Search results

The purpose of this article is investigating the impact of the spatially variable heat transfer coefficient on the thermal field in the double insulated wire.

The effect of the air boundary layer was modelled by means of changing the total heat transfer coefficient on the external perimeter of the wire. This leads to an elliptical boundary problem with Hankel’s condition dependent on the angular coordinate. The eigenfunctions of the problem were determined analytically. On the other hand, the unknown coefficients of eigenfunctions and the constants were calculated numerically by solving a respective system of algebraic equations. The steady state current rating was determined with an iterative method.

By means of the presented method, the thermal field distribution deprived of axial symmetry in the double insulated wire was determined. The obtained results have good physical interpretation and were verified with the finite element method (by means of NISA v. 16 software). The determined values of the steady-state current rating were compared with those calculated by means of the equivalent heat transfer coefficient method and the International Electrotechnical Commission (IEC) standard.

The method is applied to analyse scalar fields in layered cylindrical structures. This could be expanded to the case of a wire of any number of insulation layers. What is more, one could also consider heat sources without axial symmetry and located within the external area.

The analytical method of determining a thermal field deprived of axial symmetry in heterogeneous cylindrical system (the wire composed of three different materials) was developed.

Introduces the fourth and final chapter of the ISEF 1999 Proceedings by stating electric and magnetic fields are influenced, in a reciprocal way, by thermal and mechanical fields. Looks at the coupling of fields in a device or a system as a prescribed effect. Points out that there are 12 contributions included ‐ covering magnetic levitation or induction heating, superconducting devices and possible effects to the human body due to electric impressed fields.

The features of coated wire product are measured by the flow and heat transport occurring in the interior of dies. Therefore, an understanding of characteristics of polymers momentum, heat mass transfer and wall shear stress is of great interest. Enhancement of heat transfer rate is fundamental need of wire coating process. Therefore, this study aims to investigate the effect of suspended nanoparticles in heat and mass transport phenomena of third-grade liquid in post-treatment of wire coating process. Buongiorno model for nanofluid is adopted. Two cases of temperature dependent viscosity are considered.

The governing equations are modelled with the help of steady-state conservation equations of mass, momentum, energy and nanoparticle concentration. Some appropriate dimensionless variables are introduced. Numerical solutions for the nonlinear problem are developed through Runge–Kutta–Fehlberg technique. The outcome of sundry variables for dimensionless flow, thermal and nanoparticle volume fraction fields are scrutinised through graphical illustrations.

The study’s numerical results disclose that the force on the total wire surface and shear stress at the surface in case of Reynolds Model dominate Vogel’s Model case. Impact of nanoparticles is constructive for force on the total wire surface and shear stress at the surface. The velocity of the coating material can be enhanced by the non-Newtonian property.

This study may provide useful information to improve the wire coating technology.

Effect of nanoparticles in wire coating analysis by using Brownian motion and thermophoresis slip mechanisms is investigated for the first time. Two different models for variable viscosity are used.

Distributed temperature sensing (DTS) can identify locations and factors of seepage in embankments. Inspired by the classical transient hot-wire method (THW), the focus of this paper is to investigate the feasibility and propose a calibrated method of seepage velocity monitoring using the optical fiber DTS.

According to the definition and the measurement of thermal conductivity, the nominal thermal conductivity, which comprehensively reflects the influence of heat transfer and seepage factors, is proposed and the corresponding solution is also derived. Then, a flume testing platform of an embankment seepage monitoring system composed of the optical fiber heat-up subsystem, the seepage controlling subsystem and the optical fiber DTS subsystem is designed and built. Meanwhile, the data processing and assistant analysis subsystem (DPAAS) is also developed to effectively acquire the experimental data of concerned locations and obtain the corresponding nominal thermal conductivity under various seepage conditions. Based on these setups, a series of laboratory flume experiments are carried out under controlled velocities and heating powers.

The plots of recorded temperature rise versus natural logarithm of time allow the calculation of nominal thermal conductivities, and then the seepage velocity monitoring model particular to the experimental setup is successfully established with satisfactory precision.

