U.S. patent application number 10/476040 was filed with the patent office on 2004-10-21 for refrigerating cycle device.
Invention is credited to Funakura, Masami, Nishiwaki, Fumitoshi, Okaza, Noriho.
Application Number | 20040206109 10/476040 |
Document ID | / |
Family ID | 18998013 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040206109 |
Kind Code |
A1 |
Nishiwaki, Fumitoshi ; et
al. |
October 21, 2004 |
Refrigerating cycle device
Abstract
A refrigerating cycle apparatus including a compressor of
compressing carbon dioxide (CO.sub.2) refrigerant, a radiator of
cooling the refrigerant pressurized by the compressor, a pressure
reducing valve that is arranged more downstream of the radiator
along the refrigerant flow and depressurizes and expands the cooled
refrigerant, and an evaporator that heats the refrigerant
depressurized by the pressure reducing valve, wherein the
refrigerant flow path of the radiator and/or said evaporator is has
a diameter of 1 mm or less; and a refrigeration lubricant of which
main component is a polar oil miscible with the CO.sub.2
refrigerant is utilized.
Inventors: |
Nishiwaki, Fumitoshi;
(Nishinomiya-shi, JP) ; Funakura, Masami;
(Neyagawa-shi, JP) ; Okaza, Noriho; (Kusatsu-shi,
JP) |
Correspondence
Address: |
Allan Ratner
RatnerPrestia
One Westlakes Berwyn Suite 301
PO Box 980
Valley Forge
PA
19482-0980
US
|
Family ID: |
18998013 |
Appl. No.: |
10/476040 |
Filed: |
May 18, 2004 |
PCT Filed: |
May 21, 2002 |
PCT NO: |
PCT/JP02/04904 |
Current U.S.
Class: |
62/468 ;
62/114 |
Current CPC
Class: |
F28F 1/022 20130101;
F28D 1/05391 20130101; F25B 2309/061 20130101; F25B 9/008 20130101;
F28F 1/40 20130101 |
Class at
Publication: |
062/468 ;
062/114 |
International
Class: |
F25B 043/02; F25B
001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2001 |
JP |
2001-153508 |
Claims
1. A refrigerating cycle apparatus, comprising a compressor of
compressing carbon dioxide (CO.sub.2) refrigerant, a radiator of
cooling the refrigerant pressurized by said compressor, a pressure
reducing valve that is arranged more downstream of said radiator
along the refrigerant flow and depressurizes and expands the cooled
refrigerant, and an evaporator that heats the refrigerant
depressurized by said pressure reducing valve, wherein the
refrigerant flow path of said radiator and/or said evaporator has a
diameter of about 1 mm or less; and refrigeration lubricant of
which main component is a polar oil miscible with said CO.sub.2
refrigerant is utilized.
2. The refrigerating cycle apparatus according to claim 1, wherein
said refrigerant flow path is some thin through-holes formed in
flat tubes.
3. The refrigerating cycle apparatus according to claim 1, wherein
an ester oil, an ether oil, polyalkyleneglycol oil, polycarbonate
oil, or a mixed oil thereof is used as said refrigeration
lubricant.
4. The refrigerating cycle apparatus according to claim 1, wherein
the moisture content contained in said refrigeration lubricant is
100 ppm or less.
5. The refrigerating cycle apparatus according to claim 2, wherein
said thin through-holes are thin holes with inside grooves in which
grooves are formed on the inner surface.
6. The refrigerating cycle apparatus according to claim 5, wherein
the groove shape of said through-holes with inside grooves is
trapezoidal.
Description
TECHNICAL FIELD
[0001] The present invention relates to a refrigerating cycle
apparatus such as a refrigerating machine and an air-conditioning
machine using carbon dioxide (hereinafter denoted as CO.sub.2) as
the main refrigerant.
BACKGROUND ART
[0002] At present, fluorocarbons containing chlorine but not
containing hydrogen (hereinafter denoted as CFC) and fluorinated
hydrocarbons containing both chlorine and hydrogen (hereinafter
denoted as HCFC) are used as the refrigerants in the refrigerating
cycle apparatus in air conditioners, refrigerators, freezers,
vending machines, heat pump hot water suppliers and the like
because these refrigerants are stable in physical properties and
easy in handling.
[0003] The CFC and HCFC refrigerants, however, have characteristics
to promote the depletion of the ozone layer, and accordingly the
adoption of the fluorinated hydrocarbons which do not contain
chlorine but contain hydrogen in the molecular structure
(hereinafter denoted as HFC) as the alternative refrigerants has
been proposed. Additionally, because the CFC, HCFC and HFC
refrigerants have characteristics to promote global warming, the
adoption of natural refrigerants having an extremely feeble effect
on global warming as the alternative refrigerants has been
proposed.
[0004] Because among even the natural refrigerants, however,
hydrocarbons (hereinafter denoted as HC) are strongly flammable so
that there is the danger of catching fire and exploding, and the
ammonia refrigerant is toxic so that there is a problem that a
hazard possibly occurs at the time of leakage thereof, the adoption
of the CO.sub.2 refrigerant which is nonflammable, nontoxic and low
in price has been considered.
