U.S. patent application number 09/328858 was filed with the patent office on 2001-09-06 for method of improving performance of refrigerant systems.
Invention is credited to BEIMESCH, BRUCE J., SCHNUR, NICOLAS E..
Application Number | 20010019120 09/328858 |
Document ID | / |
Family ID | 23282763 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019120 |
Kind Code |
A1 |
SCHNUR, NICOLAS E. ; et
al. |
September 6, 2001 |
METHOD OF IMPROVING PERFORMANCE OF REFRIGERANT SYSTEMS
Abstract
A method of improving performance of refrigerant systems such as
refrigerators and air conditioners that utilize a refrigerant
working fluid. The working fluid consists essentially of a heat
transfer fluid and a lubricant that is miscible and is otherwise
compatible with the heat transfer fluid at all operating
temperatures of the refrigerant system. The method is directed
particularly to chlorine-free fluoro-group organic fluids and more
particularly to hydrofluorocarbon heat transfer fluids. The
preferred lubricants comprise polyol ester basestocks and
compounded polyol esters that are highly miscible with such
hydrofluorocarbon heat transfer fluids.
Inventors: |
SCHNUR, NICOLAS E.;
(CINCINNATI, OH) ; BEIMESCH, BRUCE J.; (CRESCENT
SPRINGS, KY) |
Correspondence
Address: |
COGNIS CORPORATION
2500 RENAISSANCE BLVD., SUITE 200
GULPH MILLS
PA
19406
|
Family ID: |
23282763 |
Appl. No.: |
09/328858 |
Filed: |
June 9, 1999 |
Current U.S.
Class: |
252/68 |
Current CPC
Class: |
C10M 105/38 20130101;
C10M 171/008 20130101; C10N 2040/50 20200501; C10M 2211/06
20130101; C10N 2040/34 20130101; C10M 2207/282 20130101; C10N
2040/36 20130101; C10M 2207/281 20130101; C10N 2040/30 20130101;
C10M 2207/283 20130101; C10N 2040/44 20200501; C10N 2040/38
20200501; C10M 2209/109 20130101; C09K 5/045 20130101; C09K 2205/24
20130101; C10N 2040/40 20200501; C10N 2040/00 20130101; C10N
2040/42 20200501; C10M 2211/022 20130101; C10M 2207/286 20130101;
C10N 2040/32 20130101 |
Class at
Publication: |
252/68 |
International
Class: |
C09K 005/00; C10M
101/00 |
Claims
What is claimed is:
1. A process of improving the performance of a refrigerant system
comprising a compressor, condenser, expansion device and
evaporator, the process comprising the step of employing in the
system a working fluid consisting essentially of a heat transfer
fluid and a lubricant that is miscible with the heat transfer fluid
over the entire operating conditions of the system.
2. The process according to claim 1 wherein the heat transfer fluid
is a chlorine-free fluoro-group organic heat transfer fluid.
3. The process according to claim 2 wherein the fluoro-group
containing heat transfer fluid is a hydrofluorocarbon.
4. The process according to claim 3 wherein the lubricant comprises
an ester of alcohols that contain at least two --OH groups and a
monocarboxylic acid in which at least 22 number percent of the acyl
groups in the ester are either straight chain and contain from
three to six carbon atoms or have a carbon bonded to three other
carbon atoms and contain up to nine carbon atoms.
5. The process according to claim 4 wherein the lubricant consists
essentially of an ester in which at least 92% of alcohol moieties
in the esters of all alcohols containing at least two --OH groups
are moieties derived from alcohols selected from the group
consisting of pentaerythritol, dipentaerythritol,
2,2-dimethyl-1,3-propanediol, and 2,2dimethyl-1-butanol.
6. A process of improving the performance of a refrigerant system
in which the system undergoes the steps of compression,
condensation, expansion and evaporation said process comprising the
further step of incorporating in the system a working fluid
consisting essentially of a chlorine-free fluoro-group containing
heat transfer fluid and a lubricant composition consisting of
esters of alcohols containing at least two --OH groups and at least
one carboxylic acid.
7. The process according to claim 6 wherein the fluoro-group
containing heat transfer fluid is selected from the group
consisting of difluoromethane, pentafluoroethane,
1,1-difluoroethane, 1,1,1-tetrafluoroethane,
1,1,1,2-tetrafluoroethane, and mixtures thereof.
8. The process according to claim 6 wherein the lubricant consists
essentially of an ester formed from an alcohol comprising
pentaerythritol and dipentaerythritol and an acid mixture in which
acyl groups used to from the ester are derived from acyl groups
having 5, 6, 7, 8, 9 and 10 carbon atoms.
9. The process according to claim 8 wherein at least 98% of the
monocarboxylic acids are derived from acyl groups having 5, 7 or 9
carbon atoms.
10. The process according to claim 6 wherein at least 98% of the
monocarboxylic acids are derived from acyl groups having 5 or 9
carbon atoms.
11. The process according to claim 9 wherein at least 98% of the
alcohol moieties in the ester are derived from pentaerythritol and
dipentaerythritol and the acyl groups used to make the ester are
derived from a mixture of about 43 wt. % 3,5,5-trimethylhexanoic
acid, about 37 wt. % n-pentanoic acid and about 20 wt. % of a
mixture of 2-methylbutanoic acid and 3-methylbutanoic acid.
12. A process of improving the performance of an air conditioner
comprising a compressor, condenser, expansion device and
evaporator, the process comprising the step of employing in the
system a working fluid consisting essentially of a heat transfer
fluid and a lubricant that is miscible with the heat transfer fluid
over the entire operating conditions of the systems.
13. The process according to claim 12 wherein the heat transfer
fluid is a hydrofluorocarbon and the lubricant is an ester formed
from an alcohol comprising pentaerythritol and dipentaerythritol
and an acid mixture derived from acyl groups having 5, 6, 7, 8, 9
and 10 carbon atoms.
14. The process according to claim 13 wherein the hydrofluorocarbon
heat transfer fluid is selected from the group consisting of
difluoromethane, pentafluoroethane, 1,1,-difluoroethane,
1,1,1,-trifluoroethane, 1,1,1,2-tetrafluoroethane and mixtures
thereof.
15. The process according to claim 13 wherein the ester lubricant
is formed from a carboxylic acid mixture in which at least 22 no %
of the acyl groups in the acid mixture are selected from the group
consisting of straight chain acid of three to six carbon atoms, an
acid containing up to nine carbon atoms in which at least one
carbon atom is bonded to three other carbon atoms and mixtures
thereof.
16. The process according to claim 13 wherein the ester includes up
to 8 percent by weight of at least one additive.
17. A process of improving the performance of a refrigerator
comprising a compressor, condenser, expansion device and
evaporator, the process comprising the step of employing in the
system a working fluid consisting essentially of a heat transfer
fluid and a lubricant that is miscible with the heat transfer fluid
between -27.degree. C. and +30.degree. C.
