Pre-sedimentation basins are considered as the major and important components in water treatment process through conventional method. Because of the high cost of constructing these basins, which is approximately 30% of the total costs of water treatment plants, modeling and optimum performance of pre-sedimentation basins are very important. In pre-sedimentation basins, because of the existence of velocity gradients, secondary and rotational flows occur. In order to increase the performance of a pre-sedimentation basin (clarifier), it is essential to have a uniform and calm flow field. The use of suitable baffle configurations may help forming favorable flow field and increase the efficiency of the pre-sedimentation basins. In order to find the proper position of a baffle in a rectangular sedimentation basin, computational investigations are performed. The first step to optimize pre-sedimentation basin is accurate calculation of the velocity field and the volume of rotation zones. Flow guiding blades can also be used to depreciate the inlet jet and reduce turbulent kinetic energy. Because of the flow complexity and also the effects of scale, physical models can not solely provide a clear understanding of the physics governing the flow field and it is necessary to study this phenomenon numerically along with field and experimental studies. The first step to optimize pre-sedimentation basins is accurate simulation of the velocity field and the volume of rotation zones. In the present study, numerical simulation of flow was investigated in a pre-sedimentation basin using SSIIM and Fluent models. Continuity and momentum equations were solved using finite volume method. Flow analysis was done steady by the SIMPLE algorithm for velocity and pressure coupling. Discrete method of continuity equations, momentum, turbulent kinetic energy, Reynolds stress drop and discretion of pressure equation are standard. The numerical results were calibrated with experimental results of Shahrokhi et al. (2011) and Imam et al. (1984). Flow simulation was performed in 3D and flow velocity profiles were compared with the experimental results in different sections of a pre-sedimentation basin. Then, in order to sedimentation investigation in the pre-sedimentation basin, advection and dispersion equation of sediment concentration was solved simultaneously with the governing equations of flow. The results of the vertical distribution of sediment concentration profiles in different sections of the basin were compared with the experimental and numerical results of other researchers. Finally, the effect of flow guiding blades on the flow pattern and the efficiency of sedimentation in the pre-sedimentation ponds were investigated. The comparison showed that there is a good agreement between numerical and experimental study with an average error of 6%. Flow rate is one of the effective parameters on creating a rotational zone inside the basins. With increasing the inlet flow rate from 0.002 to 0.01 cubic meters per second, the length of the rotational zone has increased 25% and the width of the rotating zone has increased 45%. The secondary and rotational currents formed at the entrance of the basin are two small rotational zones and approaching the middle of the basin and formation of flow separation zones, the number of rotating areas and their dimensions have increased. From the beginning to the middle of the basin, the shear stress is increased. In the sections x = 0.46 m and x = 0.82 m, the amount of shear stress is maximum. Amount of energy in the middle of the depth has decreased by 40% compared to the water level and about 60% compared to the floor of the sedimentation basin. It showed that there is a good agreement between the numerical and experimental results. It also indicated high ability of SSIIM in predicting distribution of sediment concentration profiles in pre-sedimentation basins. With increasing flow depth, the sediment concentration decreases. In the section x = 1.58 m, the sediment concentration near the free surface is 44 mg L-1, which decreased by 57.48% compared to the concentration of sediment in the basin bed. In the case without the guide blade, near the free surface of the stream, the sediment concentration was decreased. Also, in the middle of the basin, due to the turbulence of the flow and the rotational areas, the secondary current strength was maximal and decreased as it approached the end of the basin.

Settling basins are one of the most essential structures for the separation of inflow sediments. This structure is established to enhance the water quality after the river-basins and water channels. Numerous studies have been conducted on the design of this structure and different methods have been provided to increase its efficiency. However, the use of simple settling basins with the minimum cost which can provide the ideal targets has been the focus of designers. In this study, the effect of flow-guiding plates and the angle between these and the inflow, and the impact of water depth in the basin on the trap efficiency of the settling basins were considered. For testing, 4 blades with specific length and angle were installed. This experiment was repeated for 3 different lengths and 3 angles. The results of the experiments showed that with the enhancement of the depth of water to 10 centimeters to 30 centimeters, while the basin had no flow-guiding plates, increased the trap efficiency of the basin by 4.9 percent. Also, by the use of flow-guiding plates in the suitable and best length and angle (in this study, the suitable size of blades was 22.5 centimeters and the best position was by the angle of 30 degrees); with the maximum of the water depth of 30 centimeters, the trap efficiency was increased by 13.3 percent. The sensitivity analysis done showed that the depth of water had the most effect on the trap efficiency of the basin and the changes in the lengths and angles of the blades position had the similar effects of the basin trap efficiency.

