Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2180598
TITLE OF THE INVENTION
REFRIGERANT TUBES FOR HEAT EXCHANGERS
BACKGROUND OF THE INVENTION
The present invention relates to tubes for
passing a refrigerant therethrough, i.e., refrigerant
tubes, for heat exchangers, and more particularly to
refrigerant tubes for condensers and evaporators for
use in air-cooling systems for motor vehecles.
The term "aluminum" as used herein and in the
claims includes pure aluminum and aluminum alloys.
JP-B-45300/1991 discloses a condenser for
use in air-cooling systems for motor vehicles which
comprises a pair of headers arranged at right and
left in parallel and spaced apart from each other,
parallel flat refrigerant tubes each joined at its
opposite ends to the two headers, corrugated fins
arranged in air flow clearances between the adjacent
refrigerant tubes and brazed to the adjacent refrigerant
tubes, an inlet pipe connected to the upper end of the
left header, an outlet pipe connected to the lower end
of the right header, a left partition provided inside
the left header and positioned above the midportion
thereof, and a right partition provided inside the
right header and positioned below the midportion thereof,
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the number of refrigerant tubes between the inlet pipe
and the left partition, the number of refrigerant tubes
between the left partition and the right partition and
the number of refrigerant tubes between the right
partition and the outlet pipe decreasing from above
downward. A refrigerant flowing into the inlet pipe in
a vapor phase flows zigzag through the condenser before
flowing out from the outlet pipe in a liquid phase.
Condensers of the construction described are called
parallel flow or multiflow condenser, realize higher
efficiencies, lower pressure losses and supercompact-
ness and are in wide use recently in place of conven-
tional serpentime condensers.
It is required that the flat refrigerant tube
for use in the condenser have pressure resistance since
the refrigerant is introduced thereinto in the form of
a gas of high pressure. To meet this requirement and
to achieve a high heat exchange efficiency, the refrig-
erant tube used is in the form of a flat aluminum tube
which comprises upper and lower walls, and a reinforcing
wall connected between the upper and lower walls and
extending longitudinally.
However, the reinforcing wall provided in the
refrigerant tube forms independent parallel refrigerant
2 passages in the interior of the tube. Air flows
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orthogonal to the parallel refrigerant passages, so that the
heat exchange efficiency is consequently higher in the
refrigerant passage at the air inlet side than in the
passage at the air outlet side. Accordingly, gaseous
refrigerant is rapidly condensed to a liquid in the
refrigerant passage at the upstream side, whereas the
refrigerant still remains in the passage at the downstream
side. When the entire structure of the tube is considered,
the refrigerant therefore flow unevenly, failing to achieve
a high heat exchange efficiency.
The object of the present invention is to provide
a refrigerant tube for use in heat exchangers which achieves
a high heat exchange efficiency.
SUMMARY OF THE INVENTION
The present invention provides a refrigerant tube
which fulfills the above object and which comprises a flat
aluminum tube having parallel refrigerant passages and
comprising upper and lower walls and a plurality of
reinforcing walls, the reinforcing walls extending
longitudinally of the tube and spaced apart from one another
by a predetermined distance, the flat aluminum tube being
formed of an aluminum sheet, the reinforcing walls each
comprising a ridge projecting from the aluminum sheet and
integral therewith, the reinforcing walls being each formed
with a plurality of communication holes for causing the
parallel refrigerant passages to communicate with one
another therethrough, each of the reinforcing walls being 10
to 40% in opening ratio which is the proportion of the area
of all the communication holes in the reinforcing wall to
the surface area of the reinforcing wall.
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The refrigerant to be passed through the parallel
refrigerant passages flows through the communication holes
widthwise of the tube to spread to every part of all the
passages, whereby portions of the refrigerant become mixed
together. Accordingly no temperature difference occurs in
the refrigerant between the passages, with the result that
the refrigerant undergoes condensation at the upstream side
and at the downstream side alike, flowing uniformly to
achieve an improved heat exchange efficiency. The opening
ratio which is the proportion of all the communication holes
in the reinforcing wall to this wall influences thermal
conductance. When within the range of 10 to 40%, the
opening ratio results in satisfactory thermal conductance,
whereby the heat exchange efficiency of the refrigerant tube
can be further improved. The opening ratio is limited to
the range of 10 to 40% because if the ratio is less
than 10%, the thermal conductance does not increase and
further because the conductance no longer increases even if
the ratio exceeds 40%, entailing an increase only in
coefficient of friction. The opening ratio in the range
of 10 to 40% is preferably 10 to 30%, more prefer-
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ably about 20%.