18. The process according to claim 17 wherein the heat transfer
fluid is selected from the group consisting of difluoroethane,
pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluoroethane,
1,1,1,2-tetrafluoroethane and mixtures thereof.
19. The process according to claim 17 wherein the lubricant is an
ester formed from an alcohol comprising pentaerythritol and
dipentaerythritol and an acid mixture in which the acyl groups used
to form the ester are derived from acyl groups having 5, 6, 7, 8, 9
and 10 carbon atoms.
20. A process according to claim 17 wherein the heat transfer fluid
is 1,1,1,2-tetrafluoroethane and the lubricant consists of an ester
formed from an alcohol selected from the group consisting of
pentaerythritol, dipentaerythritol, tripentaerythritol and mixtures
thereof and an acid consisting of about 43 wt %
3,5,5-trimethylhexanoic acid, about 37 wt % n-pentanoic acid and
about 20 wt % of a mixture of 2-methylbutanoic acid and
3-methylbutanoic acid.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method or process of improving
performance of refrigerant systems such as refrigerators and air
conditioners that utilizes a working fluid. The working fluid
consists essentially of a chlorine-free fluoro-group containing
heat transfer fluid and a lubricant that is miscible and is
otherwise compatible with the heat transfer fluid over the
operating temperature of the system. The heat transfer fluid is
preferably a hydrofluorocarbon. The lubricant preferably comprises
an ester formed from an alcohol containing at least two --OH groups
and a carboxylic acid that is substantially or exclusively
monovalent.
BACKGROUND OF THE INVENTION
[0002] Refrigerant systems such as refrigerators and air
conditioners collectively consume enormous amounts of energy.
Energy consumption of refrigerant systems is likely to increase as
a result of the replacement of chlorine-containing heat transfer
fluids with chlorine-free organic heat transfer fluids for the
purpose of protecting the ozone layer.
[0003] The replacement of R-22 (difluoromonochloromethane) with a
chlorine-free hydrofluorocarbon heat transfer fluid illustrates
this problem. R-22 has very good thermodynamic properties resulting
in a lower volume replacement per ton of refrigeration than other
commercial heat transfer fluids. Accordingly, refrigerant systems
utilizing R-22 require less energy than systems utilizing other
heat transfer fluids including expected replacement heat transfer
fluids for R-22.
[0004] An improvement in the performance of refrigerant systems
would help alleviate the energy inefficiencies resulting from the
replacement of chlorine-containing heat transfer fluids with better
thermodynamic properties. In fact, even a small improvement in the
performance of refrigerant systems can translate into large
monetary savings given the enormous amounts of energy being
consumed by these systems. Such improvements in performance would
also benefit the environment as any reduction in energy
requirements will reduce the adverse effect on the environment
caused by energy production.
[0005] Accordingly, it is an object of this invention to improve
the performance of refrigerant systems in terms of reducing their
energy requirements. It is also an object to improve such
performance with working fluids that are compatible with and remain
stable in refrigerant systems over long periods of operation.
SUMMARY OF THE INVENTION
[0006] It has now been found that the performance of a refrigerant
system such as in air conditioners, refrigerators, freezers, soda
fountain dispensers and other cooling devices is improved by using
working fluids consisting essentially of a heat transfer fluid and
lubricant that are miscible over the operating temperature range of
the system. This finding applies to a refrigeration system
consisting of an apparatus which includes a compressor, a
condenser, an expansion device and evaporator in fluid flow
relationship. A preferred apparatus is of the sealed compressor
type wherein the lubricant which lubricates the moving parts of the
refrigeration apparatus is miscible with the heat transfer fluid
during the operation of the apparatus.
[0007] This finding applies to working fluids consisting
essentially of chlorine-free organic heat transfer fluids,
preferably hydrofluorocarbons, and lubricants comprising ester base
stocks or compounded esters. The ester lubricants are formed from
alcohols containing at least two --OH groups and a carboxylic acid
that is substantially or completely monovalent. At least part of
the acid constituent is preferably formed from straight chain acids
of three to six carbon atoms or acids of three to nine carbon atoms
with at least one carbon bonded to three other carbon atoms.
[0008] The esters are preferably formed from mixtures of alcohols
and acids to utilize feedstocks of such mixtures. The lubricant may
also comprise mixtures of esters. The lubricant can be formed from
only the ester or an ester compounded with one or more
additives.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Other advantages of the present invention will be readily
appreciated as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings wherein:
[0010] FIG. 1 shows a schematic of the refrigeration system used in
the test program.
[0011] FIG. 2 is a graph showing coefficient of performances of a
smooth tube coil type refrigerant apparatus using a miscible
working fluid of Example 1 compared with coefficient of performance
for the same apparatus using an immiscible working fluid of Example
A.
[0012] FIG. 3 is a graph showing the percentage difference in
coefficient of performances of a smooth tube type refrigerant
apparatus using the miscible working fluid of Example 1 compared
with coefficient of performance for the same apparatus using
immiscible working fluid of Example A.
[0013] FIG. 4 is a graph showing coefficient of performances of a
microfin tube type refrigerant apparatus using a miscible working
fluid of Example 1 compared with coefficient of performance for the
same apparatus using immiscible working fluid of Example A.
[0014] FIG. 5 is a graph showing the percentage difference of
coefficient of performance of a microfin tube type refrigerant
apparatus using a miscible working fluid of Example 1 compared with
coefficient of performance for the same apparatus using immiscible
working fluid of Example A.
[0015] FIG. 6 is a graph showing coefficient of performance of a
microfin tube type refrigerant apparatus using miscible working
fluids of Example 1 and 2.
[0016] FIG. 7 is a graph showing the percentage differences of
coefficient of performance of a microfin tube type refrigerant
apparatus using miscible working fluids of Examples 1 and 2
compared with coefficient of performance for the same apparatus
using immiscible working fluid of Example A.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Except in the operating examples, or where otherwise
expressly indicated, all numerical quantities in this description
indicating amounts of material or conditions of reaction and/or use
are to be understood as modified by the term "about" in defining
the broadest scope of the invention. Practice of the invention
within the boundaries corresponding to the exact quantities stated
is preferable however.
[0018] A typical refrigeration system to which this invention
applies is illustrated by the schematic set forth in FIG. 1. Such
systems would include air conditioners, refrigerators, freezers,
soda fountain dispensers as well as other cooling devices. The
schematic of the refrigeration system illustrates a typical
operation cycle of a refrigeration apparatus 10 which includes the
steps of compression, condensation, expansion and evaporation of a
heat transfer fluid. In the apparatus 10, compressed heat transfer
fluid carrying some lubricant is discharged through a tube 12 to a
condenser 14. The condensed heat transfer fluid and lubricant then
pass to an expansion valve 16 and there to an evaporator 18. The
evaporator 18 substantially vaporizes the heat transfer fluid and
the vapor and liquid phases of the heat transfer fluid and the
lubricant are conveyed through tube 12 to a compressor 20. In the
compressor 20, the vapor is compressed and discharged through tube
12 for recirculation through the refrigeration apparatus 10. The
schematic also indicates the presence of thermocouple probes (T) 22
used to calculate evaporator energy transfer, pressure transducers
(P) 24 to measure the absolute pressure (P) and changes in pressure
(.DELTA.P) at the condenser 14 and evaporator 18, a mass flow meter
26 to measure refrigerant flow rate and a sight glass 28. In the
refrigeration cycle illustrated by FIG. 1, the liquid phase of the
heat transfer fluid and lubricant remain miscible.
