7. fluidized ,packed , spouted bed

8/12/2019 7. Fluidized ,Packed , Spouted Bed

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CHE 391

Chemical engineering lab I

Experiment 7

Pressure drop studies in Packed bed, Fluidized bed and Spouted

bed

Date of submission: 21/1/10Date of experiment: 14/1/10

Submitted by

Name: Purushottam Sinha Roll No.:(Y7327)

Name: Rishi Raj Singh Roll No.:(Y7360)

Department of Chemical EngineeringIndian Institute of Technology Kanpur


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Contents

Introduction 3Objectives 5Theory and Formulae 6Experimental setup 9Procedure 10Observation and Results 11Rotameter calibration 12Fluidized bed 13Packed bed 21Spouted bed 24Discussion 29Precautions 30Answers to Questions 30Nomenclature 32References 33


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INTRODUCTION

Fluidized Bed:

A fluidized bed reactor(FBR) is a type of reactor device that can be used tocarry out a variety of multiphase chemical reactions. In this type of reactor,

a fluid (gas or liquid) is passed through a granular solid material (usually a

catalyst possibly shaped as tiny spheres) at high enough velocities to

suspend the solid and cause it to behave as though it were a fluid. A

uniform fluidization which is the most desirable regime of operation of

industrial fluidized beds is prone to instabilities. At the fluid flow increases,

bubbles of clear fluid are formed at the bottom of the bed and these

bubbles travel to the surface.This process, known as fluidization, imparts

many important advantages to the FBR. As a result, the fluidized bed

reactor is now used in many industrial applications. It is extensively

employed in a heat exchanger, catalytic and non-catalytic reactors, ion

exchange, drying, coating adsorption etc.

Packed beds:

In chemical processing, a packed bedis a hollow tube, pipe, or other vessel

that is filled with a packing material. The packing can be randomly filled

with small objects like Raschig rings or else it can be a specifically designed

structured packing. The purpose of a packed bed is typically to improvecontact between two phases in a chemical or similar process. Packed beds

can be used in a chemical reactor, a distillation process, or a scrubber

where large area is necessary to provide intimate contact between two

phases, gas-liquid or liquid-liquid.

Spouted beds:

In this a gas jet is injected into a bed of large-sized particles stored in a

vessel, usually with a conical bottom. Spouted beds are used for drying

grains. Following figures show these different types of beds.


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Figure:Fluidized Bed Figure:Packed Bed

Figure:Spouted Bed


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OBJECTIVES

Fluidized bed:

To study the fluidization characteristics of a bed of sand by air.To study the effect of particle Reynolds number on void fraction. To calculate fluidization efficiency.

Packed bed:

To verify the relationship between the velocity of the fluid andpressure drop per unit length of packing.

To verify Ergun's equation.

Spouted bed:

To determine pressure drop per unit length as a function ofsuperficial air velocity.


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THEORY & FORMULAE

Packed bed:

As a fluid passes through the bed it does so through empty spaces in the

bed. The voids form continuous channels throughout the bed. While the

flow may be laminar in some region it is turbulent in other channels. The

resistance due to friction per unit length of the bed can be taken as the :

(1)sum of viscous drag forces which is proportional to the first power offluid velocity v and

(2)inertial forces which are proportional to the square of the fluidvelocity. The pressure drop per unit length is given as

(8)

Where

P: pressure drop across column

Z: packed bed heightg: viscosity (air)

: fractional void volume

gc: Newtons law proportionality factor

ap: square feet of packing surface in a cubic foot of packed volume

g: fluid (air) density

Fluidized bed:

When a fluid passes upwardsthrough a bed of solids there will be certain

pressure drop across the bed required to maintain the fluid flow.Depending

upon the bed geometry, and particle characteristics the fluidization

phenomenon occur at a particular fluid velocity.

G

ddg

G

Z

P

p

g

pcg

75.1)1(1501

3


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In a fluidized bed of height L, the total upward force due to pressure

difference must be equal to the buoyant weight of solids

where is called the porosity of the bed.

At the onset of fluidization, the pressure drop across the bed equals the

weight of bed per unit area of cross section. This gives a minimum

fluidization velocity

(3))1(150

)g-(dV

32

p

fmf

mffs

mf

The simplified expression for minimum fluidization velocity given by Kunni

and Levenspiel are as under.