The communication holes are so sized in cross
section as to permit the refrigerant to smoothly flow
therethrough between the adjacent passages, to be free
of the likelihood of becoming clogged with a flow of
solder during brazing and to in no way impair the pressure
resistance of the tube. The pitch of the communication
holes is such that the holes will not lower the pressure
resistance of the tube while permitting the refrigerant
to smoothly flow across the reinforcing walls.
The communication holes formed in the plurality
of reinforcing walls are preferably in a staggered
arrangement when seen from above.
The pitch of the reinforcing walls in the
widthwise direction of the tube is preferably up to 4 mm.
A lower heat exchange efficiency will result if the
pitch is in excess of 4 mm.
The height of the reinforcing walls is prefer-
ably up to 2 mm. If the wall height is over 2 mm, not only
difficulty is encountered in fabricating a compacted
heat exchanger, but the resistance to the passage of air
also increases to result in an impaired heat exchange
efficiency.
The present invention will be described in
greater detail with reference to the accompanying
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drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view in cross section showing a
flat refrigerant tube of Embodiment 1 of the present
invention;
FIG. 2 is an enlarged fragmentary view of the
tube shown in FIG. 1;
FIG. 3 is an enlarged view in section taken
along the line 3-3 in FIG. 1;
FIG. 4 is a cross sectional view showing how
to produce an aluminum sheet by rolling for fabricating
the refrigerant tube of Embodiment 1 of the invention;
FIG. 5 is a cross sectional view showing how
to form cutouts in the upper edges of ridges of the
aluminum sheet shown in FIG. 4;
FIG. 6 is a view in section taken along the
line 6-6 in FIG. 5;
FIG. 7 is a view in longitudinal section showing
how to form the ridges and the cutouts in the upper edges
thereof by a single step;
FIG. 8 is an enlarged fragmentary perspective
view showing the refrigerant tube of Embodiment 1 of
the invention while it is being fabricated;
FIG. 9 is a cross sectional view of a flat
refrigerant tube according to Embodiment 2 of the
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invention;
FIG. 10 is a cross sectional view of a flat
refrigerant tube according to Embodiment 3 of the
invention;
FIG. 11 is a cross sectional view of a flat
refrigerant tube according to Embodiment 4 of the
invention;
FIG. 12 is a cross sectional view of a flat
refrigerant tube according to Embodiment 5 of the
invention;
FIG. 13 is a cross sectional view of a flat
refrigerant tube according to Embodiment 6 of the
invention;
FIG. 14 is a graph showing the result of
Evaluation Test 1, i.e., the relationship between the
average quality X of refrigerant and the thermal
conductance hA;
FIG. 15 is a graph showing the result of
Evaluation Test 2, i.e., the relationship between the
average quality X of refrigerant and the heat transfer
coefficient h;
FIG. 16 is a graph showing the result of
Evaluation Test 3, i.e., the relationship between the
opening ratio and the thermal conductance hA at an aver-
age quality X of refrigerant of 20%, 50% or 80%, and
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the relationship between the opening ratio and the
coefficient of friction f when the average quality X of
refrigerant is 50%;
FIG. 17 is a graph showing the result of
Evaluation Test 4, i.e., the relationship between the
opening ratio and the heat transfer coefficient h at an
average quality X of refrigerant of 20%, 50% or 80%,
and the relationship between the opening ratio and the
coefficient of friction f when the average quality X of
refrigerant is 50%;
FIG. 18 is a graph showing the result of
Evaluation Test 5, i.e., the relationship between the
refrigerant pressure loss APr and the quantity of heat
radiated through unit front area, Q/Fa, as established
for condensers comprising refrigerant tubes; and
FIG. 19 is a front view showing a condenser
wherein flat refrigerant tubes are used.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 19 shows a condenser comprising flat
refrigerant tubes embodying the invention. The
condenser comprises a pair of headers 61, 62 arranged
at left and right in parallel and spaced apart from
each other, parallel flat refrigerant tubes 63 each
joined at its opposite ends to the two headers 61, 62,
corrugated fins 64 arranged in air flow clearances
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between the adjacent refrigerant tubes 63 and brazed to
the adjacent refrigerant tubes 63, an inlet pipe 65
connected to the upper end of the left header 61, an out-
let pipe 66 connected to the lower end of the right 62,
a left partition 67 provided inside the left header 61
and positioned above the midportion thereof, and a
right partition 68 provided inside the right header 62
and positioned below the midportion thereof, the number
of refrigerant tubes 63 between the inlet pipe 65 and
the left partition 67, the number of refrigerant tubes
63 between the left partition 67 and the right partition
68 and the number of regrigerant tubes 63 between the
right partition 68 and the outlet pipe 66 decreasing in
this order. A refrigerant flowing into the inlet pipe
65 in a gas phase flows zigzag through the condenser
before flowing out from the outlet pipe 66 in a liquid
phase.