[0019] The invention is believed to pertain to a substantial
variety of heat transfer fluids including both chlorine-free and
chlorine-containing organic compounds. Of particular interest are
the chlorine-free fluoro-group containing organic compounds,
especially hydrofluorocarbons. The most preferred
hydrofluorocarbons are difluoromethane, pentafluoroethane,
1,1-difluoroethane, 1,1,1-trifluoroethane,
1,1,1,2-tetrafluoroethane, and mixtures thereof.
[0020] The invention relates to lubricants that are miscible and
compatible with a heat transfer fluid at all operating temperatures
of a refrigerant system. Of particular interest are lubricants that
comprise or consist essentially of ester base stocks or esters
compounded with additives. The esters suitable for this invention
are esters of alcohols that contain at least 2, or more preferably
at least 3, --OH groups in unesterified form.
[0021] In the preparation of polyol ester lubricants intended to be
miscible with chlorine-free fluoro-group containing organic
compounds, the use of certain polyols and acids and proportions of
polyols and acids are preferred as disclosed herebelow. It is
preferred, for example, with increasing preference in the order
given, that for lower viscosity esters at least 62, 78, or 90 no. %
of the alcohol moieties of the esters according to this invention
contain no more than 18, more preferably no more than 10, still
more preferably no more than 8 carbon atoms. Also independently, it
is preferred, with increasing preference in the order given, that
at least 62, 81, or 90 no. % of the alcohol moieties in the
ester(s) contain at least one carbon atom bonded to four other
carbon atoms by single bonds, or in other words, a "neo" carbon
atom. Independently and preferably with increasing preference, at
least 62, 81, 90 or 98 no. % of the alcohol moieties for the esters
are those derived from pentaerythritol, with the formula
C--(CH.sub.2OH).sub.4, from dipentaerythritol, with the formula
(HOCH.sub.2).sub.3CCH.sub.2OCH.sub.2C- (CH.sub.2OH).sub.3 and from
2,2-dimethyl-1,3-propanediol (more commonly known as neopentyl
glycol) with the formula (H.sub.3C).sub.2C(CH.sub.2OH)- .sub.2and
from 2,2-dimethylol-1-butanol (more commonly known as
"1,1,1-trimethylolpropane" or "TMP"). Independently and preferably
with increasing preference at least 81, 90 or 98% of the alcohol
moieties are derived from pentaerythritol or dipentaerythritol.
When higher viscosity ester lubricants are needed it is preferred
with increasing preference that at least 22, 33, 48 and 68 no. % of
the alcohol moieties are derived from dipentaerythritol.
[0022] Unsaturated as well as saturated alcohols may be used for
esters according to this invention. Saturated alcohols are
preferred. Also, substituted alcohols as well as unsubstituted
alcohols may be used, but it is preferred that the alcohols used
have no substituents other than alkoxy groups, fluoro groups,
and/or chloro groups. As with the acids or acyl groups to be used
for esters according to this invention, generally unsubstituted
alcohols are more economical and are most preferred for that
reason.
[0023] The carboxylic acids used to make the ester preferably
contain a sufficient fraction of acyl groups that satisfy at least
one of the following two criteria. The acyl groups must either
contain nine carbon atoms or less and include at least one carbon
atom bonded to three other carbon atoms by single bonds and/or be
straight chain with three to six carbon atoms. In order for the
esters to satisfy the miscibility requirements of the invention, it
is preferable that at least 22 number percent (hereinafter "no. %")
of the acyl groups in the ester or ester mixtures that are
lubricants and/or base stocks according to the invention meet at
least one of these criteria. With increasing preference in the
order named the no. % of acyl groups meeting one or both of these
criteria would be at least 33, 42, 50, 67, 86, or, for low
viscosity lubricants, 92.
[0024] Additionally and independently, the no. % of acyl groups
containing at least nine carbon atoms will not be greater than 81,
or with increasing preference not greater than 67, 56, 45 or 33. It
is also preferred that at least 90 no. % of the acyl groups in all
the esters used according to the invention have no more than twenty
carbon atoms each.
[0025] Either pure esters or mixtures of esters meeting the above
criteria may be effectively used in many embodiments of the
invention. Generally, mixtures of esters are more economical,
because they may be prepared from commercially available starting
materials without costly purification as a prerequisite. In one
embodiment of the invention, mixtures of esters are preferred for
performance reasons as well as economy. Where moderate to high
viscosity lubricants are needed, it is preferred with increasing
preference that at least 12, 16, 21, 29, 33 or 40 no. % of the acyl
groups in the esters to be used for the invention contain at least
7, more preferably at least 8 and most preferably 9 carbon atoms
each. The preferred acid with 8 carbons is 2-ethylhexanoic acid and
with 9 carbon atoms is 3,5,5-trimethylhexanoic acid.
[0026] A highly desirable constituent is the tetraester of
pentaerythritol with an acid mixture of about 57 weight percent
iso- or i-pentanoic acid, which for purposes of the specification
is defined as a mixture of n-pentanoic acid, 2-methylbutanoic acid,
and 3-methylbutanoic acid with about 43 weight percent
3,5,5-trimethylhexanoic acid. Additionally and independently, iso-
or i-pentanoic acid may with increasing preference make up at least
3, 5, 7, 11 or 14 no. % as needed to improve the miscibility of the
ester lubricant with the heat transfer fluid.
[0027] Generally, mixtures of acids are preferred. For most
purposes the preferred acids are acids having 5, 7 and 9 carbon
atoms. It is preferred with increasing preference that at least 60,
68, 75, 81, 92 and 98 no. % of the acyl groups have 5, 6, 7, 8, 9,
10, or more preferably 5, 7, or 9 carbon atoms and even more
preferably have 5 or 9.
[0028] For lubricants and/or base stocks according to the invention
in the lower viscosity ranges, substantially all of the acyl groups
in the esters are preferably monovalent ones. For higher viscosity
ranges, some divalent acyl groups are preferred, as it is believed
that esters containing two or more alcohol moieties joined by such
divalent acyl groups, with all the other hydroxyl positions on the
alcohols corresponding to those esterified by monoacyl groups, are
particularly advantageous types of esters for use according to this
invention. (An "alcohol moiety" in any ester is defined herein as a
connected part of the ester that would remain if all acyl groups
were removed from the ester. An acyl group may be denoted herein as
an "acid moiety" in an ester). If one or more of the acyl groups in
an ester is divalent, the ester is denoted herein as a "complex
ester"; such esters preferably include two alcohol moieties, which
may be the same or different, but are both of the type already
described below. Esters according to the invention with only one
alcohol moiety and with all monovalent acyl groups may be denoted
herein as "single polyol esters".