Considering the complexity of water flow in embankments, a seepage flume that matches the natural system, allowing for larger experimental model scales, various water temperatures, various engineering materials and a wider range of seepage velocities, should be investigated in future.

The combined THW and DTS method provides promising potential in real-time seepage monitoring of embankment dams with the help of the developed DPAAS.

In this work, we performed a flume testing of seepage velocity monitoring platform using optical fiber distributed-temperature sensing for embankments based on the transient hot-wire method. Through the testing of data, the seepage velocity monitoring model particular to the experimental setup was established. The results presented here are very encouraging and demonstrate that the DTS system can be used to monitor the temperature and the seepage factors in field applications.

The electromagnetic field and cooling system of a high power switched reluctance motor (SRM) are studied numerically. The geometry of the motor and its main components are established using a computer-aided design software in the actual size. This study aims to evaluate the resulting thermal losses using the electromagnetic analysis of the motor.

In the electromagnetic analysis, the Joule’s loss in the copper wires of the coil windings and the iron losses (the eddy currents loss and the hysteresis loss) are considered. The flow and heat transfer model for the thermal analysis of the motor including the conduction in solid parts and convection in the fluid part is introduced. The magnetic losses are imported into the thermal analysis model in the form of internal heat generation in motor components. Several cooling system approaches were introduced, such as natural convection cooling, natural convection cooling with various types of fins over the motor casing, forced conviction air-cooled cooling system using a mounted fan, casing surface with and without heat sinks, liquid-cooled cooling system using the water in a channel shell and a hybrid air-cooled and liquid-cooled cooling system.

The results of the electromagnetics analysis show that the low rotational speed of the motor induces higher currents in coil windings, which in turn, it causes higher copper losses in SRM coil windings. For higher rotational speed of SRM, the core loss is higher than the copper loss is in SRM due to the higher frequency. An air-cooled cooling system is used for cooling of SRM. The results reveal when the rotational speed is at 4,000 rpm, the coil loss would be at the maximum value. Therefore, the coil temperature is about 197.9°C, which is higher than the tolerated standard temperature insulation material. Hence, the air-cooled system cannot reduce the temperature to the safe temperature limitation of the motor and guarantee the safe operation of SRM. Thus, a hybrid system of both air-cooled and liquid-cooled cooling system with mounting fins at the outer surface of the casing is proposed. The hybrid system with the liquid flow of Re = 1,500 provides a cooling power capable of safe operation of the motor at 117.2°C, which is adequate for standard insulation material grade E.

The electromagnetic field and cooling system of a high power SRM in the presence of a mounted fan at the rear of the motor are analyzed. The thermal analysis is performed for both of the air-cooled and liquid-cooled cooling systems to meet the cooling demands of the motor for the first time.

This paper gives a review of the finite element techniques (FE) applied in the area of material processing. The latest trends in metal forming, non‐metal forming and powder metallurgy are briefly discussed. The range of applications of finite elements on the subjects is extremely wide and cannot be presented in a single paper; therefore the aim of the paper is to give FE users only an encyclopaedic view of the different possibilities that exist today in the various fields mentioned above. An appendix included at the end of the paper presents a bibliography on finite element applications in material processing for the last five years, and more than 1100 references are listed.

The paper aims to propose a parallel algorithm in order to increase speed and efficiency of an analysis of transient thermal field in layered DC cables.

Initial-boundary problem of thermal field was discretized by means of implicit finite difference method in cylindrical coordinates. A two-stage time decomposition method was applied to introduce parallel computations. An assumed duration of the transient state was decomposed. The system of algebraic equations was being solved with the use of a conjugate gradient method (with diagonal preconditioning) in all time intervals simultaneously.

A method for solving (with the use of parallel computing system) the transient heat conduction equation in a DC cable consisting of arbitrary number of material layers was given. The dependence of the convective heat transfer coefficient on the location on the perimeter of the cable and on its surface temperature (which introduced non-linearity in the boundary condition) was taken into account. The influence of the determined field on the efficiency of the heat source was also taken into consideration in the model.