(5)1000Re

5.24

)g-(dV

(4)20Re1650

)g-(dV

P

2

p

P

2

p

f

fs

mf

f

fs

mf

Pressure drop across a fixed bed (Erguns Equation):

(6)

Fluidization efficiency = (GF GE)/GF (7)

Where

GF: Mass velocity of fluid theoretically required to produce fluidization,

kg/s.m2

GE: Mass velocity of fluid actually causing initial expansion of bed, kg/s.m2

(2)LAW-1

(1))g-)(-(1L

s

s

fs

P

p

g

pcg ddg

G

Z

P

)1(15013


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Spouted bed:

In the spouted state the pressure drop across the bed arises out of two

parallel resistances, namely that of the spout in which dilute phasetransport is occurring, and that of the annulus which is downward moving

packed bed with counterflow of gas.The fluid is injected vertically through a

centrally located small opening at the base of the vessel. At sufficiently high

fluid velocity, the overall bed becomes a composite of dilute phase central

core with upward moving solids entrained by a concurrent flow of fluid and

a dense phase annular region with counter current percolation of fluid. A

conical base with fluid coming from the apex is used to obtain better fluid

motion and to avoid dead spaces in the vessel. For a bed of height H the

minimum fluidization pressure drop is given by the following equation:Pf= H (sf)(1 ) g (9)

If we assume that annulus as a loose packed bed with viscous flow, Munuro

and Hattori showed that the pressure gradient along the bed length is:

(10)

On integrating this equation for a bed of height H, it gives the spouting

pressure drop by the following equation:

Ps= (sf)(1-mf)(0.75H) (11)

The corresponding pressure dropPsfor a fully turbulent flow in annulus

is given by:

-Ps = (sf) (1-) g (9H/14) (12)

3

11))(1(H

zg

dz

dPfs


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EXPERIMENTAL SETUP

Figure: Line diagram of the experimental set up is shown.


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PROCEDURE

Rotameter calibration: Air was allowed to flow through the Rotameter only for one minute and the

volume of air flow through the wet gas flow meter was noted.

The procedure was repeated for several different Rotameter readings.

Packed bed The Rotameter reading was adjusted to a particular flow rate and the pressure

drop in the packed bed was measured by the manometer.

The procedure was repeated at different flow rates and the pressure differencereadings were taken for each of the flow rates.

Fill calibrated beaker with balls used to pack the bed, upto 100 ml mark. Nowpour water from another calibrated beaker upto 100ml mark. Note down the

initial and final reading of the water level in the beaker and thus calculate

voidage.

Fluidized bed 100 gm of Resin was weighed and added to the column. The initial height of the bed was noted. The average height of the bed and the pressure drop were measured using

manometer at different flow rates of air when the bed was fluidized.

The experiment was repeated with additional 100 gm of Resin followed byanother 100 gm of Resin.

Spouted bed 100 gm of Resin was added to the spouted bed.

The initial height of the bed was noted. The average height of bed and the pressure drop were measured usingmanometer as a function of flow rate of air.

The experiment was repeated with additional 100 gm of Resin followed byanother 100 gm of Resin.


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OBSERVATIONS AND RESULTS:

Specifications:

Diameter of Pipe ID = 7.7 cmLower Diameter of Conical Section Din = 3.4 cm

Length of conic section = 15.7 cm

Density of Air at room temperature f= 1.185 kg/m3

Viscosity of Air at room temperature f= 1.8*10-5

kg/m3

Diameter of Resin Particle dp = 0.0231 cm.

Density of Resin s= 2300 kg/m3

Diameter of Glass beads dp = 6 mm.

Density of Glass beads s = 2500 kg/m3

Porosity of packed bed = 0.45

Least Counts

Rotameter Reading M=0.01 units Manometer reading H =0.1 cm. Scale = 0.1 cm Balance=0.01 gm


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Rotameter Calibration:

Table 1: Rotameter calibration data

Rotameter Reading Divisions Flow Rate ( L/ min ) Flow Rate (10-

m /s

)

0.1 380 19.5 3.25

0.2 775 38.75 6.50

0.3 1130 56.5 9.17

0.4 1380 69 12.25

0.5 1990 99.5 15.50


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Fig 1: Rotameter Calibration curve

y = 30.25x + 0.259

0

2

4

6

8

10

12

14

16

18

0 0.1 0.2 0.3 0.4 0.5 0.6

flow

ratein(10^-4

m2/s)

rotameter reading

flow rate

flow rate

Linear (flow rate)


