نشریه علوم و مهندسی جداسازی
سال پنجم شماره 2 (پیاپی 10، پاییز و زمستان 1392)

In this study the absorption of carbon dioxide from an air stream has been investigated in rotating packed bed. At first, hydrodynamics experiments have been done to determine the flow pattern and pressure drop at two cases, single phase and two phase flow. Then, absorption experiments have been done by using water, MEA and DEA solution with different weight percent. The effect of parameters such as rotational speed, gas and liquid flow rate, type and concentration of solution on absorption efficiency investigated. Results showed that increasing of rotational speed, liquid flow rate and solution concentration increases absorption efficiency. In contrast, increasing in gas flow rate leads to decreases in efficiency. Hydrodynamics analysis showed that pressure drop increases by liquid and gas flow rates.

Separation of minerals by flotation is based on the differences of surface properties between the valuable minerals and the gangue. However, some particles float by entrainment mechanism which is a nonselective process. There are different methods to determine the amount of particles which is floated by entrainment. In this paper a new method applied to determine entrainment in collectorless flotation of chalcopyrite of Mazraeh mine. Effect of parameters including impeller speed, pulp density, time, frother amount was investigated for chalcopyrite entrainment. In collectorless flotation, by controlling pulp potential (Eh), the hyrophobicity of particles prevented and so the net fraction of particles moved to concentrate by entrainment were calculated. Under optimum conditions of pulp density = 10%, it was observed that impeller speed = 908rpm, frother amount = 20g/t and flotation time equal to 1.1min, chalcopyrite entrainment minimize to 0.6 %.

In this study the absorption of carbon dioxide from an air stream has been investigated in rotating packed bed. At first, hydrodynamics experiments have been done to determine the flow pattern and pressure drop at two cases, single phase and two phase flow. Then, absorption experiments have been done by using water, MEA and DEA solution with different weight percent. The effect of parameters such as rotational speed, gas and liquid flow rate, type and concentration of solution on absorption efficiency investigated. Results showed that increasing of rotational speed, liquid flow rate and solution concentration increases absorption efficiency. In contrast, increasing in gas flow rate leads to decreases in efficiency. Hydrodynamics analysis showed that pressure drop increases by liquid and gas flow rates.

In this paper, comparison between irreversibilities of different parts weir-type cascade solar still for a particular day has been carried out. By writing unsteady exergy balance for different parts of solar still system such as glass cover, brackish water and absorber plate, some equations are obtained for different irreversibilities of the system based on climatic and operating parameters. Simulation results show that in input mass flow rate 0.065 kg/min, the largest value of irreversibility rate belongs to absorber plate among of all of irreversibility rates of the system. Irreversibility rate of absorber plate in input mass flow rate 0.065 kg/min is 84.17% of all of system irreversibility rates. Whereas irreversibility rates in other parts of solar still can be neglected. Also study on exergy fractional shows that evaporative exergy fractional have more significant with respect to convective and radiational exergy fractional.

Today, more than 90% of world steel production accounts for continuous casting method. One of the main problems of this method is alumina nozzle clogging. In this study, modification of alumina inclusions into the calcium aluminate phases was investigated. Calcium carbide and calcium oxide were added to the steel melt and hence chemical composition of secondary phases was studied using a Scanning Electron Microscope. Both qualitative and quantitative analyses were performed. The results showed that the addition of calcium oxide to the surface of the killed aluminum molten metal leads to the gradual formation of the calcium aluminate phases. Furthermore, the addition of calcium carbide does not have the considerable effect on the formation of calcium aluminate phases and in turn, calcium oxide in the top slag prevents the nozzle clogging problem.

In this paper a two-dimensional unsteady state detailed mathematical formulation is developed for the numerical modeling of the behavior of a channel of a hygroscopic compact matrix. Considering proper control volume and some assumptions, governing equation is derived. Initial and boundary equation as well as auxiliary equation are used to close governing equations. Modeling results are validated by experimental data and numeric heat and mass balances. The profiles of temperature and humidity in the desiccant layer and air flow rate are resulted and can be used for optimum design of desiccant channel. Furthermore, effect of axial heat and mass diffusion inside the desiccant are examined as well as number of nodes in the desiccant layer. Results prove that axial heat and mass diffusion can be omitted and number of nodes can be reduced without significant effect in the result precision.

Shear yield stress as a rheological property of suspensions affects the efficiency of some of the mineral processing methods such as solids liquid separation, grinding, classification, and tailings disposal. In this work, effect of solids concentration, fines extent, pH and temperature on the shear yield stress of the final tailings suspension of concentration plant 1 at Sarcheshmeh Copper Complex was investigated and eventually their impact on solids liquid separation was analyzed. The shear yield stress was calculated using the slump test results and the analytical model presented by Pashias. Results indicated that, with the extent of fines the shear yield stress increased considerably. An increase in flocculant dosage up to 10 g/t resulted in a significant increase in the shear yield stress. While, with the flocculant dosages higher than 20 g/t, increasing the flocculant dosage led to a slight increase in the shear yield stress. An increase in shear yield stress leads to a decrease in compressibility of suspension and as a result the efficiency of solids liquid separation decreases. These achievements can be beneficial to the efficiency of thickening and filtering.