U.S. patent application number 10/642766 was filed with the patent office on 2005-04-07 for non-hcfc refrigerant mixture for an ultra-low temperature refrigeration system.
Invention is credited to Weng, Chuan.
Application Number | 20050072957 10/642766 |
Document ID | / |
Family ID | 28791808 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050072957 |
Kind Code |
A1 |
Weng, Chuan |
April 7, 2005 |
Non-HCFC refrigerant mixture for an ultra-low temperature
refrigeration system
Abstract
Methods and apparatus for a refrigeration heat exchanger section
useful in circulating a substantially non-HCFC refrigerant mixture
which comprises: a compressor means, an auxiliary condenser, a
first condenser, a second condenser, a third condenser, a subcooler
and a liquid/gas separator, wherein a subcooled refrigerant liquid
mixture taken as bottoms from the liquid/gas separator is
distributed and expanded by a first expansion means and a second
expansion means to form first and second expanded streams,
respectively, such that the first expanded stream is returned to
the auxiliary condenser and compressor in order to avoid
overheating of the compressor.
Inventors: |
Weng, Chuan; (Weaverville,
NC) |
Correspondence
Address: |
BAKER + HOSTETLER LLP
WASHINGTON SQUARE, SUITE 1100
1050 CONNECTICUT AVE. N.W.
WASHINGTON
DC
20036-5304
US
|
Family ID: |
28791808 |
Appl. No.: |
10/642766 |
Filed: |
August 19, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10642766 |
Aug 19, 2003 |
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10305188 |
Nov 27, 2002 |
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6631625 |
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Current U.S.
Class: |
252/67 |
Current CPC
Class: |
F25B 2400/23 20130101;
C09K 2205/13 20130101; F25B 9/006 20130101; C09K 2205/12
20130101 |
Class at
Publication: |
252/067 |
International
Class: |
F25D 001/00 |
Claims
1. A method of creating a non-hydrochlorofluorocarbon refrigerant
mixture, capable of providing temperatures as low as about
-150.degree. C., comprising the steps of: adding
non-hydrochlorofluorocarbon refrigerants to refrigerant R740.
2. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; any one
refrigerant from the group consisting of R134a; R152a and R290; any
one refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; and any one refrigerant from the group consisting
of R23, R116, R170, R508a, R508b and R1150.
3. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; any one
refrigerant from the group consisting of R134a; R152a and R290; any
one refrigerant from the group consisting of R236ea, R245ca and
R245fa; and any one refrigerant from the group consisting of R23,
R116, R170, R508a, R508b and R1150.
4. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; R50; any
one refrigerant from the group consisting of R134a; R152a and R290;
any one refrigerant from the group consisting of R236ea, R245ca and
R245fa; and any one refrigerant from the group consisting of R23,
R116, R170, R508a, R508b and R1150.
5. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; R50; any
one refrigerant from the group consisting of R134a; R152a and R290;
any one refrigerant from the group consisting of R227ea, R236fa,
RC318, R600 and R600a; and any one refrigerant from the group
consisting of R23, R116, R170, R508a, R508b and R1150.
6. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R50; any one
refrigerant from the group consisting of R134a, R152a and R290; any
one refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; and any one refrigerant from the group consisting
of R23, R116, R170, R508a, R508b and R1150.
7. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consists of: R14; R50; any
one refrigerant from the group consisting of R236ea, R245ca and
R245fa; any one refrigerant from the group consisting of R227ea,
R236fa, RC318, R600 and R600a; any one refrigerant from the group
consisting of R134a, R152a and R290; and any one refrigerant from
the group consisting of R23, R116, R170, R508a, R508b and
R1150.
8. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consists of: R50; any one
refrigerant from the group consisting of R236ea, R245ca and R245fa;
any one refrigerant from the group consisting of R227ea, R236fa,
RC318, R600 and R600a; any one refrigerant from the group
consisting of R134a, R152a and R290; and any one refrigerant from
the group consisting of R23, R116, R170, R508a, R508b and
R1150.
9. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; any one
refrigerant from the group consisting of R134a; R152a and R290; any
one refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; any one refrigerant from the group consisting of
R236ea, R245ca and R245fa; and any one refrigerant from the group
consisting of R23, R116, R170, R508a, R508b and R1150.
10. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consists of: R14; R50; any
one refrigerant from the group consisting of R236ea, R245ca and
R245fa; any one refrigerant from the group consisting of R227ea,
R236fa, RC318, R600 and R600a; and any one refrigerant from the
group consisting of R23, R116, R170, R508a, R508b and R1150.
11. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; any one
refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; any one refrigerant from the group consisting of
R236ea, R245ca and R245fa; and any one refrigerant from the group
consisting of R23, R116, R170, R508a, R508b and R1150.
12. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R50; any one
refrigerant from the group consisting of R134a; R152a and R290; any
one refrigerant from the group consisting of R236ea, R245ca and
R245fa; and any one refrigerant from the group consisting of R23,
R116, R170, R508a, R508b and R1150.
13. The refrigerant mixture of claim 1, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R50; any one
refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; any one refrigerant from the group consisting of
R236ea, R245ca and R245fa; and any one refrigerant from the group
consisting of R23, R116, R170, R508a, R508b and R1150.
14. A non-hydrochlorofluorocarbon refrigerant mixture for use in a
refrigeration system capable of providing temperatures as low as
about -150.degree. C., consisting of: R740 and at least four
non-hydrochlorofluorocarbon refrigerants.
15. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; any one
refrigerant from the group consisting of R134a; R152a and R290; any
one refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; and any one refrigerant from the group consisting
of R23, R116, R170, R508a, R508b and R1150.
16. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; any one
refrigerant from the group consisting of R134a; R152a and R290; any
one refrigerant from the group consisting of R236ea, R245ca and
R245fa; and any one refrigerant from the group consisting of R23,
R116, R170, R508a, R508b and R1150.
17. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; R50; any
one refrigerant from the group consisting of R134a; R152a and R290;
any one refrigerant from the group consisting of R236ea, R245ca and
R245fa; and any one refrigerant from the group consisting of R23,
R116, R170, R508a, R508b and R1150.
18. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; R50; any
one refrigerant from the group consisting of R134a; R152a and R290;
any one refrigerant from the group consisting of R227ea, R236fa,
RC318, R600 and R600a; and any one refrigerant from the group
consisting of R23, R116, R170, R508a, R508b and R1150.
19. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R50; any one
refrigerant from the group consisting of R134a, R152a and R290; any
one refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; and any one refrigerant from the group consisting
of R23, R116, R170, R508a, R508b and R1150.
20. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; R50; any
one refrigerant from the group consisting of R236ea, R245ca and
R245fa; any one refrigerant from the group consisting of R227ea,
R236fa, RC318, R600 and R600a; any one refrigerant from the group
consisting of R134a, R152a and R290; and any one refrigerant from
the group consisting of R23, R116, R170, R508a, R508b and
R1150.
21. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R50; any one
refrigerant from the group consisting of R236ea, R245ca and R245fa;
any one refrigerant from the group consisting of R227ea, R236fa,
RC318, R600 and R600a; any one refrigerant from the group
consisting of R134a, R152a and R290; and any one refrigerant from
the group consisting of R23, R116, R170, R508a, R508b and
R1150.
22. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; any one
refrigerant from the group consisting of R134a; R152a and R290; any
one refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; any one refrigerant from the group consisting of
R236ea, R245ca and R245fa; and any one refrigerant from the group
consisting of R23, R116, R170, R508a, R508b and R1150.
23. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; R50; any
one refrigerant from the group consisting of R236ea, R245ca and
R245fa; any one refrigerant from the group consisting of R227ea,
R236fa, RC318, R600 and R600a; and any one refrigerant from the
group consisting of R23, R116, R170, R508a, R508b and R1150.
24. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R14; any one
refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; any one refrigerant from the group consisting of
R236ea, R245ca and R245fa; and any one refrigerant from the group
consisting of R23, R116, R170, R508a, R508b and R1150.
25. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R50; any one
refrigerant from the group consisting of R134a; R152a and R290; any
one refrigerant from the group consisting of R236ea, R245ca and
R245fa; and any one refrigerant from the group consisting of R23,
R116, R170, R508a, R508b and R1150.
