Simulation of Hydrodynamic Characteristics of Glass Beads in Gas-Liquid-Solid Three Phase Fluidized Beds by Computational Fluid Dynamics

Transcription

1 Journa of Enineerin Technooy and Education, Vo. 8, No.2 June 2011, pp Simuation of Hydrodynamic Characteristics of Gass Beads in Gas-Liquid-Soid Three Phase Fuidized Beds by Computationa Fuid Dynamics Khanh-Toan Nuyen, Shyh-Chour Huan* Department of Mechanica Enineerin Nationa Kaohsiun University of Appied Sciences Kaohsiun, Taiwan, R.O.C. *E-mai: Abstract A computationa fuid dynamics mode used to understand the hydrodynamics of three phase fuidized bed is presented in this paper. In the present investiation, an attempt has been made to study the compex hydrodynamics of three phase fuidized bed; bed expansion, hodup of two phases, bed pressure drop, fuidized bed voidae and veocity profie. The mode is deveoped by usin the commercia CFD code Fuent 6.2. The dra mode for simuatin is used Gidaspow mode. The main focus on for anayzin the resuts is on the coumn with 1.5m heiht and diameter 0.1m. Euer-Euer mutiphase fow approach is capabe of predictin the overa performance of as-iquid-soid fuidized bed. The resuts obtained show that the iquid hodup increased with the inet iquid veocity, as hodup increased with the fow rate of as and decreased with an increase in the iquid fow rate. Key words: Fuidized bed, Bed pressure drop, Gas hodup, Liquid hodup, Bed expansion, Three-phase fuidized bed. 1. Introduction Gas-iquid-soid fuidization aso known as three phase fuidization is a subject of fundamenta research since the ast three decades due to its industria importance [1]. Three phase fuidized bed are used in a wide rane of chemica, petrochemica, refinin, pharmaceutica, biotechnooy, food and environmenta industries. The successfu desin and operation of a as-iquid-soid fuidized bed system depends on the abiity to accuratey predict the fundamenta characteristics of the system, such as the hydrodynamics, heat and mass transfer and mixin of each phase characteristics. Recent research with bubbe coumns frequenty focuses on the foowin topics: as hodup studies [2], bubbe characteristics [3], fow reime investiations and computationa fuid dynamics studies [4], oca and averae heat transfer measurements [5]. Many numerica studies are focused on investiation the effects operatin conditions on the hydrodynamic of fuidized bed. Athouh most of studies have been directed towards the understandin of individua characteristics fuidized bed. The objective of this study has been investiated the compex hydrodynamics of three phase fuidized bed; bed expansion, hodup of two phases, bed pressure drop, fuidized bed voidae and veocity profie Nationa Kaohsiun University of Appied Sciences, ISSN

2 Simuation of Hydrodynamic Characteristics of Gass Beads in Gas-Liquid-Soid Three Phase Fuidized Beds by Computationa Fuid Dynamics Mathematica mode The simuation of fuidized bed was performed by sovin the equations of continuity, momentum conservation usin Fuent 6.2 CFD software. A mutifuid Euer mode, which considers the conservation of mass and momentum for three phases, was appied. The overnin equation can be summarized as foows [6]: Mass conservation equations of as, iquid, and soid phases: t t t v ( ρ ) + ( ε ρ u ) = 0 ε (1) ( ρ ) + ( ε ρ u ) = 0 v ε (2) ( ρ ) + ( ε ρ u ) = 0 s s s s v ε (3) s Momentum conservation equations of as, iquid and soid phases: t ε v v v ( ρ ε u ) + ( ρ ε u u ) = v v T P + ( ε μeff, ( u + ( u ) ) + ρ ε + M i, (4) t ε v v v ( ρε u ) + ( ρε uu ) = v v T P + ( ε μeff, ( u + ( u ) ) + ρε + M i, (5) t ε v v v ( ρsε sus ) + ( ρsε susus ) = v v T s P + ( ε sμeff, s ( us + ( us ) ) + ρsε s + M i, s (6) The mode equations described above are soved usin the commercia CFD software packae FLUENT 6.2, the 2D computationa eometry of the fuidization coumn have been enerated by usin commercia software GAMBIT as shown in Fi. 1. After eometry creation, a uniform mesh has been enerated with map structured quadriatera eements. Totay 6000 ces with size of each ce 0.005m x 0.005m have been used for computation. The overnin equations were sover usin eement finite voume method. The FLUENT sover needs to be specified so that GAMBIT knows what types of boundary conditions are aowed. The boundary conditions such as veocity-inet, pressure outet, wa and defaut interior have been set. Then the rid has been exported as a mesh fie from GAMBIT to be used in FLUENT for soution. The initia partice heiht is 0.213m and the initia void fraction in the packed bed is Spherica ass bead with diameter of 2.18mm and 4.00 mm and density 2470k/m3 are used. The coefficient of restitution is set to 0.9.