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FLUIDIZED BED:

Sample Calculation:

Weight of Resin = 100 gm = 0.1 kg

Rotameter Reading = 0.3

Bed height, L = 2.2 cm = 0.022 m

Manometer Reading = 1.1 cm = 0.011 m

Flow Rate = 0.000917 m3/s (from calibration curve)

Crosssectional area = 3.14*(0.077)2/4 = 4. 654*10-3m2

Superficial velocity = 0.197 m/s

Porosity, e = 1((0.1 kg) / ((0.022 m)* (2300 kg/m3)*(4.654*10

-3m

2)) = 0.575

Reynolds No. = (1.185 kg/m3)*(0.197m/s)*(0.000231m) / (1.8*10

-5Pa.sec) = 2.915

Hence, ln (Re) = 1.0700

Pressure drop, -P= (15901.185)*9.8*.011 = 171.27 Pa

Hence, ln (-P)= 5.1432

Table 2: Data for Fluidized Bed with 200 gm Resin

Rotameterreading

Bed

height

(cm)

Manometer

reading

(cm)

Flow

rate Q

(m3/sec)

Superficial

velocity

vo(m/s)

Porosity()

Reynolds

number

(Re)

-P (Pa) ln(Re) ln(-P)

0.23 4.70 2.3 0.000721 0.1634 0.3574 2.516 355.81 0.9230 5.8743

0.30 4.75 2.4 0.000933 0.2113 0.3642 3.255 371.28 1.1802 5.9169

0.34 4.90 2.5 0.001054 0.2387 0.3836 3.677 386.75 1.3021 5.9577

0.39 5.0 2.5 0.001205 0.2730 0.3960 4.204 386.75 1.4362 5.9577

0.42 5.1 2.6 0.001296 0.2935 0.4078 4.521 402.22 1.5088 5.9969


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Fig 2: Plot of ln (-P) vs. ln (Re) for fluidized bed with 100gm

Resin

5.86

5.88

5.9

5.92

5.94

5.96

5.98

6

6.02

1 1.1 1.2 1.3 1.4 1.5 1.6

ln(-

deltaP)

ln ( Re )

ln( - delta P)

4.64

4.72

4.8

4.88

4.96

5.04

5.12

0.15 0.17 0.19 0.21 0.23 0.25 0.27 0.29 0.31 0.33

bedheight(cm)

superficial velocity ( m/s )

bed height vs superficial velocity


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Fig 3: Bed height vs. superficial velocity for 100 gm Resin in

fluidized bed

Fig 4: Porosity of bed vs. Re for 100 gm Resin in fluidized bed

Calculation of minimum fluidization velocity (vmf), fluidization efficiency, Froude

number at vmfand Repat =1

Bed weight = 100gmFrom fig-3

vmf, exp = 0.163 m / s

From equation-3,

vmf, theo = (0.0002312*(23001.185)*9.8*0.575

3/ (150*(1-0.575)*1.8*10

-5) = 0.199 m / s

Fluidization efficiency = (0.1990.163)*100 / 0.199 = 18.09% (using equation-7)

Rep (=1) = 7.27 (by extrapolation)

gdp

2

mfv

numberFroude

Froude number = 11.73

0.35

0.36

0.37

0.38

0.39

0.4

0.41

0.42

2 2.5 3 3.5 4 4.5 5

porosity(e)

reynolds number Re

reynolds number (Re) vs porosity (e)


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Rotameter

reading

Bed

height

(cm)

Manometer

reading (cm)

Flow

rate Q

(m3

/s)

Superficial

velocity

vo(m/s)

Porosity

()

Reynolds

number

(Re)

-P (Pa) ln(Re) ln(-P)

0.21 5.9 2.9 0.000661 0.1497 0.3601 2.3058 448.63 0.8354 6.1061

0.29 6.1 3.0 0.000903 0.2045 0.3811 3.1498 464.1 1.1473 6.1401

0.34 6.3 3.1 0.001054 0.2387 0.4007 3.6773 479.57 1.3021 6.1728

0.39 6.5 3.15 0.001235 0.2798 0.4192 4.3103 487.30 1.4610 6.1888

0.42 6.9 3.15 0.001387 0.3141 0.4528 4.8378 487.30 1.5764 6.1888

Fig 5: Plot of ln (-P) vs. ln (Re) for fluidized bed with 200gmResin

6.1

6.125

6.15

6.175

6.2

0.7 1 1.3 1.6 1.9

ln(-deltaP)

ln (Re)

ln(Re) vs ln(-delta P)


