verify the principle results mentioned above at last.

The Large Helical Device (LHD), which is a heliotron/torsatron device with two helical coils, is designed so that the current in each helical coil can be controlled independently. Unbalancing these currents leads to spatial axis configurations. The bootstrap current is found to be strongly affected by any imbalance between these currents. When the ratio of the currents in the two helical coils is small enough, a bootstrap current flows in a direction so as to decrease the rotational transform because of the enhancement of the bumpiness component of the magnetic field as well as of the spatial axis component. This leads to improved stability

We have developed a novel, radiofrequency thermal therapy device designed to improve local control of large solid tumours using heat in the range 55-90 degrees C. The device is a solenoid or helical coil designed to be loosely wound inside a tumour and excited with radiofrequency energy. Typically, we associate a uniform axially directed magnetic field with a solenoid coil, which when time varying, results in an electric field inside the coil, which lies mainly in the circumferential direction. In addition to this magnetically induced electric field, there exists a less familiar axially directed electric field inside the coil. Previous investigators have demonstrated the presence of this secondary axial electric field both experimentally and theoretically. Our design exploits the size and uniformity of these electric fields, for heating and coagulating a large tissue volume with a single applicator. The loosely wound solenoid is constructed from Nitinol, an electrically conductive shape memory alloy that permits the minimally invasive percutaneous insertion of the coil through a single cannulating delivery needle. To demonstrate the potential of this device and to determine the optimal frequency of operation, phantom tissue models and finite-element calculation models using COMSOL 3.2 were used to characterize frequency- and geometry-dependent trends in absorption rate density (ARD), which is proportional to electric field intensity. Radial and axial ARD profiles were measured, calculated and evaluated to determine the frequency and geometry best suited for producing large, homogenous coagulation volumes. Based on the trade-off between radial and axial uniformities of the ARD profiles, a 2 cm diameter coil with a 4 cm length and 1 cm pitch, operated at 27.12 MHz, produced the optimal heating pattern, as determined using tissue-mimicking phantom models.

We have developed a novel, thermal therapy device designed to improve local control of large solid tumours using heat in the range 55-90 degrees C. The device is a helical coil designed to be loosely wound inside a tumour and excited with radiofrequency energy at 27.12 MHz. This design exploits the size and uniformity of the electric fields generated by magnetic induction inside this solenoidal geometry for heating and coagulating a large target volume. The use of the electrically conductive shape memory alloy Nitinol for the coil and an external ground plane permit the minimally invasive percutaneous insertion of the coil through a single cannulating delivery needle. To demonstrate the feasibility of this device, phantom models and finite-element models using COMSOL 3.2 were used to characterize uniformity of the radial and axial ARD (absorption rate density) profiles of different monopolar coil geometries. COMSOL 3.2 was also used to calculate temperature profiles and distributions produced by these coils in a non-perfused tissue-mimicking domain following a 10 min heating period. ARD results showed that optimum radial and axial uniformities were achieved with a 0.75 cm pitch and 3 cm length for a 1.5 cm diameter coil, and a 1.4 cm pitch and 4.2 cm length for a 2 cm diameter coil. These coils were able to produce lesions in excised bovine liver of 4 cm x 4.5 cm and 3.5 cm x 6.5 cm, respectively. Predicted temperature profiles showed similar profile sizes and shapes in a non-perfused domain, with the absolute temperature rise determined by the source input to the coil. These results demonstrate the potential of this interstitial, monopolar induction coil device for heating large tumours using a single applicator delivered through a single needle insertion.

An attempt has been made to arrive at a better characterizing dimensionless group for steady isothermal flow of Newtonian fluids in helically coiled circular tubes. Pressure drop versus flow rate data has been experimentally obtained for helical coils made from thick-walled polyethylene tubing. Generalized pressure drop correlations have been developed in terms of Euler number, Eu, Reynolds number, Re, and the obtained geometrical group, Grhc = (d0.85Deq0.15/Lc), where d is the inside diameter of the tube, Deq is the equivalent diameter which accounts for the torsion effect, and Lc is the length of the coil. The Fanning friction factor for helical coil tube is found to depend on Reynolds number and a geometrical number, d/Deq, separately both, and not by a dimensionless number obtained by any combination of Reynolds number and some geometrical number as is the case of Dean number, De = Re √(d/D), where D is the diameter of the coil. There exist four regimes of flow for the flow through helical-coiled circular tubes. The obtained pressure drop correlations are simple to use.

The formulae for calculating the magnetic field produced by the finite size helical coil with rectangular cross section [J. Todoroki: Kakuyugo Kenkyu 57 (1987) 318] are extended to the case with an arbitrary polygonal cross section. The formulae for the calculation of the vector potential are also presented.

