Iranian Journal of science and Technology (B: Engineering)
Volume:32 Issue: 6, Dec 2008

In this paper the performance characteristics of a turbocharger twin-entry radial inflow gas turbine with asymmetrical volute and rotor tip diameter of 73.6 mm in steady state and under full and partial admission conditions are investigated. The employed method is based on one dimensional performance prediction which is developed for partial admission conditions. Furthermore, this method is developed for the asymmetrical volute of the turbine considering the flow specifications. Experimental investigation of the research was carried out on special test facilities under full and partial admission conditions for a wide range of speeds. A comparison of experimental and modeling results shows good agreement. Interestingly, the turbine maximum efficiency occurs when the shroud side inlet mass flow is higher than that of the hub side.

A steady state model was developed for a hollow fiber membrane contactor to describe gas absorption performance. Countercurrent absorption of pure CO2, pure SO2, CO2-N2 and SO2-N2 mixtures in diethanolamine solution (DEA), and water as the absorbent were investigated. The model is able to predict gas phase concentration and the velocity profile in the axial direction inside the shell, as well as the liquid concentration profile in both the axial and radial direction inside the fibers. A numerical scheme was proposed to solve the simultaneous mathematical expressions that were obtained based on concepts of mass transfer, and the results were validated with experimental data found in the literature. Axial variations of gas velocity, gas concentration and a two dimensional concentration profile of the liquid phase were compared for three absorbing systems, including low (CO2-water), moderate (CO2-DEA) and high (SO2-water) absorption rates. The effect of chemical reaction on the importance of external resistance was also studied using this model. It was found that the shell side and membrane resistances are negligible in comparison with the liquid resistance in low absorption rates, for example in a CO2-water system, however they have significant effects when the chemical reaction is fast and the absorption rate is high, such as SO2-water system.

In this study the effect of the presence of a drag reducing agent (DRA) on the pressure drop in cocurrent horizontal rough pipes carrying annular flow of air and crude oil is investigated. An experimental set-up is constructed. The test section of the experimental set-up consists of two rough pipes of galvanized iron, 8.8m long and having 2.54cm and 1.27cm ID. The DRA applied is a polyalpha-olefin (polyisobutylene). The pressure drop, both in the presence and the lack of DRA, has been calculated using the experimental data obtained. The results show that the addition of DRA could be effective up to certain doses of DRA, after which, the pressure drop is kept constant. A percentage drag reduction of about 45 is observed at some experimental conditions.

Application of pulsating pressure is a new and effective method to improve the formability of the tube hydroforming process. However, the factors that cause this improvement are still unclear. In this paper, the forming mechanism of pulsating free bulge hydroforming of tubes is studied using both finite element simulation and experiment. The effects of oscillating pressure on deformation behavior, thickness distribution, strain path and friction force are examined. It is shown that for a constant pressure path, the wall thickness decreases quickly up to bursting; whereas for the pulsating pressure, the thickness decreases gradually, and thus, local thinning is prevented by oscillating internal pressure. Formability is improved due to an increase of the longitudinal compressive strain and better wrinkling behavior. Small harmonic wrinkles appear and are removed during the pulsating process, hence, by this mechanism bursting and wrinkling are prevented, causing improvement of formability.

Most mineral processing system models include variables that have both systematic errors (bias) and associated randomness. Therefore, in analyzing these models it is essential to incorporate their uncertainties. In general, there are a couple of different methods of variance or uncertainty analysis used by analysts such as sensitivity analysis, Monte Carlo simulation, etc. In this paper, the law of propagation of errors (LPE) and one of the favorite analysis tools, the Monte Carlo simulation using Latin hypercube sampling, are presented. Limitations of the LPE are emphasized and simple applications of these two methods in mineral processing are also briefly shown. A case study of evaluating the variance of semi-autogenous (SAG) power draw in a grinding circuit is presented as well. Using Monte Carlo simulation showed that the mean power draw of the Sarcheshmeh SAG mill is about 9349.75 kW with a standard deviation of 983.2 kW, with the highest frequency occurring between 9058.5 and 9862.5 kW. Comparing the results of LPE and Monte Carlo simulation for the Sarcheshmeh SAG mill power draw showed that the mean is slightly higher than calculated, (9441.1kW), while its standard deviation is lower than the other one.

This article describes a study of the application of a roll bonding technique to MS90(CuZn10) alloy strips and steel sheets using a chromized interlayer. It was found that the overall bond between these two metals resulted from two different types of bonds: a block bond, linking the MS90 alloy strips and chromium topcoat layer, and a blank bond, linking the MS90 alloy strips and bare steel surface in the area where the chromium coating has been fragmented. This study investigated the effects of plating time on the thickness of the coating layers and of the area fraction of the blank bond on the bond strength. The overall bond strength depends mainly on the strength and the area fraction of the blank bond. A linear relationship model exists between the overall bond strength and the area fraction of the blank bond. The bond strength of the blank bond was eight times greater than that of the block bond. The area fraction of the blank bond increased with increasing the coating thickness up to 55 µm, but thereafter decreased due to the rotation of the chromium blocks.