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fluidized bed


5.7

6

6.3

6.6

6.9

7.2

0.12 0.15 0.18 0.21 0.24 0.27 0.3 0.33

Bedheightin(cm

)

superficial velocity ( m/s)


0.3

0.35

0.4

0.45

0.5

2 2.5 3 3.5 4 4.5 5

porosity(e)

reynolds number (Re)

porosity vs reynolds number


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Bed weight = 200gm

From fig-6,

vmf, exp = 0.160 m / s

From equation-3,

vmf, theo = (0.0002312*(23001.185)*9.8*0.597

3/ (150*(1-0.597)*1.8*10-5) = 0.235 m / s


Rep(=1) = 6.723 (by extrapolation)

gdp

2

mfvnumberFroude



Rotameter

reading

Bedheight

(cm)

Manometer

reading (cm)

Flow rate

Q (m3/s)

Superficialvelocity

vo(m/s)

Porosity

()

Reynoldsnumber

(Re)

-P

(Pa)ln(Re) ln(-P)

0.22 7.1 3.5 0.000691 0.1565 0.3619 2.4113 541.45 0.8801 6.2942

0.3 7.3 3.6 0.000933 0.2113 0.3794 3.2553 556.92 1.1802 6.3224

0.34 7.5 3.7 0.001054 0.2387 0.3960 3.6773 572.39 1.3021 6.3498

0.39 7.7 3.7 0.001205 0.2730 0.4116 4.2048 572.39 1.4362 6.3498

0.45 8.4 3.7 0.001387 0.3141 0.4607 4.8378 572.39 1.5764 6.3498


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Fig 8: Plot of ln (-P) vs. ln (Re) for fluidized bed with 300gm

Resin

6.25

6.3

6.35

6.4

0.7 0.9 1.1 1.3 1.5 1.7

ln(-deltaP)

ln ( Re)

ln ( - delta P) vs ln (Re)

7

7.4

7.8

8.2

0.15 0.17 0.19 0.21 0.23 0.25 0.27 0.29 0.31 0.33

bedheight(cm)

superficial velocity ( m/s )



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fluidized bed




Bed weight = 300gm

From fig-9,

vmf, exp = 0.169 m / s

From equation-3,

vmf, theo = (0.0002312*(23001.185)*9.8*0.618

3/ (150*(1-0.618)*1.8*10-5) = 0.275 m / s


Rep(=1) = 9.422 (by extrapolation)

gdp

2

mfvnumberFroude


0.3

0.34

0.38

0.42

0.46

0.5

2.2 2.7 3.2 3.7 4.2 4.7 5.2

porosity(e)


Reynolds number(Re)

vs porosity (e)


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PACKED BED:Sample Calculation:


Bed Height = 31.5 cm = 0.315 m

Manometer Reading = 0.4 cm = 0.004 mFlow Rate = 0.00309*0.2-0.00001=0.000608 m3/s

Flow velocity = (0.608*10-3

m3/ sec) / (4.654*10

-3m

2) = 0.130 m / sec

Reynolds Number, Re = (1.185 kg/m3)*(0.130 m/sec)*(0.006 m)/(1.8*10

-5Pa.sec) =

51.602

- P/Lp= (0.004 m)*(9.8 m/sec2)*((9971.185) kg/m

3) / (0.315 m) = 123.92 Pa / m

fp, exp = = (123.92 Pa /m)*0.453*(0.006 m) / ((1-0.45)*( 0.130 m/sec)

2) = 7.21

fp, theo=

= 150*(1-0.45) / 51.602 + 1.75 = 3.348

Table 5: Data for Packed Bed with glass balls as packing material

Rota-

meter

Reading

Manometer

reading

(cm)

Flow

velocity

vo(m/s)

Porosity

()

Reynolds

number

(Re)

