United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-98/029 April 1998
Project Summary
Heat Transfer Evaluation of
HFC-236fa In Condensation and
Evaporation
S.-M. Tzuoo and M.B. Pate
The shell-side heat transfer perfor-
mance of hydrofluorocarbon (HFC)-
236fa, which is considered to be a po-
tential substitute for chlorofluorocar-
bon (CFC)-114 in Navy shipboard chill-
ers, was evaluated in this study for
both conventional finned [1024- and
1575-fpm (fins-per-meter)] tubes and
high performance enhanced (Turbo-CII,
-B, and -Bll) tubes.
Condensation of oil-free HFC-236fa
was conducted on 1024- and 1575-fpm,
and Turbo-CII tubes. Pool boiling on
four tube types (1024- and 1575-fpm,
and Turbo-B and -Bll) was tested not
only for pure HFC-236fa but also for
HFC-236fa mixed with 1 and 3% lubri-
cant by weight. The polyolester lubri-
cant used has a viscosity 340 SSU at
37.8°C (100°F) and the trade name of
Castrol Icematic SW-68. The above
tubes, which have nominal outside di-
ameters of 19.1 mm (3/4-in.), were evalu-
ated at a saturation temperature of 40 C
for condensation and 2 C for pool boil-
ing over the heat flux range of 15 to 40
kW/m2.
Heat transfer was improved for
HFC-236fa by using the high perfor-
mance enhanced tubes. Specifically, the
Turbo-CII tube performed better than
the two conventional finned tubes in
condensation testing, while the perfor-
mance of the Turbo-B and -Bll tubes
was superior to the two conventional
finned tubes in pool boiling testing.
The maximum increase in heat
transfer coefficient for the Turbo-CII
tube was 80% relative to the 1024-fpm
tube and 70% relative to the 1575-fpm
tube, while for the Turbo-B tube, it was
0.7 and 1.2 times greater than for the
1024-and 1575-fpm tubes, respectively.
In addition, the Turbo-BII tube gave boil-
ing heat transfer coefficients up to 80%
larger than those of the Turbo-B tube.
The heat transfer performance of
HFC-236fa was compared with the CFC-
114 and HFC-236ea data obtained in
earlier studies using the same test fa-
cility. For all tube types tested, except
the Turbo-CII tube, the heat transfer
results showed that HFC-236fa per-
formed better than CFC-114 and HFC-
236ea during both shell-side conden-
sation and pool boiling. The heat trans-
fer coefficients for HFC-236fa during
condensation were up to 40% larger
than those for CFC-114 and up to 30%
larger than those for HFC-236ea, while
the pool boiling coefficients were up to
80% higher for HFC-236fa compared
with CFC-114 and up to 70% higher
compared with HFC-236ea. The con-
densation heat transfer coefficients for
the Turbo-CII tube were similar for both
HFC-236fa and -236ea; the deviation
was within 10%. The effects of com-
pressor oil on heat transfer perfor-
mance during pool boiling were inves-
tigated. The presence of up to 3% oil
(by weight) in HFC-236fa affected the
boiling performance by less than a 10%
deviation from the pure HFC-236fa re-
sults for all but one of the tubes tested.
The Turbo-BII tube, the only exception,
showed an increase in boiling coeffi-
cients of up to 30% over the pure-re-
frigerant values for the testing with 1%
oil and up to 15% with 3% oil.
This report was submitted by Iowa
State University under the sponsorship
of the U.S. Environmental Protection
Agency (EPA) with funding from the
EPA/Department of Defense/Department
of Energy Strategic Environmental Re-
-------
search and Development Program
(SERDP).
This Project Summary was devel-
oped by EPA's National Risk Manage-
ment Research Laboratory, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
This research evaluated the heat
transfer coefficients for HFC-236fa during
condensation and pool boiling on the out-
side of a single horizontal tube with a
nominal outside diameter of 19.1 mm (3/
4-in.). Two types of integral finned (1024-
and 1575-fpm) tubes and three types of
high performance enhanced (Turbo-CII, -
B, and -Bll) tubes were tested for the heat
transfer performance of HFC-236fa. Inte-
gral finned tubes tested are presently used
in Navy shipboard heat exchangers to en-
hance heat transfer, while three high per-
formance enhanced tubes, which were pro-
duced by advanced manufacturing tech-
niques, were tested to evaluate their po-
tential for improving the heat transfer per-
formance of chillers but have not yet been
used in shipboard chillers.
Saturated pool boiling was also in-
vestigated for HFC-236fa mixed with 1
and 3% oil by weight. A miscible
polyolester oil with a viscosity of 340 SSU
at 37.8°C was added to HFC-236fa, in
order to assess the effects of the oil's
presence on the boiling heat transfer per-
formance.
