Iranian Journal of science and Technology (B: Engineering)
Volume:34 Issue: 5, oct 2010

Fluid flow and heat transfer are computed through a rib-roughened duct of square cross-section. The staggered ribs are attached along the two opposite walls of the channel to augment heat transfer. Simulations are performed with an incompressible SIMPLEC finite volume collocated code. Five different versions of k- and k- turbulence models are employed. The molecular Prandtl number is 0.71 and the Reynolds number based on the bulk velocity and the height of the channel is 100000. The predicted flow field and heat transfer show a relatively good agreement with the experimental results for different employed turbulence models, although the predicted flow field results are much better than the heat transfer results.Employing a variable turbulent Prandtl number according to the Kays and Crawford relation shows only a small difference in the estimated turbulent heat transfer fluxes. The influence of constant turbulent Prandtl numbers ranging from 0.5 to 0.92 is also examined and it is found that it has a significant effect on the simulation results of the heat transfer.

Bree’s cylinder was used to show different material behaviors under constant mechanical and cyclic thermal gradient loadings. Bree showed different behaviors with the help of a diagram known by his name as Bree’s diagram. In this research, the problem was reconsidered without his simplified hypothesis. The used material model is nonlinear kinematic hardening. The two dimensional problem and the Poisson’s effect were considered. In order to obtain the Bree’s diagram, return mapping algorithm was used. The results showed that the one dimensional model of Bree is conservative and the bi-dimensional Bree’s diagram does not correspond to the complete model.

The secondary suspension of most new EMU and DMU rail vehicles is equipped with air springs, to offer a good ride comfort to passengers. Air springs are a very important isolating component, which guarantees good ride comfort during the trip. In most rail–vehicle models developed by researchers, the thermo–dynamical effects of air springs in the rail–vehicle dynamics are not considered and secondary suspension is modeled by simple springs and dampers. As the performance of suspension components, especially for air springs, have significant effects on rail–vehicle dynamics and the ride comfort of passengers, a complete nonlinear thermo–dynamical air spring model, which is a combination of two different models, is introduced. Results from field tests show remarkable agreement between the proposed model and experimental data. Effects of air reservoir volume and the connecting pipes'' length and diameter on the system performances are investigated here.

Enormous loss of production time in machining, handling and assembly operations is caused mainly by resources’ unavailability. For this reason companies, both large and small, should optimize the production processes with the detection and elimination in advance of the majority of possible mistakes and disturbances that could cause deadlocks in the production process. The optimization tools which are available on the market are usually too expensive for smaller companies, which search for their competitive position in small quantity production. Therefore, a low cost simulation tool for the optimization of the resource present management is presented in this paper, where resources are treated as one of the main parameters in the production process and which could also enable smaller companies to optimize their production processes from the resource presence viewpoint.

The paper presents a procedure for forecasting the lead times of production orders on the basis of past actual lead time data. A customer for a particular production order will select the best bidder. It is rather risky to make a bid just on the basis of sales experience. A procedure is therefore proposed by which, on the basis of the actual lead times of operational and assembly orders processed in the company''s workplaces in the past, the expected lead time of a planned production order can be forecasted. The result of the proposed procedure for forecasting lead times is an empirical distribution of possible lead times for a production order. On the basis of this distribution, it is possible to forecast the probable lead time of a production order, taking into account a confidence interval. Using the proposed procedure, the sales department can make a delivery time forecast for the customer of the planned production order. As an illustration of using the procedure for forecasting lead times of production orders, a case study is presented: lead time of production order for the «tool for manufacturing the filter casing» was forecasted; the tool is manufactured by a Slovenian company.

Nickel-titanium alloy (Ni-Ti) rotary dental instrument files are devices which are commonly used in the field of endodontics for root canal preparation. However, Ni-Ti file breakage is common and is often caused by excessive hand pressure by the endodontist during a root canal preparation. The present solution is to automate the control of file failure (caused by pressure) through the development of a fuzzy logic controller to maintain the file breakage. Both in vitro and in vivo experiments were conducted to gather enough data to observe the system behavior and to modify the control system. In vivo results showed that a fuzzy logic control system was able to improve the file life up to 22% compared to existing rotary instrument control systems. Thus the fuzzy logic system presented in this paper not only improves the filing process performance, but reduced the time and costs spent by the endodontist as well through maximizing the use of file life and preventing file failures with the use of an applied intelligent control system.

