Table Of ContentA STUDY OF THE HEAT TRANSFER BETWEEN A FALLING
DROP OF LIQUID AND A RISING STREAM OF GAS
A Thesis
Presented to
the Faculty of the Department of Chemical Engineering
The University of Southern California
In Partial Fulfillment
of the Requirements for the Degree
Master of Science in Chemical Engineering
by
Charles T. Foy
January 1950
UMI Number: EP41725
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This thesis, written by
Charles Terrance Foy
under the guidance of hT.?.... Faculty Committee,
and approved by all its members, has been
presented to and accepted by the Council on
Graduate Study and Research in partial fulfill
ment of the requirements for the degree of
Master of Science in
Chemical Engineering
Date..
Faculty Committee
Chairman
TABLE OF CONTENTS
CHAPTER PAGE
I. THE PROBLEM AND DEFINITIONS OF TERMS USED. . . . 1
The problem................................. 1
Statement of the problem ........ 1
Importance of the study.................... 1
Nomenclature and definitions of terms used , . 2
Thesis organization. . . . ............ . . . 2
II. REVIEW OF THE LITERATURE 3 .
Limitations of previous study................ 4
III.. EQUIPMENT AND EXPERIMENTAL PROCEDURE ......... 5
Apparatus ................... 5
Materials................. 8
Experimental procedure ..................... 9
IV. EXPERIMENTAL RESULTS......................... 12
Heat balances............................... 12
Correlation of the data............... 15
V. SUMMARY AND CONCLUSIONS....................... 24
Summary..................................... 24
Discussion................................. 24
Conclusions................................. 27
BIBLIOGRAPHY..................... 28
APPENDIX A. ORIGINAL DATA................... 30
APPENDIX B. SAMPLE CALCULATIONS................... 39
APPENDIX C. SAMPLE DESIGN CALCULATIONS............. 46
CHAPTER I
THE PROBLEM AND DEFINITIONS OF TERMS USED
For quite- sometime engineers in the field of heat
transfer have been faced with the problem of heating gases.
The problem has always presented a great deal of difficulty
because of the low coefficients obtained when attempting to
transfer heat to or from a gaseous medium. Since these co
efficients are so small, large heat transfer areas are re
quired for this service. These large exchangers cost a
great deal of money. Hence engineers have attempted in
various ways to reduce the size of these exchangers YriLthout
reducing their efficiency. A notable example of this is
the finned-tube units.
THE PROBLEM
Statement of the problem. It was the purpose of this
investigation (l) to construct an apparatus to study the
heat transfer between a falling drop of liquid and a rising
stream of gas, (2) to correlate the data collected on the
apparatus, and (3) to obtain heat transfer coefficients for
the design of heat exchangers.
Importance of the study. Except in large installa
tions, no effort is made to utilize the sensible heat of hot
gases for the BTU content alone. The extremely low heat
transfer coefficients obtained in gas to liquid or gas to
gas exchangers makes it economically unsound to do so.
Therefore vast amounts of heat are wasted by industry.
An exchanger of the type proposed herein makes re
covery of this heat more feasible. This- might result in a
substantial saving of fuel.
nomenclature and definitions of terms used. The
nomenclature and definitions will conform to the standard
system of Nomenclature for Chemical Engineering Unit Oper
ations as defined in the Transactions of the American Insti
tute of Chemical Engineer s,-*- except as noted.
Thesis organization. The first chapter.will cover
the problem and the definitions of the terms used. There
will be four other chapters. The second chapter will be a
review of the literature. The third chapter will cover the
experimental work with a description of the apparatus and
the method of its utilization. Chapter four will contain
the experimental results. Finally, chapter five will con
tain the summary and conclusions.
"Standard System of Nomenclature for Chemical En
gineering Unit Operations," Transactions of the American In
stitute of Chemical Engineers. 40:251-67 X1944- ) •
CHAPTER II
REVIEW OF THE LITERATURE
A review of the literature indicated that a great
deal of research has been done in the phase of the heat
transmission field which concerns itself with the transfer
of heat between gases and liquids. The greatest amount of
work has been on heat transfer through metal surfaces where
the liquid and gas do not come into contact with each other.
Also, a considerable number of articles have been written
on the subject of simultaneous heat and mass transfer. In
this case the liquid and the gas are in direct contact with
each other. The problem is complicated, however, by the
fact that this simultaneous transfer is taking place. Al
though an exhaustive search of the literature was made, no
articles could be found on the subject of heat transfer be
tween liquids and gases in direct contact with each other,
and where the vapor pressure of the liquid was sufficiently
low to insure negligible simultaneous mass transfer.
One article was found, however, where the transfer of
heat was studied betv/een gases and streamlined solids having
the same shape as a falling drop of liquid. This investi
gation was carried out by Hughes'and Coy.^ They tested in
p
J. A. Hughes and E. Coy, !,0n the Cooling of Cylinders
in a Stream of Air," Philosophical Magazine. (6) 31:118, 1916.
a wind tunnel a steamheated copper model having a stream
lined contour similar to that of a tear drop. The inlet and
exit air temperatures were measured and the gas film heat
transfer coefficients were calculated over a wide range of
air velocities. Their data was correlated by plotting
ht% vs on log—log paper. De is the effective diameter,
equal to the total perimeter divided by If . It was found
that lower coefficients were obtained v/hen the model was
reversed so that the air approached the pointed end of the
tear.
LIMITATIONS OF PREVIOUS STUDY
The greatest limitation of this study by Hughes and
Coy3 is that it only holds true for metal streamline shapes.
The results of the investigation presented herewith indicate
that their correlation cannot be used to compute gas film
coefficients when liquid droplets are employed. In the
latter case, higher coefficients were obtained due to the
violent mixing of the liquid in the droplet.
3
J. A. Hughes and E. Coy, loc. cit.
CHAPTER III
EQUIPMENT AND EXPERIMENTAL PROCEDURE
APPARATUS
The equipment used in this investigation is shown in
Figure 1. It consisted essentially of a drop forming mecha
nism, an enclosed space through which the liquid droplets fell
counter-current to the rising stream of gas, and a liquid
reservoir. Details of the drop forming mechanism are shown
in Figure 2.
The liquid from the reservoir was pumped through a
one-half inch iron pipe directly to the drop forming mechanism
where it flowed through the small stainless steel capillary
tubes, 0.05 inch O.D. The liquid emerged from these tubes
in the form of droplets. Within the drop forming mechanism,
the liquid was kept at a constant level by using an overflow
pipe, thus insuring a constant rate of flow.
The droplets fell through a six inch diameter stove
pipe lagged with one sixteenth inch asbestos. The height of
the column could be varied by adding or subtracting sections
of pipe. The bottom of the column tapered to one inch in
diameter and, at this point, the exit temperature of the
droplets was measured by a calibrated thermometer. Approxi
mately six inches above the tapered section, a trough was
6
Thermometer-; exitgas
Thermometer} fa Jet h<fo/<t-
Drop forming mechanism
V / ,y
6 Store pipe - asbestos tagging
'-fayt/icL oferf/ow /me
7roi/y/7 to catch /ipaicf running
e/oxrn the inflate of the store /npe
Gas distributor
tine used to frteasure
A ig u/ct through mput
VvV AAAI S/ectr/c heaters
f/yare /
Fxper/ mental Apparatus