3 250 Khanh-Toan Nuyen, Shyh-Chour Huan Fi. 1 Mesh created in GAMBIT In present work the converence criteria of a the residua has been taken as 10-3 for each scaed residua component. A time step of 0.001s with 40 iterations per time step was chosen. Inet boundary conditions are a uniform iquid and as veocity at the inet, and outet boundary condition is pressure boundary condition, which is set as 1.013x105Pa. Wa boundary conditions are no-sip boundary condition for the iquid phase and free sip boundary condition for the soid phase and as phase. In FLUENT, sover is set as sereated which soves the equations individuay. The phase-couped SIMPLE aorithm, which is an extension of the SIMPLE aorithm to mutiphase fows, is appied for the pressure-veocity coupin. In this aorithm, the coupin terms are treated impicity and form part of the soution matrix. First order discretization schemes for the convection terms are used. The simuation is carried out ti the system reached the quasi-steady state. For a simuations, the time-averaed quantities are obtained for the time interva between t1=18s and t2=22s. Tabe.1 shows the boundary and initia conditions for fuidized bed coumn. Tabe.1 Description of system used in simuation Physica and process parameters Cyindrica coumn Diameter of coumn (m) 0.1 Heiht of coumn (m) 1.5 Density of soid (k/m3) 2470 Gass bead mean partice size (mm) 2.18, 4 Initia bed heiht (m) Initia soid hodup (%) 0.59 Superficia as veocity (m/s) Liquid phase (water) (0C) 30 Liquid Viscosity, (Pas) Liquid Density, (K/m3) Gas phase (air) (0C) 30 Gas Viscosity, (Pas) e-05 Gas Density, (K/m3) 1.225

4 Simuation of Hydrodynamic Characteristics of Gass Beads in Gas-Liquid-Soid Three Phase Fuidized Beds by Computationa Fuid Dynamics Resuts and discussion The simuations have been carried out ti the system reached the quasi-steady state, the averaed fow variabes are time independent. This can be achieved by monitorin the expanded bed heiht or phase voume fractions. For a simuation, time-averaed quantities are obtained for the time interva between t1=18s and t2=22s. Fi. 2 a series of soid voume fraction from the simuation with Gidaspow dra mode is presented. They show the variation in the bed profie with time. The bed expansion ratio becomes aso are. For this case the inet air veocity m/s, the inet water veocity 0.12m/s and the initia soid bed heiht of 21.3cm have been used. Initiay water and as diffused into the bed and bean to saturate the interstices amonst the soid partices with an initia porosity of There is not observed fow in the bed. This was represented by the radua expansion of the yeow-orane coor reion just before 0.2s. After that the bed becomes fuidized. Whie simuatin the fuidized bed the profie of bed chanes with time. Time (second): Fi. 2 Contour of voume fraction of soid at [Vw=0.12m/s, V=0.0375m/s, Hs=0.213m, Dp=2.18mm] But after the profie of bed has not chane the sinificant difference in overa bed. This indicates that the fuidized bed has come to a quasi-steady state and we take a the information for resuts from this. It can be observed from the fiure that, the bed profie is amost the same between s of simuation time. 3.1 Phase dynamics Soid, iquid and as phase dynamics have been represented in the form of contours pots. Contours of voume fractions of soid, iquid and as in the coumn obtained at water veocity of 0.12 m/s; air veocity of m/s; initia static bed heiht of m and ass beads of diameter 2.18 mm in 1.5 m heiht coumn after the achievin quasi steady state at t=22s have been shown in Fi. 3.