26. The refrigerant mixture according to claim 14, wherein said
non-hydrochlorofluorocarbon refrigerants consist of: R50; any one
refrigerant from the group consisting of R227ea, R236fa, RC318,
R600 and R600a; any one refrigerant from the group consisting of
R236ea, R245ca and R245fa; and any one refrigerant from the group
consisting of R23, R116, R170, R508a, R508b and R1150.
27. (Cancelled)
28. (Cancelled)
29. (Cancelled)
30. (Cancelled)
31. (Cancelled)
32. (Cancelled)
33. (Cancelled)
34. (Cancelled)
35. (Cancelled)
36. (Cancelled)
37. (Cancelled)
38. (Cancelled)
39. (Cancelled)
Description
FIELD OF INVENTION
[0001] The present invention relates generally to an apparatus for
low temperature refrigeration systems. More particularly, the
present invention relates to a non-hydrochlorofluorocarbon
(non-HCFC) design of a refrigerant mixture for an ultra-low
temperature refrigeration system.
BACKGROUND OF THE INVENTION
[0002] In refrigeration systems, a refrigerant gas is compressed in
a compressor unit. Heat generated by the compression is then
removed generally by passing the compressed gas through a water or
air cooled condenser coil. The cooled, condensed gas is then
allowed to rapidly expand into an evaporating coil where the gas
becomes much colder, thus cooling the coil and the inside of the
refrigeration system box around which the coil is placed.
[0003] Ultra-low and cryogenic temperatures ranging from
-95.degree. C. to -150.degree. C. have been achieved in
refrigeration systems using a single circuit vapor compressor.
These systems typically use a single compressor to pump a mixture
of four or five chlorofluorocarbon (CFC) containing refrigerants to
reach an evaporative temperature of as low as -160.degree. C.
[0004] Environmental concern over the depletion of the ozonosphere
has increased pressure on refrigerator manufacturers to
substantially reduce the level of CFC-containing refrigerants used
within their systems. Although non-CFC refrigerant mixtures have
been developed, it has been discovered that most of these
refrigerant mixtures cannot simply be substituted for
CFC-containing refrigerants in currently available refrigeration
systems due to the different thermodynamic properties of the
refrigerants.
[0005] The present inventor has discovered that using non-CFC
refrigerants in conventional ultra-low and cryogenic temperature
systems cause an imbalanced flow of the refrigerants in the
refrigeration circuit, which reduces the cooling capability of the
refrigerants to the compressor. Such low levels of compressor
cooling can cause a system to fail due to compressor
overheating.
[0006] Furthermore, given that HCFC refrigerants do contain
chlorine, that over time can affect the ozone layer as well as CFC
refrigerants, the present inventor has developed a novel
autocascade ultra-low and cryogenic temperature refrigeration
system which is capable of operating with non-HCFC refrigerant
mixtures. These non-HCFC refrigerant mixtures are non-toxic,
chemically stable, commercially available and compatible with most
of the standard refrigeration oils and compressor materials.
Normally, one component of a non-CFC refrigerant mixture, i.e.,
hydrochlorofluorocarbon (HCFC), is a regulated ozone depleting
chemical. However, the present invention uses a non-HCFC
refrigerant mixture which has no ozone depleting properties at all,
i.e., the mixture is primarily composed of hydrofluorocarbon (HFC)
refrigerants and hydrocarbons.
[0007] As shown in FIG. 7, an index called the Ozone Depletion
Potential (ODP) has been adopted for regulatory purposes. The ODP
of a compound is an estimate of the total ozone depletion due to 1
Kg of the compound divided by the total ozone depletion due to 1 Kg
of CFC-11 refrigerant. Thus, the ODP shows relative effects of
comparable emissions of the various compounds.
[0008] Unlike the CFC-containing refrigeration systems which do not
cause overheating of the compressor, the present inventor has
discovered that the substantially non-HCFC refrigeration systems
must provide additional liquid return to the compressor in order to
avoid overheating thereof and eventual failure of the system.
[0009] The present inventor has been able to overcome the
overheating of the compressor when using substantially non-HCFC
refrigerants in a single compressor autocascade system. This is
accomplished by providing a specially-designed capillary tube or
expansion means disposed downstream of the first liquid/gas
separator such that liquid refrigerants are returned directly to
the auxiliary condenser and then to the compressor. This feature
enables larger than normal quantities of refrigerants of higher
boiling points to be rapidly returned to the compressor, which
results in excellent operating conditions of the compressor and
avoids overheating thereof.
