Document Sample

International Journal of Civil JOURNAL OF CIVIL ISSN and Technology (IJCIET), INTERNATIONALEngineering May (2014), pp. 51-60 © IAEME 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, ENGINEERING AND TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) IJCIET Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2014): 7.9290 (Calculated by GISI) ©IAEME www.jifactor.com SIMULATION MODEL TO PREDICT VELOCITY AND PRESSURE DISTRIBUTION INSIDE THE HYDROCYLONE IN WATER TREATMENT PLANT Dr. AlaaHusaeenAl-Fatlawi Head of Environmental Engineering Department, College of Engineering, University of Babylon, Iraq ABSTRACT The objective of this research work is to predict the velocity and pressure distribution inside a hydrocylone which used water as a liquid phase and inert/solid particles as a solid phase. Inside diameter of this hydrocyclone is 85mm. The proportions of each dimension proposed by Bradley are used in this work. In this study, turbulent and swirling flow within a hydrocyclone is simulated by using commercial computational fluid dynamics (CFD) code 'FLUENT' v14.0, Gambit 2.4.6, Tecplot 360, CFD post computer software’s . The results clearly showed the contours and diagrams of pressure and velocity inside the hydrocyclone. The pressure diagram indicates that pressure in center of surface is less than the walls, while the velocity distribution is (7.173 m/s) which agreed with the inlet theoretical velocity of (7.18 m/s). Keywords: Hydrocyclone, Computational Fluid Dynamic, Fluent. I. INTRODUCTION One of the main purposes for which the hydrocyclone was created is to promote solid liquid separation, particles separation, classification in different fields such as in environmental, mineral and mining, power plants, and chemical processes. A general hydrocylone consist of conical section connected to a cylindrical section. The hydrocylone is fitted with a tangential inlet and enclosed by an end plate with an axially mounted overflow outlet. The concept of separation in hydrocylone based on the principle of centrifugal force to separate, remove or to classify solids from bulk fluid, the shape of particles, size and density have a direct effect on the separation efficiency. Continuous researches and studies were carried out to increase the efficiency of hydrocyclones, for that, it is very important to have a very good understanding of flow patterns, and motion trajectories of particles inside the hydrocylone. In general, the swirling flow pattern inside the 51 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME hydrocylone is the main flow feature of separation, in addition to several minor flow patterns associated with the rotational flow and influence the trajectories of the particles. The tangential velocity is a direct factor on which the centrifugal force depended on, so, its accurate determination is crucial in prediction of the fractionation performance of hydrocyclones. In other words, the operation conditions also affecting the hydrocylone performance not only the relationship between the size of particle and hydrocylone centrifugation,Wen, (2003) The purpose of this paper is to illustrate the value of computational fluid dynamic as a perfect tool to investigate the flow pattern inside a hydrocylone, which is based on the design and operation conditions. However, because of the complication of boundary layers and the separation which are highly out of equilibrium, it has been very difficult to predict the flow inside a hydrocylone, but the development of computational fluid dynamic has solved the challenge of strongly swirling. The CFD technique is combined with the finite element algorithm and used to predict an initial design to be able to understand the efficiencies of different hydrocyclone designs and modes of operation, which then undergoes operational trials to confirm the effectiveness. II. BACKGROUND AND PREVIOUS STUDIES Dlamini, et al., (2005), studied a CFD simulation of a single phase hydrocyclone flow field. In this study; the researchers investigated the hydrodynamics of a hydrocyclone which present a complex internal flow structure as the numerical simulation of which remains a nontrivial task. They reported on three-dimensional water-only computational fluid dynamics (CFD) hydrocyclone flow field predictions and highlighted some of the issues concerned with the development of a CFD model incorporating an air core. The potential for the application of CFD as a hydrocyclone design tool is also discussed. Shojaeefard, et al., (2006), have investigated the behavior of water flow and particles trajectory inside a hydrocyclone by means of numerical and experimental methods and results have been compared together. To have a numerical simulation, CFD software was used, andfor modeling flow the RNG k–e model applied. Finally, the effect of particle size on hydrocyclone performance has been studied. It was found that the grade efficiency and number of particle that exit from underflow of the hydrocyclone is increased when bigger particles is used.A series of experiments has been carried