U.S. patent application number 14/418467 was filed with the patent office on 2015-06-18 for parallel-flow type heat exchanger and air conditioner equipped with same.
The applicant listed for this patent is Sharp Kabushiki Kaisha. Invention is credited to Kazuhisa Mishiro, Madoka Ueno, Takeshi Yoshida.
Application Number | 20150168072 14/418467 |
Document ID | / |
Family ID | 50236951 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150168072 |
Kind Code |
A1 |
Ueno; Madoka ; et
al. |
June 18, 2015 |
PARALLEL-FLOW TYPE HEAT EXCHANGER AND AIR CONDITIONER EQUIPPED WITH
SAME
Abstract
A parallel-flow type heat exchanger (1) is provided with two
vertical-direction header pipes (2, 3), and a plurality of
horizontal-direction flat tubes (4) that connect the header pipes
with each other. The plurality of horizontal direction flat tubes
are divided into a plurality of groups each comprising a plurality
of flat tubes, and each of the groups constitutes a coolant path
that lets coolant flow from one vertical-direction header pipe to
the other. The upper limit for the number of flat tubes that
constitute a coolant path for one turn is obtained from a
prescribed numerical formula.
Inventors: |
Ueno; Madoka; (Osaka-shi,
JP) ; Mishiro; Kazuhisa; (Osaka-shi, JP) ;
Yoshida; Takeshi; (Shizuoka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sharp Kabushiki Kaisha |
Osaka-shi, Osaka |
|
JP |
|
|
Family ID: |
50236951 |
Appl. No.: |
14/418467 |
Filed: |
August 7, 2013 |
PCT Filed: |
August 7, 2013 |
PCT NO: |
PCT/JP2013/071301 |
371 Date: |
January 30, 2015 |
Current U.S.
Class: |
165/144 |
Current CPC
Class: |
F24F 1/0059 20130101;
F24F 13/30 20130101; F24F 1/14 20130101; F28F 1/022 20130101; F28D
1/05375 20130101; F28D 1/0233 20130101 |
International
Class: |
F28D 1/053 20060101
F28D001/053; F28D 1/02 20060101 F28D001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2012 |
JP |
2012-194111 |
Claims
1. A parallel-flow heat exchanger of a side-flow type, comprising:
two header pipes extending in a vertical direction; and a plurality
of flat tubes extending in a horizontal direction and coupling
together the header pipes with each other, wherein the plurality of
flat tubes are grouped such that each group comprises a plurality
of flat tubes, each group constituting a one-turn refrigerant path
through which refrigerant is passed from one to the other of the
two header pipes extending in the vertical direction, an upper
limit of a number of flat tubes constituting the one-turn
refrigerant path is determined to be within a range of .+-.2 of a
value calculated using, when the parallel-flow heat exchanger is
used in an outdoor unit of an air conditioner, the formula
n<3.0.times.10.sup.-4.times.Q+8.0, (A) and when the
parallel-flow heat exchanger is used in an indoor unit of an air
conditioner, the formula n<4.2.times.10.sup.-4.times.Q+7.9, (A)
where n represents the number of flat tubes constituting the
one-turn refrigerant path; and Q represents rated capacity, given
in watts (W).
2. The parallel-flow heat exchanger according to claim 1, wherein
the heat exchanger is used in an outdoor unit of an air
conditioner, and a lower limit of the number of flat tubes
constituting the one-turn refrigerant path is determined using the
formula
n.gtoreq.(.alpha.Q+.beta.).times.[(1.4.times.10.sup.-16).times.L/(d.times-
.A'.sup.2)].sup.0.5. (B) where .alpha.=0.0161; .beta.=8.86; d
represents a hydraulic diameter, given in meters (m); and A'
represents a refrigerant passage cross-sectional area of one flat
tube, given in square meters (m.sup.2).
3. The parallel-flow heat exchanger according to claim 1, wherein
the heat exchanger is used in an indoor unit of an air conditioner,
and a lower limit of the number of flat tubes constituting the
one-turn refrigerant path is determined using the formula
n.gtoreq.(.alpha.Q+.beta.).times.[(1.4.times.10.sup.-16).times.L/(d.times-
.A'.sup.2)].sup.0.5. (B) where .alpha.=0.0228; .beta.=6.62; d
represents a hydraulic diameter, given in meters (m); and A'
represents a refrigerant passage cross-sectional area of one flat
tube, given in square meters (m.sup.2).
4. An air conditioner comprising a parallel-flow heat exchanger
according to claim 2 as an outdoor unit of the air conditioner.
5. An air conditioner comprising a parallel-flow heat exchanger
according to claim 3 as an indoor unit of the air conditioner.
Description
TECHNICAL FIELD
[0001] The present invention relates to a parallel-flow heat
exchanger of a side-flow type, and to an air conditioner
incorporating it.
BACKGROUND ART
[0002] A plurality of flat tubes are arranged between a plurality
of header pipes such that a plurality of refrigerant passages
inside the flat tubes communicate with the interior of the header
pipes, with fins such as corrugated fins arranged between the flat
tubes. So built are parallel-flow heat exchangers which are used
widely in air conditioners for vehicles and in outdoor units of air
conditioners for buildings, for instance.