In the present study, analysis of fluid flow and heat transfer in the entrance and the periodically fully developed region of a channel with porous baffles in a staggered arrangement, is numerically studied. The Navier-stokes and Brinkman-Forchheimer equations are used to model fluid flow in open and porous regions. The flow is assumed to be laminar. A finite volume based method, in conjunction with the SIMPLE algorithm, is used to solve the equations. The local thermal equilibrium model is adopted in the energy equation to evaluate solid and fluid temperatures. The effect of parameters, such as baffle height, baffle spacing, Reynolds number and thermal conductivity ratio between the porous baffles and the fluid, on the flow field and local heat transfer rate is analyzed at two values of Darcy number. Considering the effect of geometrical and physical characteristics of the porous baffles and flow parameters on the developing velocity profile and the local Nusselt number, it can be concluded that the developing length, as well as the value of fully developed Nusselt number, are affected by these parameters, while, in the case of conventional thermally developed duct flow, the Nusselt number is independent of these parameters. The results indicate that the local heat transfer coefficient significantly depends on the formation and variation of the recirculation caused by the porous baffles, so that, in cases where use of porous baffles leads to a recirculation zone, the local Nusselt number in the entrance region is less than that of the fully developed region. It is also shown that the heat transfer performance ratio is significantly improved for high Prandtl number fluids.

The present study is investigated to checking the effect of cooling film on turbine blade. The geometric model which is used in this study has the same dimensions with the one which was used for the experimental tests by Akkad [1]. At geometric simulation the semi-cylindrical and flat blade attached to it have been used for showing the front edge of the blade. Geometric model is gridded by GridGenTM software and fluid flow is simulated by FluentTM solver. Blowing ratio is defined as a ratio of the cooling mass flux and mainstream. Simulation is done for different values of 0.5 Blowing ratio and 1, and with the k-ε and k-ω turbulence model. It is assumed that the value of the free turbulence intensity at stream is 0/75%. The results show that the cooling film has more efficacies at downstream for low blowing ratio and also in the output adjacency of the cooling jet it can be observed that the blowing ratio growth causes to increase the efficacy of cooling film.

Energy conversion efficiency of water to the water flow depends on the blade of the turbine wheel depends on the blade surface. Heat water in a collision with turbine blades, friction on the surface of the water during passage through the turbine blades, nozzle head loss and air friction resistance pelton turbine energy resources are wasted. When the water jet passes around the turbine blades, ideal against the current because of non-slip surface and thus the boundary layer is created. The formation of the boundary layer and its thickness depends on the blade surface roughness. In this research the mathematical relationships to help the border layer, a model for the calculation of the flow passing through the wasted power of pelton turbine blade is presented in which the effect of the friction and pressure changes on the flow along the path of the blade come into account.

Convective heat transfer from a flat plate, which is enhanced by an oscillating blade, was numerically investigated at the present study. It was assumed that the blade is made of a rigid and thin plate and it is vertically oriented at the top of the target plate. Numerical analysis was performed using commercial software ANSYS Fluent 6.3 and the periodic oscillation of the blade was modeled by the moving mesh method. Conservation equations of mass, momentum and energy was solved in 2-D and transient form for the laminar airflow with constant physical properties. Constant temperature was considered for the plate and the details of both the flow and thermal fields were determined. The distribution of convective heat transfer coefficient was then calculated for the target plate. The effect of various parameters including the amplitude and frequency of the blade oscillation as well as the geometrical parameters was investigated on the convective heat transfer from the target plate. The results indicated that a wider area of the plate was affected by increasing the oscillation amplitude of the blade. Convective heat transfer was also enhanced over the entire target plate as the rotational Reynolds number was increased.

