Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO91/09089 PCT/US90/06996
Is ':`2~
AZEOTROPE-LIKE COMPOSITIONS OF
1,1,1,2-TETRAFLUOROETHANE ~ND l~l-DIFLVOROETH~NE
FIELD OF THE INVENTION `
This invention ~elate6 to azeotrope-like
compo~ition6 of 1,1,1,2-tetrafluocoethane and
l,l-difluocoethane. The~e mixture~ a~e u~eful a6
10 cefrigerant~ for heatinq and cooling applications.
.
BACKGROUND OF THE ~NVENTION
Fluorocarbon ba6ed fluids have found widespread u6e
15 in indu6try for ce~rigeration, air conditioning and heat
pump application6.
Vapoc compres6ion is one focm o refrigecation. In
its simple6t ocm, vapoc compce6sion involve6 changing the
20 cefrigecant rom the liquid to the vapoc phase through
heat ab60rption at a low pre6suce and then from the vapoe
to the liquid pha~e theough heat removal at an elevated
pre6~uce. Fie6t, the refrigerant is vaporized in the
evaporator whlch i6 ln contact with the body to be
25 cooled. The pre66ure in the evapocatoc i6 6uch that the
boiling point o the cefrigerant i6 below the te~pecatuce
o the body to be cooled. Thu6, heat flow6 com the body
to the rerigerant and cau~e6 the refrigerant to
vaporize. The vapoc ormed i6 then removed by means Of a
30 compressoe in order to maintain the low pre~sure in the
evaporator. The temperature and pressure of the vapoc ace
then cai6ed thcough the addition of mechanical energy by
the compeessoc. The high ece6sure vapor then pas6es to
the condenser whereupon heat exchange6 with a
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cooler medium. The 6en5ible and latent heats are
removed with subsequent conden~ation. The hot liquid
ref~igerant then pas6e6 to the expansion valve and i6
ready to cycle again.
~ hile the prlmary purpo6e of refrigeration i~ to
remove energy at low temperature, the primary purpose
of a heat pump i5 to add energy at higher temperature.
Heat pumps are considered reverse cycle 6ystem~ becau~e
for heating, the operation of the conden6er is
interchanged with that of the refrigeration evaporator.
Certain chloro~luorocarbons have gained
widespread use in refrigeration applications including
air conditioning and heat pump applications owing to
their unique combination of chemical and phy~ical
propertie~. The ~ajocity oS ce~rigecants utilized in
vapoc compces~ion ~ystem~ are eithec single component
fluid~ or azeotcopic mixtuce~. Single component ~luids
and azeotropic mixtures are chacacterized a~
con6tant-boiling because they exhibit isothermal and
isobaric evaporation and conden6ation. The u~e of
azeotropic mixtures as ref rigerantB ifl ~nown in the
art. See, ~or example, R.C. Downing, "Fluorocacbon
2 Refrigerants Handbook", pp. 139-15~, Prentice-HalI,
198B, and U.S. Patents 2,101,993 and 2,641,579.
Azootropic or azeotcope-like compo~ition~ are
desired because they qo not ~ractionate upon boiling or
30 evaQoration. This behavior iB desirable becau~e in the
pre~iou~ly desccibed vapor compre~sion equipment with
~hich the~e refrigerants are e~ployed, condensed
material is generated in preparation for cooling or for
heating purpoae~, and unless the refrigerant
35 compo~ition i~ constant boiling, i.e. i6 azeotrope-
like, fractionation and ~egregation will occur upo~
evaporation and condensation and undesirable
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refrigerant distribution may act to upser the cooling
or heatinq.
Non-azeotropic mixture~ have been di6clo6ed a6
refrigerants, se2, e.g., U.S. Patent 4,303,536, but
have not ~ound widespcead u6e in comme~cial
application6 even though the ability of non-azeotropic
refeigerant blends to exhibit improved thermodynamic
performance ha6 often been di6cu66ed in the literature.
See, e.g., T. Atwood, "NARBS - The Promise and the
Proble~", American Society o ~echanical Engineers,
Winter Annual Meetin~, paper 86-WA/HT-61, 19a6 and ~.O.
