International Journal of Engineering
Volume:12 Issue: 2, May 1999

The purpose of this paper is to introduce a different type of converter circuit used to drive switched reluctance motors. It continues with detailed discussion on the resonant converter armed at minimizing or eliminating the transistors switching losses. Finally the drive has been tested on a disc-type reluctance motor for the perfomance and functionality.

Abstract The kinetics and mechanism of bainite transformation have been studied in Fe-Cr-Mo-V-Ti-C steel high speed dilatometry backed by thermodynamic analysis. The complete transformation of austenite, however, has not occurred at any reported temperature. Obtained results confirm the incomplete reaction phenomenon with the cessation of the bainite transformation well before the paraequilibrium is achieved. These experimental data indicate that bainitic ferrite is formed by a displacive transformation mechanism, but soon afterwards, excess of carbon is patitioned into the residual austenite. The results are discussed in terms of the mechanism of bainite transformation.

An axisymmetric jet issued from a sharp edged circular convergent nozzle has been studied experimentally in the near field at Reynolds number 5.3x104 to search the saddle shape behavior of mean velocity and the role of mean static pressure in the jet flow. Due to the vena contracta effect the centerline mean velocity of the jet increases about 4.2% of its exit value and corresponding decrease of mean static pressure is found in the potential core of the jet. Streamwise mean velocity shows saddle shape profile adjacent to the mixing layer near the exit (due to secondary current). Velocity peaks are associated with corresponding drop of mean static pressure. This saddle shape behavior is found to die down at the end of the potential core. The geometric virtual origin is at downstream of the nozzle tip and the entrainment rate is increased nonlinearly with the axial distance. A partial self-preservation of mean velocity is attained earlier than that of mean static pressure.

This paper describes the use of image processing to measure lightness changes of fabric appearance. The lightness changes due to dyeing, washing and exposure to light treatments are studied. These properties are measured by using the changes in the intensity levels of the fabrics image and the L* obtained by a spectrophotometer. For each case, analysis of variance (ANOVA) is carded out and the correlation between the intensity level and L* is computed. This study also investigates the use of angular power spectrum (APS) to quantify the variation in fabric surface protrusion due to washing.

The transient response of passivated metallic electrode system under potential step was analyzed based on a linear model, and a technique for calculating the parameters characterizing the growth and dissolution of passive film was proposed. It is believed that the information which is expected to be gained from the impedance measurement can be obtained by this technique and that this technique is superior to impedance measurement as it is much more rapid than the latter.

In this paper, the effects of horizontal stress and dimensions of barrier pillars on the stability of drifts hr been investigated. An elastoplastic hybrid finite/boundary element program has been used. A plastic analysis of stresses in barrier pillars above the drifts in one of the underground coal mines with inclined seams is examined. Computed stresses and safety factor controur lines around the drifts and in a barrier pillar are shown. It is shown that the extent of the yielding zone in barrier pillars depends on the dimension of the barrier pillar. Also the extent of the yielding zone above the drift depends on the location of the drift relative to the barrier pillar. In this analysis, a modified Hock and Brown failure criterion has been used.

The occurrences of huge reserves of garnet deposits have been reported from different parts of Iran specially those of Kohe-E-Gabri area which is very high grade in nature. These deposits can not be directly used as abrasives, filter aid and many others because of some impurities present. To know the mineralogical composition, the type of garnet, the shape of the particles, the chemical character and the mesh of the grind all of which play a vital role in finding out suitable flowsheet design, the samples have been subjected to detailed mineralogical and microscopic studies, sieve analysis, liberation studies and chemical analysis. The results indicate that, the type of garnet is anderadite with relative grade of 75% and most of the particles shape are of edged type rather than rounded one and this is to be taken in to account while using them as abrasives and filter aids. Quartz, Calcite, Wollastonite, Magnetite and Hematite are the impurities present in the order of abundance and liberation studies show that the optimum mesh of the grind is about 600 microns. Based on the characterization studies, it was suggested that the gravity and magnetic methods would be the suitable separation techniques for removing the impurities. Therefore, the beneficiation studies have been carried out with, table, spiral, multigravity and magnetic separators. In all gravity techniques due to higher specific gravity of magnetite, this particular mineral has been separated with garnet in concentrate which is removed later with a magnetic separator. Finally based on the preliminary characterization and beneficiation studies, it''s possible to upgrade the garnet deposits of Rafsanjan area to the tune of more than 95% garnet with recovery of above 87%. The results obtained are not only encouraging but also form original and distinct contribution to the beneficiation of garnet in general, and to that of Kohe-E-Gabri area in particular.