- P/Lp(Pa/m)

fp, exp =

fp, theo

0.21 0.4 0.1496 0.45 59.8605 122.13 3.490 3.253

0.26 0.7 0.1838 0.45 73.5546 213.73 4.045 2.9730.33 1.3 0.2318 0.45 92.7265 396.92 4.727 2.7200.37 1.6 0.2592 0.45 103.6818 488.52 4.653 2.6180.40 1.8 0.2797 0.45 111.8983 549.59 4.494 2.5540.44 2.4 0.3071 0.45 122.8537 732.79 4.971 2.4820.48 2.8 0.3345 0.45 133.8090 854.92 4.889 2.4220.50 3.2 0.3482 0.45 139.2867 977.05 5.157 2.396

2

3

)1( vL

dP p

2

3

)1( vL

dP p


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Fig 11: fp, exp vs. Re for Packed Bed

Fig 12: Pressure Drop per unit bed length vs. Re for Packed Bed

2

3

4

5

6

50 70 90 110 130 150

fp(theoretical)&fp(experimental)

reynolds number(Re)

fp vs Re

f exp

f theo

0

100

200

300

400

500

600

700

800

900

1000

50 70 90 110 130 150

DeltaP/L(N/m^3)

Reynolds number (Re)

Pressure drop/length Vs Re


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SPOUTED BED:

Sample Calculation:


Bed height = 8.6 cm = 0.086m

Manometer Reading = 5.4 cm = 0.054 m

-P = ((1590 1.185) kg/m3)*(0.086 m)*9.8 = 840.8 Pa

-Pviscous= ((23001.185) kg/m3)*(1-0.685)*9.8*(3*0.054/4) = 457.24 Pa

-Pturbulent= ((23001.185) kg/m3)*(1-0.685)*9.8*(9*0.054/14) = 391.92 Pa

Table 6: Data for Spouted Bed with 100 gm Resin

Rotameterreading

Bed

height

(cm)

Manometerreading (cm)

Flow

velocity

vo(m/s)

Porosity()

Reynolds

number

(Re)

(-) P(Pa)

(-)

Pviscous(Pa)

(-)

Pturbulent

(Pa)

0.12 8.4 5.4 0.1667 0.6666 322.29 835.50 308.14 264.16

0.15 8.6 5.0 0.2056 0.6744 397.50 773.61 315.48 270.45

0.19 8.7 4.8 0.2574 0.6781 497.78 742.66 319.14 273.59

0.25 9.0 4.5 0.3352 0.6888 648.19 696.25 330.15 283.02

0.30 9.2 4.2 0.4001 0.6956 773.54 649.83 337.49 289.31

Fig 14: Porosity vs. Re for 100 gm Resin in Spouted Bed

0.62

0.64

0.66

0.68

0.7

0.72

0.74

0.76

0.78

0.8

0.976962528 1.986599388 2.996236248 4.005873108 5.015509968

Porosity Vs Re

Porosity Vs

Re


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Using fig 14,

Fluidization occurs at Re = 1.98,

mf= 0.696

Fig 15: Comparison between -P, -Pviscousand -Pturbulentfor 100

gm Resin in Spouted Bed


Rotameter

reading

Bed

height

(cm)

Manometer

reading (cm)

Flow

velocity

vo(m/s)

Porosity

()

Reynolds

number

(Re)

(-) P

(Pa)

(-)

Pviscous(Pa)

(-)

Pturbulent

(Pa)

0.1 11.9 8.8 0.0642 0.545 0.9761370.194 914.4805 783.840

0. 12.5 7.1 0.1306 0.567 1.9861105.497 914.4805 783.840

0.3 14.5 6.6 0.1970 0.626 2.9961027.646 914.4805 783.840

0.4 15.5 6.3 0.2634 0.650 4.005980.9344 914.4805

783.8404

0.5 17 6.1 0.3298 0.681 5.015949.7936 914.4805 783.8404

0

100

200

300

400

500

600

700

800

900

200 400 600 800

deltaP(Pa)


delta P vs reynolds number

delta P (viscous)

delta P (turbulent)

delta P ( experimental)


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Fig 16: Porosity vs. Re for 200 gm Resin in Spouted BedUsing fig-16,

Fluidization occurs at Re = 2.23, mf= 0.588

Fig 17: Comparison between -P, -Pviscousand -Pturbulent for 200


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.976962528 1.986599388 2.996236248 4.005873108 5.015509968