[0029] An independent constraint on the ratio between monovalent
and higher valency acids to be reacted is that too large a fraction
of acids with more than one valence may result in an undesirable
amount of high molecular weight polymer, in view of the fact that
all or substantially all of the alcohol(s) to be reacted also have
at least two reactive groups. For this reason, it is increasingly
preferred that the ratio of equivalents from monovalent acids to
the equivalents from divalent or higher valent acids reacted be at
least 1, 1.76, or 2.69. Also, the amount of acyl groups with
valence higher than 2 preferably is no more than 2 no. % of the
total of all acyl groups.
[0030] It is preferred, with increasing preference in the order
given, that at least 55, 67, 81, or 92 no. % of the divalent acyl
groups in esters used according to this invention have from 4 to
12, or more preferably from 6-9 carbon atoms, and it is
independently preferred, with increasing preference in the order
given, that at least 55, 67, 81, or 92% of the monovalent acyl
groups in the esters contain no more than 18, more preferably no
more than 9, still more preferably no more than 7, carbon
atoms.
[0031] Additionally and independently, it is desirable that for
adequate solubility in highly fluorinated refrigerant heat transfer
fluids, the ratio of the no. % of acyl groups in the ester(s) that
contain 8 or more carbon atoms and are unbranched to the no. % of
acyl groups in the ester(s) that are both branched and contain not
more than six, preferably not more than five, carbon atoms will not
be greater than 1.56, more preferably not greater than 1.21, or
still more preferably not greater than 1.00.
[0032] Saturated and unsaturated acyl groups may both be used, but
saturated ones are preferred. Also, substituted as well as
unsubstituted acyl groups may be used in esters according to the
invention, but it is preferred that the acyl groups have no
substituents other than alkoxy, fluoro and/or chloro groups.
Generally unsubstituted acyl groups are most economical and are
most preferred for that reason.
[0033] Independently of all other preferences, it is increasingly
more preferred that no more than 20, 14, 9, 5 and 2 no. % of the
oxygen atoms in the esters to be used in a composition according to
the invention be chemically bonded (as distinct from "hydrogen
bonded") to a hydrogen atom.
[0034] For each of the esters which form the lubricant composition
of the invention, it is possible to obtain the same esters by
reacting acid derivatives such as acid anhydrides, acyl chlorides,
and esters of the acids instead of reacting the acids themselves.
The acids are generally preferred for economy and are exemplified
herein, but it is to be understood that the esters defined herein
by their reactive components with acids can be equally well
obtained by reaction of alcohols with the corresponding acid
derivatives.
[0035] Concerning the reactive components of the esters which form
the lubricant composition of the invention, it is to be understood
that although only the desired alcohols and acids are explicitly
specified, some amount of the sort of impurities normally present
in technical or industrial grade products may be tolerable in most
cases. For example, "tech pentaerythritol" (PE) normally contains
on the order of 85-90 weight % of mono PE, along with 10-15 weight
% of dipentaerythritol ("DPE") and 0-3% of tripentaerythritol
("TPE"), and is quite satisfactory for making high quality esters
in many cases. Also, "commercial isopentanoic acid" normally
contains about 65 weight % n-pentanoic acid and about 35 weight %
of isopentanoic acids selected from the group consisting of
2-methylbutanoic acid and 3-methylbutanoic acid.
[0036] In practice, it has been found that reaction between the
alcohol(s) and the acid(s) reactants of the respective esters
proceeds more effectively if the quantity of acid charged to the
reaction mixture initially is enough to provide an excess of 10-25%
of equivalents of acid over the equivalents of alcohol reacted with
the acid. (An equivalent of acid is defined for the purposes of
this description as the amount containing one gram equivalent
weight of carboxyl groups, whereas an equivalent of alcohol is the
amount containing one gram equivalent weight of hydroxyl groups.)
The composition of the mixture of acids and alcohols that have
actually reacted can be determined by analysis of the ester product
for its acyl group content.
[0037] In making the ester product, according to this invention,
the acid reacted will be lower boiling than the alcohol(s) reacted
and the product ester(s). When this condition obtains, it is
preferred to remove the bulk of any excess acid remaining at the
end of the esterification reaction by distillation, most preferably
at a low pressure such as 1-5 torr.
[0038] After such vacuum distillation, the product is often ready
for use as a lubricant blending stock according to this invention.
If further refinement of the products is desired, the content of
free acid in the product after the first vacuum distillation may be
further reduced by treatment with epoxy esters, as taught in U.S.
Pat. No. 3,485,754 or by neutralization with any suitable alkaline
material such as lime, alkali metal hydroxides, or alkali metal
carbonates.
[0039] If treatment with epoxy esters is used, excess epoxy esters
may be removed by a second distillation under very low pressure,
while the product of reaction between the epoxy ester and residual
acid may be left behind in the product without harm. If alkali
neutralization is used as the refinement method, subsequent washing
with water, to remove any unreacted excess fatty acid neutralized
by the alkali, is strongly preferred before using the product is
forming a lubricant ester blend.
[0040] Under some conditions of use, the ester base stock described
herein will function satisfactorily as a complete lubricant. It is
generally preferable, however, for a complete lubricant to contain
other materials generally known in the art as additives, such as
oxidation resistance and thermal stability improvers, corrosion
inhibitors, metal deactivators, lubricity additives, viscosity
index improvers, pour and/or floc point depressants, detergents,
dispersants, foam promoting agents, antifoaming agents, anti-wear
and extreme pressure resistance additives and acid scavangers. Many
additives may impart both anti-wear and extreme pressure resistance
properties, or function both as a metal deactivator and a corrosion
inhibitor. Cumulatively, all additives preferably do not exceed 8%
by weight, or more preferably do not exceed 5% by weight, of the
total compounded lubricant formulation.
[0041] An effective amount of the foregoing additive types is
generally in the range of 0.01 to 5% for the antioxidant compound,
0.01 to 5% for the corrosion inhibitor component, from 0.001 to 5%
for the metal deactivator component, from 0.5 to 5% for the
lubricity additives, from 0.01 to 2% for each of the viscosity
index improvers and pour and/or floc point depressants, from 0.1 to
5% for each of the detergents and dispersants, from 0.001 to 0.1%
for foam promoting agents or anti-foam agents, and from 0.1-2% for
the anti-wear and extreme pressure resistance components, and 0.05
to 2% for the acid scavenger. All these percentages are by weight
and are based on the total weight of the lubricant composition. It
is to be understood that more or less than the stated amounts of
additives may be more suitable to particular circumstances or
applications, and that a single molecular type or a mixture of
types may be used for each type of additive component.
[0042] The foregoing examples are intended to be merely
illustrative and not limiting, except as circumscribed by the
appended claims.