In addition, the comparative heat
transfer performance of HFC-236fa and -
236ea, and CFC-114 was made in order
to evaluate the possibility of replacing CFC-
114 with HFC-236fa. The first two refrig-
erants are non-ozone depleting alterna-
tives for CFC-114. Both CFC-114 and
HFC-236ea were tested earlier in the cur-
rent test facility.
Objectives and Scope
This study not only evaluated the
shell-side heat transfer coefficients of an
environmentally safe refrigerant, HFC-
236fa, during condensation and pool boil-
ing for two integral finned (1024- and 1575-
fpm) tubes and three high performance
enhanced (Turbo-CII, -B, and -Bll) tubes
but also compared the heat transfer per-
formance of the tubes tested with HFC-
236fa. In addition, the comparison of the
heat transfer coefficients for HFC-236fa
and -236ea and CFC-114 was also an
important objective, where HFC-236fa and
HFC-236ea are potential alternative re-
frigerants for CFC-114.
Using the same test facility which al-
lows analysis of condensation and pool
boiling, measurements were conducted on
a single-tube configuration at a saturation
temperature of 2°C for pool boiling and at
40°C for condensation over the heat flux
range of 15 to 40 kW/m2.
Two integral finned (1024- and 1575-
fpm) tubes were tested for both shell-side
condensation and pool boiling. In addi-
tion, the Turbo-CII tube, designed to en-
hance condensation, was tested during
shell-side condensation while the en-
hanced boiling Turbo-B and -Bll tubes
were tested in pool boiling.
The comparative heat transfer perfor-
mance of the high performance enhanced
tubes with the conventional finned tubes
was made for HFC-236fa in this study.
Heat transfer results for CFC-114 and
HFC-236ea and -236fa were also com-
pared with each other. CFC-114 and HFC-
236ea were tested previously in the same
test facility. In addition, the effects of oil in
the refrigerant on the heat transfer perfor-
mance during pool boiling were assessed
for HFC-236fa in this research.
The heat transfer coefficients for the
integral finned tubes were used as a
baseline for comparing the heat transfer
performance of the high performance en-
hanced tubes. All the tubes compared had
the same tube outside diameter of 19.1
mm (3/4-in.).
Experimental Apparatus
Even though the same test rig was
used in all the experiments, different ex-
perimental arrangements were required for
testing condensation and pool boiling. The
main components of the test facility in-
cluded the test section, tubes under test,
closed water loop, closed refrigerant loop,
glycol/water chiller, and data acquisition
system.
The heat transfer experiments were
performed in a cylindrical, stainless steel
chamber. On the top of the test section
are two ports which are passageways for
vapor. The test section also has two other
ports on the bottom to serve as liquid
paths.
The closed water loop consists mainly
of a storage tank, two triplex diaphragm
pumps, a flowmeter, an immersion heater,
and a dual-tube heat exchanger. The
heater and heat exchanger were used to
control the water temperature.
The glycol/water mixture was pumped
through a chiller with a 105-kW (30-ton)
cooling capacity and could be supplied
through manifolds to the dual-tube heat
exchanger, two condensers, and a
subcooler.
During condensation tests, a stain-
less steel boiler was used to vaporize
refrigerant before it reached the test sec-
tion. For evaporation tests, a subcooler
and two condensers were utilized to con-
dense refrigerant after it was boiled in the
test section.
Condensation Results
Heat transfer coefficients were ob-
tained for condensation of HFC-236fa on
three tube types— 1024- and 1575-fpm,
and Turbo-CII tubes. A comparison of re-
sults for these tubes with the previously
obtained results of CFC-114 and HFC-
236ea was made.
The best heat transfer performance
with HFC-236fa was provided by the high
performance Turbo-CII tube, indicating an
increase in heat transfer coefficients of
around 20 to 80% with respect to the
1024-fpm tube, and about 40 to 70% with
respect to the 1575-fpm tube.
The HFC-236fa performed better than
CFC-114 and HFC-236ea during conden-
sation for all the tube types tested except
the Turbo-CII tube. The HFC-236fa yielded
a maximum increase of 40% compared
with CFC-114 and 30% compared with
HFC-236ea. The condensation heat trans-
fer coefficients produced by the Turbo-CII
tube were similar for both HFC-236fa and
-236ea. Data were not taken on the Turbo-
CII tube with CFC-114.