Mc~inden et al., 'l~ethods for Comparing the Performance
of Pure and Mixed Refrigerants in the Vapo~ Comp~e~sion
Cycle", Int. J. Refri~. 10, 31B (19~7). Becau6e
non-azeotropic miKtures may fcactionate dueing the
refcigeration cycle, they ~equire ceetain hardwa~e
change~. The added difficulty in changing and
6ervicing refrigeeation equipment i8 the pcimary ceason
that non-azeotropic mixtures have been avoided. The
situation i~ further complicated if an inadvertent leak
in the ~yste~ occurs during such use or service. The
composition of the mix~ure could change, affecting
system peessures and system performance. Thu~, if one
component of the non-azeotropic mixture i8 ~lammable,
fractionation could shift the composition into the
fla~able region with potentially adver~e con~equence6.
Tho art is continually seeking new fluorocarbon
based azeotrope-like mixtuces which offer alternatives
for refrigeration and heat pump applications.
~urrently, envieonmentally acceptable
Sluorocarbon-base~ refrigerants ace of particular
interest becau~e the fully halogenated
chlorofluorocarbons have been implicated in cau~ing
environmental peoblems associated with the depletion of
the earth~s protective ozone
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làyer. Mathematical model~ have sub6tantiated that
hydrofluorocarbons like 1,1,1,2-tet~afluoroethane
~HFC-134a) and l.L-difluoroethane ~HFC-152a), will not
adver~ely affect atmo~pheric chemistry becau~e their
contribution to 6tratospheric ozone depletion and
global warming in compari~on to the fully halogenated
specie~ is negligible.
The substitute materials must alBo po6~e88 those
propertie6 unique to the CFC's including chemical
~tability, low toxicity, non-fla~mability, and
efficiency in-u~a. The latter characteri6tic i8
important, for example, in refrigeration applications
like air conditioning where a 10BB in refrigerant
thermodynamic performance or energy efficiency ~ay
produce secondary environmental effects due to
incceaBed fos8il fuel u~age arising from an increased
de~and for electrical energy, Furthecmore, the ideal
CFC cefrigerant substitutQ would not require major
engineering changes to conrentional vapor compres~ion
technology current}y used with CFC cefrigerants.
It i~ accordingly an object of this invention to
provide novel azeotrope-like compositions based on
l,l,l,Z-tetrafluoroethane and l,l-difluoroethane whic~
25 are useful in cooling and heating applications.
Another object of the invention iB to provide
novel environmentally acceptable ce~rigerants for use
30 in the a~or-mentloned application~.
Other ob3ects and advantages of the invention
will become apparent trom the following description.
SUMMAaY OP THE INVPNTION
The invention relates to novel environmentally
acceptable azeotrope-like compositions of
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WO91/09089 PCT/US90/06996
.
1,1,1,2-tetrafluoroethane and L,l-difluoroethane which
are u~eful in heating and cefrige~ation application6.
DESCRIPTION OF THE INVENTION
In accordance with the invention, novel
azaotrope-like compo~ition6 have been discovered
compri~ing 1.1,1,2-tetrafluocoethane and
l,l-difluocoethane. The azeot~ope-like compo~ition~
comprise from about 5 to about 90 weight percent
1,1,1,2-tetrafluoroethane and from about 10 to about 95
weight percent l,l-difluoroethane and have a vapor
pre~sure of about 76 p6ia ~ 5 p6ia at 20C. These
compo6itions a~e azeotrope-like because they exhibit
e66entially con~ta~t vapor pre66ure ver~u6 compo6ition
and e66entially identical liquid and vapor compositions
ove~ the aforementioned ~ange6.
In a pceferred embodiment of the invention, 6uch
azeotrope-like compo6ition6 compei6e from about 40 to
about 85 weight percent l,l,L,Z-tetrafluoroethane and
from about 15 to about 60 veight peccent 1,1-
difluoroethane and have a vapor pre66uce of 76 p6ia , 3
p6ia at ZOC.
