United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-98/033 April 1998
Project Summary
Heat Transfer Evaluation of
HFC-236ea with High
Performance Enhanced Tubes in
Condensation and Evaporation
S.-M. Tzuoo and M.B. Pate
This research evaluated the heat trans-
fer performance of pure hydrofluorocarbon
(HFC)-236ea for high performance en-
hanced tubes which had not been pre-
viously used in Navy shipboard chill-
ers. Shell-side heat transfer coefficient
data are presented for condensation
on a Turbo-CII tube, pool boiling on
Turbo-B and -Bll tubes, and spray
evaporation on Turbo-B and -CM tubes
and a 1575-fpm (1575-fins-per-meter)
tube. These tubes have nominal out-
side diameters of 19.1 mm (3/4-in.),
and they were evaluated at a satura-
tion temperature of 2%C (35.6%F) in
evaporation and 40%C (104%F) in con-
densation.
The condensation and pool boiling
results for the high performance en-
hanced tubes in this study were com-
pared with the results for a plain tube
and two integral finned tubes (1024-
and 1575-fpm tubes), which were evalu-
ated in an earlier study. The compari-
son shows that the high performance
enhanced tubes are able to promote
heat transfer processes better than the
plain tube, and especially better than
the integral finned tubes that are cur-
rently being used with chlorofluorocar-
bon (CFC)-114 in Navy shipboard chill-
ers. It was found that the Turbo-CII, -
Bll, and -B tubes performed best in
condensation, pool boiling, and spray
evaporation, respectively. The conden-
sation heat transfer coefficients for the
Turbo-CII tube were approximately 2
times those for the two integral finned
tubes and 5 to 10 times those for the
plain tube. During pool boiling, the
Turbo-BII tube provided 1.2 to 1.7 times
the heat transfer coefficients of the
Turbo-B tube, 1.7 times the values of
the 1024-fpm tube, 1.9 to 2.4 times the
values of the 1575-fpm tube, and 3
times the values of the plain tube. Dur-
ing spray evaporation, the Turbo-B tube
provided 1.2 times and 1.7 times the
heat transfer coefficients of the Turbo-
CII and the 1575-fpm tubes, respec-
tively.
The comparative heat transfer per-
formance of spray evaporation with
pool boiling was made by using Turbo-
B and 1575-fpm tubes. For the range of
liquid refrigerant feed rates evaluated,
the superiority of spray evaporation
over pool boiling was found to exist
only at low heat loads.
This report was submitted by Iowa
State University under the sponsorship
of the U.S. Environmental Protection
Agency (EPA) through the EPA/Depart-
ment of Defense/Department of Energy
Strategic Environmental Research and
Development Program (SERDP).
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Air Pollution Pre-
vention and Control Division, 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 trans-
fer performance of pure HFC-236ea dur-
ing condensation, pool boiling, and spray
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evaporation on the outside of high perfor-
mance enhanced tubes that had not pre-
viously been installed in Navy shipboard
heat exchangers. Specifically, shell-and-
tube heat exchangers in Navy shipboard
chillers currently use integral finned tubes
(1024- and 1575-fpm tubes) and CFC-
114 as the working refrigerant.
Since HFC-236ea is free of stratospheric
ozone depleting substances and consid-
ered as a prospective substitute for re-
placing CFC-114 that is harmful to the
ozone layer, an investigation was initiated
to determine the heat transfer performance
of HFC-236ea. In a previous study, Phase
I, the comparative heat transfer perfor-
mance of CFC-114 and HFC-236ea was
determined for a plain tube and two types
of conventional finned (1024- and 1575-
fpm) tubes.
The high performance enhanced tubes
evaluated in this research included Turbo-
Cll, -B, and -Bll tubes. The Turbo-CII tube
is commercially designed to enhance shell-
side condensation, while the Turbo-B and
-Bll tubes are commercially suggested for
use in nucleate boiling. None of these
tubes had been previously installed in ship-
board heat exchangers. The heat transfer
coefficients of HFC-236ea were measured
for condensation, pool boiling, and spray
evaporation occurring on the outside of a
single horizontal tube with a nominal out-
side diameter of 19.1 mm.
Objectives and Scope
The objective of this study was to deter-
mine the optimum tube types for shell-
side heat transfer of HFC-236ea during
condensation, pool boiling, and spray
evaporation. An additional objective was
to compare the heat transfer performance
for evaporation of HFC-236ea during pool
boiling and spray evaporation.
Three types of high performance en-
hanced tubes that had not been previ-
ously installed in shipboard chillers were
investigated: (1) a Turbo-CII tube in con-
densation testing as well as in spray
evaporation testing, (2) a Turbo-BII tube
in pool boiling tests, and (3) a Turbo-B
tube tested for both pool boiling and spray
evaporation. In addition to these high per-
formance enhanced tubes, a 1575-fpm
tube was also tested for spray evapora-
tion.
The results for the high performance
enhanced tubes in the study reported here
(Phase II) were compared with those for
the conventional finned tubes tested ear-
lier (Phase I). The comparative heat trans-
fer performance of HFC-236ea for spray
evaporation with pool boiling was also
made by using Turbo-B and 1575-fpm
tubes.
Measurements were conducted on a
single-tube setup at a refrigerant satura-
tion temperature of 2%C for both pool
boiling and spray evaporation and at 40%C
for condensation. The tested range of heat
fluxes was from 15 to 40 kW/m2for con-
densation and pool boiling, and 10 to 30
kW/m2for spray evaporation.
Experimental Apparatus
The experimental arrangements required
for testing condensation, pool boiling, and
spray evaporation are illustrated in Fig-
ures 1 through 3, respectively. The main
components of the test facility include the
test section, tubes under test, closed wa-
ter loop, closed refrigerant loop, glycol/
water chiller, and data acquisition system.