[0005] A refrigerating cycle apparatus using the CO.sub.2
refrigerant has a configuration in which the high pressure line is
operated under the supercritical region because the critical
temperature of the CO.sub.2 refrigerant is 31.degree. C. A commonly
used refrigerating cycle apparatus is constructed by connecting
together by piping a compressor which compresses the refrigerant to
elevate the pressure thereof, a four way valve according to need, a
radiator which cools the refrigerant, a pressure reducing valve
which reduces the pressure of the refrigerant such as a capillary
tube and an expansion valve, an evaporator which evaporates and
gasifies the refrigerant and the like; and the refrigerant is
circulated in the interior of the apparatus to conduct cooling or
heating operation.
[0006] As the heat exchanger used in the radiator and evaporator of
the refrigerating cycle apparatus using the CO.sub.2 refrigerant, a
heat exchanger referred to as a microtube heat exchanger is used. A
microtube heat exchanger is composed of flat tubes internally
provided with a plurality of thin through-holes (the refrigerant
flow path) and fins arranged between the flat tubes for the purpose
of increasing the heat transfer area for the external fluid (for
example, the air). The thin through-holes have a circular sectional
shape and are of the order of 1 mm in hole size.
[0007] Additionally, as the refrigeration lubricant for the
CO.sub.2 refrigerant, mineral oils have been frequently used from
the viewpoint of the excellent lubricity thereof (see the
reference: B. E. Fagerli, "Development and Experiment with a
Hermetic CO.sub.2 Compressor," Proceeding of the 1996 International
Engineering Conference at Purdue, 229-234).
[0008] Incidentally, a mineral oil is a nonpolar oil and hence
immiscible with the CO.sub.2 refrigerant. The refrigeration
lubricant discharged from the compressor into the cycle together
with the refrigerant flows through the refrigerant flow paths in
the radiator and evaporator in the form of oil drops or oil film
coating the tube inner wall in a ring shape. This causes the heat
transfer inhibition and the increase of the pressure loss, and
becomes the cause for the dimensional enlargement and efficiency
degradation of the heat exchanger. Particularly, the heat transfer
degradation ascribable to the refrigeration lubricant is remarkable
in the evaporator which is not operated in the supercritical
region.
[0009] Additionally, the present inventor has found that in the
case of the microtube heat exchanger, the refrigerant flow path
consists of very thin heat transfer tubes of the order of 1 mm in
hole size, and hence the effect of the heat transfer inhibition and
pressure loss due to oil films and oil drops formed on the tube
inner wall is larger as compared to the refrigerant flow path
having a large sectional area of a pipe diameter of the order of 5
mm as has been applied to the conventional HFC refrigerants.
Detailed description will be made below on the content of the above
described finding.
[0010] FIGS. 6 and 7, respectively, are the graphs showing the
characteristics of the evaporating ability and pressure loss in the
evaporator, which has the flat tubes each consisting of microtubes
having hydraulic diameter of 1.2 mm as the refrigerant flow path.
As the refrigeration lubricant, a mineral oil that is a nonpolar
oil immiscible with the CO.sub.2 refrigerant is used. The
horizontal axis in each figure represents the oil circulation rate
that is obtained by dividing the oil (refrigeration lubricant)
circulation quantity by the refrigerant circulation quantity. It
can be seen that in the case of an immiscible oil, the heat
transfer coefficient is remarkably decreased due to the increase in
the oil circulation rate and the pressure loss is remarkably
increased.
[0011] The calculated values obtained from a variety of
experimental data including the data presented in FIGS. 6 and 7 on
the basis of the correlation formulas which will be described below
are in good agreement with the evaporation heat transfer
coefficient and pressure loss values of the flat tubes in the case
where the oil and CO.sub.2 refrigerant are circulated.
[0012] In other words, as for the evaporation heat transfer
coefficient, the Liu-Winterton correlation formula, generally known
as the correlation formula for the evaporation heat transfer
coefficient in the tube, has been modified using the parameter Kfh
taking account of the oil mixing effect on the nucleate boiling
heat transfer coefficient, while as for the forced convection heat
transfer coefficient, a modification has been made in which the
values of the physical properties of the liquid are replaced with
the values of the mixed properties of the refrigerant and oil.
[0013] (Equation 1)
h=a.multidot.{(E.multidot.hl).sup.2+(S.multidot.h
pool).sup.2}.sup.0.5 (Formula 1)
[0014] (Equation 2)
h
pool=55.multidot.Pr.sup.0.12.multidot.{-logPr}.sup.-0.55.multidot.M.sup.-
-0.5.multidot.q.sup.0.67.multidot.Kfh (Formula 2)
[0015] Here, h denotes the evaporation heat transfer coefficient, a
denotes a constant, hl denotes the forced convection heat transfer
coefficient for the case where only the liquid phase is assumed to
flow, h pool denotes the pool boiling heat transfer coefficient,
and E and S, respectively, are the parameters representing the
extents of the forced convection and nucleate boiling.