out in a laboratory with a hydrocyclone. Comparison shows that, there is a good agreement between the CFD models and experimental result. George and Tudor, (2007), studied a numerical study of liquid-solid separation process inside the hydrocyclones with double cone sections. The major objective of this study was, using the modern numerical techniques, to investigate particle transport processes within a hydrocyclone with double cone sections, were the wastewater is depurated. This investigation consists of calculations of the fluid flow inside the hydrocyclone, including particle trajectory, pressure losses and separation efficiencies. The hydrocyclone has modeling with the proper geometrical relationship between the cyclone diameter, inlet area, vortex finder, apex orifice, and sufficient length providing retention time to properly separation particles. Obtained results of calculations were numerically verified as well as compared with results published in the subject literature. The model predicted the velocity particle and fractional recovery of solid particles requirements given the dimensions of the cyclone, the physical properties of the fluid, and the volumetric flow rate. Murthy and Udaya, (2012), studied parametric CFD studies on hydrocyclone, this research article encompasses development of hydrocyclone simulation methodology through validation with suitably designed experiments at a range of process conditions and further understanding on the parametric design and operating conditions. The salient features of the methodology included Eulerian primary phase flow field generation through steady state simulation using RSM turbulence modeling, and evaluation of particle distribution behavior through discrete phase modeling using 52 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME particle injection technique. The results are validated with water throughput, split and cyclone cut size while classifying fly ash. The results have indicated a reasonable matching between the simulated and the experimental values. The studies revealed that the cyclone cut size increases with an increase in vortex finder diameter, a decrease in the spigot diameter, decrease in the inlet velocity of the fluid, and decrease in the viscosity of the fluid. Figure 1: Schematic diagram of hydrocylone,Murthy and Udaya, (2012) III. OBJECTIVE OF STUDY Proper hydrocyclone design is essential for achieving maximum performance and ensuring the maximum and most reliable solids separation efficiency. However, there is still a lack of detailed understanding of hydrocyclone flow behavior and separation mechanism that occur in hydrocyclone, thus, more researches are needed in order to achieve these targets. Up to date, the design of the solid liquid hydrocyclones has relied on empirical experience, and more recently on CFD and numerical modeling, which has had some success owing to the improvement of computing power. Still, CFD models require a large amount of computing power, and simulations are time consuming and costly (Severino, 2007) So, this work aims to use the latest computer programs such as AutoCAD 3D Mechanical, Gambit 2.4.6, Ansys Fluent V.14, TecPlot 360 and CFD Post to predict the velocity and pressure profile inside a hydrocylone. IV. MODELING OF WATER FLOW IN HYDROCYCLONE For a dilute fluid suspension, the incompressible Navier–Stokes equations supplemented by a suitable turbulence model are appropriate for modeling the flow in a hydrocyclone. The most popular turbulence model in use for engineering applications is the k–e model where the scalar variables k and e represent the kinetic energy of turbulence and its dissipation rate, respectively. The standard k– e model was used to represent the turbulence in the equipment. The model was used to predict the water flow rates in the two outlet streams for different inlet velocities of water (Shojaeefard, et al., 2006). 53 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME For this model, both mass conversion equation and continuity conversion equation have been solved: a) Mass Conversation Equitation The continuity or mass conversion equation can be written as follows: + ( ) = Sm … (1) This equation is the general form of the mass conversion equation; it is valid for the incompressible and compressible flows as well. The (Sm) term represent the mass added to the continuous phase from the dispersed second phase, i.e. solid particles added to the liquid phase. For 2D axisymmetric geometries, the continuity equation is given by:- + ( )+ ( )+ = Sm … (2) Where is the axial coordinate, is the radial coordinate, is the axial velocity, and is the radial velocity b) Momentum Conversation Equitation The following equations describe the transport of momentum in an inertial (non-accelerating) reference frame:- ρ ρ = ρ ρ … (3) Where ρ is the static pressure, is the stress tensor (described below), and ρ is the gravitational body force. contains other source terms that may arise from resistances, sources, etc. The stress tensor is given by: µ …(4) Where µ is the molecular viscosity, I is the unit