[0010] As such, the overall performance of the non-HCFC autocascade
system is comparable to its counterpart of the CFC autocascade
system. This is evidenced by the fact that both systems have
similar pull down rates and compressor operating conditions at
standard 90.degree. F. ambient.
[0011] The present invention also provides many additional
advantages which shall become apparent as described below.
SUMMARY OF THE INVENTION
[0012] The present invention overcomes the need for using CFC or
HCFC refrigerant mixtures in a refrigeration system by utilizing
refrigerants R14, R23, R50, R116, R134a, R152a, R170, R236fa,
R236ea, R245fa, R245ca, RC318, R290, RR508a, R508b, R600, R600a,
R740 and R1150 in various 5, 6 and 7-component mixtures. To achieve
desired properties, these refrigerants may be used in a "cocktail"
mixture (e.g., R600a or R600; R290; R170 or R1150; R50; and
R740).
[0013] It is therefore a feature of the present invention to
provide a non-HCFC ultra-low temperature refrigerant mixture that
can safely be applied in the field as needed without the risks
associated with CFC or HCFC ultra-low temperature refrigerants.
[0014] It is another feature of the present invention to provide a
refrigeration heat exchanger section which is capable of
circulating a substantially non-HCFC refrigerant mixture which
comprises: a compressor means, an auxiliary condenser, a first
condenser, a second condenser, a third condenser, a subcooler means
and a liquid/gas separator, wherein the improvement is
characterized by: a means for distributing a subcooled refrigerant
liquid mixture from the liquid/gas separator to a first expansion
means and a second expansion means for forming first and second
expanded streams, respectively; and a first conduit means for
returning the first expanded stream to the auxiliary condenser and
the compressor; and a second conduit means for delivering the
second expanded stream to the first condenser.
[0015] More specifically, the refrigeration heat exchanger section
preferably comprises: a compressor means; an auxiliary condenser
connected to receive and cool the refrigerant mixture discharged
from the compressor means; a first liquid/gas separator connected
to received the cooled refrigerant mixture discharged from the
auxiliary condenser, wherein a subcooled refrigerant liquid mixture
is taken as bottoms and a gaseous refrigerant liquid mixture is
taken overhead; a means for distributing the subcooled refrigerant
liquid mixture to a first expansion means and a second expansion
means to form a first expanded stream and a second expanded stream,
respectively; a first conduit means for returning the first
expanded stream to the auxiliary condenser and the compressor.
[0016] The high pressure flow of the heat exchanger circuit further
comprises: a first condenser connected to receive the gaseous
refrigerant mixture from the liquid/gas separator; a second
liquid/gas separator connected to receive the gaseous refrigerant
mixture from the first condenser, wherein a subcooled liquid
refrigerant mixture is taken as bottoms and a gaseous refrigerant
mixture is taken overhead; a second condenser connected to receive
the gaseous refrigerant mixture which is taken overhead from the
second liquid/gas separator; a third condenser connected to receive
at least a portion of the gaseous refrigerant mixture taken from
the second condenser; and a subcooler means connected to receive
the gaseous refrigerant mixture from the third condenser.
[0017] The low pressure flow of the heat exchanger circuit further
comprises: a distributor means connected to receive the refrigerant
mixture from the subcooler means, the distributor means is capable
of separating the refrigerant mixture into a first stream and a
second stream; a third expansion means connected to receive the
first stream, thereby forming a third expanded stream; a third
conduit means for delivering the third expanded stream to the
subcooler means; a fourth expansion means connected to received the
second stream, thereby forming a fourth expanded stream; a fourth
conduit means for delivering the fourth expanded stream to a
storage tank; a fifth conduit means for delivering the fourth
expanded stream from the storage tank to the third condenser; a
sixth conduit means disposed between the third condenser and the
second condenser such that the fourth expanded stream from the
third condenser is delivered to the second conduit means; a sixth
expansion means connected to receive the subcooled liquid
refrigerant mixture from the second liquid/gas separator, thereby
forming a fifth expanded stream; a seventh conduit means for
delivering the fifth expanded stream to the second condenser; an
eighth conduit means for delivering the fifth expanded stream from
the second condenser to the first condenser; a second conduit means
for delivering the second expanded stream to the first condenser; a
ninth conduit means for delivering the second expanded stream and
the fifth expanded stream from the first condenser to the auxiliary
condenser; and a tenth conduit means for delivering the first,
second and fifth expanded streams from the auxiliary condenser to
the compressor.
