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MECHANISM OF MOISTURE MOVEMENT IN THE
DRYING OF ORGANIC GRANULAR SOLIDS
by
Edward w. Jerger
A Dissertation Submitted to the
Graduate Faculty In Partial Fulfillment of
The Requirements for the Degree of
DOCTOR OF PHILOSOPHY
Major Subject: Theoretioal and Applied Mechanics
Approved:
In Charge ofMajor Work
(jieAd of Major Department
Dean of'Graduate College
Iowa State College
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UMI Number: DP13303
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TABLE OF CONTENTS
Page
INTRODUCTION............................................ 1
Definition of Drying............................... 1
Importance of Drying as a Unit Operation.......... 3
Theories of Drying................................. b
Drying schedule............................... 6
Constant rate period.......................... 9
Falling rate period........................... 13
Diffusion..................................... lb
Capillary flow................................ 16
Gravity....................................... 17
Convection.................................... 17
Porous flow theory............................ 17
Vaporization condensation theory............. 18
PSYCHROMETRIC RELATIONS................................. 19
Perfeot Mixtures................................... 19
Partial pressures............................. 20
Humidity........................................... 22
Dew point..................................... 22
Adiabatic saturation.......................... 22
Wet and dry bulb temperatures................ 25
The Psyohrometrlc Chart............................ 26
Barometric pressure correction for standard
pressure psychrometrio chart................ 26
THEORETICAL DEVELOPMENT................................. 30
Dimensional Analysis............................... 30
Analytical Analysis........... Jb
DESCRIPTION OF APPARATUS................................ bb
Air Conditioner.................................... bb
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Page
Steam humidifier. ............................ 44
Filters......................................... 47
Steam ooils..................................... 4?
Chilled water ooil ............... 48
Cooling ooil.............................. 48
Air washer...................................... 48
Fan............................................. 46
Drying Unit....................... 49
Electric heaters................................ 49
Drying cabinet.................................. 50
Instrumentation...................................... 50
Temperatures.................................... 50
Air flow........................................ 51
TE3TS AND PROCEDURE....................................... 52
Preparation of Samples............................... 52
Methods Used in Tests................................ 53
Accuracy of Measurements............................. 59
Calculations......................................... 6 0
SUMMARY OF RE3ULTS........................................ 62
CORRELATION AND INTERPRETATION OF EXPERIMENTAL WORK...... 71
Treatment of Soybean Data....................... 71
Illustrative Problem................................. 78
Treatment of Corn Data............................... 81
CONCLUSIONS............................................... 84
REFERENCES................................................ 85
ACKNOWLEDGMENT............................................ 86
APPENDIX.................................................. 87
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ABBREVIATIONS
atm atmospheres
om oentimeters
cfm cubic feet per minute
DS dry solid
fpm feet per minute
gin grams
hp horsepower
hr hours
in. inches
lb pound
psl pounds per square inch
psf pounds per square foot
sq ft square feet
sq cm square centimeters
rpm revolutions pe|> minute
°F temperature in degrees
°C temperature in degrees
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INTRODUCTION
Definition of Drying
In general, the term drying la loosely used to desorlbe a
process of liquid or vapor removal from solids, liquids, or
gases. Consequently, the term drying is often so misapplied
that the true significance of drying is confused. A rigorous
definition of drying would exclude many of the "so-called "
industrial drying applications.
Drying, then, is uniquely defined as the partial or com
plete removal of evaporable liquids from a mixture of the
liquid xtflth the solids, other liquids, or gases; by thermal
means. The inclusion of the restriction, "by thermal means,"
separates true drying from a meohanlcsl separation of liquids
from a mixture of the liquid with solids, other liquids, or
gases. Yet it is still difficult to distinguish between dry
ing and evaporation or distillation. In fact, there is only
a hair line difference between them, and it appears that the
difference is based merely on the nature of the equipment used
in eaoh process.
A striking example of the miJuse of the term drying is
illustrated in the Industrial reference to the drying of paints
and varnishes. Paints and varnishes (in accordance with the
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