Shape memory alloy (SMA) actuators often operate under a complex state of stress for an extended number of thermomechanical cycles in many aerospace and engineering applications. Hence, it becomes important to account for multi-axial stress states and deformation characteristics (which evolve with thermomechanical cycling) when calibrating any SMA model for implementation in large-scale simulation of actuators. To this end, the present work is focused on the experimental validation of an SMA model calibrated for the transient and cyclic evolutionary behavior of shape memory Ni49.9Ti50.1, for the actuation of axially loaded helical-coil springs. The approach requires both experimental and computational aspects to appropriately assess the thermomechanical response of these multi-dimensional structures. As such, an instrumented and controlled experimental setup was assembled to obtain temperature, torque, degree of twist and extension, while controlling end constraints during heating and cooling of an SMA spring under a constant externally applied axial load. The computational component assesses the capabilities of a general, multi-axial, SMA material-modeling framework, calibrated for Ni49.9Ti50.1 with regard to its usefulness in the simulation of SMA helical-coil spring actuators. Axial extension, being the primary response, was examined on an axially-loaded spring with multiple active coils. Two different conditions of end boundary constraint were investigated in both the numerical simulations as well as the validation experiments: Case (1) where the loading end is restrained against twist (and the resulting torque measured as the secondary response) and Case (2) where the loading end is free to twist (and the degree of twist measured as the secondary response). The present study focuses on the transient and evolutionary response associated with the initial isothermal loading and the subsequent thermal cycles under applied constant axial load. The experimental results for the helical-coil actuator under two different boundary conditions are found to be within error to their counterparts in the numerical simulations. The numerical simulation and the experimental validation demonstrate similar transient and evolutionary behavior in the deformation response under the complex, inhomogeneous, multi-axial stress-state and large deformations of the helical-coil actuator. This response, although substantially different in magnitude, exhibited similar evolutionary characteristics to the simple, uniaxial, homogeneous, stress-state of the isobaric tensile tests results used for the model calibration. There was no significant difference in the axial displacement (primary response) magnitudes observed between Cases (1) and (2) for the number of cycles investigated here. The simulated secondary responses of the two cases evolved in a similar manner when compared to the experimental validation of the respective cases.

Uniformity of magnetic fields are of great importance especially in magnetic resonance studies, namely in magnetic resonance spectroscopy applications (NMR, FMR, ESR, EPR etc.) and magnetic resonance imaging applications (MRI, FMRI). Field uniformity is also required in some other applications such as eddy current probes, magnetometers, magnetic traps, particle counters etc. Here we proposed a coil winding regime, which follows the surface of a spheroid (an ellipsoid of rotation); in light of previous theoretical studies suggesting perfect uniformity for a constant ampere per turn in the axial direction thereof. We demonstrated our theoretical results from finite element calculations suggesting 0.15% of field uniformity for the proposed structure, which we called a Spheroidal Helical Coil.

The large helical device (LHD) type fusion power reactor has many advantages in operations such as steady state and no active plasma current. The magnet system of the LHD-type fusion device consists of superconducting helical coils and superconducting poloidal coils. Since the helical coil is a complicated three-dimensional structure, designs of the coil and the supporting structure have to be performed carefully. Clarifying the mechanical behavior during coil excitation is very important for a design of the coil system. The mechanical behavior for components in the helical coil can be estimated using a simplified two dimensional axisymmetric model which has a mean radius of curvature of the actual helical coil. To evaluate the accuracy of this simplified model, stress distribution was calculated with three-dimensional finite element model and the result was compared with that of the simplified model. The stress distribution of a candidate design of LHD-type helical reactor was estimated by using the simplified model and the result showed that the stress / strain level were within the reasonable range for composed materials.

This paper deals with a determination of the effective resistance and inductance of a helical coil of great length, composed of thin wire, wound on a cylinder whose radius is large in comparison with that of the wire. The pitch of the winding is not small, so that the problem cannot be treated by the method of Cohen. The method employed depends upon the use of a type of "helical coordinates" defining the position of any point, and of the general theorem relating to orthogonal systems of coordinates. A solution is obtained for the internal and external forces, corresponding to a given impressed electro-motive force, in the form of a Fourier series of which only the initial terms require calculation. The value of the effective current across any section is obtained, and thence the inductance and resistance. The results are of simple character, and are expressed in general in terms of the ber and bei functions of Lord Kelvin, whose results for a straight wire appear as a limiting case. Certain particular cases are worked out in detail and formulae obtained in terms of elementary functions which are suitable for a very high or a low frequency. Their necessary limitations are also examined numerically. For a high frequency, it is found that the change of self-inductance due to twisting of the wire tends to vanish, and that the change of resistance tends towards a value independent of the frequency.

The incomplete circuit formed by a single turn ABC of a helix of pitch p, which lies on a cylinder of radius a, is completed by a straight link CA, of length p, parallel to the axis of the cylinder. Through any point O on this axis are taken rectangular axes Ox, Oy, Oz. Of these, Ox is the axis of the cylinder, and Oz is parallel to the shortest distance between Ox and CA. The components H1, H2, H3 of the magnetic force at O, due to a current in the circuit, are found for the case when p/a is small.