[0016] Additionally, as for the pressure loss, to the
Lockhart-Martinelli correlation formula generally known as the
two-phase flow pressure loss correlation formula, a modification
has been made in which the values of the physical properties of the
liquid are replaced with the values of the mixed properties of the
refrigerant and oil.
[0017] (Equation 3)
.DELTA.P=.phi..sup.2.multidot..DELTA.Pf.multidot.Kfp (Formula
3)
[0018] Here, .phi. denotes the Martinelli parameter, .DELTA.Pf
denotes the pressure loss for the case where only the liquid phase
is assumed to flow, and Kfp is a correction parameter.
[0019] FIG. 8 is a characteristic diagram (a representative
example) showing the evaporation heat transfer coefficient and
pressure loss of the CO.sub.2 refrigerant obtained from the above
described correlation formulas. The horizontal axis represents the
oil circulation rate obtained by dividing the oil circulation
quantity by the refrigerant circulation quantity. Besides, the
vertical axis represents the quantity in percent which is obtained
by dividing the ratio of heat transfer coefficient based on the
value assumed to be 100 for the oil circulation rate of 0% by the
ratio of pressure loss based on the value assumed to be 100 for the
oil circulation rate of 0%. In other words, the ordinate value
becomes 100 when the oil circulation rate is 0%, and the smaller
than 100 is the ordinate value, the larger is the heat transfer
coefficient depression due to the oil circulation rate increase
and/or the larger is the pressure loss due to the oil circulation
rate increase.
[0020] Additionally, FIG. 8 also shows the characteristics for the
thin tubes with different hydraulic diameters De, and reveals that
the smaller is the hydraulic diameter De, the larger is the heat
transfer coefficient depression and/or the larger is the pressure
loss increase.
[0021] Thus, for the purpose of more detailed examination, FIG. 9
shows the relation between the (heat transfer coefficient/pressure
loss) reduction rate in relation to the oil circulation rate
increase from 0% to 4% and the hydraulic diameter De. It can be
seen that the (heat transfer coefficient/pressure loss) reduction
rate is sharply increased when the hydraulic diameter De is
decreased further from the order of 1 mm. In other words, it is
shown that when the hydraulic diameter De is made further thinner
than the order of 1 mm, the immiscible oil allows the oil film to
be formed on the tube inner wall or the oil drops to be scattered
in the interior of the tube, and hence the depression of the heat
transfer coefficient becomes large and/or the increase of the
pressure loss becomes large.
[0022] A first invention of the present invention is a
refrigerating cycle apparatus, comprising a compressor of
compressing carbon dioxide (CO.sub.2) refrigerant, a radiator of
cooling the refrigerant pressurized by said compressor, a pressure
reducing valve that is arranged more downstream of said radiator
along the refrigerant flow and depressurizes and expands the cooled
refrigerant, and an evaporator that heats the refrigerant
depressurized by said pressure reducing valve,
[0023] wherein the refrigerant flow path of said radiator and/or
said evaporator is thin tubes of 1 mm or less; and
[0024] Refrigeration lubricant of which main component is a polar
oil miscible with said CO.sub.2 refrigerant is utilized.
[0025] A second invention of the present invention is the
refrigerating cycle apparatus according to the first invention of
the present invention, wherein said refrigerant flow path is a
plurality of thin through-holes formed in flat tubes.
[0026] A third invention of the present invention is the
refrigerating cycle apparatus according to the first invention of
the present invention,. wherein an ester oil, an ether oil,
polyalkyleneglycol oil, polycarbonate oil, or a mixed oil thereof
is used as said refrigeration lubricant.
[0027] A fourth invention of the present invention is the
refrigerating cycle apparatus according to the first invention of
the present invention, wherein the moisture content contained in
said refrigeration lubricant is 100 ppm or less.
[0028] A fifth invention of the present invention is the
refrigerating cycle apparatus according to the second invention of
the present invention, wherein said thin through-holes are thin
holes with inside grooves in which grooves are formed on the inner
surface.
[0029] A sixth invention of the present invention is the
refrigerating cycle apparatus according to the fifth invention of
the present invention, wherein the groove shape of said
through-holes with inside grooves is trapezoidal.