5 252 Khanh-Toan Nuyen, Shyh-Chour Huan Voume fraction Soid Liquid Gas Fi. 3 Contours of voume fraction of soid, iquid and as at [Vw=0.12m/s, V=0.0375m/s, Hs=0.213m, Dp=2.18mm] The coor scae iven to the eft of each contours ives the vaue of voume fraction correspondin to the coor. The warm coor correspond to area with hih ascendin voume fraction of phase, contrast the cod coors depict the reion with hih descendin voume fraction of phase respectivey. The contours for ass beads iustrates that bed is in fuidized condition. The contours for water iustrates that voume fraction of water (iquid hodup) is ess in fuidized part of the coumn compared to remainin part. The contour for air iustrates that as hodup is sinificanty more in fuidized part of the bed compared to remainin part. 3.2 Bed expansion In as-iquid-soid system with increase in iquid veocity at a constant as veocity, the expanded bed heiht increases and the void of the bed aso increases. The resut from CFD shows an increase in the bed expansion with the iquid veocity at a constant as veocity. It can be seen from the contours of soid voume fraction (shown in Fi. 4). Contours of voume fractions of soid in the coumn obtained over a rane of superficia iquid veocities 0.06m/s, 0.08m/s, 0.1m/s and 0.12 m/s, the constant inet as veocity m/s, initia static bed heiht of m and ass beads of diameter 2.18 mm in 1.5 m heiht coumn. There is steady increase in bed heiht with increase superficia iquid veocity. The increase in iquid superficia veocity increases the enery input to the coumn, eadin to the increase in both circuation and turbuence.

6 Simuation of Hydrodynamic Characteristics of Gass Beads in Gas-Liquid-Soid Three Phase Fuidized Beds by Computationa Fuid Dynamics 253 Liquid veocity (m/s) Fi. 4 Contour pot of soid voume fraction with variation inet iquid veocity at [V=0.025m/s, Hs=0.213m,Dp=2.18mm] In industria fuidized bed reactors, it is important to find out the fuidized bed hih accuratey. Such as the importance of the bed heiht in desin are the positionin of the heat transfer equipment and the soids withdrawa pipes. From the theoretica point of view, the bed is characterized by the presence of partices and the free board by the absence of partice. There is no correspondence to the bed heiht in the resuts of CFD computationa modein. Post-processin of the void fraction distribution is required to determine the expansion. One possibiity is to time averae the data and then inspect downward in the free board to find the ocation where the void fraction fas beow a specific vaue. This method has the same roundwork as that of the visibiity check of the probe tip. Faiure of this technique has been reported at hih fuidization veocities due to the diute of the upper reion of the bed, which in turn may cause biased prediction of bed heiht [7]. In the present work, the bed heiht can be determined by takin X-Y pot of the soid voume fraction of ass beads on Y-axis whie heiht of the coumn at X-axis as shown in Fi. 5. The point where the soid fraction sharpy decreases to zero vaue can be taken as the heiht of the bed. Fi. 6 show the pot of expanded bed heiht with iquid veocity obtained at different constant of inet as veocity. It is indicated from the fiure that there is siht different in the expanded bed heiht with increase in the as veocity. Other meanin of the fiure, it shows that the bed expands when the water veocity increases. Concusion, bed expansion is the stron function with superficia iquid veocity and weak function with as veocity. Bed expansion increases with increase of both the iquid veocity and the as veocity.