Porosity Vs Re

Porosity

Vs Re

0

200

400

600

800

1000

1200

300 500 700 900 1100

deltaP(Pa)


delta P vs reynolds number

delta P (viscous)

delta P (turbulent)



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Rotameter

reading

Bed

height

(cm)

Manometer

reading

(cm)

Flow

velocity

vo(m/s)

Porosity

()

Reynolds

number

(Re)

(-) P

(Pa)

(-) Pviscous(Pa)

(-)

Pturbulent

(Pa)

0.114 17.8 0.0642 0.4201 0.976 2771.529 1371.7208 1175.7607

0.214.9 8.2 0.1306 0.4551 1.986 1276.772 1371.7208 1175.7607

0.316 8 0.1970 0.4925 2.996 1245.631 1371.7208 1175.7607

0.417.5 7.8 0.2634 0.5360 4.005 1214.49 1371.7208 1175.7607

0.5 18.5 7.6 0.3298 0.5611 5.015 1183.349 1371.7208 1175.7607

Fig 18: Porosity vs. Re for 300 gm Resin in Spouted Bed

Using fig-18,

Fluidization occurs at Re = 1.986,

0

0.1

0.2

0.3

0.4

0.5

0.6

0.976962528 1.986599388 2.996236248 4.005873108 5.015509968

Porosity Vs Re

Porosity

Vs Re


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mf = 0.455

Fig 19: Comparison between -P, -Pviscousand -Pturbulentfor 300


400

500

600

700

800

900

1000

1100

1200

1300

400 600 800 1000

deltaP


delta P vs reynolds number (Re)

delta P (viscous)

delta P (turbulent)



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DISCUSSION:

Packed Bed:1. Value of f exp first decreases then remains almost constant with Re that is

initially it is in laminar zone then in turbulent zone.

2. There is huge difference between f exp and f theo which might be because oflarge experimental error or Erguns equation might not fit into this system.

3. Pressure Drop per unit bed length increases with Re in almost exponential way.FluidizedBed:

4. It is found that the pressure first increases, then decreases and then assumes aconstant value (fluidization point) with increase in flow rate for 100gm,200gm

and 300 gm Resin which is in agreement with theory.5. Porosity initially remains constant until fluidized point then increases almost

linearly with Re .

6. Bed height also remains constant until fluidized point then increases linearly withsuperficial velocity . Significant rise in bed height can be observed at the time of

fluidization.

7. The minimum fluidization velocity increased with increase in weight of solidparticles, i.e, increased initial bed height. However, since the experiment was

done for only three initial bed heights, a trend could not be traced.

Spouted Bed:1. Porosity initially remains constant until fluidized point then increases with Re .2. Initially there is large difference between experimental and theoretical values of

pressure difference but as Re increases this difference decreases . This

discrepancy may be blamed on the inherently unstable nature of the system. The

manometer readings fluctuate a lot and occasional entrapment of air bubble also

affects the readings. Thus the readings are at best approximate.


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PRECAUTIONS

Fluid flow rates are limited to the range over which the bed is fluidized. If the

velocity is much higher than Vmf, there can be excessive loss of material carried

out from the bed and there may also be unacceptable particle damage due to

excessive operating velocity.

The Bed height and the readings in the manometer should be carefullymeasured since it can introduce large amount of human error.

When a particular bed is being studied, we must ensure that all the valves of theother two beds are closed.

ANSWERS TO QUESTIONSFluidized Bed

A1.Advantages and Disadvantages of fluidization:

The chief advantage of fluidization are that the solid is vigorously agitated by the fluid

passing through the bed, and the mixing of the solid ensures that there are practically

no temperature gradients in the bed even with quite exothermic or endothermic

reactions.

The main disadvantage of gas-solid fluidization is the uneven contacting of gas and solid.

Erosion of vessel internals

Attrition of solids: Because of attrition, the size of the solid particles is getting reduced

and possibility for entrapment of solid particles with the fluid is more.

A2.When fluidizing Resin with water, the particles move further apart and their motion

becomes more vigorous as the velocity is increased, but the bed density at a given

velocity is same in all sections of the bed. This is called particulate fluidization and is

characterized by a large but uniform expansion of the bed at high velocities.