[0018] There has been outlined, rather broadly, the more important
features of the invention in order that the detailed description
thereof that follows may be better understood, and in order that
the present contribution to the art may be better appreciated.
There are, of course, additional features of the invention that
will be described below and which will form the subject matter of
the claims appended hereto.
[0019] In this respect, before explaining at least one embodiment
of the invention in detail, it is to be understood that the
invention is not limited in its application to the details of
construction and to the arrangements of the components set forth in
the following description or illustrated in the drawings. The
invention is capable of other embodiments and of being practiced
and carried out in various ways. Also, it is to be understood that
the phraseology and terminology employed herein, as well as the
abstract, are for the purposes of description and should not be
regarded as limiting.
[0020] As such, those skilled in the art will appreciate that the
conception upon which this disclosure is based may readily be
utilized as a basis for the designing of other structures, methods
and systems for carrying out the several purposes of the present
invention. It is important, therefore, that the claims be regarded
as including such equivalent construction insofar as they do not
depart from the spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a block diagram of the single compressor
refrigeration system according to the present invention.
[0022] FIG. 2 is a non-HCFC autocascade heat exchanger section
according to the present invention.
[0023] FIG. 3 is a non-HCFC autocascade heat exchanger section in
accordance with another embodiment of the present invention.
[0024] FIG. 4 is a conventional CFC-based autocascade heat
exchanger section.
[0025] FIG. 5 is a graph depicting the pull down rates of CFC
refrigerants in a conventional autocascade system at 90.degree. F.
ambient.
[0026] FIG. 6 is a graph depicting the pull down rates of non-HCFC
refrigerants in an autocascade system according to the present
invention at 90.degree. F ambient.
[0027] FIG. 7 illustrates the Ozone Depletion Potentials of CFC,
HCFC and HFC refrigerants.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0028] Referring now to the Figures, in FIG. 1 there is shown a
Single compressor ultra-low and cryogenic temperature refrigeration
systems, as shown in FIG. 1, pump refrigerants through a condenser,
heat exchanger section and evaporator coils in a closed circuit
loop to provide temperatures as low as -150.degree. C. The heat
exchanger section and evaporator coils referred to in FIG. 1 are
specifically described in FIG. 2. The conventional refrigeration
compressor and condenser referred to in FIG. 1 are not shown in
FIG. 2. The air-cooled or water-cooled condenser cools the
compressor and removes BTU's from the refrigerant by partially
changing the refrigerant mixture from vapor to liquid, whereas the
liquid/gas separator separates liquid refrigerant from vapor and
returns lubricating oil to the compressor. The heat exchangers use
the thermophysical properties of the refrigerants to effect the
cooling process. The evaporator coils permit the flow of
refrigerant at ultra-low temperatures to absorb heat from the
freezer interior, delivering this heat to the condenser for
removal.
[0029] For example, a non-HCFC refrigerant mixture used with this
system is the combination of five refrigerants R-134a
(CF.sub.3CFH.sub.2); R-23 (CHF.sub.3) or R-508 (R-23+R-116b); R-14
(CF.sub.4); R-600 (C.sub.4F.sub.10) or R-600a (CH(CH.sub.3).sub.3);
and R-740 (argon, Ar). The -95.degree. C. systems use a similar
heat exchanger configuration. The following Table 1-1 is arranged
and grouped by refrigerant normal boiling points (NBP).
1TABLE 1-1 NBP NBP NBP NBP Refrigerants 44.degree. F. 4.degree. F.
-13 .degree. F. -108.degree. F. NBP NBP NBP ASHRAE# to 78.degree.