7 254 Khanh-Toan Nuyen, Shyh-Chour Huan Bed expansion vs Superficia iquid veocity Bed expansion (cm) V= m/s V=0.025 m/s V= m/s V=0.05 m/s Fi. 5 XY pot of soid voume fraction at [Vw=0.12m/s, V=0.0375m/s, Hs=0.213m, Dp=2.18mm] Fi. 6 CFD simuation resuts of bed expansion behavior at [Dp=2.18mm, Hs=0.213m] The other characterize of the bed expansion shoud to investiation here that bed expansion with different partices size. Two partice sizes, 2.18mm and 4mm were used to study the effect of partice size on the bed expansion. Fiure 7 comparison of bed expansion of two different ass beads with over a rane of superficia iquid veocities 0.06m/s, 0.08m/s, 0.1m/s and 0.12 m/s, the constant inet as veocity 0.025m/s, initia static bed heiht of 0.213m in 1.5m heiht coumn. The fiure is indicated that the bed expansion depends on the size of partices. In detais, bed expansion increase with the sma partices and decrease with are partices. Aso increasin the iquid veocity the bed heiht has been found to increase with both partices. 3.3 Liquid hodup Fi. 8 shows the variation of iquid hod up with inet iquid veocity at different constant as veocity. It has been observed that with the increase superficia iquid veocity the iquid hod up increases. Other of meanin can see from the fiure, the iquid hodup can not observed ceary at different constant as veocity. When the inet as veocity increases, the iquid hodup increases sihty. Concusion, iquid hodup has stron function with superficia iquid veocity, but it is weak function with inet as veocity. Fi. 9 shows the variation of iquid hod up with inet iquid veocity at constant as veocity of two different partice size ass beads. It is observed from the fiure that the iquid hodup decreases with increase in partice diameter.

8 Simuation of Hydrodynamic Characteristics of Gass Beads in Gas-Liquid-Soid Three Phase Fuidized Beds by Computationa Fuid Dynamics 255 Bed expansion vs Superficia iquid veocity for two different ass beads Liquid hodup vs Superficia iquid veocity 85 Bed expantion (%) Dp=2.18 mm Dp=4 mm Liquid hodup (%) V= m/s V=0.025 m/s V= m/s V=0.05 m/s Fi. 7 Comparison of bed expansion of two different ass beads at [V=0.025m/s, Hs=0.213m] Fi. 8 Liquid hod up variation with inet superficia iquid veocity for different inet as veocity Fi.10 indicated the averae soids hodup in the fuidized bed with different superficia iquid veocity at inet as veocity 0.025m/s and initia static bed heiht of 0.213m in 1.5m heiht coumn. It is observed that the averae soid hodup in the fuidized bed increase with the increase the soid partice size. Other meanin from the fiure 10, it expains the reason for fiure 9, because the riser soid hodup increase in the fuidized bed and the iquid hodup decrease effectivey. 85 Liquid hodup vs Superficia iquid veocity for different partice Soid hodup vs Superficia iquid veocity for different partices Liquid hodup (% Dp=2.18 mm Dp=4 mm Soid hodup (%) Dp=2.18 mm Dp=4 mm Fi. 9 Liquid hod up variation with inet iquid veocity for different partices size at [V =0.025 m/s, Hs=0.213 m] Fi. 10 Soids hodup variation with inet iquid veocity for different partices size at [V=0.025m/s, Hs=0.213m] 3.4 Gas hodup Gas hodup is the key parameter to characterize the hydrodynamics of three phase fuidized bed systems. The as hodup depends on as veocity and superficia iquid veocity, coumn eometry (diameter and heiht), physica properties of the as and iquid, partice concentration and physica properties of the partices. In present work, we are focused on study the effect of superficia iquid veocity, partices size and as veocity on the as

9 256 Khanh-Toan Nuyen, Shyh-Chour Huan hodup. Gas hod up is obtained as mean area-weihted averae of voume fraction of the as phase at sufficient number of axia positions in the fuidized portion of the bed. As it can be seen from the XY pot (Fi. 11) of as (air) voume fraction aon the axis of the coumn that the voume fraction of air is not the same at a positions in the fuidized portion of the coumn, it varies with axia position and radia position. Hence area weihted averae of voume fraction of air is determined at heihts 0.05 m apart aon the enth of the coumn. These vaues are averaed to ive the averae as hodup in the bed. Gas hodup vs Superficia iquid veocity Gas hodup (%) V= m/s V=0.025 m/s V= m/s V=0.05 m/s Fi. 11 XY pot of air voume fraction at [Vw=0.12m/s,V=0.025m/s, Dp= 2.18mm, Hs= 0.213m] Fi. 12 Variation of as hodup with iquid veocity for different vaues of as veocity at [Dp= 2.18mm,Hs=0.213m] The variation of as hodup with superficia iquid veocity obtained from CFD simuation is shown in Fi. 12 at different vaues of constant as veocity. The fiure shows that the as hodup has been found to decrease with the increasin of inet superficia iquid veocity. However the variation of fractiona as hodup with iquid veocity is sma. It has been presented by [8] that the fractiona as hodup is practicay unaffected by iquid veocity except at very hih superficia iquid veocity rane. The decrease in as hodup with iquid veocity may possiby be due to the fact that at hiher iquid veocity the bubbes are fast driven by the iquid. The residence time of the as hodup is ikey to decrease [9]. The effect of as fow rate on as hod up is shown in Fi. 13. The fiure reveas that as the as hod up increases with increase in as fow rate. Because of hih as veocity, hih turbuent intensity and hih mixin between three phases (G L S). The resuts from the fiure show pay more predominant roe of the inet as veocity in the as hodup. In Fi. 14 the variation of fractiona as hodup with superficia iquid veocity at a constant as veocity for different ass beads sizes have been represented. The resut indicated that the as hodup decreases with iquid veocity ike the above findin. The fiure reported that the partice size increases the as hod up decreases. Thus the effect of partice size on the as hod up becomes sinificant with increasin as veocity.