The refrigerant tubes 63 for use in the above
condenser are concerned with the present invention.
Refrgigerant tubes embodying the invention will be
described below. The following embodiments are all 10
to 40% in opening ratio which is the proportion of
all communication holes in each reinforcing wall to the
reinforcing wall. The communication holes formed in
a plurality of reinforcing walls are all in a staggered
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arrangement.
Embodiiment 1
This embodiment is shown in FIGS. 1 to 3. A
refrigerant tube T1 for heat exchangers is formed by a
flat aluminum tube 7 having parallel refrigerant
passages 6 in its interior and comprising flat upper
and lower walls 1, 2, left and right vertical side walls
3, 4 connected respectively between the left side edges
of the upper and lower walls 1, 2 and between the right
side edges thereof, and a plurality of reinforcing walls
5 connected between the upper and lower walls 1, 2,
extending longitudinally of the tube and spaced apart
from one another by a predetermined distance. The
reinforcing walls 5 are each formed with a plurality of
rectangular communiction holes 8 for causing the parallel
refrigerant passages 6 to communicate with each other
therethrough,
The flat aluminum tube 7 is prepared from
upper and lower two aluminum sheets 9, 10 by vertically
bending the lower sheet 10 at its opposite side edges,
joining the bent side edges to the respective side edges
of the upper aluminum sheet 9 so as to define a hollow
portion by the two aluminum sheets 9, 10.
The reinforcing walls 5 are formed by parallel
ridges 11 projecting inward from the lower wall 2 and
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joined to the inner surface of the upper wall 1. The
rectangular communication holes 8 are formed by
rectangular cutouts 12 provided in the upper edge of
each ridge 11 at a predetermined spacing and having
their openings closed by the upper wall 1.
The refrigerant tube T1 is produced by the
following method.
With reference to FIG. 4, an aluminum sheet
blank in the form of a brazing sheet covered with a
brazing filler metal over the lower surface and having
a thickness greater than that of upper and lower walls
of the refrigerant tube to be produced is first rolled
by a pair of upper and lower rolls 13, 17. The upper
roll 13 has parallel annular grooves 14 arranged at
a spacing, first small-diameter portions 15 formed at
the respective outer sides of the arrangement of
grooves 14 and each having a periphery of the same
diameter as the bottom faces of the grooves 14, and
second small-diameter portions 16 positioned externally
of the respective first small-diameter portions 15 and
having a smaller diameter and a greater width than the
portions 15. The lower roll 17 is provided, at its
respective outer ends, with large-diameter portions 18
each having an outer end face flush with that of the
second small-diameter portion 16 and having a smaller
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width than the portion 16. The peripheral surfaces of
the rolling rolls 13, 17 form a flat portion 19
providing the lower wall 2 by thinning the sheet blank
to a specified thickness. The rolls 13, 17 also form
ridges 11 projecting from the flat portion 19 integral-
ly therewith by means of the annular grooves 14.
Further formed at the respective side edges of the flat
portion 19 are upright portions 20 each including an
inner stepped part 20a with the same height as the
ridges 11, and a thin wall 20b extending upward from
the outer edge of the stepped part 20a. Thus, the
rolling operation produces a rolled aluminum sheet 21.
As shown in FIGS. 5 and 6, the rolled aluminum
sheet 21 is then passed between a pair of upper and
lower rolls 22, 24. The upper roll 22 has rectangular
protrusions 23 arranged at a predetermined spacing at
a position corresponding to each of the parallel annular
grooves 14 in the upper roll 13 for the preceding step.
This rolling operation forms rectangular cutouts 12 in
the upper edges of the respective ridges 11 at the
predetermined spacing, whereby the lower aluminum sheet 10
is obtained.