F. to 30.degree. F. to -43.7.degree. F. to -154.degree. F.
-198.degree. F. -258.degree. F. -302.degree. F. R14 E R23 D R50 F
R116 D R134a C R152a C R170 D R236ea A R236fa B R227ea B R245ca A
R245fa A R508a D R508b D R600 B R600a B R740 G R1150 D RC318 B R290
C Note: NBP = Normal Boiling Point
[0030] Other possible non-HCFC refrigerant mixture combinations are
as follows from Table 1-1:
[0031] Mixture 1: A+C+D+E+F+G
[0032] Mixture 2: A+C+D+E+G
[0033] Mixture 3: A+C+D+F+G
[0034] Mixture 4: B+C+D+E+F+G
[0035] Mixture 5: B+C+D+E+G
[0036] Mixture 6: B+C+D+F+G
[0037] Mixture 7: A+B+D+E+F+G
[0038] Mixture 8: A+B+D+E+G
[0039] Mixture 9: A+B+D+F+G
[0040] Mixture 10: A+B+C+D+E+F+G
[0041] Mixture 11: A+B+C+D+E+G
[0042] Mixture 12: A+B+C+D+F+G
[0043] It should be noted that G (R-740) is required in all of the
above non-HCFC refrigerant mixtures (see Table 1-1). These
combinations are for -140.degree. C./-150.degree. C. freezers in
which one refrigerant can be pulled out of each alphabetical group
A to G (see Table 1-1) in order to make a viable mixture.
[0044] For freezers operating between -60.degree. C. to -95.degree.
C., the mixture combinations would exclude group G (R-740). Each
mixture combination has a workable composition range of about
.+-.10 % per refrigerant. For example, if a mixture is a
5-component mixture, (e.g., Mixture 8, A+B+D+E+G) then the
composition for a component would be about 10 to 30 percent by
volume.
[0045] FIG. 2 is a schematic diagram for a -150.degree. C. non-HCFC
autocascade heat exchanger section, wherein a mixture of non-HCFC
refrigerant is pumped from liquid line 1 taken from the condenser
shown in FIG. 1 through liquid/suction heat exchanger 3 to produce
a mixture of gases and liquids at 225 psi and room temperature.
This liquid/gas mixture is then pumped through auxiliary condenser
7 via conduit 5 and exits therefrom via conduit 9. After flowing
through auxiliary condenser 7 the liquid/gas mixture reaches a
temperature of approximately -10.degree. F.
[0046] For example, at -10.degree. F. and a pressure of about 220
psi, refrigerants R-600, R-134a and R-23 become subcooled liquids,
and sink to the bottoms of a vertically-mounted liquid/gas
separator 11. The subcooled liquid mixture is then distributed and
expanded by two capillary tube 13 and 15. The expanded liquid flows
from capillary tube 13 and 15 to conduits 17 and 21, respectively,
to join the return flow of low pressure refrigerant fluids.
[0047] Meanwhile, R-14 and R-740, along with traces of the other
refrigerants of higher boiling points, continue to flow through the
tube side of first condenser 23 via conduit 25. The temperature of
the R-14 and R-740 after passing through first condenser 23 is
approximately -67.degree. F. The traces of R-23 are subcooled to a
liquid phase after passing through first condenser 23 such that it
passes from conduits 35 and 37 into liquid/gas separator 39. Liquid
R-23 and some gases are expanded by capillary tube 41 and pumped
via conduits 43 and 45 to the tube side of second condenser 47.
After passing through second condenser 47, the liquid R-23 is mixed
in conduit 27 with the expanded mixture from conduit 21 and
returned to the shell side of first condenser 23.
[0048] The R-14 and argon gas exiting first condenser 23 via
conduit 35 are pumped via conduit 49 to the shell side of second
condenser 47, exiting therefrom via conduit 51 at a typical
temperature of -130.degree. F. This temperature and the high side
pressure of 215 psig allow a portion of the R-14 to be subcooled
and sent via conduit 53 to capillary tube 55 where it is expanded
and pumped via conduit 57 to cool the tube side of third condenser
59. However, a majority of the R-14 and R-740 are passed through
the shell side of third condenser 59 to conduit 61 and into the
tube side of subcooler 63. Most of the R-14 and R-740 exit
subcooler 63 via conduit 65 at a temperature of -220.degree. F.