The current research has studied the piezoelectric blade sensor from different views in order to control the oscillations of the circular cylinder present upstream of the piezoelectric blade and to control the fluctuating fluid flow around the blade using the force on the piezoelectric blade. The desired arrangement of a piezoelectric blade is placed downstream of a circular cylinder and with the help of a certain limit of blade oscillations, the hardness coefficient of the cylinder spring is applied from 65 (N/M) in normal condition to 100 (N/M) in the necessary condition. The controller as well as in other cases, the damping rate increases from zero to 0.02 (Nm/S) and in this way, the oscillations of the cylinder are controlled. In the same way, by controlling the oscillations of the cylinder, its effect on the oscillations of the blade, which is located downstream, has been investigated under the title of feedback effects. By controlling the feedback of the force on the piezoelectric blade in a closed loop, it is possible to monitor the displacement of the tip of the blade and the force on the piezoelectric blade. In these studies, it has been determined that in the case where the specific limit of the controller is 0.7 mm of the oscillations of the piezoelectric blade tip, due to the earlier application of the controller compared to the specific limit of 1 and 2 mm of the oscillations of the blade tip, the oscillations of the cylinder are Also, by comparing the state where the controller is included in the circuit compared to the state without the controller, it is clear that the oscillations of the blade and cylinder have been controlled to some extent.

Triangular weirs (Triangular vanes) and footing are measures which causes to control the scour in outer bend and keep out scouring hole from the outer bend. In this study, the main purpose is to experimentally study the effect of using both footing and triangular weirs on sedimentation and erosion of a bed of flume bend under different flow conditions (Froude numbers 0.243, 0.262, 0.292 and 0.321). Tests were conducted using triangular weirs with distance of 8 times of the effective length installed at an angle of 30 degree from the upstream bank. Footing width and effective length of triangular weirs were selected one-fifth the width of the canal. The results showed that using footing combined with the triangular weirs caused to reduce maximum scour depth at the toe of weirs and prevent from its extension to outer bend. Using footing reduced 70 percent maximum scour depth at the toe of weirs. Moreover using footing combined with triangular weirs had a little effect on flow diversion from outer bank towards the center of flume. The results show that using footing along with triangular weirs increased 9 percent maximum scour depth of thalweg and did not change the thalweg distance from the outer bank.

In pool-type research reactors, utilizing thermal column irradiation facilities through the fission process in the core, gamma rays are produced and absorbed by lead slab as a gamma rays shield of thermal column. Consequently, heat is generated in the lead slab surface which induces flow by the thermal buoyancy force. In the present work, 3D, CFD simulation of flow and heat transfer in a channel, formed by the thermal column and core edge, is considered. The aim is to obtain the temperature distribution on the lead surface and also a solution to prevent boiling, which may occur on the lead surface. It is observed that the hot spot on the lead surface exceeds the boiling point in natural convection mechanism. Therefore, the grid plate is extended underneath the channel so that water can flow through the channel and exit to the plenum causing forced convection to be established as an effective way to eliminate the boiling occurrence.

In this study, a three-dimensional simulation model has been carried out to investigate the flow pattern and the effect of picket fences on the performance of the settler in the solvent extraction plant in the Miduk copper complex. The effect of picket fences on the settler and their arrangements, flow distribution blades, separation of phases and the droplet size distribution has been investigated with CFD simulations.  The simulation has been carried out with an Eulerian-Eulerian method in conjunction with the incorporated MUSIG model which is based on a population balance equation and takes into account the break up and coalescence models of droplets.  The simulation of settler shows that feed spouting velocity was propagated for long distances in the settler and dispersion band continues to the end of the settler. By setting one picket fence in the settler, velocity vectors transmitted and the width of dispersion band decreased which as a result increasing droplet size. By increasing number of picket fences dispersion band almost disappears. The inspection of distribution of droplet size at different points in the settler showed that the presence of picket fences increases the size of droplets. Finally, the effect of closed to opened (C/O) area ratio of the picket fences on the performance of the settler was studied. The results showed that by increasing the C/O ratio, some circulation appears in the flow which causes a negative effect on phase separation.