Vapor pha~e co~po~ition6 containing in exces~ of
about 80 weight peecent 1,1,1,2-tetrafluoroethane were
detormined to be nonflammable in aic at ambient
cond~tions uring the Bureau of Mine~ - ~tyle eudiomete~
apparatus. ~ ",
The azeotcope-like compo6ition6 of thi~
invention, co~pri6ed of HFC-152a ant HFC 134a, do not
~egregate. In addition, they exhibit a number of
advantage~ over dichlorodifluoromet~àne (CFC-12),
HFC-134, and HFC-152a. Foc example, the azeotrope-like
mixture6 are non-flammable above 80 veight percent
HFC-134a the~eby teducing the hazard of explo~ion
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WO91/09089
PCT/US9~/06996
; 2~695Q9 6
which mi~ht occur if flammable HFC-152a vapor6 were
u6ed, stored, or handled in pu~e ~orm.
The~e azeotrope-like mixtures al50 exhibit zero
ozone depletion potential and low atmo6pheric lifetime
hence they contribute negligibly to the greenhou6e
warming effect. This i6 contra6ted with the hiqh ~zone
depletion potential and corre6pondinqly high greenhouse
warming potential of CFC-L2.
The energy efficiency and co~liny capacity of
the azeotrope-like compo6ition6 of the invention are
superior to tho6e of pure HFC-134a and, in addition,
the 134a~152a compo6ition6 provide 6ignificantly
reduced direct and indirect gceenhou6e warming
potential ove~ puce HFC-134a,
The azeotroeic compo6ition6 of thi6 invention
uniquely pos6es6 all o~ the desireable featuces of an
ideal eef rigerant i,e,, safe eo use, non-flammable,
zero ozone depletion potential, negligible greenhouse
warming effect, and attractive energy/cooling
perfocmance compared to the mo6t relevant pure
eluoromethane or fluocoethane ~luid6; i.e.,
fluococarbon refcigerants boiling between -19 C and
-30 C (this range repre~ents the boiling point range
for the majority of currently u~ed air conditioning and
refrigecant working Sluids), In summary, when
HFC-15Za/HPC-134a are combined in ef~ective amounts, a
non-flammable, non-segregating, envi~onmentally
acceptable azeotrope-like refrigerant having impcoved
thecmodynamic performance re6ult6.
The ter~ ~azeotrope-likel~ i6 u6ed herein for
mixtures of the invention because in the claimed
Proeortion6~ the comeo6ition~ of
1,1,1,2-tetrafluoethane and 1,1-difluoroethane are
con6tant boiling oc es6entially con6tant boilinq. All
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. _7~ ' 2~ 9
compo6ition~ within the indicated range~, a~ well as
certain compo6itionE outside the indicated ~anges, are
azeotrope-like, as de~ined moce pa~ticularly below.
From fundamental pcinciple~, the thermodynamic
state of a fluid i~ defined by four variables:
pre66ure, temperature, liquid compo~ition, and vapor
compo6ition, or P-T-~-Y, respectively. An azeotrope is
a unique chaeacteri6tic of a sy6tem of two Qr more
component6 where X and Y a~e equal at a 6tated P and
T. In p~actice thi6 mean6 that the CompQnent6 cannot
be 6eparated during a phase change, and therefore are
u6e~ul in the cooling and heating application~
de6ccibed above.
For the purpo~e6 of thi~ di6cus6ion, by
azeotrope-like compo6ition i~ intended to mean that the
compo6ition behave~ like a true azeot~ope in tecms of
thi6 con6tant boiling chacacteri6tics or tendency not
to ~ractionate upon boiling o~ evaporation. Thu6, in
such 6y6tems, the co~po6ition o~ the vapor formed
during the evaporation is identical or sub6tantially
identical to the oriqinal liquid composition. Hence,
during boiling or evaporation, the li~uid compo6ition,
25 if it changes at all, change~ only slightly. Thi~ i~
contrasted ~ith non-azeotrope-like composition~ in
- ~hich the liquid and vapor compositions change
sub~tantially during evaporation or condensation.