[0043] Examples of suitable oxidation resistance and thermal
stability improvers are diphenyl-, dinaphthyl- and
phenyl-naphtyl-amines, in which the phenyl and naphthyl groups can
be substituted, e.g., N,N'-diphenyl phenylenediamine,
p-octyldiphenylamine, p,p-dioctyldiphenylamine, N-phenyl-1-naphthyl
amine, N-phenyl-2-naphthyl amine, N-(p-dodecyl)-phenyl-2-napthyl
amine, di-1-naphthylamine, and di-2-naphthylamine; phenothiazines
such as N-alkylphenothiazines, imino(-bisbenzyl); and hindered
phenols such as 6-(t-butyl) phenol,
4,4'-methylenebis(-2,6-di-(t-butyl)phenol), and the like.
[0044] Examples of suitable cuprous metal deactivators are
imidazole, benzamidazole, 2-mercaptobenzothiazole,
2,5-dimercaptothiadizaole, salicylidine-propylenediamine, pyrazole,
benzotriazole, tolutriazole, 2-methylbenzamidazole, 3,5-dimethyl
pyrazole, and methylene bis-benzotriazole. Benzotriazole
derivatives are preferred. Other examples of more general metal
deactivators and/or corrosion inhibitors include organic acids and
their esters, metal salts, and anhydrides, such as
n-oleyl-sarcosine, sorbitan monooleate, lead naphthenate,
dodecenyl-succinic acid and its partial esters and amides, and
4-nonylphenoxy acetic acid; primary, secondary, and tertiary
aliphatic and cyloaliphatic amines and amine salts of organic and
inorganic acids, such as oil-soluble alkylammonium carboxylates;
heterocyclic nitrogen containing compounds, such as thiadiazoles,
substituted imidazolines, and oxazolines; quinolines, quinones, and
anthraquinones; propyl gallate; barium dinonyl naphthalene
sulfonate; ester and amide derivatives and alkenyl succinic
anhydrides or acids, dithiocarbamates, dithiophosphates, amine
salts of alkyl acid phosphates and their derivatives.
[0045] Examples of suitable lubricity additives include siloxane
polymers, polyoxyalkene polymers, polyalkyleneglycol and long chain
derviative of fatty acids and natural oils, such as esters, amines,
amides, imidazolines, and borates.
[0046] Examples of suitable viscosity index improvers include
polymethacrylates, polybutenes, styrene-acrylate copolymers and
ethylene-propylene copolymers.
[0047] Examples of suitable pour point and/or floc point
depressants include polymethacrylates such as
methacrylate-ethylene-vinyl acetate terpolymers; alkylated
naphthalene derivatives, and products of Friedel-Crafts catalyzed
condensation of urea with naphthalene or phenols.
[0048] Examples of suitable detergents and/or dispersants include
polybutenylsuccinic acid amides; polybutenyl phosphonic acid
derivatives; long chain alkyl substituted aromatic sulfonic acids
and their salts; and methyl salts of alkyl sulfides, of alkyl
phenols, and of condensation products of alkyl phenols and
aldehydes.
[0049] Examples of suitable anti-foam agents include silicone
polymers, siloxane polymers and polyoxyalkene polymers and some
acrylates.
[0050] Examples of foam promoters include silicone polymers with a
different molecular structure than the silicone polymers used as
anti-foam agents, siloxane polymers and polyoxyalkene polymers.
[0051] Examples of suitable anti-wear and extreme pressure
resistance agents include sulfurized fatty acids and fatty acid
esters, such as sulfurized octyl tallate; sulfurized terpenes;
sulfurized olefins; organopolysulfides; organo phosphorus
derivatives including amine phosphates, alkyl acid phosphates,
dialkyl phosphates, aminedithiophosphates, trialkyl and triaryl
phosphorothionates, trialkyl and triaryl phosphines, and
dialkylphosphites, such as amine salts of phosphoric acid monohexyl
ester, amine salts of dinonylnaphthalene sulfonate, triphenyl
phosphate, trinaphthyl phosphate, diphenyl cresyl and dicresyl
phenyl phosphates, naphthyl diphenyl phosphate,
triphenylphosphorothionate; dithiocarbamates, such as an antimony
dialkyl dithiocarbamate; chlorinated and/or fluorinated
hydrocarbons, and xanthates.
[0052] Examples of suitable acid scavengers are epoxy compounds
having at least one epoxy compound in its molecule. Preferred acid
scavengers are compounds having at least one glycidyl ester group
including aliphatic glycidyl ethers such as propylene glycol,
diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol
diglycidyl ether and 1-propanol diglycidyl ether; aromatic glycidyl
ethers such as phenyl glycidyl ether, cresyl glycidyl ether and
glycidyl ether of bisphenol A - alkylene oxide adduct and
polyalkylene glycol diglycidyl ether. In the diglycidyl ether of
polyalkylene glycol or other alkylene oxide adducts, preferable
constitutive alkylene groups are ethylene, propylene, butylene,
etc. and the preferable molecular weight thereof is 1000 or
less.
[0053] Under some conditions of operation, it is believed that the
presence in lubricants of the types of polyether polyols that have
been prominent constituents of certain prior art lubricant base
stocks reported to be useful with fluorocarbon refrigerant working
fluids are less than optimally stable and or inadequately
compatible with some of the most useful lubricant additives. Thus,
in one embodiment of this invention, it is preferred that the
lubricant base stocks and lubricant be substantially free of such
polyether polyols. By "substantially free", it is meant that the
compositions contain no more than about 10% by weight, preferably
no more than about 2.6% by weight and more preferably no more than
about 1.2% by weight of the materials noted.
[0054] In formulating a working fluid according to this invention,
the selected heat transfer fluid and the lubricant components of
the working fluid should have chemical characteristics and be
present in such a proportion to each other that the lubricant
remains miscible with the heat transfer fluid over the entire range
of working temperatures to which the working fluid is exposed
during operation of a refrigeration system in which the working
fluid is used. Such systems vary enormously in terms of their
operating conditions. Accordingly, it is often adequate if the
working fluid remains miscible up to +30.degree. C., although it is
increasingly more preferable if the working fluid remains miscible
up to 45.degree., 60.degree., 71.degree. and at least 100.degree.
C. Similarly, it is often adequate if the working fluid remain
miscible when chilled to 0.degree. C., although it is increasingly
more preferable if the working fluid remain miscible down to
-15.degree., -27.degree., -42.degree., -50.degree., -57.degree. and
-60.degree. C. Miscible working fluids consisting essentially of
chlorine-free fluoro-group containing heat transfer fluids and
blended ester lubricants can be obtained as described above.
Miscibility over a temperature range for working fluids containing
up to 1, 2, 4, 10 and 15% by weight of lubricant is successively
more preferable.
[0055] In the practice of the invention, working fluids consisting
essentially of a refrigerant heat transfer fluid and lubricant base
stock or compounded lubricant is used in a process of operating
refrigerant systems in such a manner that the working fluid
improves performance of the refrigerant system.