10 Simuation of Hydrodynamic Characteristics of Gass Beads in Gas-Liquid-Soid Three Phase Fuidized Beds by Computationa Fuid Dynamics 257 Gas hodup vs Gas veocity Gas hodup vs Superficia iquid veocity for different partice Gas hodup (%) Vw=0.06 m/s Vw=0.08 m/s Vw=0.1 m/s Vw0.12 m/s Gas hodup (%) Dp=2.18 mm Dp=4 mm Gas veocity (m/s) 0.3 Fi. 13 Gas hodup with as veocity for 2.18mm ass beads at Hs=0.213m Fi. 14 Variation of as hodup with iquid veocity for different ass beads size at [V=0.025m/s, Hs=0.213m] 3.5 Bed voidae The bed voidae is defined as the fraction of the bed voume occupied by both iquid and as phases and as such directy proportiona to the expanded bed heiht. The effect of superficia iquid veocity on bed voidae is shown in Fi.15. The fiure reveas that as the bed voidae increases with increase inet superficia iquid veocity. It is cear from this that the bed voidae increases with increase of both the iquid veocity and the as veocity. The bed voidae is a stron function of iquid veocity, but is a weak function of as veocity. Fi. 16 shows the variation of bed voidae with inet iquid veocity at constant as veocity of two different partice size ass beads. The fiure indicated that the bed voidae increases with sma partice size. Aso the bed voidee increases when the superficia iquid increases. The axia pressure drop in a fuidized bed varies from hiher vaue at the bottom of the bed to zero vaue at top of the coumn in the aue pressure scae. Simiar variation has been observed in the CFD simuation resut as shown in Fi. 17 the contour pot of the static aue pressure Bed voidae vs Superficia iquid veocity Bed voidae vs Superficia iquid veocity for two ass beads Bed voidae (%) V= m/s V=0.025 m/s V= m/s V=0.05 m/s Bed void (%) Dp=2.18 mm Dp=4 mm Fi. 15 Variation of bed voidae with iquid veocity at different vaues of as veocity for 2.18mm ass beads at Hs=0.213m Fi. 16 Variation of bed voidae with superficia iquid veocity for different ass beads size at [V=0.025m/s, Hs=0.213m]

11 258 Khanh-Toan Nuyen, Shyh-Chour Huan 3.6 Pressure drop The fiure represented the contours of static aue pressure (mixture phase) in the coumn obtained at water veocity of 0.12m/s and air veocity of 0.025m/s. The bed pressure drop can be determined from the difference of pressure at the inet (bottom) and the outet (top). Bed pressure drop vs Superficia iquid veocity Bed pressure drop (Pa) V= m/s V=0.025 m/s V= m/s V=0.05 m/s 4500 Fi. 17 Contour of static aue pressure at [Vw=0.12m/s, V=0.025m/s, Dp=2.18mm, Hs=0.213m] Fi. 18 Variation of pressure drop with iquid veocity for different vaues of as veocity at [Dp=2.18mm,Hs=0.213m] It is know that the pressure has a sinificant effect on the hydrodynamics of three phase fuidized beds. The effect of superficia iquid veocity on the pressure drop is mainy part in the process of investiation fuidized bed. Fi 18 shows the pot of bed pressure drop with iquid veocity obtained at different inet vaues of as veocity. It is indicated that pressure drop increases when superficia iquid veocity is increased. But at hiher inet as veocity, the as hodup is more and increase in iquid veocity cause a decrease in the as hodup (increase in iquid hodup), so eadin to increase in pressure drop. Other of meanin can see from the fiure, the pressure drop is not observed ceary at different constant as veocity. When the inet as veocity increases, the pressure drop increases sihty. Concusion, pressure drop has stron function with superficia iquid veocity, but it is weak function with inet as veocity. 3.7 Chane in veocity profie with simuation time Veocity manitudes of iquid and soid ass beads with time has been obtained at the inet superficia iquid veocity of 0.12m/s and the inet as veocity of 0.025m/s by takin mean area weihted at bed heiht of m are shown in Fi.19 and Fi. 20 respectivey. The initia inet veocity of iquid in the coumn at time of zero second is 0.12 m/s. The maximum veocity of iquid has been found to 0.325m/s at time of 4th second as shown in Fi. 19.