I~ the vapor and 11quid phases have identical
compositions, then it can be ~hown, on a rigocous
thecmodynamic ba~is, that the boiling point ver~us
composition curve pas6es through an absolute maximum or
an absoluto minimum at thi~ compo~ition. If one of the
35 t~o conditions, identical liquid and vapor compo~ition6
or a minimum or ma%imum boiling point, are shown to
eXi6t, then the sy~tem i5 an azeotrope, and the other
condition mu6t ~ollow.
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WO91/09089 PCT/US90/06996
2~599 -8- ~
One way to determine whether a candidate mixtuce
i8 aze`otrope-like within the meaning o~ thi6 invention,
is to d}still a 6ample thereo~ undec conditions ~i.e.,
resolution - numbec of plate6) which would be expected
to separate the mixture into it6 sepa~ate components.
If the mixture i~ non-azeotrope or non-azeotrope-like,
the mixture will fractionate, i.e., ~eparate into it~
va~ious components with the lowest boiling component
distilling of~ first, and 60 on. If the mixture is
azeotrope-like, 60me finite amount of the ~irst
distillation cut will be obtained which contains all of
the mixture component6 and which i~ con6tant boiling or
behaves as a single sub6tance. This phenomenon cannot
occur if the mixture i6 not azeotrope-like, i.e., it i5
l not part of an azeotrope 6ystem.
It follows from the above that another
characteri6tic o~ azeotrope-liko compo6ition6 i6 that
thece i6 a range of compo~itions containing the sa~e
component6 in vacying proportions which are azeotrope-
like. All such compo6itions ace intended to be covered
by the term azeotrope-like as u6ed herein. A6 an
example, it i3 well known that at different pres6ure6
tha composition of a given azeotrope will vary at least
slightly as does the boiling point of the compo6ition.
Thus, an azeotrope of A and B repre~ents a unique type
of relationship but with a variable compo~ition
depending on the temperature and/or pressure. A~ i~
readily under~tood by persons skilled in the art, the
boiling point of an azeotrope will vary with the
pre6~ure.
In one proces~ embodiment of the invention, the
azeotrope-like co~po~ition~ of the invention may be
35 uset in a method for producing cooling which compri6e~
condensinq a cefrigerant compci~ing the azeotrope-like
compo6ition~ and thecea~ter evaporating the re~rigerant
in the vicinity of the body to be cooled.
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In anothe~ proce~6 embodiment of the invention,
the azeotrope-like compo6ition~ of the invention may be
used in a method ~o~ producing heating which utilize6
conden~ing a refcige~ant in the vicinity of the body to
be heated and thereafte~ evaporarlng the cef~igecant.
Fo~ pucpo6e~ of thi6 application, the proce66
embodiments for producing cooling or heatin~, discu66ed
above, will gene~ally be referred to a~ heat exchange
applications.
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The L,1,1,2-tetcafluoroethane and
l,l-difluoroethane component6 of the novel
azeotrope-like compo6ition6 of the invention are known
matecial~. prefecably they 6hould be u~ed in
sufficiently high purity ~o as to avoid the
intcoduction of advec6e influences upon the constant
boiling propeetie~ of the 6ystem.
It 6hould be unter~tood that the pce6ent
20 compo6ition6 may include additional components 60 as to
form new azeot~ope-like composition6. Any such
compo6itions a~e considered to be within the 6cope of
the pcesent invention as long a6 the compo6itions ace
es6entially constant boiling and contain all the
25 e~sential components de~ceibed herein.
In attition, the azeotrope-like compo6itions of
tho invention may include components which may not form
new azeotrope-like composition~. In paeticular,
lubcicants like those discussed in U.S. Patent
4,755,316 may be adaed without depatting f~om the 6cope
of the invention..
35The pce~ent invention i5 mo~e fully illustrated
by the following non-limiting Examples.
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W091/09089
PCT/~S90/06996
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E~AMPLE 1
This example show6 that certain compositi~ns of
1,L,1,2-tetra~luo~oeehane and l,l-difluoroethane a~e
a~eotrope-li~e, i.e., exhibit es6entially identical
liquid and vapo~ composition6, and are con6tant
boiling, i.e., exhibit e6sentially constant vapo~
p~e66ure ver~us compo6ition within thi~ canqe.