Beds of solids fluidized with air usually exhibit what is called aggregative or bubbling

fluidization. At superficial velocities much greater than Vmfmost of the gas passes

through the bed as bubbles or voids which are almost free of solids, and only a smallfraction of the gas flows in the channels between the particles.

And Froudes number is Fr= V/dp*g V= Superficial Velocity

dp=particle diameter g=acceleration due to gravity


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31

A3. Yes, type of distributor does matter. A good distributor is one which is

compatible to the particle size and can create maximum pressure drop for given flow

rate.

A4. The simplest description of the expansion of a bubbling fluidized bed is derived

from the Two-Phase Theory of fluidization of Toomey and Johnstone (1952). This theoryconsiders the bubbling fluidized bed to be composed of two phases; the bubbling phase

(the gas bubbles) and the particulate phase (the fluidized solids around the bubbles).

The particulate phase is also referred to as the emulsion phase. The theory states that

any gas in excess of that required at incipient fluidization will pass through the bed as

bubbles. Thus, in bubbling fluidization, bed expansion at velocities beyond minimum

bubbling velocity is due to the presence of bubbles.

A5.Yes, under similar condition the conversion in fluidized bed is more than the fixed

bed because the contact surface area increases as well as the conditions are

uniformly distributed in the fluidized bed.

Spouted Bed

A1.Gasification, bed dryers, used for plastic recycle and catalytic decomposition.

A2.In spouted bed the fluid flow is upward and density of particle is low while in moving

bed the density of particle is and flow direction is downwards.

A3. Minimum spouting velocity is the superficial velocity of the fluid at which spouting

starts. Maximum spouting velocity is the superficial velocity of the fluid at which

spouting seizes and turn to fluidized bed. Maximum spouting pressure drop

corresponding to maximum spouting velocity.

Packed Bed

A1.The pressure drop decreases if the size of particle is increased.

A2.The maximum diameter of sphere can be the diameter of the tube.

A3.If packing is made of particle of diameter D1 and D2 then the porosity will not beuniform. Average porosity will be in between the porosity of that of D1 and D2. If

porosity increases then pressure drop decreases.


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32

NOMENCLATURE

P Pressure Drop in a Bed N/m2

Ptheoretical Theoretical Drop in a Bed N/m2

H Difference in the level of fluid in manometer. cm

f Density of fluid flowing in the Column. Kg/m3

s Density of solid packed in the column. Kg/m3

Void Fraction or Porosity

mf Void Fraction at minimum fluidization.

f Viscosity of Fluid. Pa-s.A Cross Section Area of Column. cm

2

dp Diameter of Resin particles. cm

Din Inner Diameter of Spouted Column. cm

D Diameter of Column. cm

g acceleration due to gravity.m/s2

Fr Froudes Number

Q Volumetric Flow Rate. lit/s

Rep Reynolds Number of particle.

V0 Superficial Velocity. cm/s

Vmf Velocity at minimum fluidization. cm/s

Ws Weight of the bed

Fp, f Friction factor


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REFERENCES*1+. McCabe W. and Smith J.C., Unit Operations of Chemical Engineering, 4

thEdition,

McGraw Hill, New York, (1985).

*2+. Fan S. and Liang, Principles of solid-gas flows, Cambridge University Press, pg 223-

226, 1998.

[3]http://inls.ucsd.edu/grain/fluidbed/

[4]http://www.cesiweb.com/images/fig2.gif

[5]. Mcketta J.J., Encyclopedia of Chemical Processing and Design, Marcel Dekker, pg

56-61, 1985

*6+. Yang W.C., Handbook of Fluidization and Fluid-Particle Systems, Marcel Dekker, pg

65-80, 2003.

*7+. Gupta, S.K., Momentum Transfer Operations, Tata McGraw-Hill Publishers, 1979.

*8+. Perry, J.H. (Editor), Chemical Engineering Handbook, 4th

Ed., McGraw Hill, 1963
http://inls.ucsd.edu/grain/fluidbed/http://inls.ucsd.edu/grain/fluidbed/http://inls.ucsd.edu/grain/fluidbed/http://www.cesiweb.com/images/fig2.gifhttp://www.cesiweb.com/images/fig2.gifhttp://www.cesiweb.com/images/fig2.gifhttp://www.cesiweb.com/images/fig2.gifhttp://inls.ucsd.edu/grain/fluidbed/

7. fluidized ,packed , spouted bed

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