IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2006 | Volume:30 | Issue:B3|Papers Count:12

In order to assess the variation of ground vibration intensity, if any, due to the use of three different blasting methods and two different types of explosives, a large number of monitored ground vibrations was analysed in an open cut coal mine. This work involved 86 sets of blast data for different types of blasting when ANFO and Slurry explosives were used in this mine. Statistical analysis of the data sets resulted in 5 of the best fitting empirical relationships between peak particle velocity and scaled distance with excellent values of coefficients of correlations. A comparison of the analytical work revealed that the level of ground vibration varies significantly with the changing method of blasting and/or explosive type. The roles of these factors have been quantified. The rate of the vibration reduction, due to the variation of blasting modes and/or explosive type, varies within each blasting method. These rates are higher in lower ranges of scaled distances, but converge to an almost constant rate at certain scaled distances. The range of this rate varies from 45.77% to 89.34% for free face blasting, and from 38.72% to 56.28% for a buffered blast, depending on the explosive type and scaled distance. It was also observed that one of the two site-specific parameters in the empirical vibration criterion is influenced significantly by the variation of the blasting method and explosive type. However, the other parameter is not much affected by these two factors, and is shown to be more loyal to ground conditions.

In the case of noncircular journal bearings, as opposed to circular journal bearings, the orientation of bearing with respect to a given load direction can be a design parameter. This orientation may be defined in terms of an angle, which in the present work is being referred to as the mount angle. The purpose of the work presented in this paper is to study the effect of the mount angle on the theoretical static and dynamic characteristics of three types of gas-lubricated noncircular bearings. It is found that the effect of the mount angle happens to be more pronounced at low compressibility numbers. Also, among the three types of bearings, the effect of the mount angle is more significant in two lobe bearings in comparison to the three and four lobe bearings.

The present study is concerned with the effect of fuel droplet size on the complex soot process in a turbulent liquid-fuelled combustor. A hybrid Eulerian-Lagrangian method is employed to model the reactive flowfield inside the combustor. Equations governing the gas phase are solved by a control-volume based semi-implicit iterative procedure, while the time-dependent differential equations for each size of the fuel droplets are integrated by a semi-analytic method. The processes leading to soot consist of both formation and combustion. Soot formation is simulated using a two-step model, while a finite rate combustion model with the eddy dissipation concept is implemented for soot combustion. Also, mathematical models for turbulence, combustion, and radiation are used to take into account the effects of these processes. Results reveal the significant influence of liquid fuel droplet size on soot emission from turbulent spray flames under different equivalence ratios, inlet air temperatures, and combustor wall temperatures. The predictions show that reduction of spray droplet size considerably decreases soot emission from spray flames.

Solid desiccants have long been used in dehumidification and cooling systems. Many investigators have presented mathematical work on it, but there is a considerable discrepancy between published values and experimental values. A mathematical model has been derived to show the dehumidification trend of a desiccant dehumidifier with no rotation. In this model, variation of several parameters such as air humidity ratio, air temperature, water content of desiccant bed and temperature of desiccant as a function of the length of the bed and time were investigated. The mathematical model was validated by experimental results on a fixed solid desiccant bed filled with silica gel. The results indicated that the dehumidification rate along the length of the desiccant bed depends mostly on input humidity ratio, air stream velocity, heat and mass transfer from the air stream to the bed and the Ackermann heat transfer correction factor. By increasing input air relative humidity and temperature more than 50% and 95°C, respectively, the Ackermann factor corrected the heat transfer coefficient up to 4%. The results also showed that air stream velocity was one of the most effective parameters on the dehumidification rate of the wheel.

An integrated analysis methodology composed of four components: visual modeling, simulation, diagnosis and reduction of bottleneck processes of production lines has been presented in this paper. Various components are integrated to analyze the bottleneck process of production lines including process parameters and production planning. In this method, 3D dynamic modeling, which includes physical and logical modeling, is the basis to define the entire layout, the visual simulation and the diagnosis of the production line. Simulation is the most crucial part for acquiring many data to quickly diagnose the bottleneck processes in the production line. The reducing method of bottleneck processes, which includes two anti-bottleneck ways, local expansion and bypass reducing, is the premise to redesign the production line. Because the result of each following steps can be fed back to the previous steps, the bottleneck processes of the production line can be quickly diagnosed and reduced. With this method, an existing production line is virtually modeled in a computer, simulated and analyzed. Based on the simulation results, the bottleneck processes are quickly diagnosed. Some ways for reducing bottleneck processes are proposed and their simulation results are quickly achieved in the simulation environment. Results reveal that the integrated analysis method can integrate the following functions: modeling, simulation, bottleneck diagnosis and reduction of production lines, and as a result quickly diagnose the bottleneck processes, redesign the production line, and provide a preanalysis tool for the production plan.