[0056] The operable and preferred ranges of viscosity and variation
of viscosity with temperature for lubricant compositions according
to this invention are generally the same as established in the art
for lubricants to be used in refrigeration systems together with a
heat transfer fluid, particularly for a fluorocarbon and/or
chlorofluorocarbon heat transfer fluid. In general, as noted above,
it is preferred that lubricants according to this invention have
International Organization for Standardization ("ISO") viscosity
grade numbers between 15 and 320. The viscosity ranges for some of
the ISO viscosity grade numbers are given in Table 1.
1 TABLE 1 Viscosity Range in Centistokes at 40.degree. C. ISO
Viscosity Grade Number Minimum Maximum 2 1.98 2.42 3 2.88 3.53 5
4.14 5.06 7 6.12 7.48 10 9.00 11.0 15 13.5 16.5 22 19.8 24.2 32
28.8 35.2 46 41.4 50.6 68 61.2 74.8 100 90 110 150 135 165 220 198
242 320 288 352 460 414 506 680 612 748 1000 900 1100 1500 1350
1650
[0057] The preparation of ester lubricant base stocks of the
invention is described in further detail in the following
examples.
[0058] General Ester Synthesis Procedure
[0059] The alcohol and acid to be reacted, together with a suitable
catalyst such as dibutyltin diacetate, tin oxalate, phosphoric
acid, and/or tetrabutyl titanate, were charged into a round
bottomed flask equipped with a stirrer, thermometer, nitrogen
sparging means, condenser, and a recycle trap. Acid was charged in
about 15% molar excess over the alcohol. The amount of catalyst was
from 0.02 to 0.1% by weight of the weight of the total acid and
alcohol reacted.
[0060] The reaction mixture was heated to a temperature between
about 220 and 230.degree. C., and water from the resulting reaction
was collected in the trap while refluxing acids were returned to
the reaction mixture. Partial vacuum was maintained above the
reaction mixture as necessary to achieve a reflux.
[0061] The reaction mixture was sampled occasionally for
determination of hydroxyl number, and after the hydroxyl number had
fallen below 5.0 mg of KOH per gram of mixture, the majority of the
excess acid was removed by distillation after applying the highest
vacuum obtainable with the apparatus used, while lowering the
temperature to about 190.degree. C. The reaction mixture was then
cooled, and any residual acidity was removed, if desired, by
treatment with lime, sodium hydroxide, or epoxy esters. The
resulting lubricant or lubricant base stock was dried and filtered
before blending and phase compatibility testing.
EXAMPLE 1 AND A
[0062] Two refrigerant working fluids were tested in a vapor
compression refrigeration system similar to that described in FIG.
1. One of these fluids (Example A) comprises a heat transfer fluid
and a mineral oil lubricant known to be immiscible with the heat
transfer fluid. The mineral oil is an Iso 32 naphthentic
refrigeration oil. The second working fluid (Example 1) comprises a
lubricant comprising a polyol ester which is known to be miscible
with the heat transfer fluid. The heat transfer fluid used in both
Examples A and 1 is 1,1,1,2-tetrafluoroethane (R134a). The polyol
ester of Example 1 is formed from pentaerythritol and a mixture of
37 weight percent n-pentanoic acid, 20 weight percent of a mixture
of 2-methylbutanoic acid and 3-methylbutanoic acid and 43 weight
percent 3,5,5-trimethylhexanoic acid.
[0063] These refrigerant working fluids were tested in a
vapor-compression refrigeration system similar to that used in
actual buildings. This system is designed to provide approximately
3 tons of refrigeration. The refrigeration system schematic is
shown in FIG. 1. The major components of the refrigeration system
are as follows:
[0064] Evaporator
[0065] The evaporator is a cross-flow refrigerant coil. The
refrigerant flows through copper tubes, with air flowing across the
tubes. Air-side heat transfer is enhanced with aluminum fins
mounted on the copper tubes.
[0066] In the initial testing, the refrigeration system had a coil
in which inside of the copper tubes is smooth tube (smooth-tube
coil) and the tests were conducted on this coil. Later tests were
performed on an evaporator coil with microfin tubes (microfin-tube
coil). Both coils have the same design capacity of 10.5 kW (3
tons), but they differ in physical characteristics as the
microfin-tube coil is smaller than the smooth-tube coil.
[0067] The smooth tube coil has 5/8 inch nominal outer diameter
copper tubes with twelve fins per inch (12 fpi), while the
microfin-tube coil has 3/8 inch copper tubes with 15 fpi. The
microfin tube coil has around 25 percent smaller cross-sectional
area than the smooth-tube coil cross-sectional area. Also, the
volume of the microfin-tube coil on the refrigerant side is about
70 percent smaller than the same volume for the smooth-tube
coil.
[0068] Compressor
[0069] The compressor is a hermetically-sealed constant-speed
reciprocating type, designed to operate with HFC-134a refrigerant.
The compressor has accessible plugs for charging and draining
lubricant so that oil changes can be performed while the compressor
is still installed.
[0070] Expansion Valve
[0071] There are two expansion devices installed in the
refrigeration system, namely a thermostatic expansion valve and a
needle valve. Since the thermo-expansion valve has a slow response
time, the needle valve is the preferred device for flow rate
control as described in Crown, S. W., H W Shapiro and M. B. Pate.
1992. A comparison study of the thermal performance of R-12 and
R-134a. "International Refrigeration Conference--Energy Efficiency
and the New Refrigerants" (1): 187-196 (hereafter the "Crown et al
article"). In addition, the needle valve can be directly controlled
by the data acquisition system.
[0072] INSTRUMENTATION
[0073] Measuring devices used to quantitatively evaluate
refrigeration system performance are also shown in FIG. 1. The
sensors installed are thermocouple probes, pressure transducers,
flow sensors, and a watt transducer. A detailed description of each
of those sensors is provided below.
[0074] Thermocouple probes
[0075] Thermocouple probes are of the T type, and they are located
before and after each of the components of the refrigeration
system. All of the thermocouples were calibrated, and the
uncertainty of their reading is .+-.0.21.degree. C. (0.5.degree.
F.).
[0076] In addition, there are two thermocouple grids before and
after the evaporator on the air flow side. Each grid consists of 18
thermocouples equally spaced across the heat exchanger
cross-sectional area. The purpose of these grids is to accurately
calculate evaporator energy transfer on the air side. Dry and wet
bulb thermocouples are installed before and after the evaporator
for the purpose of measuring the amount of moisture in the air
stream.
[0077] Pressure transducers
[0078] Four pressure transducers installed in the refrigeration
system are used to measure absolute pressure. All of the pressure
transducers were calibrated with a dead weight tester over the
expected range of operation. The pressure transducer uncertainty is
estimated to be 1.05 kPa (0.15 psia).
[0079] Mass flowmeter
[0080] The refrigerant flow rate is measured with a mass flowmeter
that was precalibrated by the manufacturer. For accurate flow rate
measurements, it is required that refrigerant be in a liquid state
at the outlet of the condenser, which is where the flowmeter is
located. If the liquid phase requirement is met, the flowmeter can
read actual flow rate with an uncertainty of .+-.0.0075 kg/min
(0.0034 lbm/min).