The heat transfer experiments were per-
formed in a cylindrical, stainless steel
chamber. On the top of the test section,
there are two ports which are passage-
ways for vapor and five threaded ports
where spray nozzles could be installed
with compression fittings for testing spray
evaporation. The test section also has the
two other ports which serve as liquid paths
on the bottom.
The closed water loop consists mainly
of a storage tank, two triplex diaphragm
-exs—r--
j--~-q->_
-o-a-
To chiller
T ) : Thermacouple
>M/ : Thermistor
^PJ : Pressure gage
J3J : Pressure transducer
I : Liquid v: Vapor
Sight glass
Test section f "";
fP
.-•T Filter 1
Closed
water
loop
Figure 1. Schematic of test facility for condensation tests.
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To chiller
T ) : Thermacouple
^~-~\
^M) : Thermistor
PJ : Pressure gage
DJ : Pressure transducer
I : Liquid v: Vapor
t
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pumps, a flow meter, 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 then supplied through
manifolds to the dual-tube heat exchanger,
two condensers, and a subcooler.
During condensation tests, a stainless
steel boiler was used to vaporize refriger-
ant before it reached the test section. For
evaporation tests, a subcooler and two
condensers were utilized to condense re-
frigerant after it was boiled in the test
section.
Results
The heat transfer performance of HFC-
236ea for high performance enhanced
tubes during condensation, pool boiling,
and spray evaporation was evaluated and
documented. Since these tube types have
not been employed in the Navy shipboard
chillers, the results obtained in this study
can be applied to the design of new chill-
ers. Using the results for integral finned
tubes reported previously (Phase I), the
heat transfer performance of high perfor-
mance tubes was also compared with that
of integral finned tubes.
For condensation of HFC-236ea at
40%C, the high performance tube, Turbo-
Cll, performed better than the plain tube
and the integral finned tubes which were
tested earlier (Phase I). The heat transfer
coefficients for the Turbo-CII tube were
approximately 2 times those for the inte-
gral finned tubes and 5 to 10 times those
for the plain tube.
For pool boiling of HFC-236ea at 2%C,
the pair of high performance tubes, the
Turbo-BII and -B tubes, provided higher
heat transfer performance than the plain
tube and integral finned tubes, which were
tested earlier (Phase I). The Turbo-BII tube
outperformed the other tube types tested
and provided 1.2 to 1.7 times the heat
transfer coefficients of the Turbo-B tube.
In turn, the Turbo-B tube yielded 1.1 to
1.3 times the heat transfer coefficients
than the 1024-fpm tube, 1.4 to 1.5 times
the values of the 1575-fpm tube, and 1.8
to 2.2 times the values of the plain tube.
For spray evaporation of HFC-236ea at
2%C, the Turbo-B tube performed better
than the 1575-fpm and Turbo-CII tubes.
The Turbo-B tube provided heat transfer
coefficients 1.1 to 1.2 times those of the
Turbo-CII tube, and 1.6 to 1.8 times the
values of the 1575-fpm tube. With increas-
ing heat flux, the heat transfer coefficient
in spray evaporation increased until the
heat flux reached around 15 kW/m2 and
then decreased with increasing heat flux
to 30 kW/m2.
Pool boiling and spray evaporation of
HFC-236ea were compared for 1575- fpm
and Turbo-B tubes. Generally, spray
evaporation provided higher heat transfer
below the heat flux of 30 kW/m2 com-
pared with pool boiling. At a heat flux of
15 kW/m2, the heat transfer coefficients
provided by the Turbo-B and 1575-fpm
tubes in spray evaporation were 2.3 times
and 1.2 times, respectively, the values in
pool boiling. At a heat flux of 30 kW/m2,
both of these tube types provided similar
heat transfer performance in these two
different heat transfer forms.
Summary
The results of the comparisons reported
here demonstrate that substantial in-
creases in heat transfer can be obtained
with the use of the high performance en-
hanced tubes compared to the plain tube
and conventional finned tubes (1024- and
1575-fpm tubes) that are presently used
with CFC-114 in Navy shipboard chillers.
The high performance Turbo-CII tube
outperformed the two integral finned tubes
during condensation testing; the heat trans-
fer coefficients for the Turbo-CII tube were
around twice those for the two integral
finned tubes.
The high performance Turbo-BII and -B
tubes outperformed the two integral finned
tubes during pool boiling. In particular, the
Turbo-BII tube outperformed the other
tubes tested and provided heat transfer
coefficients 1.2 to 1.7 times those of the
Turbo-B tube. In turn, the Turbo-B tube
yielded 1.1 to 1.3 times the heat transfer
coefficients of the 1024-fpm tube and 1.4
to 1.5 times the values of the 1575-fpm
tube.
During spray evaporation testing, the
Turbo-B tube provided higher heat trans-
fer coefficients than both the 1575-fpm
and Turbo-CII tubes. Specifically, the
Turbo-B tube gave 1.1 to 1.2 times the
heat transfer coefficients of the Turbo-CII
tube and 1.6 to 1.8 times the values of the
1575-fpm tube.
The comparative heat transfer perfor-
mance of spray evaporation with pool boil-
ing shows that the heat transfer superior-
ity of HFC-236ea for spray evaporation
over pool boiling exists only at heat fluxes
below about 30 kW/m2.
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S.-M. Tzuoo and M.B. Pate are with Iowa State University, Ames, I A 50011.
Theodore G. Brna is the EPA Project Officer (see below).
The complete report, entitled "Heat Transfer Evaluation ofHFC-236ea with High
Performance Enhanced Tubes in Condensation and Evaporation," (Order No.
PB98-137177; Cost: $29.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air Pollution Prevention and Control Division
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-98/033
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