United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-98/037 April 1998
Project Summary
Transport Property
Measurements of HFC-236ea
J.-Y. Lin and M.B. Pate
A candidate to replace 1,2-dichloro-
tetrafluoroethane (CFC-114) in surface
craft and submarine chiller units is
1,1,1,2,3,3-hexafluoropropane (HFC-
236ea). This study is an evaluation of
transport properties of HFC-236ea, with
liquid viscosity and thermal conductiv-
ity being the two main transport proper-
ties of interest. In addition, the specific
heat and density of refrigerant/lubricant
mixtures are also provided in this study.
This study used a novel method for
simultaneously measuring viscosity and
thermal conductivity by using inline
property sensors in series with a heat
transfer measurement system. Specifi-
cally, viscosity was measured with an
inline torsional oscillation viscometer,
while thermal conductivity was mea-
sured from the knowledge of single-
phase heat transfer characteristics of
a heated test-section.
The viscosity and thermal conductiv-
ity measurements for CFC-114 were
compared with American Society of
Heating, Refrigerating and Air-Condi-
tioning Engineers (ASHRAE) data, with
agreement being within ±5% for ther-
mal conductivity and ±2% for viscosity.
For HFC-236ea, the measured data
were compared with REFPROP, a theo-
retical prediction package developed by
the National Institute of Standards and
Technology ( NIST), with average devia-
tions being within +15% in thermal con-
ductivity and -5% in viscosity.
The properties of HFC-236ea mixed
with a lubricant (Castrol oil SW68) were
also investigated. The results showed
that thermal conductivity increased with
lubricant concentration at lower tem-
peratures, while it decreased slightly at
higher temperatures. However, at high
temperatures there was no significant
difference of thermal conductivity of
refrigerant/lubricant mixtures between
various lubricant concentrations. For the
viscosity of HFC-236ea and lubricant
mixtures, the results showed significant
increases at higher lubricant concen-
trations, especially at lower tempera-
ture ranges.
[This work was funded through the
U.S. Department of Defense's Strategic
Environmental Research and Develop-
ment 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 find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
HFC-236ea is a possible replacement
candidate for CFC-114. There are several
reasons that this refrigerant shows promise to
replace CFC-114. First, the thermophysical
properties were investigated and found to
be similar to those of CFC-114. Second,
according to simulation results, the perfor-
mance of HFC-236ea is similar to that of
CFC-114 which makes it attractive as a re-
placement refrigerant for surface craft or sub-
marine chiller refrigerant. The EPA, in
cooperation with the U.S. Navy, has also
shown that HFC-236ea would have other
favorable characteristics with respect to Navy
applications.
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Objective
The objective of this study was to mea-
sure the transport properties of HFC-236ea
with and without lubricant (Castrol oil SWB8),
using a new methodology. The transport
properties of particular interest are thermal
conductivity and viscosity, with density and
specific heat also being measured. Mea-
sured data for pure refrigerant were com-
pared with other theoretical data sources
such as REFPROP. The methodology was
verified, using the properties of CFC-114.
Scope
The scope of this study was:
• Design and construct a test rig for mea-
suring transport properties with empha-
sis on thermal conductivity based on
the knowledge of single-phase heat
transfer.
• Install a viscometer in series with a heat
transfer test-section for simultaneously
measuring viscosity and thermal con-
ductivity.
• Calibrate heat transfer and heat loss
characteristics of the test-section by us-
ing refrigerants of known properties.
• Verify the accuracy of viscometer with
fluids of known viscosity.
• Measure the viscosity and thermal con-
ductivity of CFC-114 and compare
them with ASHRAE standard hand-
book data.
• Measure the viscosity and thermal con-
ductivity of HFC-236ea and compare
them with theoretical prediction data (i.e.,
REFPROP).
• Measure the viscosity and thermal con-
ductivity of HFC-236ea with lubricant.
• Develop prediction equations from
measured properties.
In this study, density, D , and specific
heat, C , for the refrigerants of interest were
also measured and discussed.
Experimental Test Facility
The experimental test rig was established
for the purpose of measuring liquid trans-
port properties of pure refrigerants, refriger-
ant mixtures, and refrigerant/lubricant
mixtures. The approach used was a combi-
nation of commercially available sensors (in
the case of viscosity and density) in series
with an electrically heated and instrumented
test section. Convection heat transfer coeffi-
cients were measured in the electrically
heated test section and from these mea-
surements, thermal conductivity and specific
heat data were obtained.
The test-section was a 3/8-in. (0.95 cm)
inner diameter by 2-m long smooth copper
tube. The measured quantities were tube
wall temperature, inlet/outlet fluid tempera-
tures, absolute and differential pressures,
viscosity, and mass flow rate. To measure
heat transfer coefficients, temperature sen-
sors were installed at various points in the
test section. Specifically, 11 T-type thermo-
couples were installed on the outer wall of
the tube at equal distances of 0.2 m, start-
ing from the inlet point and ending at the
outlet point, along the 2-m long test section.
To get more average temperature mea-
surements at the inlet and outlet locations,
two additional thermocouples were placed
0.1 m from the inlet and the outlet points on
the outer tube wall. Moreover, one thermo-
couple was placed on the outer insulated
wall surface for measuring the temperature
there. Two resistance temperature detec-
tors (RTDs) were placed at the inlet and
outlet points of the test section to measure
the respective fluid temperatures. All ther-
mocouples and RTDs were calibrated to
±0.05°C.