12 Simuation of Hydrodynamic Characteristics of Gass Beads in Gas-Liquid-Soid Three Phase Fuidized Beds by Computationa Fuid Dynamics 259 Fi.19 Pot veocity manitude of iquid at bed heiht of m versus fow time at [Vw = 0.06 m/s, V = m/s, Hs = m, Dp = 2.18 mm] Fi. 20 Pot of veocity manitude of ass beads at heiht of 0.213m versus fow time at [Vw = 0.12m/s, V = 0.025m/s, Hs = 0.213m, Dp = 2.18mm]. The veocity of ass beads initiay at the static condition in the coumn at time of zero second is zero. Maximum veocity of ass beads has been found as 0.29m/s at time of 4.5th second as shown in Fi. 20 both iquid and soid veocities in the fuidized bed have been found to increase with time at the beinnin of simuation and then it decreases showin an osciatory behavior with decreasin ampitude. It means that for a iven initia condition the veocity wi reach the maximum ony once after startin the fuidization. In three phase fuidization veocity of soid, iquid and as chanes with time and ocation in the bed. The veocity vector of ass beads of size 2.18 mm with the as inet veocity of 0.025m/s and the superficia iquid inet veocity of 0.12m/s at the soid static bed heiht of m has been shown in Fi. 21. Soids fow structure in three phase-fuidized beds shows a sine circuation pattern, where there is a centra fast bubbe fow reion in which the soids move upward and free wa reion where the soids fow downwards. It can be ceary observed that the veocity of soid at the bottom is sma and at top a the veocity vectors are showin downward trend. Because no ass beads are present in the upper section, so no veocity vectors can be seen at top reion. (Actua) (Manified view) Fi. 21 Veocity vector ass beads at [ Vw=0.12m/s, V=0.025m/s, Hs=0.213m, Dp=2.18mm] Fi. 22 Veocity profies of ass beads with different bed heiht aon radia direction in 1.5 m heiht fuidized bed at [Vw =0.12m/s, V = 0.025m/s, Hs = 0.213m, Dp = 2.18mm]

