Iranian Journal of science and Technology (B: Engineering)
Volume:33 Issue: 3, June2009

Domed roofs have been used in Iran and many other countries to cover large buildings such as mosques, shrines, churches, schools, etc. However their favorable thermal performance has allowed them to be employed in other buildings like bazaars, or market places in Iran.In this investigation, wind pressure coefficients were determined experimentally for a domed roof model in a boundary layer wind tunnel. The model was a 1/10 scale model of the dome of an old school in the city of Yazd, in the central desert region of Iran. The model included a number of windows at the collar of the dome, and a hole on its apex. A total of 48 pressure tabs were employed to measure the air pressure at various points on the dome model. Tests were run under three conditions of windows and the hole on top of the dome being open or closed.The result of this research can be used to determine the heat transfer coefficient of wind blowing on domed roofs and the passive cooling effect of such structures.

A new analytical model is developed to calculate laminar natural convection heat transfer from isothermal cones of arbitrary aspect ratio and orientation (tip downward, tip upward and horizontal) with active end for all values of Pr number. It is based on the new concept of Dynamic Body Gravity Function. This problem is also solved numerically for isothermal cones of different orientations. Results of this dynamic model for three different cones are compared with the present numerical solution and available experimental data. Excellent agreement between the present analytical model, the numerical solution and also the experimental data points in a wide range of Rayleigh number for all cones discussed shows that the present analytical method is a powerful tool for modeling laminar natural convection heat transfer from isothermal bodies.

Wire erosion discharge machining (WEDM) is a modification of electro discharge machining (EDM) and has been widely used for a long time for cutting punches and dies, shaped pockets and other machine parts on conductive work materials. The surface finish of the machined surface mainly depends on the pulse duration, open voltage, wire speed and dielectric flushing pressure. In the present work, two of the techniques, namely factorial design and neural network (NN) were used for modeling and predicting the surface roughness of AISI 4340 steel. Surface roughness was taken as a response variable measured after WEDM and pulse duration, open voltage, wire speed and dielectric flushing pressure were taken as input parameters. Relationships between surface roughness and WEDM cutting parameters have been investigated. The level of importance of the WEDM cutting parameters on the surface roughness was determined by using the analysis of variance method (ANOVA). The mathematical relation between the workpiece surface roughness and WEDM cutting parameters were established by regression analysis method. This mathematical model may be used in estimating the surface roughness without performing any experiments. Finally, predicted values of surface roughness by techniques, NN and regression analysis, were compared with the experimental values and their closeness with the experimental values determined. Results show that, NN is a good alternative to empirical modeling based on full factorial design.

Multilayered ceramic-metal composites were produced by solid state diffusion bonding of polycrystalline alumina and three Al alloys containing 1 to 2%Sr, 2% Mg and Mg + Si (5057 Al alloy). The multilayered structures were fabricated at 610°C under a compressive stress of 3 MPa for 2 hours in He-5%H atmosphere. The ceramic-metal interfaces were studied by SEM and TEM equipped with an energy dispersive spectrometer (EDS). Addition of 1 wt % Sr to Al promoted good adhesion, without producing any interfacial products, while the Al-2wt%Sr was poor in this regard due to the presence of dispersed Al4Sr, which is an intrinsic phase in the Al-Sr phase system. The Al-2%Mg alloy produced a continuous film at the interface, which was characterized as being MgAl2O4. Al alloys containing Mg and Si (5057 commercial alloy) produced not only the spinel structure (MgAl2O4), but another phase rich in Mg and Si (close to Mg2Si). These latter interfacial reaction products were not the intrinsic phases in Al-Mg alloys, but were reaction products at the Al2O3 –Al alloy interfaces.

In this study a mathematical method called PSPD (profile side-pore diffusion) based on the work of Bouffard and Dixon [10] is proposed for simulation of solute transport through the pores of a heap, considering the reaction terms. The obtained governing equations are converted into dimensionless forms and are solved by writing a computer program based on an implicit finite difference method. The solution of the model results in the outlet acid concentration profile. In order to check the accuracy of the proposed model and also for determination of effective diffusivity of sulfuric acid in copper oxide ore particles, two experimental setups are constructed, one for measurement of the effective diffusivity and the other for measuring the rate of leaching. The effective diffusivity is obtained by two different methods which reconfirm each other. The copper oxide ore of Sarcheshmeh copper complex, situated in Kerman province in Iran, was used for experimentation. The effects of different factors such as particle size, acid solution flow rate and initial acid concentration are examined on the rate of leaching in two columns of different heights.Comparison of the calculated data with experimental data under the same operating conditions shows a good agreement between them and hence validity of the proposed model was confirmed. The results show that the extraction time of copper is influenced mostly by increasing the acid solution flow rate and decreasing the column height due to decreasing the advection time.

Gol-E-Gohar iron complex is located 50km southwest of Sirjan City, Iran. Its concentrate contains sulfur and phosphor with grades of 0.5%S and 0.08%P which are higher than the steel industrial permitted limit of 0.1%S and 0.05%P. Pyrite and apatite are the main sources of sulfur and phosphor. In this work, it was attempted to decrease the S and P percentages of the concentrate using the flotation approach. In reverse flotation with the presence of xanthates, pyrite floated and fine apatite particles were conducted with water. The results of mineralogical studies indicated that the main minerals in the sample were magnetite and hematite and others were goethite, chlorite, pyrite, calcite, quartz and apatite, chalcopyrite and pyrotite in low amounts, and -75+53 microns was the pyrite liberation size with a degree of 65%. The effect of different parameters such as type and doze of collector, frother and depressant, solid content, pH, impeller speed, frothing time, conditioning time and desliming on sulfur and phosphor removal were investigated. The best results were achieved with desliming. The collector, frother and dispersant were 50g/t of KAX, 60g/t of MIBC and 200g/t of sodium silicate, pulp pH=8, and 6 minutes for conditioning time. Under the best conditions, with desliming, a concentrate with acceptable grades of Fe (70.24%), S (0.041%), and P (0.043%) were obtained. The recovery for Fe was 95.11%, and for sulfur removal, 92.24%.

Gas hydrates are dissociated to hydrate former gases and either water or ice. The enthalpy of the dissociation reaction is determined analytically using Clausius-Clapeyron equation. Two correlations are developed for calculating the enthalpies of dissociation of simple and mixed hydrates. The results show that the enthalpies of dissociation of simple and mixed hydrate calculated by this method are in good agreement with the experimental data at the quadruple point.

The paper presents numerical results for the prediction of two- dimensional laminar heat transfer to water flow at critical pressure. The set of governing equations containing continuity, momentum and energy are solved simultaneously using CFD technique. The discretized form of each equation is obtained by finite volume method and the SIMPLE algorithm is used for pressure-velocity calculations. In all of the case studies, sub-cooled water at critical pressure (22.1 MPa) enters into a duct with constant surface temperature which is near the fluid critical temperature. Numerical results show that as the fluid temperature approaches the critical temperature, the variations of fluid properties increase rapidly and cause an unusual velocity profile for this type of convective flow. In the present work, the crucial influence of fluid property variation on flow and heat transfer distributions at critical pressure is thoroughly explored.