Results and Discussion
This study used a new approach for si-
multaneously measuring several
thermophysical properties (e.g., thermal con-
ductivity, viscosity, specific heat, and den-
sity). This approach used single-phase
in-tube heat transfer knowledge to obtain
thermal conductivity. Viscosity was mea-
sured by a viscometer placed in-line with
the heat transfer test section. There are two
approaches: Approach 1, the Nusselt num-
ber (Nu) method; and Approach 2, the
Prandtl number (Pr) method. The uncer-
tainty analysis was presented in this study.
Approach 2 seems to have less uncertainty
than Approach 1, and inlet temperature, Tj,
and temperature differential, )T, do not sig-
nificantly affect the uncertainties. However,
the average temperature difference be-
tween the average wall temperature of the
test section and the average fluid tempera-
ture of the test section (/T^) is a significant
parameter that affects the uncertainties.
In Approach 1, the determination of a
calibration function (CF) by experiments
using fluids with known properties was
shown to be important for accurate thermal
conductivity measurements. Three Nu cor-
relations were used for calculating thermal
conductivity in this study, and they were
examined and discussed. Four refrigerants-
-HCFC-22, CFC-12, CFC-113, and CFC-
114-were used for calibration and verification
purposes which cover the Pr from 3 to 9
and Reynolds number based on diameter
D (Rep ) from 8,000 to 180,000. Based on
the calibration results, the CF functions were
found for three correlations examined in this
study. Approach 2 bypasses the Nu, and
thermal conductivity was found from Prwhich
is directly related to ReDand non-dimen-
sional temperature, )T. This approach was
shown to be more accurate and convenient
to use because less variables were in-
volved. A theoretical uncertainty analysis
also showed this approach to have less
uncertainty than Approach 1. The measured
results were also compared and discussed
for both approaches.
Viscosity was measured by a torsional
oscillation inline viscometer. The accuracy of
the viscosity measurement was verified with
CFC-113, CFC-12, and pure water and
shown to be within ±2% when compared
with the ASHRAE data. Other measured
properties including specific heat, density,
viscosity, and thermal conductivity were also
examined for CFC-114, compared with
ASHRAE data, and shown to be matched
closely to within ±5% for thermal conductiv-
ity, ±3% for specific heat, and ±1% for
density.
For HFC-236ea property measure-
ments, REFPROP-4.0 data were used as
a comparison with the measured data. The
deviations of measured properties from
REFPROP-4.0 are +4.8% for specific heat,
-5.0% for viscosity, ±1% for density, and
+ 15% for thermal conductivity.
A lubricant (Castrol oil SW68) was se-
lected to be mixed with HFC-236ea. Prop-
erties were measured for five lubricant
concentrations over a temperature range of
-10 to 60°C. Thermal conductivity effects
due to adding lubricant seemed to be more
significant at low temperatures than high tem-
peratures. For example, the thermal con-
ductivity was found to increase up to 40%
compared with the pure refrigerant at a low
temperature (-10°C), while this increase of
thermal conductivity was less than 8% at a
high temperature (60°C). Viscosity was
obviously affected by lubricant concentra-
tion, especially at a low temperature and
high lubricant concentration. It increased over
300% from the pure mixture at the low
temperature for a lubricant concentration of
11.6% while it increased less than 100% at
the high temperature. Curve fit equations
for both one variable (temperature) and two
variables (temperature and lubricant con-
centration) were provided for convenient
use. Other properties such as density, spe-
cific heat, thermal diffusivity, and Prwere
also determined.
Conclusions
Using the measuring method developed
in this study, viscosity and thermal conduc-
tivity data for CFC-114 were compared
with ASHRAE data with agreement being
within ±5% for thermal conductivity and ±2%
for viscosity.
For HFC-236ea property measure-
ments, REFPROP-4.0 data were used as
a comparison with the measured data. The
deviations of measured properties from
REFPROP-4.0 are +4.8% for specific heat,
-5.0% for viscosity, ±1% for density, and
+ 15% for thermal conductivity.
Viscosity and thermal conductivity mea-
surements were affected by lubricant addi
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tion to HFC-236ea, especially at low tem-
peratures and high lubricant concentrations.
At the low temperature (-10°C) for example,
viscosity increased less than 50% as oil
was added to the pure refrigerant to a lubri-
cant concentration of 7.4%, while it increased
about 100% at the high temperature (50°C)
for the same mixture concentration change.
It should also be noted that the viscosity at
the lower temperature was about triple that
at the higher temperature for the pure refrig-
erant. At the mixture concentration with 7.4%
(by mass) oil, the viscosity at the lower
temperature was nearly quadruple that at
the higher temperature. Thermal conductiv-
ity decreases at a temperature of 50°C
while thermal conductivity at -10°C increases
as the mixture changes from a pure refriger-
ant to one having 7.4% oil.
J.-Y. Lin 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 "Transport Property Measurements of HFC-236ea,"
(Order No. PB98-137185; Cost: $44.00, subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
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
CenterforEnvironmental 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-98/037
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