Baffles are used for decreasing bubbles diameter in order to increase the conversion rate along the bubbling fluidized bed reactors. The appearance of this phenomenon is due to bursting of the bubbles during the pass of bubbles from baffles. In this work, a computerized modeling and simulation have been performed in order to obtain a fundamental knowledge of the influence of the baffles on the bubble diameter and the specific mass transfer area. The height of the bed is 5m and its diameter is 0.3m. Paffles are located at 1and 2m from the bottom of the bed. A two phase model together with a comprehensive. fluid dynamical description of bubbling fluidized is presented. The effects of baffles and gas superficial velocity on the operating behavior of fluidized bed reactors are considered. The results are compared to the previously reported documents, and the experiments which have been carried out. MATLAB software is used in this simulation.

Heat transfer is a very important phenomenon for modeling heat equipment and scale up of slurry bubble reactors. For studying local heat transfer coefficient in slurry reactors, a column of 30cm diameter and of about 3m height which meets industrial reactor region was designed and constructed. In the experiments, 50-mm SiO2 powder having the same size of the catalyst of Fischer-Tropsch process was used as the solid phase and paraffin and air were used as the liquid and gas phases respectively. A specially designed heat transfer probe was used for measuring local heat transfer which consists of an electrical heat source element and two thermocouples for probing surface and fluid temperature measuring. By using this probe, local heat transfer coefficient was measured and the influence of superficial gas velocity and solid concentration were investigated. In all experiments, slurry phase height to the column diameter ratio was 4. The results showed that increasing the gas velocity from 2 to 25cm/s leads to an increase in heat transfer coefficient by about 65%; also an increase in the solid concentration increases heat transfer rate

Background and Objective: In This study the impacts of operating conditions such as aeration rate, the downcomer-to-riser cross-sectional area ratio (Ad/Ar), and liquid phase properties on the hydrodynamics and volumetric mass transfer coefficient in three-phase airlift reactors was investigated. Method: Experiments were conducted in external loop air-lift reactor with downcomer to riser cross-sectional area ratio (AD/AR=0. 14) and internal air-lift reactors with downcomer to riser cross-sectional area ratios 0. 36 and 1. Air and Water were used as gas and liquid phases, respectively and activated sludge is used as the solid phase. Findings: The liquid circulation velocity, gas holdup and mass transfer coefficient increased with an increase in the superficial gas velocity, decrease the sludge concentration and decrease downcomer to riser cross-sectional area ratio. The maximum amount of gas hold up, 0. 178 in external air-lift reactor with 1%(w/w) activated sludge in superficial gas velocity 0. 24(m/s) was observed. A model to predict the effect of activated sludge concentration, the superficial gas velocity and the downcomer-to-riser cross-sectional area ratio on the mass transfer activated sludge airlift reactors provided which with the experimental results are in good agreement. Discussion and Conclusion: The evaluation of internal and external reactors performance at different concentration and superficial gas velocity show that the air-lift reactor with external loop has better performance in comparison with internal airlift reactors.

Flotation is the most important process for concentrating mineral ores. This process may occur in any vessel such as column flotation, which has been used widely during the last decade and the conventional flotation cells. The effect of superficial feed velocity on the copper recovery was investigated using pilot-scale column flotation of "Sarcheshmeh Copper Complex". The results were compared with the conventional flotation cell data. It was reveled that for coarse particles (d(80)=90 mu m) this column could not be used instead of cells and rougher cells, but for small particles (d(80)=44 mu m) it could, For coarse particles, recovery curve demonstrated a maximum with increase in feed rate. However a minimum was observed for fine particles.

The overall flotation recovery depends on the recovery in the pulp zone as well as recovery in the froth zone. The froth retention time affects the froth recovery and it has an inverse relationship with both froth recovery and overall recovery. On the other hand, the froth retention time depends on gas rate and froth depth. The gas rate is an independent factor in induced-air flotation machines, whereas in self-aerated cells it depends on various variables and the froth depth is one of them with significant effect. Therefore, adjusting the gas rate is more complicated and more difficult in the induced-air flotation machine. This study attempts to investigate the effects of froth depth and gas rate on superficial gas velocity, froth retention time and metallurgical performance of the cell. The operation of these types of cells can be improved, by understanding the relationship between these parameters particularity the adjustment of froth depth and gas rate. Experimental tests were carried out in a 50 m3 self-aerated cell in Gol Gohar iron ore processing plant. The results showed that although the froth depth variations, changed the gas rate, but the gas rate variations did not have a significant effect on the froth retention time and the metallurgical performance. Also, the froth depth was not a good option to change the gas rate and the superficial gas velocity in this type of flotation cells, because the range of superficial gas velocity variations was low when the froth depth was changed in industrial-scale.

In this paper, a large-scale experimental study has been conducted in order to evaluate the high-velocity compaction of aluminum powder using gas Detonation Forming (GDF) processing technique. In this series of experiments, the effect of the distribution of grain particle size, initial powder mass, and loading conditions on green density and strength of compacted products were thoroughly studied. The maximum relative green density and green strength of 97. 6% and 17. 9% were achieved. Group Method of Data Handling (GMDH)-type neural network in conjunction with Singular Value Decomposition (SVD) method was exerted to model the high-velocity compaction process of aluminum powder. The main objective of this idea is to demonstrate how two characteristics of the high-velocity compaction, namely, the relative green density and strength of products vary with the changing of significant parameters, involved in GDF processing technique.

Experimental investigation conducted on Taylor bubble characteristics in a large bend including three consecutive inclinations. For this purposes, flow maps were obtained for the bend and horizontal section of upstream of the bend to define the area of this regime and mechanism of Taylor bubble formation. The effect of superficial gas-liquid velocities and the duct slope were studied on average velocity, length and frequency of bubbles. The results show, the bubble velocity and length increase as gas superficial velocity increases and the duct slope decreases. However, liquid velocity increase has decreasing effect on this characteristic. Bubble frequency is independent of slope change and reduces as gas superficial velocity increase. However, bubble frequency reduces at first and then increase as liquid superficial velocity increases. Regarding the safety regulation for industry, the minimum of the bubble frequency should be generated for the required liquid mass flow rate. Meanwhile, for the gas velocity, some optimization is required between frequency reductions with Taylor bubble velocity increase in addition to bubble length reduction. Regarding the background of the present field with shortage of results on Taylor bubbles frequency, some correlations based on the superficial Reynolds number of phases were presented for each inclination.

The vortex gas injection into plasma torch is considered as a method for reducing electrodes erosion. In order to investigate the effects of vortex gas injection on plasma structure, as well as the effect of gas viscosity on the rate of rotation, a threedimensional nonequilibrium and time-dependent non-transferred DC plasma torch model has been simulated. Viewing the general characteristics of the plasma shows that the model works well. The results have shown that if the components of the inlet gas velocity are not properly selected, it is possible that the rotary effects of the gas are greatly depleted even before the gas reaches the cathode tip and plasma formation. In this case, only the change in the axial component of the gas causes changes in the structure of the plasma. Vortex reduction is also observed during the movement of cold gases. It is observed that the change in viscosity of gas has significant effects on the rate of the vortex.