tensor, and the second term on the right-hand side is the effect of volume dilation. For 2D axisymmetric geometries, the axial and radial momentum conversion equations are given by: ( )+ ( )+ ( )=- + [rµ ( ]+ [rµ ( ] + Fx …(5) And ( )+ ( )+ ( )=- + [rµ ( ]+ [rµ ( ] - µ 2µ + Fr …(6) 54 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME Where: = + + …(7) 1- BOUNDARY CONDITIONS It was necessary to specify boundary conditions at the inlet, outlet and at the walls of hydrocyclones. Inlet velocity was used as a boundary condition, which means that the value of the velocity is specified. A uniform velocity profile was specified by introducing the inlet velocity and this gave the required mass flow rate. To determine the influence of the flow rate on the velocity field and to improve the predicted axial and tangential velocity profile, a pressure boundary was used to model the outlet conditions. At the walls, the default of no slip condition was applied, i.e. the velocity equals to zero at the wall. The normal logarithmic wall function was used to specify the flow conditions in the cells adjacent to the wall. The fluid properties at the inlet used in this study are specified in Table 1 below. Table 1: Physical properties of water and inert particles a. Water -liquid (fluid) Property Units Value(s) Density kg/m3 998.2 Cp (Specific Heat) J/kg.k 4182 Thermal Conductivity w/m.k 0.6 Viscosity kg/m.s 0.001 Molecular Weight kg/kmol 18.015 b. Inert-particles Property Units Value(s) 3 Density kg/m 1920 Cp (Specific Heat) J /kg.k 1680 Thermal Conductivity w/m.k 0.045 The hydrocyclone in this study has a 85 mm diameter of cylindrical section as shown in Figure 2. Figure 2: Hydrocyclone geometry 55 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME By using GAMBIT, pre-processing software, an unstructured triangular mesh with 1,260,881 elements has been used for the main body of hydrocyclone. The mesh is shown in Figures 3 and 4 uses unstructured triangular mesh for the main body of the hydrocyclone. In this model the tangential inlet shown is meshed for simplicity using triangular elements. Figure 3: Unstructured triangular mesh of hydrocyclone with 100% active elements Figure 4: Grid elements in the (xy) axis 2- SOLUTION STEPS In addition to solving transport equations for the continuous phase, CFD allows to simulate a discrete second phase in a Lagrangian frame of reference. This second phase consists of spherical particles dispersed in the continuous phase. CFD computes the trajectories of these discrete phase entities, as well as heat and mass transfer to/from them. The coupling between the phases and its impact on both the discrete phase trajectories and the continuous phase flow can be included. We can include a discrete phase in our CFD model by defining the initial position, velocity, size of individual particles. These initial conditions, along with our inputs defining the physical properties of the discrete phase, are used to initiate trajectory and mass transfer calculations. For this model, a discrete phase model with a tolerance of 10-5 has been used. For the operation conditions, we define gravitational acceleration in direction y (-9.86m/s2). After defining 56 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME materials, boundary conditions and operating conditions, the next step is to solve for CFD. A SIMPLE scheme pressure velocity coupling has been used for the solution method. A (10,000) iterations needed to get the peak tangential velocity in the simulation. Running of this model on a dual core computer processor toke (60 hrs), with minimum accuracy of (1e-6). V. RESULTS AND DISCUSSION Despite the simplicity of its construction of hydrocyclone, it displays a quite complex internal behavior, including features as high preservation of vorticity, vortex breakdown and flow diagram. For the stated geometry, boundary conditions, and operation conditions, the pressure distribution inside the hydrocyloneis presented in Figures 5 and 6. These figure show a half cross section of the effects of pressure on the separation and planner view for pressure distribution inside the hydrocyclone. TheseFigures clearly indicate that pressure in center of surface is less than the walls. While Figure 7 shows the path lines of particles colored by time inside the hydrocyclone. Figure 5: Vertical section for pressure distribution inside the hydrocyclone Figure 6: Planner view for pressure distribution inside the hydrocyclone 57 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME Figure 7: Path lines of particles colored by time inside the hydrocyclone It is notable that particles needs maximum (0.99 sec) to reach the underflow and (3.31 sec) to rise to the overflow. This is due to the high velocity near the wall and slow velocity in the core of hydrocyclone. An important analysis comes from the velocity profiles. The liquid axial velocity component is an indication of the magnitude of the two spirals depicted in Figure (8) and therefore determines the volumetric distribution of the product between the overflow and underflow streams. A