Fludised

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  • Topic: Fluidized bed, Fluid dynamics, Fluid mechanics
  • Pages : 10 (2300 words )
  • Download(s) : 66
  • Published : March 17, 2013
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Abstract
The characteristics associated with water and air flowing vertically upwards was investigated through a bed of coarse ballotini (glass beads with a nominal diameter of 485 microns).Different flow rates for water and air is applied to determine the pressure drop and differentiate between the fixed bed and the fluidized bed characteristics. Also the measured onset of fluidization was compared with the predicted one. From this experiment it was obtained thatthe pressure drop increase as increasing the fluid (water or air) rates until it reach constant value. In addition, the bed height is constant as flow rate increased in fixed bed and it is increased as the flow rate increased when fluidization occurred. Furthermore, it was found that the air fluid requires higher flow rate than water in order to fluidize the bed.

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Nomenclature
Symbols Dp ε ρa μ ρs ρw A Φs L D V ∆P Description particle size (mm) porosity density of air (Kg/m3) viscosity (N.s/m2) density of particle (Kg/m3) density of water (Kg/m3) bed cross-section area (m2) sphericity bed height (m) diameter (m) velocity (m/s) pressure drop (mm H2O)

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Table of contents

Abstract Nomenclature Contents List of Figures List of Tables 1. Introduction 2. Experimental Set-up 2.1 2.2 Apparatus Procedure

1 2 3 4 4 5-6 6-7 6 7 8-12 13 13 14

3. Results and Discussion 4. Conclusion 5. Reference Appendices

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List of figures
Figure1 : fixed and fluidized bed apparatus Figure2: Flow rate versus Pressure drop for experimental data Figure3: Pressure drop versus Flow rate for experimental and theoretical data. Figure4: Bed pressure drop (mm H2O) versus flow rate (L/min) obtained from the experimental data. Figure5: Bed pressure drop (mm H2O) vs. flow rate for the experimental and the theoretical value Figure6:Various steps in the air fluidization.

List of tables
Table1: Experimental and Theoretical data for water passing through a bed with glass beds. Table 2: Results and data obtained for air flowing vertically upwards through glass bed.

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1. Introduction
The upward flow of fluid through a bed of particles is a situation encountered both in nature, as with the natural movement of ground water, crude petroleum or natural gas through porous media, and in industrial operations such as backwashing filters, ion-exchange processes, extraction of soluble components from raw materials and for certain types of chemical reactor. Fluidization occurs in the bed when the superficial velocity has been reached and that the particles in the bed become fully suspended and thus the fluid-particle mixture can then act as a fluid itself (Fluidized Beds). Fluidization allows for virtually uniform temperature

distributions even when highly exothermic reactions are occurring, and since the solid particles are often used to catalyze the reaction occurring within the column, fluidization also allows for intimate contact between reactants and catalytic particles as well as uniform mixing. Fluidization of a bed of solid occurs by passing a fluid (water and air) upwards through a bed of particles supported on a distributor. Fluidization converts a bed of solid particles into an expanded mass that has many properties of a liquid. As a fluid is passed upward through a bed of particles, pressure loss due to frictional resistance increases as fluid flow also increases. At the same time, the upward drag force exerted by the fluid on the particle equal to apparent weight of particles in the bed. Fluidized bed operations are used for various situations such as drying, coating, heat transfer and polymerization reactors.

There is a specific range of velocity over which the bed remains in a fluidized state because if the fluid velocity within the bed is greater than the terminal velocity of the particles, the fluid will tend to entrain the particles and carry them out of the bed and if the velocity above the bed is less than the terminal velocity of the particles,...
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