[0081] Pitot-tube measuring station
[0082] The air flow rate is measured with a Pitot-tube measuring
station which uses a calibrated pressure transducer to measure
dynamic pressure.
[0083] Turbine flowmeter
[0084] The flow rate of the water flowing through the condenser is
measured by a calibrated turbine flowmeter. The flowmeter can
measure the water flow rate with an uncertainty of .+-.0.05 kg/min
(0.0225 lbm/min).
[0085] Watt transducer
[0086] A watt transducer precalibrated by the manufacturer is used
to measure compressor power consumption with a listed uncertainty
of .+-.0.05 kW (4 Btu/min).
[0087] Data Acquisition System
[0088] The data acquisition system consists of a computer, an
IEEE-488 GPIB (General Purpose Interface Bus) controller card, a
computer addressable digital voltmeter, and two scanners. The GPIB
controller card allowed for computer control of the scanners and
the voltmeter. All of the instruments were connected to the data
acquisition system, allowing constant updating of the system
operating parameters and storing of the information in the computer
memory.
[0089] In order to compare the system performance for different
types of working fluids, testing and data taking must be done at
the same operating conditions. Therefore, it was necessary to
define an operating point by assigning values to the independent
parameters. Six different parameters could be controlled during
testing, and, as such, they can be considered to be independent
parameters. Four out of six independent parameters were kept
constant:
[0090] 1. Superheat at the compressor inlet is necessary so that
the refrigerant entering the compressor is in the vapor phase, thus
preventing any damage to the compressor. The refrigerant vapor was
superheated 7.5.degree. C. (13.5 F.) above the saturation
temperature corresponding to the suction pressure. This value is
representative of the superheat used in the industry for
refrigeration system applications.
[0091] 2. Refrigerant charge was investigated by operating the
system over a wide range of conditions for the case of the POE
lubricant. As the refrigerant charge was found to be an optimum at
3.6 kg (8 lbm), this same charge was used for all tests.
[0092] 3. Condenser water flow rate was kept constant at a maximum
value, which corresponds to approximately 80 kg/min (175 lbm/min)
of water mass flow rate. At high water flow rates, the condenser
performance becomes independent of the water flow rate magnitude
due to a negligible thermal resistance between the water and the
tube wall as described in Incorpera F. P. and D. P. De Witt, 1990
Fundamentals of heat mass transfer, third edition, New York: John
Wiley & Sons. Thus, the water flow rate was removed as a
variable during system testing and analysis, and as a result, the
condenser performance becomes only a function of water inlet
temperature, refrigerant flow rate, and refrigerant temperatures as
described in the Crown et al article.
[0093] 4. Air volumetric flow rate was kept constant at
approximately 1.3 m.sup.3/sec (2400 CFM). This flow rate magnitude
is close to the maximum achievable air flow rate in the test
facility and is kept constant so that it is not a variable in this
study.
[0094] 5. Four different condenser water inlet temperatures were
selected for investigating the refrigeration system performance.
These temperatures are 18.5.degree. C. (65.degree. F.), 24.degree.
C. (75.degree. F.), 32.degree. C. (90.degree. F.), and 40.5.degree.
C. (105.degree. F.), and they correspond to water temperatures
readily available and used in refrigeration applications.
[0095] 6. The three different evaporator air inlet temperatures
selected were 13.degree. C. (55.degree. F.), 18.5.degree. C.
(65.degree. F.), and 24.degree. C. (75.degree. F.) which represent
a wide range of working temperatures for air-conditioning
applications.
[0096] Combinations of these two independent variables produced 12
different operating points representing a large range of operating
conditions. Determining the refrigeration system performance over
this large range of conditions is considered important for the
working fluid baseline data for working fluids comprising the
polyol ester (POE) lubricant of Example 1 and mineral oil of
Example A.
[0097] In order to control the six independent parameters
referenced hereabove, the system is first charged with refrigerant
to an optimum amount. The condenser water was circulated at a
constant volume flow rate by operating a pump at its maximum
capacity. The air flow rate was set by adjusting the fan motor
speed to achieve a constant air stream dynamic pressure.
[0098] In order to control the remaining three independent
parameters simultaneously, the condenser water temperature is
controlled by mixing the chilled water with the condenser return
water. The air inlet temperature was kept at a desired value by
reheating the air leaving the evaporator by using a combination of
a steam coil and an electric heater. The electric heater is used to
accurately control the air temperature while the steam coil was
used to produce the bulk of the cooling load. Finally, a needle
valve was used to control the refrigerant flow rate through the
system which in turn adjusts the amount of superheat at the
compressor exit.
[0099] After the steady state operation has been reached, the data
were taken over an approximately 5 minute period. Multiple readings
of several key parameters were taken in order to reduce any
precision errors in instrumentation readings. These multiple
readings were statistically processed to access the fluctuations in
instrument readings.
[0100] The experimental procedures adopted for changing the
lubricant in the refrigerant system are important in order to
ensure that the refrigerant lubricant in the compressor is of an
acceptable purity.
[0101] The lubricant oil change was performed in accordance with
the triple-flush procedure outlined in Byrne J. J., M Shows and M.
W. Abel. Investigation of flushing and cleanout methods for
refrigeration equipment to ensure system compatibility. Final
report. ARTI MLLR Project Number 660-52502. The triple-flush is a
method for the removal of the mineral oil from an installation
containing R-12 when it is retrofitted with HFC-134a. The same
procedure was used in this project to replace the polyolester
refrigerant lubricant with the mineral oil. The method requires
three lubricant changes to remove any traces of residual mineral
oil which reduces the residual oil to less than 1 percent by
volume.
[0102] An industry recognized indicator of refrigerant system
performance is the coefficient of performance (COP). Coefficient of
performance is defined as the useful energy transfer (i.e.,
evaporator capacity) divided by the energy consumed. The
coefficient of performance was measured for working fluids of
Examples 1 and A for air inlet temperatures of 13.degree. C.,
18.degree. C. and 24.degree. C. and for condenser water inlet
temperatures of 18.5.degree. C., 24.degree. C., 32.degree. C. and
40.5.degree. C. The results of these measurements are set forth in
Table 2. In Table 2, the working fluid of Example 1 is identified
as "POE lubricant" and the working fluid of Example A is identified
as "Mineral Oil".
[0103] As shown in FIG. 2 the refrigerant system operation is more
efficient with the POE lubricant than with the mineral oil. This is
illustrated by the relatively higher unbroken lines representing
COP results with the miscible working fluid of Example 1
(identified as "POE 1") is the dotted lines for the COP results for
the immiscible working fluid of Example A (identified as "MO").
This result indicates that the performance of refrigerant systems
is improved by the use of miscible refrigerant working fluids and
that such performance improvement results in energy savings.
[0104] FIG. 2 also indicates that COP can vary greatly due to
varying air and water temperatures. These differences are
illustrated by establishing a reference point corresponding to an
air temperature of 13.degree. C. and a water temperature of
18.5.degree. C. It can then be observed that an increase in air
temperature from the reference point of 13.degree. C. to 24.degree.