locus or envelope of zero axial velocity is a significant feature of this velocity component and divides the outer downward flowing and the inner upward flowing fluid layers. The axial velocities increase with distance from the envelope, with the inner spiral having a considerably higher maximum velocity. Figure 8: Axial velocity vs radial position The tangential velocity (Figure 9) increases traversing towards the core of the hydrocyclone, before decreasing rapidly at the interface with the air core. The associated velocity gradients are steepest in the region below the vortex finder. The tangential velocity profiles assume a compound vortex structure, known as a Rankine vortex, which constitutes free and forced vortices near the hydrocyclone wall and the central vertical axis, respectively. A parabolic peak, intermediate between the two vortex regions, marks a gradual transition between the two distinct and uniquely defined vortex structures. 58 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME Figure 9: Tangential velocity vs radial position Figure 10 shows the radial velocity inside the hydrocylone, the magnitude of radial velocity is much smaller than that of the tangential or axial velocity which agree with what (Kelsal, 1952) proposed. However, very little information is available about this velocity component. In practice, the tangential and axial velocities are usually measured (Leeuwner and Eksteen, 2008). Figure 10: Radial velocity vs radial position The model also gives the contour of pressure as shown in Figure 11, The pressure is high in the upper wall of the hydrocyclone, meanwhile inside the air-core is the lower pressure. Those results are agreed with theory. Figure 11: Pressure vs radial position 59 International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 5, May (2014), pp. 51-60 © IAEME VI. CONCLUSIONS It can be concluded that the velocity, pressure and flow pattern within a hydrocyclone chamber can be modeled using CFD. This will easily allow researchers studying how changes in the shape of hydrocyclone will influence its operating performance. The ability of modern supercomputers allows the approximation of three-dimensional flow pattern in hydrocyclones to be investigated. That will give in a near future a better understanding of hydrocyclone performance. REFERENCES [1] Rama Murthya, UdayaBhaskarb, (2012), “Parametric CFD studies on hydrocyclone”, Research Development and Technology, Tata Steel Ltd, Jamshedpur, 831007, India & ArcelorMittal Global R & D, 3001 E. Columbus Drive, East Chicago, IN 46312, USA. [2] Severino, G. J., (2007), "Mechanistic Modeling of Solid-Liquid Separation in Small Diameter Hydrocyclones", The Graduate School, University of Tulsa, USA. [3] Wen-Ching Yang, (2003), "Handbook of Fluidization and Fluid-Particle Systems", Published March 19th 2003 by CRC Press. [4] Kelsal, D.F., 1952,"A study of the motion of solid particles in a hydraulic cyclone", Transactions of the Institution of Chemical Engineers. 30, 87– 108. [5] Leeuwner M.J and Eksteen J.J., (2008), “Computational fluid dynamic modelling of two phase flow in a hydrocyclone”, Department of Process Engineering, University of Stellenbosch. [6] Dlamini M.F. , Powell M.S., and Meyer C.J., (2005),“ A CFD Simulation Of A Single Phase Hydrocyclone Flow Field”, Department of Chemical Engineering, UCT, Rondebosch, Cape Town, South Africa. [7] Shojaeefard M. H., Noorpoor A.R., Yarjiabadi H., Habibian M., (2006), “Particle Size Effects on Hydrocyclone Performance”, Automotive Engineering Department, Iran University of Science and Technology. Islamic Republic of Iran. [8] George Ipate, Tudor Căsăndroiu, (2007), “Numerical Study of Liquid-Solid Separation Process inside the Hydrocyclones with Double Cone Sections”, Department of Biotechnical Systems, University “Politehnica”, Bucharest, Romania. [9] A. Rizk, A. Aldeberky and N. Guirguis, (2014), “Comparison Between Natural Cross and Hybrid Ventilation for Hot Climate by using CFD”, International Journal of Civil Engineering & Technology (IJCIET), Volume 5, Issue 2, pp. 71 - 80, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [10] R Radhakrishanan and A Praveen, (2012), “Sustainability Perceptions on Wastewater Treatment Operations in Urban Areas of Developing World”, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 1, pp. 45 - 61, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. 60

DOCUMENT INFO

Shared By:

Categories:

Tags:

Stats:

views: | 0 |

posted: | 6/6/2014 |

language: | Unknown |

pages: | 10 |

OTHER DOCS BY iaemedu

Docstoc is the premier online destination to start and grow small businesses. It hosts the best quality and widest selection of professional documents (over 20 million) and resources including expert videos, articles and productivity tools to make every small business better.

Search or Browse for any specific document or resource you need for your business. Or explore our curated resources for Starting a Business, Growing a Business or for Professional Development.

Feel free to Contact Us with any questions you might have.