The multiplicity of protrusions 23 are in a
staggered arrangement so that the cutouts 12 are formed
in the upper edges of the parallel ridges 11 in a
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staggered arrangement when seen from above. That is to say,
the cutouts 12 formed in each of the plurality of
reinforcing walls are in a staggered arrangement relative to
the cutouts formed in an adjacent reinforcing wall of the
plurality of the reinforcing walls.
The above method of producing the lower aluminum
sheet 10 requires two steps for forming the ridges 11 having
the cutouts 12. As shown in FIG. 7, however, these
ridges 11 with the cutouts 12 can be formed by a single step
by using in combination with the lower roller 17 of the
first step an upper roll 26 which is formed in each of
parallel annular grooves 14 with protrusions 25 arranged at
a predetermined spacing and having a height smaller than the
depth of the grooves.
On the other hand, the flat upper aluminum sheet 9
is prepared which comprises a brazing sheet having opposite
surfaces each covered with a brazing filler metal layer. As
seen in FIG. 8, the upper aluminum sheet 9 has at each of
its opposite side edge portions an upper surface in the form
of a slope 27 slanting outwardly downward. With reference
to FIG. 2, each side edge portion of the upper aluminum
sheet 9 is placed on the stepped part 20a of the upright
portion 20 of the lower aluminum sheet 10, and the thin
wall 20b (indicated in a broken line) is crimped onto the
slope 27 of the upper aluminum sheet 9. Subsequently, the
lower surface of the upper sheet 9 is brazed to the stepped
parts 20a of the upright portions 20 of the lower sheet 10
and to the top ends of the ridges 11 thereof, whereby the
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refrigerant tube Tl is fabricated.
The peripheral surface of the upper rolling
roll 13 may be formed with indentations and projections
which are triangular wavelike in cross section, or
knurled. The lower aluminum sheet 10 then obtained has
projections and indentations extending longitudinally
thereof over the entire inner surface, or has an inner
surface formed with latticelike projections or indenta-
tions. This gives an increased surface area to the lower
wall 2.
Embodiment 2
FIG. 9 shows this embodiment, i.e., a refrig-
erant tube T2 for use in heat exchangers. The tube T2
has the same construction as Embodiment 1 except that
the tube T2 has left and right side walls 28, 29 of
double structure, communication holes 30 in the form of
an inverted trapezoid,and a plurality of relatively low
upward projections 31 integral with the lower wall 2,
extending longitudinally thereof and spaced apart from
one another for giving a heat transfer surface of increased
area. The holes 30 can be provided by forming trape-
zoidal cutouts 32 in the upper edges of the ridges 11.
The tube T2 comprises a flat aluminum tube 33,
which is prepared by bending opposite side edges of
upper and lower two aluminum sheets 34, 35, fitting the
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bent side edges of one of the two aluminum sheets 34, 35
respectively over the bent side edges of the other
aluminum sheet and joining the fitted portions so as to
define a hollow portion by the sheets 34, 35.
Stated more specifically, the side walls 28,
29 are formed by the following method. Upright portions
36 having the same height as the reinforcing walls 5
are provided respectively at opposite sides of the lower
aluminum sheet 35, and a slope 38 slanting outwardly
upward is formed at the bottom edge of each upright
portion 36. As indicated in a broken line in FIG. 9, on
the other hand, a depending portion 37 is formed at each
of opposite sides of the upper aluminum sheet 34, the
portion 37 being in contact with with the outer side face
of the upright portion 36 and projecting downward
slightly beyond the lower surface of the lower wall 2.
The downward projections 37a of the depending portions
37 are crimped onto the respective slopes 38 of the
lower aluminum sheet 35, and the portions where the
upper and lower aluminum sheets 34, 35 are in contact
with each other are brazed.
Embodiment 3
FIG. 10 shows this embodiment, i.e., a
refrigerant tube T3 for use in heat exchangers, which
comprises a flat aluminum tube 39. The tube 39 is
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prepared from an aluminum sheet 40 in the form of a
brazing sheet having a brazing filler metal layer on one
surface thereof, by folding the sheet at the midportion
of its width like a hairpin with the brazing layer out
so as to form a hollow portion, bending opposite side
edges to an arcuate shape and joining the side edges in
butting contact with each other. The tube 39 therefore
has circular-arc left and right side walls 41, 42.
