Journal Of Applied Fluid Mechanics
Volume:2 Issue: 1, Jan-Feb 2009

Circulation regions always exist in settling tanks. These regions would result in short-circuiting enlargement of the dead zone and high flow mixing problems and avoid optimal particle sedimentation. Therefore, the main objective of the tank design process is to avoid formation of the circulation zone, which is known as dead zone. Experiments show that the tank performance can be improved by altering the geometry of the tank which leads to a different velocity distributions and flow patterns. In this paper, the presence of a baffle and its effect on the hydrodynamics of the flow field has been investigated in a primary settling tank. Hydrodynamics of the flow field in these basins is sophisticated. Therefore a numerical simulation has been provided to discover such flow field. Then, the flow structure was simulated by an unsteady two-phase finite volume method, with VOF (Volume of Fluid) model. Besides, the RNG turbulence model was used in the numerical calculations. Successively, in order to validate the mentioned method and for a better understanding of the phenomenon, experimental tests have been carried out using ADV (Acoustic Doppler Velocimeter) and a 0.2 m breadth rectangular model tank. Results depict the ability of this model in predicting the velocity profiles and circulation districts. Eventually, the optimum position of the baffle for enhancing the performance of the primary settling tank was determined by applying the above mentioned numerical scheme.

Aim of the paper is to investigate effects of variable thermal conductivity and heat source/sink on flow of a viscous incompressible electrically conducting fluid in the presence of uniform transverse magnetic field and variable free stream near a stagnation point on a non-conducting stretching sheet. The equations of continuity, momentum and energy are transformed into ordinary differential equations and solved numerically using shooting method. The velocity and temperature distributions are discussed numerically and presented through graphs. Skin-friction coefficient and the Nusselt number at the sheet are derived, discussed numerically and their numerical values for various values of physical parameter are presented through Tables.

Aim of the paper is to investigate the effects of linearly varying viscosity and thermal conductivity on steady free convective flow of a viscous incompressible fluid along an isothermal vertical plate in the presence of heat sink. The governing equations of continuity, momentum and energy are transformed into coupled and nonlinear ordinary differential equations using similarity transformation and then solved using Runge-Kutta fourthorder method with shooting technique. The velocity and temperature distributions are discussed numerically and presented through graphs. Skin-friction coefficient and Nusselt number at the plate are derived, discussed numerically and their numerical values for various values of physical parameters are presented through Tables.

We propose to study the natural convection flow resulting from the interaction of a fire with walls that surround it. Indeed, when a fire occurs in a tunnel or in a tower block, it creates a thermal plume causing a heating of the neighbouring walls. This heating by thermal radiation of the walls creates a phenomenon of thermosiphon which interacts with the plume. To study this flow we simulated the problem at the laboratory where we placed a rectangular source heated by Joule effect at the entrance of an open-ended vertical canal. The flow visualization by laser plan and the exploration of the thermal and dynamic fields inside the canal enabled us to describe the flow structure. In order to better characterize this flow, we carried out a fine analysis by studying the spectra of temperature fluctuations. This spectral analysis allowed us to clarify the energetic evolution of the vortexes during their ascension and verify some known spectral laws.

An attempt has been made to investigate the various parameters affecting the fluid behaviour, partially filled in a rotating cylinder. When the cylinder is rotating at ‘high’ speed, a liquid forms a hollow cylinder. Different patterns are observed in the fluids for the rotatioal speeds below a critical speed. This study should give us some insight into molten metal behaviour during centrifugal casting. An extensive experimental investigation is required to obtain an appropriate functional relationship by knowing and understanding some dimensionless parameters. Here the effect of dimensionless parameters ε (which is 2 g/ω2d, where g, ω and d denotes gravitational acceleration, container rotation rate and inner diameter of liquid cylinder) and G (number of times the gravity) was studied as variation of rotation speed, viscosity and aspect ratio of the mould.

This paper deals with the movement of water in a natural unsaturated zone, focusing on infiltration-redistribution system. Infiltration refers to the downward movement of water due to the gravitational force and redistribution defines the upward movement of water due to the capillary rise. Under natural conditions, the movement of water through an infiltration-redistribution depended upon the relations among water content, hydraulic conductivity and tension of soil pore. Various combinations of water balance concepts, Richards’ equation, soil-physics theory and capillary height concepts were applied to mathematically model the movement of water through infiltration-redistribution system. The accuracy and computational efficiency of the developed model were evaluated for the case study. Besides the laboratory scale sand/soil columns with the inner diameter of 10.4 cm were investigated in order to provide the supporting data for model calibration. Sand/soil layers were packed with a bulk density of 1.80 and 1.25 g/cm3, respectively. The infiltration was sprayed uniformly at the soil surface with the constant rate of 66.1 and 7.18 cm3/h for sand and soil columns, respectively. The redistribution process was developed by which water arriving at the column base enter to the sand/soil column due to capillary rise. The laboratory observations were simulated using the developed model. The results indicate that the developed model could well estimate the movement of water in the infiltration-redistribution system that observed in the case study and the experiments

Transient thermal behavior of a vertical storage tank of adomestic solar heating system with a mantle heat exchanger has been investigated numerically in the charging mode. It is assumed that the tank is initially filled with uniform cold water. At an instant of time, the hot fluid from collector outlet is uniformly injected in the upper section of the mantle heat exchanger and after heat transfer with the fluid inside the tank, withdrawn from the bottom part of the heat exchanger. The conservation equations in the cylindrical coordinate and in axis-symmetric condition have been used according to the geometry under investigation. Governing equations have been discretized by employing the finite volume method and the SIMPLER algorithm has been used for coupling between momentum and pressure equations. The Low Reynolds Number (LRN) k −ω model is utilized for treating turbulence in the fluid. First, the transient thermal behavior of heat storage tank and the process of formation of thermal stratification in the heat storage tank were investigated. Then, the influence of Rayleigh number in the heat storage tank, Reynolds number in the mantle heat exchanger and vertical positioning of mantle on the flow and thermal fields and the formation of the thermal stratification was investigated. It is found that for higher values of Rayleigh number, a more suitable thermal stratification is established inside the tank. Also it is noticed that increasing the incoming fluid velocity through the mantle heat exchanger causes a faster formation of the thermalstratification. A superior thermal performance was achieved when the mantle heat exchanger is positioned at the middle height of the storage tank.

In this work, a 19-bit Incompressible Generalized Lattice Boltzmann (IGLB) method has been proposed for three-dimensional incompressible fluid flow simulation, for the first time. Equilibrium moments in moment space are derived from an incompressible BGKLB method. The incompressible Navier–Stokes equations can be recovered through the Chapman-Enskog multi-scale expansion without artificial compressible effects. To compare the performance of proposed model, several benchmark problems (such as a cubic lid-driven cavity flow, flow over a backward-facing step, and a double shear flow) are solved and the results are compared with those of both 19-bit Incompressible BGK Lattice Boltzmann (IBGKLB) method and existing CFD simulations. It is shown that the stability and accuracy of the 19-bit IGLB method is better than those of the 19-bit IBGKLB method; in fact with the IGLB model we can increase the Reynolds number by factor of 2.5 and still get stable results. The proposed 3-D IGLB method is successfully expanded and applied to simulation of the 3-D incompressible buoyancy driven flows. The results of the 3-D steady-state natural convection in an air-filled differentially heated cubic cavity obtained by the extended model comply well with the existing data in literature. In addition, natural convection from a discrete heat source which is mounted flush with the bottom wall of a horizontal enclosure is simulated. The obtained results indicate that the proposed method is very convenient for simulation of thermally driven flow problems.