DISCLOSURE OF THE INVENTION
[0030] The present invention solves such problems found in the
conventional refrigerating cycles as described above and takes as
its object the provision of a compact refrigerating cycle apparatus
with high efficiency using the CO.sub.2 refrigerant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic block diagram showing the
refrigerating cycle apparatus in an embodiment 1 of the present
invention;
[0032] FIG. 2 is a schematic view showing the structure of a heat
exchanger used in the embodiment 1 of the present invention;
[0033] FIG. 3 is a schematic view showing the structure of a heat
transfer tube used in the heat exchanger in the embodiment 1 of the
present invention;
[0034] FIG. 4 is an enlarged schematic view of the structure of the
important part of the heat transfer tube of the heat exchanger used
in the refrigerating cycle apparatus in an embodiment 2 of the
present invention;
[0035] FIG. 5 is an enlarged schematic view of the structure of the
important part of the heat transfer tube of the heat exchanger used
in the refrigerating cycle apparatus in an embodiment 3 of the
present invention;
[0036] FIG. 6 is a graph showing the characteristics of the
evaporation ability against the oil circulation rate in the
evaporator, which has flat tubes in which microtubes of 1.2 mm in
hydraulic diameter are used as the refrigerant flow path;
[0037] FIG. 7 a graph showing the characteristics of the pressure
loss against the oil circulation rate in the evaporator utilizing
flat tubes in which microtubes of 1.2 mm in hydraulic diameter are
used as the refrigerant flow path;
[0038] FIG. 8 is a graph showing the characteristics of the thin
tubes different in the hydraulic diameter De;
[0039] FIG. 9 is a graph showing the relation between the (heat
transfer coefficient/pressure loss) reduction rate and the
hydraulic diameter De for the case where the oil circulation rate
is increased from 0% to 4%;
[0040] FIG. 10 is a graph showing the tensile strength
characteristic diagram of PET resin after the test when an
autoclave test has been performed; and
[0041] FIG. 11 is a graph showing the elongation characteristic
diagram of PET resin after the test when an autoclave test has been
performed.
DESCRIPTION OF SYMBOLS
[0042] 1, 31, 41 Flat tube
[0043] 2 Thin through-hole
[0044] 3 Heat exchanger
[0045] 9 Fin
[0046] 11 Compressor
[0047] 12 Radiator
[0048] 13 Pressure reducing valve
[0049] 14 Evaporator
[0050] 15 Oil separator
[0051] 16 Auxiliary heat exchanger
[0052] 17 Sub pressure reducing valve
[0053] 32, 42 Thin hole with inside grooves
BEST MODE FOR CARRYING OUT THE INVENTION
[0054] Description will be made below on the embodiments of the
present invention with reference to the accompanying drawings.
[0055] (Embodiment 1)
[0056] FIG. 1 shows a schematic block diagram showing the
refrigerating cycle apparatus in an embodiment 1 of the present
invention. FIG. 2 is a schematic view showing the structure of a
heat exchanger used in the radiator and evaporator, and FIG. 3 is a
schematic view showing the structure of the heat transfer tube used
in the above described heat exchanger.
[0057] In FIGS. 1 to 3, reference numeral 11 denotes a compressor,
12 denotes a radiator having a plurality of thin through-holes 2
formed in the flat tube 1 as the refrigerant flow path, 13 denotes
a pressure reducing valve, and 14 denotes an evaporator having a
plurality of thin through-holes 2 formed in the flat tubes 1 as the
refrigerant flow path; these are connected together by piping to
form a closed loop that constitutes a refrigerating cycle in which
the CO.sub.2 refrigerant is circulated along the direction of the
arrows written in the figure.
[0058] Furthermore, an auxiliary heat exchanger 16 is arranged to
perform heat exchange between the refrigerant flow path in the heat
release section that is the refrigerant flow path falling in the
range from the outlet of the radiator 12 to the inlet of the
pressure reducing valve 13 and the refrigerant flow path in the
evaporation section that is the refrigerant flow path falling in
the range from the outlet of the evaporator 14 to the suction part
of the compressor 11.
[0059] Additionally, an oil separator 15 is arranged between the
compressor 11 and the radiator 12. Here is a configuration in which
the refrigeration lubricant separated in the oil separator 15 is
made to return to the compressor 11 through the intermediary of a
sub pressure reducing valve 17 along an auxiliary path 18 connected
by piping to the compressor 11. Incidentally, the part of the
refrigeration lubricant that has not been separated in the oil
separator 15 comes to flow together with the refrigerant in the
radiator 12 and the evaporator 14 in the refrigerating cycle.
[0060] Additionally, as FIGS. 2 and 3 show, the heat exchanger 3
used in the radiator and evaporator has a configuration in which a
plurality of the plate-like flat tubes 1 (heat transfer tubes),
each having a plurality of thin through-holes 2 penetrated in the
lengthwise direction, are laminated in the thickness direction of
the plate shape approximately with the predetermined intervals, and
both lengthwise ends of the plate shape are inserted into a pair of
header pipes 4, 5. For the purpose of coping with the high pressure
in the supercritical state and improving the heat transfer
coefficient in tubes, the hole diameter of the thin through-holes 2
is made to be as small as about 1 mm, and additionally the
sectional shape thereof is made to be circular.
[0061] Additionally, in the pair of the header pipes 4, 5 are
arranged partition plates 6 that partition the interior of each
header pipe in to a plurality of partitions along the lengthwise
direction. Additionally, a refrigerant inlet 7 for introducing the
refrigerant into the heat exchanger 3 is arranged on either of the
pair of the header pipes 4, 5, and a refrigerant outlet 8 for
discharging the refrigerator from the heat exchanger 3 is arranged
on either of the pair of the header pipes 4, 5. A plurality of the
plate-like flat tubes 1 are arranged along the thickness direction
approximately at even intervals, and fins 9 (wavy fins) are
arranged between the flat tubes 1 for the purpose of enlarging the
area for heat transfer to the external fluid (for example, the
air).