Vapoe liquid equilib~ium expeeiments were
pe~formed by p~eparing mixture6 o~ ~FC-134a and
HFC-152a in an appeoximately 150 cubic centimeter
ve6sel. The ve~sel, equipped with a magnetically
driven stirrer and a 0-300 psia pres6ure transducer
accurate to + 0.2%, was submerged in a constant
temperature bath controlled to within + 0.02C. Once
thermal equilibrium was attained, as deteemined by
con~tant vapoe peessure ceadings, vapor and liquid
6amples weee withdra~n ~com th~ ve6sel and analyzed by
standaed gas chromatographic technique6. Thi~
procedure wa6 repeated at three nominal composition6 o~
approximately 25, 50 and 70 mole peccent HFC-134a in
HFC-152a, and at threo tempecaturea, -20, 20 and 60C.
Table I sum~ari2e~ tho results of these expeeiments.
T~e data ~hown in Table I inticate that the
vapor and liquid compo~itions aro essentially identical
within tho eYpoci~ental uncectainty of + 2.0 weight
percent unit a~ociated with the chromatographic
analy~is. The ~apor pce66uce data measured at -20C
show a minimum vorsus composition wbich is evidence o~
azeotropic behavior. Tho vapor pees~ures of the blends
are essentially con6tant to within + 5 psia ove~ the
composition range from aboue 5 to about 90 weight
percent HFC-134a and ~ro~ about ~0 to about 95 weight
percent HFC-152a~ that i6, these blends are constant
boiling oe az-oteope-like.
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WO91/89089 PCT/US90/06996
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EXAMPLE 2 2
This example show6 that azeotrope-like
HFC-134a/HFC-L52a blends have certain pec~ocmance
advantage6 when compared to FC-134a alone.
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The perfo~mance of a ref~igerant at specific
operating condition6 can be mea6ured by the coefficient
of performance and the capacity of the refriqerant.
The coefficient of perfocmance, COP, i~ a unive~sally
accepted measure, e~pecially u6eful in repce6enting the
relative thermodynamic efficiency of a refrigerant in a
6pecific heating or cooling cycle involving evaporaeion
1 5 'S~
HFC-13~-/H~C-lS2- V~por Llquid tqulllbrl~ D-t~
T~np~r~tur~ ~quid Co~po~tion~ V-po~ Compo~ition* V~por Prossuro
20(~C)~t. S H~C-13~) (~t. ~ HFC-13~) (p8i~
-20.0 0.0 0.0 17~8
-20.0 36.0 35.9 17.1
-20.0 6~.1 63.~ 17.2
-20.2 77.~ ~9.5 17.7
-20.0 100.0 100.0 19.3
2520.0 o.o o,o 74.7
20.0 3~.~ 36.~ 75.0
20.1 60.8 63.~ 76.t
20.0 78.~ 80.1 ?9.0
20.0 100.0 100.0 82.9
60.0 0.0 0.0 218.9
3060.0 3~.7 36.7 219.5
60.~ 60.8 63.2 225.7
60.3 78.0 79.~ 233.5
60.0 100.0 100.0 2~3.9
~ Weight percent HFC-134-a in HFC-152a
or condensation of the re~cigerant. In refcigeration
engineecing this ter~ expce~se~ the ratio of usoful
cefcigecation to the energy appliet by the compcessor
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W091/09089
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in compres6ing the vapor. The capacity of a
refrigerant repre6ents the volumetric efficiency o~ the
refriqerant. To a compre660r engineer this value
expresses the capability of a co~pres60r to pump
quantitiefi of heat for a given volumetric ~low rate of
re~rigerant. In other word~, given a 6pecific
compre660r, a refrigerant with a higher capacity will
; deliver more cooling or heating power.