Low carbon steel sheets have many applications in industries, especially in automotive parts, therefore it is necessary to study formability of these steel sheets. Forming limit diagram (FLD) is one of the strong pieces of equipment used to study the formability of sheet metals. In this study, FLDs have been determined experimentally for three grades ST12, ST14, and Interstitial free (IF) by conducting punch-stretching experiments using suitably designed and fabricated tools. Formability observed from FLDs has been correlated with mechanical properties and formability parameters like punch type, punch diameter, friction between punch and sheet, work hardening exponent (n) and plane-anisotropy (r) of the sheets. Results have indicated that forming strains in IF and ST14 steel sheets are higher than ST12 and higher n×r values and thickness are desirable to raise the forming strains. The sheet orientation can be effective and in addition, depends on the strain path .For example, forming limit strains in 45 angles with respect to the rolling direction are less than that for 0 and 90 within the right band of FLDs.

Silicium-Based Ceramics were investigated to determine the effect of microstructural parameters and densification on thermal stress resistance to fracture initiation during thermal shock testing. The different materials and microstructures were obtained by changing parameters such as the type of powder, additive, forming process and sintering condition. Critical temperature differences (DTc), after water quenching, are discussed in relation to change in Young's module of elasticity, a variable affecting thermal shock. The maximum thermal shock resistance of dense Si3N4 has been achieved after completing conversiona®b, the changes in grain morphology toward elongated grain and the relative crystallization of the second phase. These characteristics are produced by a higher percentage of the powder in the  a-phase, high Y2O3, and the sintering condition at a higher temperature (2000°C), longer soaking times (1h) and load application at the beginning of thermal cycle.

Due to certain advantages in (semi-)Autogenous-Ball mill circuits in most of the high throughput ore grinding units of mineral processing plants, much attention is paid to optimize mill performance. Despite the maturity of the grinding mill mechanical design, the efficiency of the grinding media has previously been ignored. Different liner materials and shapes are used in different situations (in a variety of ore types and operational conditions), but the best economically and operationally chosen for one operation is not the same for the other. In this research, the possibility of establishing a relationship between liner/lifter wear rate and variations in the composition (SiO2% and FeO%) of an iron ore is investigated. The ore belongs to a magmatic high grade iron ore deposit located at Chadormalu mine in the province of Yazd, Iran. A significant change in the mineralogical composition of the ore was observed during the sampling days which resulted in the variation of the feed ore work index. Measurements and determination of liner/lifter wear rates and patterns concluded that the critical liner segments posed too much abrasion during ore grinding. By performing the metallurgical analysis of liner materials and after correlation of wear rate with ore composition, it was concluded that the homogeneity in the metallurgical microstructure of the alloyed steel (such as the uniform distribution and amounts of the constituent phases) has a great influence on the response of the liner/lifter to the variations of ore composition. Magnetite with a greater abrasion index than hematite, also in finer particles, is responsible for additional wear rate (abrasion) in liners, but hematite with greater toughness/grindability (work index) exists in the mill with larger particle sizes, thus it could produce wear on liner parts with less tolerance to impact as is the situation for martensitic steels.

In this work MoO3 was added to the Mn-Zn ferrite with the basic composition of (52mol% of Fe2O3, 34mol% of MnO, 14mol% of ZnO) at concentrations of 0.08, 0.5, 1 and 5 wt%. The optimum sintering condition was determined based on maximum Q factor values. The microstructure of the sintered samples was studied using SEM. The magnetic properties were characterized by determining Q factor and Curie temperature. Results showed that the addition of MoO3 increased Curie temperature and noticeably decreased linear shrinkage. The Q factor was maximized at a concentration of 0.5 wt% MoO3 making this value the best.