Heat transfer studies in fluidized bed region of gas-solid systems

119 Pages·04.109 MB·English

by  Brazelton, William Thomas

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NAME AND ADDRESS DATE

NORTHWESTERN UNIVERSITY
HEAT TRANSFER .STUDIES IN
FLUIDIZED BED REGION OF GAS - SOLID
SYSTEMS
A DISSERTATION
SUBMITTED TO THE GRADUATE SCHOOL
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
for the degree
DOCTOR OF PHILOSOPHY
DEPARTMENT OF CHEMICAL ENGINEERING
BY
WILLIAM THOMAS BRAZELTON
EVANSTON, ILLINOIS
DECEMBER, 1951
1952.
ProQuest Number: 10061028
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TABLE OF CONTENTS
List of Figures and Tables 1
Acknowledgement 3
Summary 4
Introduction 6
General Principles of Fluidization 6
Heat Transfer by Convection 11
Review of Previous Investigation 13
Heat Transfer in Fluidized Beds 17
Materials and Equipment 23
Gas-Solid System 23
Heat Transfer Equipment 23
Air Supply and Measurement 27
Heating Section 28
Temperature Measurement 32
Measurement of Pressure Drop 34
Supporting Screen 34
Equipment for Visual Studies 35
Sight Tube 35
Gas Flow 35
Bed Support 37
Pressure Drop Measurement 37
Procedure 38
Operation of the Heat Transfer Unit 38
Solids Introduction 38
653414
Air Supply and Metering 38
Heating Control 38
Temperature Measurement 39
Operation of the Visual Unit 39
Results and Conclusions 41
Discussion of Results 41
Correlation of Experimental Data 51
Conclusions 65
Nomenclature 67
Appendix 69
Calculation Methods 69
Tables 72
Bibliography
1
LIST OF FIGURES AND TABLES
Page No*
General Plot of Temperature Variation with Height of
Fluidized Bed 21
Photomicrographs of Spherical Solid Particles 24
Photograph of Heat Transfer Unit 25
Flow Diagram of the Heat Transfer Unit 26
Cross Section of Heating Unit 29
Iron-Constantan Guard Thermocouples in Transite Cylinder 31
Copper-Constantan Thermocouples in the Tube 33
Photograph of Equipment for Visual Studies 36
A, Typical Radial Temperature Profile in Fluidized Bed 42
B« Typical Longitudinal Temperature Traverse (Wall and
Air)
Typical Longitudinal Variations of Heat Transfer 44
Coefficient within the Fluidized Bed
Influence of Superficial Mass Velocity upon Bed Density 45
A* No. 3 Bead, Dp = 0.04371'
B. No. 5 Bead, Dp = 0.0350*’
C. No. 7 Bead, Dp = 0.021S”
D. No. 10 Bead, Dp = 0.0132"
E. No. 13 Bead, Dp « 0.0060"
Variation of Heat Transfer Coefficient with Superficial 47
Mass Velocity (No. 7 Bead, Dp = 0.0218)
Variation of Heat Transfer Coefficient with Superficial 48
Mass Velocity at Constant Particle Diameter
Variation of Heat Transfer Coefficient with Particle
Diameter at Constant Superficial Mass Velocity 50
2
Figure Page No.
15. Heat Transfer Correlation, Stanton Number versus 52
Reynolds Number
.
16 Variation of Fraction Solids with Reynolds Number
at Constant Particle Diameter 54
17. Heat Transfer Correlation, Product of Stanton Number
and Fra'ction Solids versus Reynolds Number 55
18. Variation of Stanton Number with Fraction Solids at
Constant Reynolds Number 57
19. Final Heat Transfer Correlation, Product of Stanton
Number and the 1.3 Power of Fraction Solids versus
Reynolds Number 58
.
20 Test of Final Heat Transfer Correlation Incorporating
Data from the Literature 60
21. Variation of the Ratio DE/Dp with the Ratio 62
.
22 Variation of the Ratio GmaX/G with the Ratio ^3
LIST OF TABLES
Table I Physical Properties of Spherical Glass Beads 72
II Primary Heating Elements 73
III Secondary Heating Elements 74
IV Data Obtained in the Heat Transfer Unit 75
V Data Obtained in the Visual Unit 79
3
ACKNOWLEDGMENT
The author is deeply grateful to Dr. George Thodos whose guidance
and encouragement made possible the completion of this work* For
time, effort and ideas advanced, special acknowledgement is due Mr*
August H* P ritzlaff, J r., the w riterfs colleague in the construction
and operational phases of this effort*
4
SUMMARY
Heat transfer coefficients were evaluated in a system of spherical
solid particles fluidized in an air stream, the major controlled variables
being air through put and particle diameter* The fluidized beds were
screen supported in a copper tube 1*959 inches in diameter with heat
being transferred from these tube walls to the fluidizing gas* The
primary heat supply was from electrical resistance heaters with heat
loss minimized through use of a secondary electrical heat guard system.
The spherical beads used were of glass ranging in size from 0,0060 inches
in diameter to 0,04-37 inches and were suspended in air flowing at
superficial mass velocities ranging from 227 to 3780 pounds per hour
per square foot. Measured heat transfer coefficients varied between 7*8
and 63 B.t.u*/hour per square foot per degree Fahrenheit,
Assuming a relatively simple heat transfer mechanism, involving
a consideration of an actual mean velocity of air through the void
spaces of the fluidized bed and a transport of heat affected by the
movement of the individual particles, a form of representing heat
transfer data was proposed. The equational form recommended, representing
the data of these studies within an average deviation of 10$ is:
where:
N ^ « Stanton number, h/ CpGmax
N^e = Reynolds number, %GmaX/ ^
1- f a Fraction solids
h = Heat transfer coefficient, B ,t.u,/(hr0)(sq* ft,)(°F)