[0062] Besides, the CO.sub.2 refrigerant is used as the refrigerant
and polyalkyleneglycol oil (PAG oil) that is a polar oil is used as
the refrigeration lubricant, the moisture content of which is
adjusted to be 100 ppm or lower.
[0063] In the next place, description will be made below on the
operation of the refrigerating cycle apparatus that has such a
configuration as described above.
[0064] The CO.sub.2 refrigerant compressed in the compressor 11
takes a high temperature and high pressure state, and is introduced
into the radiator 12. In the radiator 12, the CO.sub.2 refrigerant
does not take the gas/liquid two phase state when the CO.sub.2
refrigerant flows in the supercritical state, releases the heat to
the media including the air and water, and is further cooled in the
refrigerant flow path of the auxiliary heat exchanger 16 in the
heat release section, which is from the outlet of the radiator 12
to the inlet of the pressure reducing valve 13. The CO.sub.2
refrigerant is depressurized in the pressure reducing valve 13 to
take a low-pressure gas/liquid two-phase state, and is introduced
into the evaporator 14. In the evaporator 14, the CO.sub.2
refrigerant absorbs the heat from the air and the like, and takes a
gaseous state in the refrigerant flow path of the auxiliary heat
exchanger 16 in the evaporation part, which is from the outlet of
the evaporator 14 to the suction part of the compressor 11, and is
again sucked into the compressor 11.
[0065] Through repeating such a cycle as described above, the
heating action is made in the radiator 12 by heat release and the
cooling action is made in the evaporator 14 by heat absorption. In
this connection, in the auxiliary heat exchanger 16, heat exchange
occurs between the relatively high temperature CO.sub.2 refrigerant
leaving the radiator 12 and going to the pressure reducing valve 13
and the relatively low temperature CO.sub.2 refrigerant leaving the
evaporator 14 and going to the compressor 11. Accordingly, the
CO.sub.2 refrigerant having left the radiator 12 is further cooled
and then depressurized in the pressure reducing valve 13, and hence
the enthalpy is decreased at the inlet of the evaporator 14 to
increase the enthalpy difference between the inlet and outlet of
the evaporator 14, and the endothermic ability (cooling capacity)
is thereby increased.
[0066] Furthermore, detailed description will be made below on the
operation of the heat exchanger 3 acting as the radiator 12. As
shown by the arrows in FIG. 2, the refrigerant in the supercritical
state flows through the refrigerant inlet 7 into the space above
the partition plate 6 in the header pipe 4, (1) flows into the
upper portion of the header pipe 5 through the thin through-holes 2
in the plurality of the flat tubes 1 inserted into the portion
above the partition plate 6 in the header pipe 4, (2) flows through
from the upper portion to the middle portion (the space above the
partition plate 6) of the header pipe 5, (3) flows in through the
thin through-holes 2 in the flat tubes 1 into the middle portion of
the header pipe 4, (4) flows through from the middle portion to the
bottom portion of the header pipe 4, and (5) flows in through the
thin through-holes 2 in the flat tubes 1 into the bottom portion
(the space beneath the partition plate 6) of the header pipe 5 and
flows out from the refrigerant outlet 8 at a low temperature.
[0067] In the present embodiment, polyalkyleneglycol oil (PAG oil)
that is a polar oil is used so that the refrigeration lubricant
discharged from the compressor together with the CO.sub.2
refrigerant into the cycle is miscible in the CO.sub.2 refrigerant.
Consequently, even when the refrigerant flow path, which is thin
tubes of 1 mm or less, no oil film that is to be thermal resistance
is formed on the inside wall surface of the thin through-holes 2 of
the flat tubes 1 constituting the refrigerant flow path of the
radiator, and hence no degradation of the heat transfer performance
occurs so that it is possible to effectively take advantage of the
high heat transfer coefficient that is possessed by the
CO.sub.2refrigerant in the supercritical state. Additionally,
because no oil film is formed on the inside wall surface of the
thin through-holes 2 and no oil flows as oil drops, no increase of
the pressure loss is brought on. Consequently, the intratube heat
transfer rate is very high and the performance degradation caused
by pressure loss can be suppressed, which makes it possible to make
the radiator compact and high in performance.
[0068] In the case of the evaporator, the CO.sub.2 refrigerant
taking the low-pressure gas/liquid two-phase state flows, together
with the refrigeration lubricant, into the thin through-holes 2 of
the flat tubes 1 constituting the refrigerant flow path in the
evaporator, and flows therein as annular mist flow while being
evaporated by absorbing heat from the air and the like.