Thickness of compound layers formed on the surface of pure iron during the nitriding process was analytically calculated and compared with experimental data in the gaseous and plasma nitriding. Plasma nitriding was carried out on a high purity iron substrate at a temperature of 550oC in an atmosphere of 75 vol. % H2 and 25 vol. % N2 for various nitriding times. The thickness of compound layers was evaluated by several characterization techniques including optical microscopy, SEM and XRD. Using the Fick''s first diffusion law and a mass conservation rule, two separate equations were developed for predicting the thickness of the binary compound layers; epsilon (ε) and gamma prime (γ''), in terms of the nitriding process parameters. The results of modelling indicated good agreement with the experimental data, provided that appropriate correction factors are applied. The flexibility and reliability of the models were increased by introducing two factors, Kε and Kγ''; the calculated curves corresponded well with both gaseous and plasma nitriding experimental data.

Phase variation of potential field data can be used as an interpretation method. This idea appears in edge detection with tilt angle or phase angle. The advantages of this quantity are its independency to body magnetization direction and also its easy computations. In this paper variations of this quantity termed local wave number are used for source parameter estimation such as body depth and susceptibility, which can be used without any prior information about source geometry. This method was applied on synthetic magnetic data and on the real magnetic data of an area in the Sar-Cheshme region. Using this method, causative body depth varies from 15 to 100 meters in different locations of the studied area, which is in agreement with the existing drilling information and forward modeling.

The Arghash gold deposit includes two oxidized and sulfide zones. In this work, separate samples from mineralogical zones and drilling cores of both oxidized and sulfide zones were taken, in which the gold head grades were 2. 5ppm and 0. 8ppm, respectively. Microscopic studies of polished and thin sections of the samples showed that the Arghash mineralization was simple and composed of pyrite, iron oxide and hydroxide. To process the Arghash oxidized sample, the gravity separation treatment with a jig and shaking table were employed and different experiments were performed. The results obtained from these experiments were not acceptable as the gold particles were disseminated in fine sizes. The grade of the gold in the jig concentrate using feed size fractions of -2360+500 microns was 3. 4ppm and in the shaking table using two feed size fractions of -500+75 and -300+75 microns was 3. 8ppm and 2. 4ppm respectively. The gold recovery in the jig test was 34% and for the shaking table test were 20. 7% and 25. 88% for the two size fractions. Because of the very low recovery obtained from gravity concentrations, cyanidation tests were carried out using an oxidized sample. Based on these experiments, the optimum value for size (d80), cyanide concentration, pH and cyanidation time were determined as 75 microns, 1000ppm, 10. 5 and 24 hours, respectively, which yielded 90% recovery. The sulfide sample was used in the cyanidation process. The recovery of direct cyanidation on the sulfide sample was relatively low (about 66%); therefore, the sulfide zone of Arghash belongs to the «refractory gold» type. Thus as pretreatment, the sulfide part of the sample was separated by flotation. The optimum parameters for separation including the feed size (80% passing), collector dosage, frother dosage, pulp density and conditioning time were defined as 74 microns, 100g/t, 40g/t, 30% and 5 minutes, respectively. Roasting and ultrafine grinding procedures were also used for the sample pretreatment. The cyanidation test was then done using a flotation tail and roasted and very fine ground flotation concentrate. The maximum gold recovery (approximately 90%) was obtained by cyanidation of the roasted flotation concentrate.

In the present paper, the effect of heat treatment on the surface roughness of AISI 4140 steel has been investigated by use of paired t-test and one way analysis of variance (ANOVA). The paired t-test was performed to determine the differences between the means before and after heat treatment. One way ANOVA was used to further evaluate the effect of heat treatment on the difference in variances between two groups. According to the statistical analysis, it was concluded that heat treatment has decreased the surface roughness at the 95% confidence level. The improvement of surface roughness varies from 37% to 45% with various combinations of experimental parameters.