,OILING
HEAT
TRANSFER
r
John
C.
Chen
$&*
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.
rooh haven
~ational Laboratory
\
Upton,
New
Yor
December
26.
1962
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A
CORRELATION
FOR
BOILING
HEAT
TRANSFER
TO
SATURATED
FLUIDS
IN
CONVECTIVE
FLOW
..John
C.
Chen
PBSTRACT
An
additive mechanism of micro- and macro-convective heat
'transfer was formulated to represent boiling heat transfer
with net vapor generation to saturated,' non-metallic
'flui'ds
in convective.flow. The final equations are:
.
h
=
rnic
h= h
+h
mic
mac
The second equation
will
be recognized as the Dittus-Boelter
equation
yith the additional factor
F.
The two functions F
j.
and
S
are defined as
where
ke
is
the effective Reynolds number for the two-phase
fluid and
AT
is
'the effective superheat for bubble growth. F
e
and
S
were obtained as functions of the Martinelli parameter
and the two-phase Reynolds
number, respectively.
The correlation was tested with available data: for water
and .organic fluids. Data from different sources which could
not be satisfactorily
.
.
correlated by existing correlations were
shown to be quite well correlated by the one presently proposed.
The average deviation between calculated and measured boiling
coefficients for all data points from nine experimental cases
was
211%.
Brookhaven National Laboratory, Upton,
N.
Y.
.
Introduction
It
has become almost a tradition that any paper dealing
with the
sdject
of boiling heat transfer should start by
.
'
recognizing 'the complexity of the phenomenon.
This complex-
ity
is
especially evident in the case of convective boiling
with net generation of vapor. Under these condition, the
heat transfer is effected
by
the
various
flow parameters
and
the vapor quality as well as by the parameters which are per-
,'tinent in pool boiling. Figure la illustrates
the
wide range
of local conditions and different flow regimes which could
exist along the length of a boiler for such a case. Figure
.
1b.illustrates typical fluid and wall temperature profiles'
corresponding to these various flow regimes. In the sub-
.'
cooled region, both the fluid and the wall temperatures in-
. .
'
crease as the liquid gains sensible heat.
At
the point where
nucleate boiling starts, the wall temperature begins to de-
crease. The fluid temperature continues to increase until
.it
reaches
its
saturation value, from which point on,
it
de-
creases gradually corresponding to the decreasing pressure.
As
the fluid progresses into the annular flow regime with
continuously increasing vapor qualities,
it
is
seen that the
wall temperature decreases, reflecting an increasing heat
transfer coefficient. This condition often exists into the
'
fog-flow region. Finally, liquid deficiency occurs and there
is
a sudden decrease in the heat transfer coefficient with
a
corresponding
rise
in the wall temperature.
In view of the widely different conditions that could
exist at various points along a boiler,
it
is
this author's
opinion that
it
,would be entirely unprofitable either to meas-
ure over-all
"average"'coefficients or to attempt to corre-
late them. The only hope of obtaining results which can be