The butt joint 43 thus made is oblique in cross section
so as to form the joint 43 over an increased area.
Each of reinforcing walls 44 is formed by
joining a downward ridge 44a inwardly projecting from
the upper wall 1 to an upward ridge 44b inwardly project-
ing from the lower wall 2. Each of trapezoidal
communication holes 5 is formed by the combination of a
pair of trapezoidal cutouts 45a, 45b. Such cutouts 45a,
45b are formed respectively in the lower edge of the
downward ridge 44a and the upper edge of the upward
ridge 44b at a predetermined spacing.
Embodiment 4
FIG. 11 shows this embodiment, i.e., a heat
exchange refrigerant tube T4, which has two kinds of
reinforcing walls 46. The walls 46 of one kind are each
formed by a downward ridge 46a inwardly projecting from
an upper wall 1 and joined to a flat inner surface of a
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lower wall 2. The walls 46 of the other kind are each
formed by an upward ridge 46b inwardly projecting from
the lower wall 2 and joined to a flat inner surface of
the upper wall 1. The two kinds of walls 46 are
arranged alternately. Trapezoidal communication holes
47 are formed by trapezoidal cutouts 47a, 47b provided
respectively in the lower edge of the downward ridge 46a
and in the upper edge of the upward ridge 46b and have
their openings closed by one of the upper and lower
walls 1, 2. With the exception of this feature, the
present embodiment is the same as Embodiment 3.
Embodiment 5
FIG. 12 shows this embodiment, i.e., a heat
exchanger refrigerant tube T5. The tube T5 has
reinforcing walls 48 which are formed by downward ridges
48a inwardly projecting from an upper wall 1 and joined
to a flat inner surface of a lower wall 2. Trapezoidal
communication holes 49 are formed by providing trape-
zoidal cutouts 49a in the lower edges of the ridges 48a
at a predetermined spacing and closing the openings of
the cutouts 49a with the lower wall 2. The present
embodiment is the same as Embodiment 3 except for this
feature.
Embodiment 6
FIG. 13 shows this embodiment, i.e., a heat
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exchange refrigerant tube Ts, which comprises a flat
aluminum tube 50. The tube 50 is prepared from upper
and lower two aluminum sheets 51, 52 by bending opposite
side edges of the sheets to an arcuate shape toward each
other so as to form a hollow portion, butting the sheets
against each other edge to edge and joining the butted
edges. Except for this feature, the present embodiment
is the same as Embodiment 3. The left and right butt
joints 53, 54 are oblique in cross section as is the
case with Embodiment 3.
The aluminum sheet having the ridges, etc. and
used in the foregoing embodiments can be replaced by an
aluminum extrudate of specified cross section.
Examples of the invention will be described
below along with a comparative example. The refrigerant
tubes of the examples and comparative example are so
shaped as shown in FIG. 1 in cross section.
Example 1
A refrigerant tube which is 508 mm in length,
16.5 mm in the distance between side walls 3, 4, 1 mm
in the height between upper and lower walls 1, 2, six
in the number of reinforcing walls 5, 2.4 mm in the pitch
of reinforcing walls 5, 0.3 mm in the thickness of
reinforcing walls 5, 1.6 mm in the pitch P of communica-
tion holes 8, 0.8 mm in the length L of communication
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holes 8, 0.2 mm in the height H of communication holes
8, and 10% in opening ratio.
Example 2
The same refrigerant tube as that of Example 1
except that this tube is 0.4 mm in the height of
communication holes and 20% in opening ratio.
Example 3
The same refrigerant tube as that of Example 1
except that the tube is 0.6 mm in the height of
communication holes and 30% in opening ratio.
Example 4
The same refrigerant tube as that of Example 1
except that the tube is 0.8 mm in the height of
communication holes and 40% in opening ratio.
Comparative Example
The same refrigerant tube as that of Example 1
except that the tube has no communication holes in the
reinforcing walls.
Evaluation Test 1
The refrigerant tubes of Example 1 and
Comparative Example were used to determine the relation-
ship between the average quality X of refrigerant
(the fraction of vapor mass in refrigerant) and the
thermal conductance hA (h: heat transfer coefficient,
A: the area of heat transfer surface inside the refriger-
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ant tube). The method of determination was as follows.