Accordingly, the heat transfer coefficient on the inside wall
surface of the heat transfer tube significantly affects the overall
performance; in the present embodiment, similarly to the case of
the radiator, polyalkyleneglycol oil (PAG oil) that is miscible in
the CO.sub.2 refrigerant is used, and hence no oil film that is to
be thermal resistance is formed on the tube inner wall surface of
the thin through-holes 2 of the flat tubes 1 even when the
refrigerant flow path is formed using thin tubes of 1 mm or less.
Consequently, neither degradation of the heat transfer nor increase
of the pressure loss is brought on in the evaporator, which makes
it possible to make the evaporator compact and high in
efficiency.
[0069] Incidentally, in the above explanation, description has been
made on the basis of polyalkyleneglycol oil (PAG oil) as a polar
oil; even when another oil such as polyol ester oil, polyvinyl
ether oil, polycarbonate oil, or mixed oil thereof is used as a
polar oil, similar effects can be obtained because these oils are
high in miscibility in the CO.sub.2 refrigerant.
[0070] Incidentally, depending on the operation conditions, even
when a polar oil is used, the refrigeration lubricant cannot
completely be miscible with the CO.sub.2 refrigerant, and sometimes
the polar oil flows as the refrigeration lubricant in the
refrigerating cycle. However, the CO.sub.2 refrigerant is easily
soluble in the refrigeration lubricant, and hence the viscosity of
the refrigeration lubricant is remarkably reduced and the fluidity
thereof is improved. Accordingly, as compared to the conventional
cases where mineral oils that are nonpolar oils are used, the
degradation of the heat transfer and the increase of the pressure
loss become slight, which makes it possible to actualize a
high-performance heat exchanger.
[0071] Additionally, in the present embodiment, when a polar oil is
used, the polar oil is not hydrolyzed because the moisture content
contained in the refrigeration lubricant is adjusted to be 100 ppm
or less and the refrigeration lubricant is not deteriorated and
thus the reliability is not failed.
[0072] Additionally, the adjustment of the moisture content
contained in the refrigeration lubricant to 100 ppm or less makes
it possible to adjust the content of the moisture entering into the
refrigerating cycle to be 100 ppm or less, and accordingly the
effects described below occur.
[0073] The present inventor has confirmed the novel facts and
effects obtained by the above described means on the basis of the
experiments described below. The CO.sub.2 refrigerant, PET
(polyethylene terephthalate) resin film and the refrigeration
lubricant containing the moisture content of 200 ppm were sealed in
an autoclave container, and the autoclave test for the test time
period of 500 hours was performed at 140.degree. C. and at the
pressures of 8 MPa and 11 MPa. The PET resin is a commercially
time-proven resin as an insulating film in compressors for the
refrigerant R134a. The post-test tensile strength and elongation
characteristics of the PET resin are shown in FIGS. 10 and 11,
respectively. It can be seen that as compared with the pre-test
initial characteristics, the tensile strength and elongation
characteristics of the PET resin exposed to the high pressure
CO.sub.2 refrigerant are remarkably deteriorated. Additionally, it
has been revealed that the tensile strength and elongation
characteristics of the PET resin are scarcely deteriorated as
compared to the initial characteristics when the moisture content
contained in the refrigeration lubricant is adjusted to be 100 ppm
or less. Needless to say, from the market achievement, it is
apparent that the PET resin is not deteriorated in the R134a
refrigerant, and hence the deterioration phenomenon of this resin
caused by the moisture is a feature specific to the CO.sub.2
refrigerant.
[0074] From the above experimental results, it has been revealed
that an insulating film such as PET resin in the refrigerating
cycle is deteriorated in the case where the moisture content
contained in the refrigerating cycle exceeds 100 ppm, but is
scarcely deteriorated when the moisture content is 100 ppm or less.
Accordingly, in the present embodiment, the resin deterioration in
the refrigerating cycle is not caused and the reliability can be
enhanced since the moisture content entering into the refrigerating
cycle can be adjusted to be 100 ppm or less by adjusting the
moisture content contained in the refrigeration lubricant to be 100
ppm or less.
[0075] Additionally, in the present embodiment, description has
been developed on the basis of the refrigerating cycle provided
with an oil separator 15, but it is obvious that the present
invention displays the effect thereof particularly for the case
where an oil separator 15 is absent since the present invention
utilizes a polar oil soluble in the refrigerant.
[0076] (Embodiment 2)
[0077] Description will be made below on the refrigerating cycle
apparatus in embodiment 2 of the present invention with reference
to the accompanying drawing.
[0078] FIG. 4 is an enlarged schematic view of the structure of the
important part of the heat transfer tube of the heat exchanger used
in the refrigerating cycle apparatus in embodiment 2 of the present
invention. The present embodiment is different from embodiment 1 in
that a plurality of the thin through-holes, formed in the flat
tubes 31 that are the refrigerant flow path in the radiator and
evaporator, are made to be thin holes 32 with inside grooves that
are provided with a large number of small triangle-shaped grooves
on the inner surface thereof. The outer diameter (a virtual
diameter from a groove trough to the opposing groove trough) of a
thin hole 32 with inside grooves is taken to be 1 mm and the groove
depth is taken to be 0.1 mm. Polyol ester oil (POE oil) that is a
polar oil is used for the refrigeration lubricant and the moisture
content in the oil is adjusted to be 100 ppm or less.