C., while keeping the same condenser water temperature, results in
approximately a 25 percent COP increase. If the water temperature
is increased from 18.5.degree. C. to 40.degree. C. then the COP
decreases around 40 percent. Although changes in air and water
inlet temperatures have a considerable effect on COP, at the
temperature conditions tested, the COP for the refrigerant system
was with only one exception higher with the miscible working fluid
of Example 1.
[0105] The results plotted in FIG. 2 can also be presented as a
percent difference as shown in FIG. 3. The percent COP difference,
COP.sub.dif, is defined as the difference between the COPs for the
miscible working fluid with the POE lubricant and the immiscible
working fluid with the mineral oil divided by the COP for the
miscible working fluid. The value is expressed as a percentage. 1
COP dif [ % ] = COP POE - COP m oil COP m oil .times. 100 ( 1 )
[0106] Using this approach, the results plotted in FIG. 3 also show
that the system operating with the miscible working fluid (POE
lubricant) has a larger COP than the system operating with the
immiscible working fluid (Mineral oil). The percent differences are
as high as 2.5 percent. It appears from FIG. 3 that the largest
percent differences correspond to the points with the highest
evaporator temperature of 24.degree. C. (75.degree. F.) with the
COP percent difference diminishing to a fraction of a percent as
the evaporator air entering temperature decreases.
[0107] These results suggest that for an air conditioning
application operating with air entering at 24.degree. C.
(75.degree. F.) there is a $25 potential saving for every $1,000
spent on operating the refrigeration system using a miscible
working fluid in the compressor in place of an immiscible working
fluid.
[0108] These tests were repeated for the microfin-tube coil in the
same manner as for the smooth-tube coil. Specifically, effects of
miscible and immiscible working fluids on coefficient of
performance of the same refrigeration apparatus with a microfin
coil used in place of the smooth-tube coil were investigated by
comparing the refrigeration system operating points corresponding
to the same independent parameters (i.e. refrigerant charge; air
and water inlet temperatures; air and water flow rates; and amount
of superheat at the compressor inlet). The data obtained are set
forth in FIG. 4 and indicate similar system behavior for the two
types of coils.
[0109] As with the smooth-tube coil, the system operates more
efficiently with the miscible working fluid (POE) lubricant then
with the immiscible working fluid (MO) with the microfin-tube coil.
As already determined for the smooth-tube coil, the COP data shows
that there are energy savings related to the utilization of a
miscible working fluid in the microfin tube system.
[0110] FIG. 4 also reveals substantial differences in COP due to
variations in water and air temperatures. For instance the COP
decreases for 25 percent if the water temperature is increased from
24.degree. C. to 40.degree. C., and it also decreases for around 20
percent if the air temperature is reduced from 24.degree. C. to
13.degree. C. Only for a condenser water temperature of 40.degree.
C. (105 F.) are there no distinguishable difference among COP
percent differences for different air temperatures. Yet, the COP
for the refrigerant system was higher for the miscible working
fluid of Example 1 for all test conditions.
[0111] The percent COP difference, COP.sub.dif defined earlier, in
formula (1) is obtained from the COP results set forth in FIG. 4.
The COP.sub.dif results expressed in percentage are set forth in
FIG. 5. Using this approach, the results demonstrate that the
system operating with the miscible working fluid (POE lubricant)
has a larger COP than the system operating with the immiscible
working fluid (Mineral oil). The COP percent differences are as
high as about 4.5 percent, and the largest percent differences
correspond to the points with the highest evaporator temperature
24.degree. C. (75.degree. F.) and the lowest condenser water
temperature 24.degree. C. (75.degree. F.). The COP percent
difference appears to decrease with an increase in water
temperature and a decrease in air temperature.
[0112] These results suggest that for an air conditioning
application operating with air entering at 24.degree. C.
(75.degree. F.), for every $1,000 spent on operating the
refrigeration system there is a $45 potential saving in utilizing
the miscible working fluid over the immiscible working fluid in the
compressor. Accordingly, the possible energy savings related to
usage of the miscible working fluid with the microfin-tube coil are
even higher than the energy savings found for the smooth-tube coil.
This result is especially significant because micro-fin coils are
being used increasingly in refrigerant systems.
EXAMPLE 2
[0113] The coefficient of performance was measured for the
refrigeration apparatus described hereabove using a second miscible
working fluid comprising 1,1,1,2-tetrafluoroethane heat transfer
fluid and a second polyol ester lubricant (POE #2). The second
polyol ester is formed from an alcohol mixture of 65 weight percent
pentaerythritol and 35 weight percent dipentaerythritol and a
mixture of straight chain acids of 5 to 10 carbon atoms present in
the following ranges (53-63 no. % nC.sub.5; 5-15 no. % nC.sub.6;
7-17 no. % nC.sub.7; 7-17 no. % nC.sub.8; 0-10 no. % nC.sub.9 and
0-10 no. % nC.sub.10) The conditions under which the coefficient of
performance was measured for this Example 2 working fluid were the
same as those for the working fluids of Examples 1 and A. The
comparative results for COP for the miscible working fluids of
Examples 1 and 2 (expressed as POE #1 and #2) are shown in FIG.
6.
[0114] The coefficient of performance results of the working fluids
of Examples 1 and 2 are defined relative to the immiscible working
fluid of Example A in terms of a percent difference in FIG. 7 by
calculating these differences according to formula (1). The COP
percent differences for working fluids of Examples 1 and 2 (i.e.,
POE #1 and POE #2) are plotted in FIG. 7 as functions of condenser
water temperature and evaporator air temperature. The COP percent
differences data indicate that the miscible working fluid of
Example 2 improves the COP of a refrigerant system relative to the
immiscible working fluid of Example A. Specifically, the COP
percent improvement for the miscible working fluid of Example 2
over the immiscible working fluid of Example A varied from 0.1 to
5.2%. These results suggest that for an air conditioning
application operating with air entering at 13.degree. C. there is a
$52 potential saving for every $1,000 spent on operating the
refrigeration system using a miscible working fluid in the
compressor in place of an immiscible working fluid. The COP percent
improvement for the miscible working fluid of Example 1 over the
immiscible working fluid of Example A varied from 1.6 to 4.7%. The
COP percent difference values which are plotted in FIG. 7 and
discussed above are also given in Table 2. The fact that the COP
percent differences are all positive and as high as 5.2% shows that
for all test conditions, refrigerant system performance was
improved with the use of miscible working fluids.
2TABLE 2 COP Percent Differences for two POE Lubricants. Tcond =
23.9 C Tcond = 32.2 C Tcond = 40.6 C POE #1 POE #2 POE #1 POE #2
POE #1 POE #2 Tair = 13.0 C 2.58 5.20 1.58 4.11 1.83 3.64 Tair =
18.5 C 3.79 3.83 2.10 3.49 1.99 2.88 Tair = 24.0 C 4.74 4.68 3.93
3.55 1.80 0.10
* * * * *