The refrigerant tube was placed in a cooling water
channel, a refrigerant comprising HFC134a was passed
through the tube, and cooling water was passed through
the channel. After the lapse of a specified period
of time, the mass velocity G of the refrigerant was set
at 400 kg/m2=s, the refrigerant inlet temperature at
65 0 C, and the heat flux between the refrigerant and
the cooling water at 8 kW/m2. The flow rate of the
cooling water was so set as to give a Reynolds number
of 1500. The thermal conductance hA was measured at
varying values of average quality X.
The result is shown in FIG. 14, which reveals
that when the reinforcing walls are formed with
communication holes, the thermal conductance hA is
greater at any value of average quality X than when no
holes are formed.
Evaluation Test 2
The refrigerant tubes of Example 2 and
Comparative Example were used to determine the relation-
ship between the average quality X of refrigerant and
the heat transfer coefficient h by the same method as
in Evaluation Test 1. FIG. 15 shows the result.
FIG. 15 reveals that at any value of average
quality X, the heat transfer coefficierit h is greater
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when the reinforcing walls are formed with communication
holes than when no holes are formed.
Evaluation Test 3
The refrigerant tubes of Examples 1 to 4
and Comparative Example were used to determine the
relationship between the opening ratio and the thermal
conductance hA at an average quality X of refrigerant of
20%, 50% or 80%, and the relationship between the opening
ratio and the coefficient of friction f when the average
quality X of refrigerant was 50% (Reynolds number of
refrigerant: 104.), the relationships being determined
by the same method as in Evaluation Test 1. FIG. 16
shows the result.
FIG. 16 indicates that at any value of average
quality X, the thermal conductance hA is greater when
the reinforcing walls are formed with communication
holes than when no holes are formed, and that the
thermal conductance hA is especially great at an opening
ratio of 20%.
Evaluation Test 4
The refrigerant tubes of Examples 1 to 4
and Comparative Example were used to determine, by the
same method as in Evaluation Test 1, the relationship
between the opening ratio and the heat transfer coeffi-
cient h at an average quality X of refrigrant of 20%,
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50% or 80%, and the relationship between the opening
ratio and the coefficient of friction f when the average
quality X of refrigerant was 50% (Reynolds number: 104).
FIG. 17 shows the result.
FIG. 17 indicates that at any value of average
quality X, the heat transfer coefficient h is greater
when the reinforcing walls are formed with communication
holes than when no holes are formed, and that the heat
transfer coefficient h is especially great at an opening
ratio of 20%.
Evaluation Test 5
Three kinds of condensers of the multiflow type
shown in FIG. 19 were fabricated using the refrigerant
tube of Example 2 or Comparative Example. More
specifically, 37 refrigerant tubes, and corrugated fins,
22 mm in width, 7 mm in height and 1 mm in fin pitch,
were used for making a core portion measuring 326 mm in
width, 330.5 mm in height and 0.108 m2 in front area,
and opposite ends of each tube were connected to right
and left headers. No partition was provided in opposite
headers in the condenser of the type I (single pass).
The condenser of the type II had a partition inside the
left header above the midportion thereof, another
partition inside the right header below the midportion
thereof, 20 refrigerant tubes positioned above the
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partition of the left header, 11 refrigerant tubes
arranged between the two partitions, and 6 refrigerant
tubes positioned below the partition of the tight
header (three passes). The condenser of the type III
had two partitions positioned respectively in an
upper portion and a lower portion of the left header,
two partitions positioned inside the right header, one
at an intermediate level between the two partitions of
the left header and the other at a level below the
lower partition of the left header, 12 refrigerant tubes
positioned above the upper partition of the left header,
9 refirgerant tubes between the upper partition of the
left header and the upper partition of the right header,
7 refrigerant tubes positioned between the upper parti-
tion of the right header and the lower partition of the
left header, 5 refrigerant tubes positioned between the
lower partition of the left header and the lower parti-
tion of the right header, and 4 refrigerant tubes
positioned below the lower partition of the right header
(five passes). The condensers were checked for the
relationship between the refrigerant pressure loss oPr
and the quantity of heat radiated per unit front area,
Q/Fa. FIG. 18 shows the result.
FIG. 18 shows that the capacitor comprising
the refrigerant tube wherein the reinforcing walls are
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formed with communication holes at an opening ratio of
20% exhibits an improved performance over the condenser
comprising the refrigerant tube having no communication
holes in the reinforcing walls and achieves an improve-
ment even when the pressure loss is the same.
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