[0079] In this way, the thin through-holes that are the refrigerant
flow path in the heat exchanger are made to be the thin holes 32
with inside grooves in which a large number of small
triangle-shaped grooves are provided on the inner surface thereof,
and hence the heat transfer area of the refrigerant flow path is
increased and additionally the heat transfer coefficient of the
refrigerant is improved dramatically owing to the refrigerant
stirring effect provided by the minute grooves and the like.
[0080] Incidentally, in the present embodiment, since polyol ester
oil (POE oil) that is a polar oil is used, the refrigeration
lubricant discharged from the compressor into the cycle together
with the CO.sub.2 refrigerant is miscible in the CO.sub.2
refrigerant. Consequently, the oil film that is to be thermal
resistance is not formed on the tube inner wall surface of the thin
holes 32 with inside grooves in the flat tubes 31 constituting the
refrigerant flow path of the radiator and evaporator so that the
heat transfer is not degraded, and hence the high heat transfer
coefficient that is possessed by the CO.sub.2 refrigerant can be
effectively utilized.
[0081] Additionally, no oil film is formed on the tube inner wall
surface of the thin holes 32 with inside grooves, and additionally
no oil flows as oil drops so that no increase in pressure loss is
brought on. Accordingly, the heat transfer coefficient in the tubes
is very high and the performance degradation due to the pressure
loss can be suppressed, which makes it possible to make the heat
exchanger compact and high in performance.
[0082] Incidentally, even when polyol ester oil (POE oil) that is a
polar oil is used as the refrigeration lubricant, in the case where
the temperature is high in the temperature condition in the
radiator and evaporator and the weight ratio of the refrigeration
lubricant is large, the CO.sub.2 refrigerant and the refrigeration
lubricant cannot completely be miscible with each other, and hence
in some cases the oil film is slightly formed on the inner wall
surface of the heat transfer tubes which constitute the refrigerant
flow paths of the radiator and evaporator. In this case, when the
refrigerant flow path is made of thin holes of 1 mm or less, the
heat transfer coefficient tends to be degraded as described in the
section of Background Art; however, in the present embodiment, the
thin holes 32 with inside grooves in which grooves are provided on
the tube inner wall surface are used and hence the heat transfer
area is increased and the stirring effect due to the grooves is
generated so that the tube inner wall surface is not wholly coated
with the oil film. Furthermore, the CO.sub.2 refrigerant has a very
high pressure, and hence the miscible amount of the CO.sub.2 in the
refrigeration lubricant itself becomes large so that the viscosity
of the refrigeration lubricant is decreased and the fluidity
thereof is improved. Accordingly, the increase of the pressure loss
also becomes slight. In this way, the thin through-holes through
which flow the CO.sub.2 refrigerant and the polar oil are made to
be the thin holes 32 with inside grooves, and hence even under the
operation condition that the oil film is easily formed, it comes to
be possible to prevent the degradation of the heat transfer and the
increase of the pressure loss, which makes it possible to actualize
a high-performance heat exchanger.
[0083] Incidentally, in the above explanation, description has been
developed on the basis of the polyol ester oil (POE oil) used as
the polar oil; however, similar effects can be obtained even when
other polar oils are used because the polar solvents are high in
miscibility in the CO.sub.2 refrigerant.
[0084] Additionally, in the present embodiment, when a polar oil is
used, the polar oil is not hydrolyzed because the moisture content
contained in the refrigeration lubricant is adjusted to be 100 ppm
or less and the refrigeration lubricant is not deteriorated and
thus the reliability is not failed.
[0085] (Embodiment 3)
[0086] Description will be made below on the refrigerating cycle
apparatus in embodiment 3 of the present invention with reference
to the accompanying drawing.
[0087] FIG. 5 is an enlarged schematic view of the structure of the
important part of the heat transfer tube of the heat exchanger used
in the refrigerating cycle apparatus in embodiment 3 of the present
invention. The present embodiment is different from embodiment 2 in
that a plurality of the thin through-holes with inside grooves,
formed in the flat tubes 41 that are the refrigerant flow path in
the radiator and evaporator, are made to be thin holes 42 with
inside trapezoidal grooves in which the groove shape is made to be
trapezoidal. Incidentally, the outer diameter (a virtual diameter
from a groove trough to the opposing groove trough) of a thin hole
42 with inside grooves is taken to be 1 mm and the groove depth is
taken to be 0.1 mm, and the number of the grooves is identical to
that in the case of the triangular grooves (the dotted line 43 in
FIG. 5.) of the above described embodiment 2, but the groove shape
is made to be trapezoidal. Besides, polyvinyl ether oil (PVE oil),
that is a polar oil is used for the refrigeration lubricant and the
moisture content in the oil is adjusted to be 100 ppm or less.
