1 / 14

FLOW THROUGH GRANULAR BEDS AND PACKED COLUMN

FLOW THROUGH GRANULAR BEDS AND PACKED COLUMN. By: Mdm. Noor Amirah Abdul Halim. Introduction. Most of technical process, liquid or gases flow through beds of solid particles. Example: i ) A single fluid flow through a bed of granular solid

neola
Download Presentation

FLOW THROUGH GRANULAR BEDS AND PACKED COLUMN

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. FLOW THROUGH GRANULAR BEDS AND PACKED COLUMN By: Mdm. Noor Amirah Abdul Halim

  2. Introduction • Most of technical process, liquid or gases flow through beds of solid particles. • Example: i) A single fluid flow through a bed of granular solid ii) Two phase countercurrent flow of liquid and gas through packed columns.

  3. Flow of single fluid through a granular bed Single fluid flow through a granular bed or porous medium involves in; • fixed bed reactor • filtration • adsorption • seepage of underground water or petroleum

  4. Darcy Law and Permeability • Permeability measurement is conducted to determine the surface powder • Where ; • –ΔP = the pressure drop across the bed l = the thickness of the bed uc=the average velocity of flow of the fluid, defined as (1/A) (dV/dt) A = the total cross sectional area of the bed V = the volume of fluid flowing in time t K = a constant depending on the physical properties of the bed and fluid

  5. Specific surface and Voidage • The general structure of a bed of particles can often be characterized by the specific surface area of the bed and the fractional voidage of the bed . • Voidage/porosity (ε) -The fraction of the volume of the bed not occupied by solid material. It is dimensionless and given by;

  6. Specific surface area of the bed (SB) − The surface area presented to the fluid per unit volume of bed when the particles are packed in a bed. Its units are (length)^-1 • Specific surface area of the particles (S) • The surface area of a particle divided by its volume. Its units are (length)^-1 • Sand SBare not equal due to the voidage which is present when the particles are packed into a bed.

  7. If point contact occurs between particles so that only a very small fraction of surface area is lost by overlapping, then SB is given by; • For a sphere particle, S is given by;

  8. General expressions for fluid flow through beds in terms of Carman-Kozeny equations. 1.Physical model for granular bed • The pore space in the bed is assumed to be a tube with equivalent diameter (de ) which satisfies the following assumptions: • The internal surface area is equal to the surface area of particles • The free space is equal to that in granular bed. Equivalent Diameter (de)

  9. 2.Pressure drop At a steady state, and negligible gravity effect, The pressure drop per unit length is given by; Where λ is a friction coefficient determine experimentally and is superficial (empty tower) velocity

  10. Verification of model and evaluation of model parameters • The Reynolds number for a granular bed is defined as • where the average velocity is; • For laminar flow (Re <1) through granular beds, Kozeny found that λ= K/Re

  11. Thus, according to Carman-Kozeny equations, Where K= 5 (Kozeny constant) • Factors affecting pressure drop: • operation parameters: e.g., VO • • physical properties of fluid: μ , ρ • • characteristics of the bed: ε , s

  12. Dispersion in packed beds • Axial dispersion is nonideal flow phenomenon occurred in packed beds when flow rate of fluid and pressure are high • The importance of axial dispersion in liquid flow through porous beds is well known for numerous engineering applications. • Many studies concerned with diffusion and dispersion in porous media have been undertaken to understand their effects on mass and heat transfer and on chemical reactions taking place within packed beds.

  13. The axial dispersion maybe describes by a diffusion-like equations • Where, • C = fluid concentration • D= Axial dispersion coefficient • Z =Axial coordinate in packed bed • v= fluid velocity

  14. Exercise • A water moving trough a packed column of granulated silica gel at 20 ºc. The average size of the particles is around 3 mm and covered for 65% of the beds volume. Determine the specific surface area of the bed and the equivalent diameter of the pore channels through the bed. • If the Reynolds number is given by 0.89, calculate the average velocity of the water moving trough the channel of the bed. • Find the pressure drop if the length of the bed is given by 2m?

More Related