Packed Beds

Question 1

What is a column?

Answer 1

A cylindrical vessel whose height is as greater than it’s diameter

Question 2

What is Darcy’s law?

Answer 2

uc = K (-deltaP) / l

uc = induced flow
deltaP = driving pressure drop
l = depth of bed

Question 3

What is Reynolds number?

Answer 3

Re = (Rho V D) / Mu

Re = Reynolds number
Rho = Density
V = velocity
D = pipe diameter
Mu = viscosity

Inertial forces divided by viscous forces. If Re > 2000, it is turbulent flow in the pipe. If Re < 2000, it is laminar flow in the pipe.

Question 4

What is laminar flow?

Answer 4

A flow pattern in which all the particles are flowing in parallel lines.

Question 5

What is turbulent flow?

Answer 5

A flow pattern where all the particles are mixing.

Question 6

What is Darcy’s law at low Re?

Answer 6

uc = B (-delta P) / (Mu l)

uc = induced flow
B = permeability coefficient of the bed
delta P = Pressure drop
Mu = Viscosity
l = bed height

Question 7

What is specific surface area of a bed?

Answer 7

SB = A / (pi d^2 l / 4)

SB = Specific surface area of a bed (the surface area of particles presented to the fluid per unit length of the bed)
A = Total surface area in the bed
d = diameter
l = bed height

Question 8

What is voidage and how does it relate to the volume of the bed?

Answer 8

e = Vv / Vt

e = voidage
Vv = Void volume
Vt = Total volume

Vb = 1 - e

Vb = Bed volume

Question 9

How does specific surface area of the bed relate to voidage?

Answer 9

SB = S (1 - e)

SB = specific surface area of the bed
S = specific surface area of a particle
e = Voidage

Question 10

What is Carman-Kozney’s Equation?

Answer 10

B = 1 / K’’ * e^3 / (S^2 (1 - e)^2)

B = Permeability Coefficient of the bed
K'' = Kozney's constant
e = Voidage
S = Specific surface area of the particle

Question 11

What is dispersion?

Answer 11

Dispersion describes the types of self-mixing that can occur in a reactor.

Question 12

What is a quiexcent fluid?

Answer 12

A still fluid, no convection, only diffusion

Question 13

What is Fick’s law?

Answer 13

J = -D (dC / dx)

J = molar flux
D = diffusivity
C = concentration
x = distance along the vessel

Question 14

What enhances dispersion?

Answer 14

Turbulent flow and adding packing.

Question 15

What is DL and DR at Re < 10?

Answer 15

DL = DR = 0.7D

DL = Diffusion longitudinal
DR = Diffusion radial
D = Diffusivity
DL = DR < D due to tortuosity

Question 16

What is tortuosity?

Answer 16

The property of a pipe being twisted.

Question 17

What is DL and DR approximately at Re > 10?

Answer 17

DL = DR = (uc d) / 2e

DL = Longitudinal diffusivity
DR = Radial diffusivity
uc = induced flow
d = distance along the vessel
e = voidage

Question 18

What is the diffusion distance rule of thumb?

Answer 18

dD = 2 (Dt)^1/2

dD = diffusion distance
D = diffusivity
t = time