The main limitation is induced by cylindrical and coaxial structure of the consecutive layers of the system. Thermal field is generated by direct current flow only. The length of the fragment of the cable under consideration should be much greater than its diameter.

The time-spatial distribution of thermal field in the cross-section of the cable can be used for analysis of its reliability and for determination of important characteristics and parameters of the system.

A parallel algorithm of solving initial-boundary parabolic problem was proposed as a result of synthesis of three methods (finite difference, time decomposition and conjugate gradient). An algorithm of minimization of disturbances of the solution introduced at the division points was given. Equations approximating real distribution of heat transfer coefficient from the surface of the cable were proposed.

The major problem that limits the widespread use of WAAM technology is the forming quality. However, most of the current research focuses on post-process detections that are time-consuming, expensive and destructive. This paper aims to achieve the on-line detection and classification of the common defects, including hump, deposition collapse, deviation, internal pore and surface slag inclusion.

This paper proposes an in-process multi-feature data fusion nondestructive testing method based on the temperature field of the WAAM process. A thermal imager is used to collect the temperature data of the deposition layer in real-time. Efficient processing methods are proposed in this paper, such as the temperature stack algorithm, width extraction algorithm and a classification model based on a residual neural network. Some features closely related to the forming quality were extracted, containing the profile image and width curve of the deposition layer and abnormal temperature features in longitudinal and cross-sections. These features are used to achieve the detection and classification of defects.

Thermal non-destructive testing is a potentially superior technology for in-process detection in the industrial field. Based on the temperature field, extracting the most relevant features of the defect information is crucial. This paper pushes current infrared (IR) monitoring methods toward real-time detection and proposes an in-process multi-feature data fusion non-destructive testing method based on the temperature field of the WAAM process.

In this paper, the single-layer and multi-layer WAAM samples are preset with various defects, such as hump, deposition collapse, deviation, pore and slag inclusion. A multi-feature nondestructive testing methodology is proposed to realize the in-process detection and classification of the defects. A temperature stack algorithm is proposed, which improves the detection accuracy of profile change and solves the problem of uneven temperature from arc striking to arc extinguishing. The combination of residual neural network greatly improves the accuracy and efficiency of detection.

This paper gives a review of the finite element techniques (FE) applied in the area of material processing. The latest trends in metal forming, non‐metal forming, powder metallurgy and composite material processing are briefly discussed. The range of applications of finite elements on these subjects is extremely wide and cannot be presented in a single paper; therefore the aim of the paper is to give FE researchers/users only an encyclopaedic view of the different possibilities that exist today in the various fields mentioned above. An appendix included at the end of the paper presents a bibliography on finite element applications in material processing for 1994‐1996, where 1,370 references are listed. This bibliography is an updating of the paper written by Brannberg and Mackerle which has been published in Engineering Computations, Vol. 11 No. 5, 1994, pp. 413‐55.

The purpose of this paper is to present a fast and contactless measurement method to determine the spatial conductivity distribution within an intrinsically conducting polymer, more precisely a conductive rubber sheet specimen. As a consequence of the manufacturing process and the material composition, the conductivity distribution within the sheet is assumed to be inhomogeneous.

The current density distribution within the conductive rubber sheet due to an excitation current is estimated from the measured magnetic field distribution. Therefore, a GMR sensor is used to spatially sample the magnetic field above the specimen. Based on the estimated current density distribution and alternatively the local power dissipation calculated from a thermal image, the conductivity distribution within the specimen is determined. For comparison a reference measurement with a classical resistivity probe is done.

The measurement results show a good agreement between the developed and the classical method. Moreover, the developed measurement method requires less time and still offers a higher spatial resolution.

The presented results demonstrate the potential of the developed measurement method for determining the conductivity distribution within thin and planar specimens. Furthermore, conclusions can be drawn about the material homogeneity of the used test specimen.