ADDIS ABABA UNIVERISTY

ADDIS ABABA INISTITUTE OF TECHNOLOGY

GROUP NAMESID NUMBER

SUBMITTED TO
SUBMISSION DATE

Fluidization
Objectives
To experimentally determine the minimum fluidization velocity for the given bed of
particle
To qualitatively observe the behavior of a gas fluidized bed with increasing gas velocity
using a 2-D bed
THEORY
When a packed bed of particle is subjected to a sufficient high upward flow of fluid (gas or liquid)
the weight of the particles is supported by the drag force exerted by the fluid on the particles and
the particles become freely suspended or fluidized. The behavior of fluidized suspension is similar
in many aspects to that of pure liquid. Mass transfer and heat transfer rates between particles and
submerged objects (e.g. heat exchanger tubes) is greatly enhanced in fluidized beds. In addition,
rapid particle mixing allows uniformity in bed. As a result, fluidized bed are widely used for
conducting gas solid reactions (coal combustion), gas solid catalytic reaction (catalytic cracking
of petroleum), etc. several applications also utilize liquid fluidized beds (bioreactors).
Some of the important design parameters for such systems are: the minimum fluidization velocity,
bed expansion of fluidization, and pressure variation in the bed.
Minimum fluidization velocity:
The basis of the theory for prediction of minimum fluidization velocity is that the pressure drop
across the bed must be equal to the effective weight per unit area of the particles at the point of
incipient fluidization. The is expressed in mathematical form as
P = (p g)(1-M)gl (1)
Where P is the pressure drop, p and g are the densities of the particle and gas respectively.
Emis the porosity at minimum fluidization, and L is the height of the bed. The Ergun equation can
be used to calculate the pressure drop in packed beds.

Advantages of fluidized beds

The smooth liquid like flow of particle allows continuous automatically controlled
operations;
The rapid mixing of solids leads to nearly isothermal conditions throughout the reactor;
The circulation of solids between two fluidized beds makes it possible to transport the
vast quantities of heat produced or needed in large reactor;
It is suited to large scale operation;
Heat and mass transfer rate between gas and particles are high when compared with other
modes of contacting;
The rate of heat transfer between a fluidized bed and an immersed object id high; heat
exchanger with in the fluidized beds required relatively small surface area.
Disadvantages of the fluidized beds
The difficult to describe flow of gas represents an in efficient contacting system. This
becomes especially serious, when high conversion of gaseous reactants is required.
The rapid mixing of solids in the bed leads to non-uniform residence limes of solids in the
reactor.
Friable solids are pulverized and entrained by the gas: they then must be placed:
 Erosion of pipes and vessels from abrasion by particles can be serious.
At high temperature the agglomeration and sintering of the line particles can necessitate a
lowering in temperature of operation, reducing rate considerably.
Nowadays, fluidized beds are used in a large extension for a lot of processes in
chemical engineering because of the many advantages.

Apparatus used
fluidization equipment
Air

PROCEDURE
Fine solid particles were filled in the fluidization pipe: the height was recorded
Air was supplied with a low flow rate to the bed and the flow rate was measured using
a rotameter.
The gas flow rate was increased slightly and the flow rate, the pressure across the bed
and the bed height were carefully recorded
The above procedure was repeated until maximum flow rate (16 l/min) was reached.
Finally, the process was reversed starting from high flow rate and decreasing the flow
rate uniformly until 2l/min.

DATA
Fluidization
Q P(mm L P
Q (m3/s) P/H log P/H V (mm/s) log V
(l/min) water) (m) (Pa)
2 60 0.137 3.3333E-05 588.396 4294.86 3.63 0.6666 -0.18
4 97 0.138 6.6667E-05 951.2402 6893.04 3.84 1.333 0.12
6 146 0.138 1.0000E-04 1431.764 10375.10 4.02 2.000 0.30
8 187 0.145 1.3333E-04 1833.834 12647.13 4.10 2.666 0.43
10 184 0.155 1.6667E-04 1804.414 11641.38 4.07 3.333 0.52
12 192 0.170 2.0000E-04 1882.867 11075.69 4.04 4.000 0.60
14 190 0.190 2.3333E-04 1863.254 9806.60 3.99 4.666 0.67
16 192 0.200 2.6667E-04 1882.867 9414.34 3.97 5.333 0.73
Defluidization

P(mm
Q (l/min) L (m) Q (m3/s) P (Pa) P/H log P/H V (mm/s)
water) log V
 16 192 0.200 2.6667E-04 1882.867 9414.34 3.97 5.333 0.73
14 187 0.190 2.3333E-04 1833.834 9651.76 3.98 4.666 0.67
12 162 0.175 2.0000E-04 1588.669 9078.11 3.96 4.000 0.60
10 151 0.165 1.6667E-04 1480.797 8974.52 3.95 3.333 0.52
8 131 0.150 1.3333E-04 1284.665 8564.43 3.93 2.666 0.43
6 98 0.150 1.0000E-04 961.0468 6406.98 3.81 2.000 0.30
4 68 0.150 6.6667E-05 666.8488 4445.66 3.65 1.333 0.12
2 39 0.150 3.3333E-05 382.4574 2549.72 3.41 0.666 -0.18
CALCULATION
To calculate the minimum fluidization velocity using the formula:
Particle diameter=275m
Porosity () =0.343
Area of the bed = 0.05m2
particle = 2960 kg/m3
air (1 bar, 25 = 1.1839 kg/m3
air = 18.6 Pa.s
g=9.81 m/s2
(((150**V0m) *(1-M))/ (Dp2 *m3))- [(((1.75*g*V20m))/ (DP*3M)] =g (p g)
o 150**V0m=150*18.6*10-6* V0m = 2.8*10-3 * V0m
o 1-M=1-0.343=0.657
o Dp2 *m3=(2.75E(-04))2*(0.3433)=3.05*10-9
o 1.75*g*V20m=1.75*1.184* V20m=2.1 V20m
o Dp*3M=2.75*10-4 *(0.3433)=1.11E(-05)m
o g(p g)=9.81(2960-1.129)=29026.5Kgm-2s-2
157755V20m -20.699V0m-1=0
When we solve the equations we get two solutions
V1= -0.0026 and V2= 0.0025
But the negative one cant be a solution we take the positive one and v will be
V=0.0025 m/s
 4.50 logP/HVslogV
4.00 4.02 4.10 4.07 4.04 3.99 3.97 3.98 3.96 3.95 3.93
3.84 3.81
3.50 3.63 3.65
3.41
P/H
3.00
log

2.50
2.00
1.50 logP/H
From the
1.00
graph above,
0.50
the
0.00
0.18 0.12 0.30 0.43 0.52 0.60 0.67 0.73 0.67 0.60 0.52 0.43 0.30 0.12 0.18
logV
maximum value corresponds to the minimum fluidization velocity.
log V= 0.43
V = 100.43
V=2.69 mm/s

CONCLUSION
In our experiment, we have done both fluidization and defluidization in the same experiment in
order to elaborate the process better. The minimum fluidization velocity is the minimum velocity
in which the solid is fluidized. As the gas flow rate increases beyond the minimum fluidization,
the bed may continue to expand and remain homogeneous for a time. At a fairly definite
velocity, however, bubbles begin to form. Further increases in flow rate distribute themselves
between the dense and bubble phases in some ways that are not well correlated.
Extensive bubbling is undesirable when intimate contacting between phases is desired, as in
drying processes or solid catalytic reactions.