13 260 Khanh-Toan Nuyen, Shyh-Chour Huan The veocity profies of soid, iquid and as with ass beads of size 2.18 mm, inet superficia iquid veocity of 0.12 m/s and inet as veocity of m/s have been shown in Fi. 22, Fi. 23 and Fi. 24 respectivey. The ines at different bed heiht aon radia direction created in mode for cacuatin the veocity profie. A these ines represent the veocity manitude at respective bed heiht aon radia direction. Fi. 23 Veocity profies of iquid with different bed heiht aon radia direction in 1.5 m heiht fuidized bed at [Vw = 0.12m/s, V = 0.025m/s, Hs = 0.213m, Dp = 2.18mm] Fi. 24 Veocity profies of as with different bed heiht aon radia direction in 1.5 m heiht fuidized bed at [Vw= 0.12m/s, V = 0.025m/s, Hs = 0.213m, Dp = 2.18mm] The veocity profie of ass beads is indicated that the chanes in veocity manitude aon radia direction of fuidized bed coumn at different bed heihts. At the bed heiht of 0.5m, ass beads veocity profie increased and attained the maximum veocity aon radia direction is 0.375m/s. On sma further increase in bed heiht the veocity of ass beads decreases and finay veocity becomes cose to zero at 0.7m and above this the veocity manitude is zero since no soid partices are there. The veocity profie aso indicated that the manitude of veocity is more in center reion and at wa the veocity sometime is zero. The maximum iquid veocity found in the profie to be 0.45m/s at bed heiht of 0.55m. Then the iquid veocity decreases with the bed heiht above 0.7m and there is amost same veocity aon radia direction has been found when the bed heiht is between ( m). The maximum as veocity found in the profie to be 0.375m/s at bed heiht of 0.5m. Then the as veocity decreases with the bed heiht after 0.5m, finay the as veocity becomes to zero at 0.7m. 4.Concusions This work represented a computationa study of fow behavior in a fuidized bed. The CFD simuations of as-iquid-soid three-phase fow in fuidized bed have been performed by usin the commercia code, FLUENT 6.2. The mode Euer-Euer approach was used to predict phase distribution and phase veocities. Moreover, simuation has been conducted to investiate incude as, iquid and soid hod up, bed expansion, veocity distribution profies of a phases, pressure drop, and operatin variabes varied incude iquid and as veocity,

14 Simuation of Hydrodynamic Characteristics of Gass Beads in Gas-Liquid-Soid Three Phase Fuidized Beds by Computationa Fuid Dynamics 261 and partice size. The resuts of the present work of three-phase fow the foowin major concusions: - Trends of bed expansion with inet iquid veocity obtained at different inet air veocities show that bed expands when iquid veocity increases. - Trends of as hodup with inet iquid veocity obtained at different inet air veocities show that as hodup decreases when iquid veocity is increased. - Trends of pressure drop with iquid veocity obtained at different inet air veocities show that pressure drop increases when water veocity is increased. - The static pressure decreases with increase in the bed heiht. - Liquid hod up increases with inet iquid veocity. Liquid hodup is found to be heiht for sma partice size as compared with the arer size partices under same conditions in the system. - The veocity profies of both iquid and soid in fuidized bed have been increasin with time in startin and then it oes on to decrease showin the osciatory behavior with decreasin ampitude. From the initia time to the system et the quasi steady state, the veocity wi observe maximum ony once after startin the fuidization. - The manitude of veocity of a phases has been found to be more at the center reion than near the wa. - The sma partices et more veocity than the arer partices for same conditions in fuidized bed. - Bed voidae increases with the iquid inet veocity and sma partice size has more bed voidae than the arer partice size. References [1] H.M. Jena, G.K. Roy, B.C. Meikap, 2009, Hydrodynamics of a as-iquid-soid fuidized bed with hoow cyindrica partices, Chemica Enineerin and Processin 48, paes [2] M. Safoniuk, J.R. Grace, 2002, Gas hodup in a three-phase fuidized bed, A.I.Ch.E. Journa 48, paes [3] H. Li, A. Prakash, 2000, Infuence of surry concentrations on bubbe popuation and their rise veocities in three-phase surry bubbe coumn, Powder Techno 57, paes [4] B.N. Thorat, J.B. Joshi, 2004, Reime transition in bubbe coumns: experimenta and predictions, Exp Therm Fuid Sci 28, paes [5] W. Chen, T. Haseawa, A. Tsutsumi, 2003, Generaized dynamic modein of oca heat transfer in bubbe coumns, Chem En J 96, paes [6] R. Panneersevam, S. Savithri, G.D. Surender, 2009, CFD simuation of hydrodynamics of as-iquid-soid fuidized bed reactor, Chemica Enineerin Journa 64, paes [7] F. Vejahati, N. Mahinpey, 2009, CFD simuation of as-soid bubbin fuidized bed: A new method for adjustin dra aw, The Canadian Journa of Chemica Enineerin 87, paes [8] M. Safoniuk, J.R. Grace, L. Hackman, and C.A. Mckniht, 2002, Gas hod-up in a three-phase fuidized bed, AIChE J, 48, paes [9] H.M. Jena, G.K. Roy, B.C. Meikap, 2008, Prediction of as hodup in a three phase fuidized bed from bed pressure drop measurement, IChE, 86, paes [10] Fuent 6.3 Documentation., 2005, Fuent Inc.