Pool Boiling Results
Heat transfer coefficients on four tube
types (1024- and 1575-fpm, and Turbo-B
and -Bll) were determined for pool boiling
of HFC-236fa as well as HFC-236fa/oil
mixtures. The effects of oil and tube types
on the boiling heat transfer performance
of HFC-236fa were assessed. In addition,
comparison was also made for these test
tubes with the previous results of CFC-
114 and HFC-236ea in order to evaluate
the effects of refrigerant type on the boil-
ing performance.
The best heat transfer performance
with HFC-236fa was provided by the high
performance Turbo-BII tube with heat
transfer coefficients of around 2 to 2.9,
2.4 to 3.8, and 1.2 to 1.8 times the values
for the 1024- and 1575-fpm, and Turbo-B
tubes, respectively.
The HFC-236fa performed better than
CFC-114 and HFC-236ea during pool boil-
ing for all the tube types tested. The HFC-
236fa provided a maximum heat transfer
coefficient increase of 80% compared with
CFC-114 and 70% compared with HFC-
236ea.
The small amount of oil, up to 3%
concentration, present during pool boiling
was found to affect the heat transfer per-
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formance by less than 10% relative to the
pure HFC-236fa results for all but one of
the tubes tested. The exception was the
Turbo-BII tube. As noted, the Turbo-BII
tube showed the largest increase in per-
formance with a 30% enhancement at 1%
oil and a 15% enhancement at 3% oil
over the pure refrigerant value.
Summary
The heat transfer coefficients of HFC-
236fa, proposed as a CFC-114 substitute,
were measured for 1024- and 1575-fpm
conventional finned tubes and Turbo-CII,
-B, and -Bll high performance enhanced
tubes during shell-side condensation and
pool boiling on the outside of a single
horizontal tube. The high performance
enhanced tubes were found to effectively
increase heat transfer and produced higher
heat transfer coefficients than the
conventional finned tubes.
The Turbo-CII tube produced notice-
ably higher heat transfer coefficients in
condensation than the 1024- and 1575-
fpm tubes, and yielded around 1.2 to 1.8
times the values of the 1024-fpm tube
and 1.4 to 1.7 times those of the 1575-
fpm tube.
The pool boiling results for both pure
HFC-236fa and HFC-236fa with oil show
that the tube performance in descending
order was Turbo-BII and -B, and 1024-
and 1575-fpm tubes. Heat transfer coeffi-
cients for pure HFC-236fa provided by the
Turbo-B tube are 1.6 to 1.7 and 1.9 to 2.2
times those by the 1024- and 1575-fpm
tubes, respectively. The Turbo-BII tube
outperformed the other tubes tested and
produced 1.2 to 1.8 times the heat trans-
fer coefficients of the Turbo-B tube.
For the pool boiling testing, a mis-
cible polyolester oil with a viscosity of 340
SSU at 37.8°C was added to HFC-236fa.
The oil concentrations in the HFC-236fa
were 1 and 3% by weight. The oil effects
on HFC-236fa caused the boiling coeffi-
cients to deviate less than 10% from those
for the pure HFC-236fa tested with all the
tubes tested except the Turbo-BII tube.
Although the high performance Turbo-
BII tube produced the highest heat trans-
fer coefficients of all the tubes tested, it
showed larger changes in pool boiling per-
formance with the addition of oil. Specifi-
cally, the Turbo-BII tube had a 10 to 30%
increase at the 1% oil concentration over
the results for pure HFC-236fa and a 10%
decrease to 15% increase at the 3% oil
concentration.
A comparison of shell-side heat trans-
fer coefficients was made for CFC-114
and its two proposed alternative refriger-
ants; i.e., HFC-236fa and -236ea. In gen-
eral, HFC-236fa was found to have better
heat transfer performance than CFC-114
and HFC-236ea during both shell-side con-
densation and pool boiling. For condensa-
tion, HFC-236fa yielded a maximum in-
crease of 40% compared with CFC-114
and 30% compared with HFC-236ea. For
pool boiling, HFC-236fa provided a maxi-
mum increase of 80% compared with CFC-
114 and 70% compared with HFC-236ea.
Replacing CFC-114 with HFC-236fa
is desirable in terms of the heat transfer
performance based on the comparison of
CFC-114, and HFC-236ea and -236fa
made in this study. In addition, the high
performance enhanced tubes outper-
formed the finned tubes at all the testing
conditions in this research.
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S.-M. Tzuoo and M. B. Pate are with Iowa State University, Ames, IA 50011.
Theodore G. Brna is the EPA Project Officer (see below).
The complete report, entitled "Heat Transfer Evaluation ofHFC-236fa in Conden-
sation and Evaporation," (Order No. PB98-136203; Cost: $27.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-605-6000
The EPA Project Officer can be contacted at:
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT NO. G-35
EPA/600/SR-98/029
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