[0088] As described above, the heat transfer coefficient of the
refrigerant is improved dramatically because, the thin
through-holes that are the refrigerant flow path in the heat
exchanger are made to be the thin holes 42 with inside grooves in
which a large number of small trapezoid-shaped grooves are provided
on the inner surface thereof and hence the heat transfer area of
the refrigerant flow path is increased as compared to the heat
transfer tube in the above described embodiment 2 which has the
same groove depth and the same groove number of triangular grooves,
additionally the wetted perimeter length of the refrigerant flow
path is increased to decrease the hydraulic diameter, the
refrigerant stirring effect and the like are provided by the minute
grooves, and additionally, in the case of the circulating flow, the
liquid film thickness is made to be uniform owing to the increased
ability for holding the refrigerant in the grooves. Incidentally, a
high heat transfer coefficient can be achieved in the above
described embodiment 2, but the presence of the grooves sometimes
causes the inconvenience that the oil film is easily formed in the
groove trough portions; however, in the present embodiment 3, the
grooves are trapezoidal which makes the groove sectional area
larger so that the oil film is hardly formed in the groove trough
portions.
[0089] Incidentally, in the present embodiment, since polyvinyl
ether oil (PVE oil) that is a polar oil is used, the refrigeration
lubricant discharged from the compressor into the cycle together
with the CO.sub.2 refrigerant is miscible in the CO.sub.2
refrigerant. Consequently, the oil film that is to be thermal
resistance is not formed on the tube inner wall surface of the thin
holes 42 with inside grooves in the flat tubes 41 constituting the
refrigerant flow path of the radiator and evaporator so that the
heat transfer is not degraded, and hence the high heat transfer
coefficient that is possessed by the CO.sub.2 refrigerant can be
effectively utilized.
[0090] Additionally, no oil film is formed on the tube inner wall
surface of the thin holes 42 with inside grooves, and additionally
no oil flows as oil drops so that increase in no pressure loss is
brought on. Accordingly, the heat transfer coefficient in the tubes
is very high and the performance degradation due to the pressure
loss can be suppressed, which makes it possible to make the heat
exchanger compact and high in performance.
[0091] Incidentally, even when polyvinyl ether oil (PVE oil) that
is a polar oil is used as the refrigeration lubricant, in the case
where the temperature is high in the temperature condition in the
radiator and evaporator and the weight ratio of the refrigeration
lubricant is large, the CO.sub.2 refrigerant and the refrigeration
lubricant cannot completely be miscible with each other, and hence
in some cases the oil film is slightly formed on the inner wall
surface of the heat transfer tube which constitutes the refrigerant
flow path of the radiator and evaporator. In this case, when the
refrigerant flow path is made of thin holes of 1 mm or less, the
heat transfer coefficient tends to be degraded as described in the
section of Background Art; however, in the present embodiment, the
refrigerant flow path is made to be the thin holes 42 with inside
grooves in which trapezoidal grooves are provided on the tube inner
wall surface and hence the heat transfer area is further increased
as compared to embodiment 2 and the stirring effect due to the
grooves is generated so that the tube inner wall surface is not
wholly coated with the oil film. Furthermore, the CO.sub.2
refrigerant has a very high pressure, and hence the miscible amount
of the CO.sub.2 in the refrigeration lubricant itself becomes large
so that the viscosity of the refrigeration lubricant is decreased
and the fluidity thereof is improved. Accordingly, the increase of
the pressure loss also becomes slight. In this way, the thin
through-holes through which flow the CO.sub.2 refrigerant and the
polar oil are made to be the thin holes 42 with inside grooves, and
hence even under the operation condition that the oil film is
easily formed, it comes to be possible to prevent the degradation
of the heat transfer and the increase of the pressure loss, which
makes it possible to actualize a high-performance heat
exchanger.
[0092] Incidentally, in the above explanation, description has been
developed on the basis of the polyvinyl ether oil (PVE oil) used as
the polar oil; however, similar effects can be obtained even when
other polar oils are used because the polar solvents are high in
miscibility in the CO.sub.2 refrigerant.
[0093] Additionally, in the present embodiment, when a polar oil is
used, the polar oil is not hydrolyzed because the moisture content
contained in the refrigeration lubricant is adjusted to be 100 ppm
or less and the refrigeration lubricant is not deteriorated so that
the reliability is not failed.
[0094] Industrial Applicability
[0095] As can be clearly seen from the above description, according
to the present invention, the refrigerant flow path in the heat
exchanger for the CO.sub.2 refrigerant is made to be a plurality of
thin through-holes formed in flat tubes and the refrigeration
lubricant containing a polar oil as the main component is used, so
that the oil film that is to be thermal resistance and flow
resistance is not formed on the tube inner wall surface of thin
through-holes, and hence the degradation of the heat transfer
coefficient and the increase of the pressure loss in the heat
exchanger can be suppressed, which makes it possible to actualize a
compact and high-performance refrigerating cycle apparatus
utilizing the CO.sub.2 refrigerant.
* * * * *