These gases are distributed via conduits 67 and 68 to capillary
tube 69 and 70, respectively, where they are expanded to achieve a
final temperature of -260.degree. F. The expanded R-14 and R-740
from capillary tube 70 enter the shell side of subcooler 63 via
conduit 72 to cool the gases passing through the tube side of
subcooler 63. These gases then exit subcooler 63 via conduit 74 and
are joined in conduit 57 with the expanded gases contained in
reservoir or storage tank 76 (i.e., this constitutes the evaporator
coils of FIG. 1) and expanded gases from capillary tube 55 before
passing through the tube side of third condenser 59.
[0049] A portion of the R-14 and R-740 which exit second condenser
47 via conduit 51 are diverted via conduit 80 to an expansion tank
section (not shown) as needed to prevent overpressure of the system
during pull down and heavy loading situations.
[0050] Contemporaneously, the expanded liquid from capillary tube
15 is plumped via conduit 21 to conduit 27 wherein it flows to the
shell side of first condenser 23. The shell side liquid of first
condenser 23 is then merged with the expanded liquid from conduit
17 in conduit 29 and sent to the shell side of auxiliary condenser
7. The expanded liquid from conduit 29 exits auxiliary condenser 7
via conduit 31 and passes along the shell side of liquid/suction
heat exchanger 3 where it is sent via suction line 33 to a single
compressor (i.e., shown in FIG. 1). The compressor referred to in
FIG. 1 compresses the expanded liquid and delivers the compressed
liquid the condenser of FIG. 1 so as to complete the closed loop
circuit of FIG. 1. The use of capillary tube 13 allows liquid phase
refrigerants R-600 and R-134a to continue the journey of
evaporation within auxiliary condenser 7 and liquid/suction heat
exchanger 3, giving an appropriate return condition to prevent the
compressor (not shown) from overheating. Simultaneously, capillary
tube 15 will dispatch enough liquid for the cooling of first
condenser 23. The use of an additional capillary tube 13 to return
refrigerants R-600 and R-134a to the compressor accommodates the
different thermodynamic properties of the non-HCFC refrigerants.
Otherwise, sufficient liquid refrigerants would not be returned to
the compressor to avoid overheating, thereby causing failure of the
refrigeration system.
[0051] FIG. 3 is a schematic diagram for a -95.degree. C. and
-120.degree. C. non-HCFC autocascade heat exchanger section. This
is similar to the heat exchange configuration of the -150.degree.
C. non-HCFC system, except that the refrigerant charges do not
include argon in -95.degree. C. models and have less argon gas in
-120.degree. C. models. The warmer temperatures of these models
make it possible to avoid the expense of a liquid/suction heat
exchanger disposed about suction line 33 and liquid line 1.
[0052] FIG. 4 depicts a conventional CFC-autocascade heat exchanger
section which is similar to the non-HCFC systems shown in FIGS. 2
and 3, except that the subcooled liquid from liquid/gas separator
11 is only distributed and expanded via one capillary tube to the
shell side of the first condenser for cooling of the first
condenser, second condenser and the compressor. As such, the
conventional CFC system of FIG. 4 would cause the compressor to
overheat, if used with the non-HCFC refrigerants, and eventually
result in a system failure.
[0053] Conversely, if a CFC refrigerant is added to the non-HCFC
autocascade refrigeration systems according to the present
invention, then the thermodynamic operation of the system would be
completely disrupted by returning too much liquid to the auxiliary
condenser and thus causing the compressor to be flooded and
eventual failure of the compressor.
[0054] FIGS. 5 and 6 clearly show that the pull down rates at
90.degree. F. ambient are similar for both the conventional CFC
autocascade system and the non-HCFC autocascade system according to
the present invention. For example, both systems exhibit a pull
down rate at discharge after 600 minutes of about 0.192.degree.
C./min. The suction pull down rate after 600 minutes is about
0.033.degree. C./min. for the CFC system and about 0.008.degree.
C./min. for the non-HCFC system. Finally, the pull down rate at the
center temperature after 600 minutes is about 0.24.degree. C./min.
for both systems.
[0055] It should be noted that the lower temperatures at suction,
as exhibited in the non-HCFC system, are highly desirable since
these lower temperatures assist in the cooling of the
compressor.
[0056] The above description and drawings are only illustrative of
preferred embodiments which achieve the objects, features, and
advantages of the present invention, and it is not intended that
the present invention be limited thereto. Any modification of the
present invention which comes within the spirit and scope of the
following claims is considered to be part of the present
invention.
* * * * *