The performance of a 78/22 HPC-134aiHFC-152a by
weight azeotrope-like blend wa6 evaluated in a typical
automotive air conditioning unit operated under
controlled labocatory calorimeter condition~. The
compre660c and conden6er sections o~ the aic
conditioning cycle were maintained in a contcol~ed
environ~ent of 100F. Thermocouplec wece u6ed to
measure the tempecature of the air flowing to and from
the conden~ec ant tho temperatuee o~ the re~riqerant at
the discharge and suction ports o~ the compre66er as
well a~ at the cond~en~er outlet. The compressor wa~
operaeed at a constant speed of 1188 revolutiona pec
minute with an electric motor. A Watt-hour meter wa~
used to determine~the m-chanical wor~ input to the
compressor. Heat remo~al trom the conden~er
environment was ac~hieved using chilled water flowing at
a measured flow rate to a cooling coil in the conden6er
room. The capacity o~ the air conditioning 6ystem is
determined by performing an energy balance over the
condense~ coom.
The evaporatoc and expansion valve section of the
air conditioning cycle were maintained at 100P and 40%
relative humidity.~ Thermocou~les were used to measure
the temperatures o~ the refrigerant leavi~ng the
evaporatoc and leaving the accumulator. Pour pre~ure
:ransducers, located in the comp~essor suction and
discharge lines and ju~t after the condenser and
accumulator, were u~ed to mea~ure the refrigecant
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WO9l/09089 PCT/US90/06996
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pre~sure throughout the cycle. Two set~ of electrical
heate~6 in the evaporator ~oo~ wece continuously
adjusted to balance the heat ~emoved by the evapo~atoc.
Tests were pecfocmed at the above specified
conditions for three cefrigerant6, CFC-12
(dichlorodifluo~omethane3. HFC-134a and the 78/22
HFC-134a/HFC-152a azeotcope-like blend. CPC-12 is a
fully halogenated chlo~ofluoroca~bon which has been
u6ed widely in air conditioning and reeriqeration
application6. CPC-12 ha6 been determined to be a
contributor to the~depletion of the Earth~6
strato6phecic ozone layer. Each test con6i6ted of at
least two consecutive experiments whece the measured
COP's agreed to within 1%. The data for these te6ts i6
reported in Table II.
The data listed in thi~ table eor Te6t6 1-3 ~how
that the 78/22 HFC-134a/HFC-152a azeoteope-like blend
pcovites a 6.6% increase in COP over HFC-134a and a
capacity similar to that o~ HFC-134a. The blend al60
provide6 a COP and capacity comparable to, thaC attained
with CFC-12. The co~p~essor discha~ge p~es6u~e foc the
blend i8 lo~er than~that exhibited by HPC-}34a, ~hicb
aliminates the need to design air conditioning
equipment to withstand higher operating pre-6uces.
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Te6t~ ~-6 cepresents a ~oce extceme condition
wher- the aiC ~low ovee the condenser has been ceduced
30 which ce~ult~ in gr-atec di~charge pre~Ure~ and
temperatures. The HPC-134a/HFC-152a blend pco~ides a
4% impcove~ent in COP and a ~light (Z~) drop
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T~blo II
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Parform~nc- Of A 78~22 HrC-124~/HPC-152~ Bl~nd
Pres~ure ~emperature Coolin~ Compressor
Dischar~e Accumulator Disch~rge Acccumulato~ Capacity Work COP
~psia) (pgi8) ~-F) (-F) (W~tt) (Watt)
T~t 1: CFC-12
255.2 60.8 174.0 53.2 5194.7 2153.4 2.41
Te~t 2: H~C-134a
284.0 59.5 163.6 S1.3 4948.8 2224.2 2.23
Test 3: HFC-13~ FC-152a(78/22)
270.9 57.1 171.2 52.3 5069.7 2128.6 2.38
T~t ~: CFC-12
313.7 60.7 187.8 53.1 3957.~ 2332.8 1.70
T~t 5: HPC-134~
352.7 59.6 180.~ 51.3 3538.9 2B81.0 1.49
T-st 6: HPC-13~-/HPC~lSZ~78/22)
339.1 57.2 19~.~ 51.6 3603.1 2321.7 1.55
in capacity compared to HPC-134a as well a~ a reduction
in discharge pressure.
Having de~cribed the invention in detail ant by
reference to pce~erred embodiment~ thereo~, it will be
apparent that modi~ication~ and variation~ are po~sible
without departinq ~rom the ~cope o~ the in~ention
de~ined in the appended clai~.
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