[0003] An example of the structure of a parallel-flow heat
exchanger is shown in FIG. 1. The top and bottom sides of FIG. 1
correspond respectively to the top and bottom sides of the heat
exchanger. The parallel-flow heat exchanger 1 is of a side-flow
type, and comprises two header pipes 2 and 3 extending in the
vertical direction and a plurality of flat tubes 4 arranged between
them and extending in the horizontal direction. The header pipes 2
and 3 are arranged parallel to each other, at an interval in the
horizontal direction. The flat tubes 4 are arranged at a
predetermined pitch in the vertical direction. At the stage of
actual mounting in an appliance, the parallel-flow heat exchanger 1
can be installed at any angle to suit particular designs, and
therefore, in the present description, the "vertical" and
"horizontal" directions should not be interpreted strictly but be
understood to merely give a rough notion of relevant
directions.
[0004] The flat tubes 4 are elongate moldings of metal formed by
extrusion and, as shown in FIG. 2, have formed inside them
refrigerant passages 5 through which refrigerant is circulated. The
flat tubes 4 are arranged with their longitudinal direction, i.e.,
the extrusion direction, aligned with the horizontal direction, and
thus through the refrigerant passages 5, the refrigerant circulate
in the horizontal direction. The refrigerant passages 4 comprise a
plurality of refrigerant passages having the same cross-sectional
shape and the same cross-sectional area arranged in the left-right
direction in FIG. 2. Thus, in a vertical cross-sectional view, the
flat tubes 4 look like a harmonica. The refrigerant passages 5 each
communicate with the interior of the header pipes 2 and 3.
[0005] The flat tubes 4 have fins 6 fitted on their flat faces.
Used as the fins 6 here are corrugated fins, but plate fins may
instead be used. Of the fins 6 arranged in the up-down direction,
the topmost and bottom most ones have side plates 7 arranged on
their respective outer sides.
[0006] The header pipes 2 and 3, the flat tubes 4, the fins 6, and
the side plates 7 are all made of metal with good thermal
conductivity, such as aluminum. The flat tubes 4 are brazed or
welded to the header pipes 2 and 3, so are the fins 6 to the flat
tubes 4, and so are the side plates 7 to the fins 6.
[0007] The interior of the header pipe 2 is divided by two
partitions P1 and P2 into three sections S1, S2, and S3. The
partitions P1 and P2 separate the plurality of flat tubes 4 into
three flat tube groups, so that a plurality of flat tubes 4 are
connected to each of the sections S1, S2, and S3.
[0008] The interior of the header pipe 3 is divided by a single
partition P3 into two sections S4 and S5. The partition P3
separates the plurality of flat tubes 4 into two flat tube groups,
so that a plurality of flat tubes 4 are connected to each of the
sections S4 and S5.
[0009] A refrigerant introduction/discharge pipe 8 is connected to
the section S1, and another refrigerant introduction/discharge pipe
9 is connected to the section S2.
[0010] The parallel-flow heat exchanger 1 operates in the following
manner. When the parallel-flow heat exchanger 1 is used as a
condenser, refrigerant is fed into the section S1 through the
refrigerant introduction/discharge pipe 8. The refrigerant that has
entered the section S1 flows toward the section S4 through the
plurality of flat tubes 4 connecting the section S1 to the section
S4. This group of a plurality of flat tubes 4 constitutes a
refrigerant path A. The refrigerant path A is indicated by a hollow
arrow. Other refrigerant paths will be indicated by a hollow arrow
each.
[0011] The refrigerant that has entered the section S4 turns back,
then to flow toward the section S2 through the plurality of flat
tubes 4 connecting the section S4 to the section S2. This group of
a plurality of flat tubes 4 constitutes a refrigerant path B.
[0012] The refrigerant that has entered the section S2 turns back,
then to flow toward the section S5 through the plurality of flat
tubes 4 connecting the section S2 to the section S5. This group of
a plurality of flat tubes 4 constitutes a refrigerant path C.
[0013] The refrigerant that has entered the section S5 turns back,
then to flow toward the section S3 through the plurality of flat
tubes 4 connecting the section S5 to the section S3. This group of
a plurality of flat tubes 4 constitutes a refrigerant path D. The
refrigerant that has entered the section S3 is then discharged out
of it through the refrigerant introduction/discharge pipe 9.
[0014] In the present description, of the route traveled by the
refrigerant, each segment between the refrigerant
introduction/discharge pipe 8 or 9 and the next turning-back and
between one and the next turning-back is referred to as "one turn."
Thus, the refrigerant paths A, B, C, and D each count as a one-turn
refrigerant path.
[0015] When the parallel-flow heat exchanger 1 is used as an
evaporator, refrigerant is fed into the section S3 through the
refrigerant introduction/discharge pipe 9. Thereafter, the
refrigerant travels in the reverse direction the route that it
travels when the parallel-flow heat exchanger 1 is used as the
condenser. Specifically, the refrigerant passes through the
refrigerant path D, then the refrigerant path C, then the
refrigerant path B, and then the refrigerant path A to enter the
section S1, and is then discharged through the refrigerant
introduction/discharge pipe 8.
[0016] In parallel-flow heat exchangers, elaborate designs have
been made for improved performance. Examples are seen in Patent
Documents 1 to 3 identified below.
[0017] In the parallel-flow heat exchanger described in Patent
Document 1, inside a plurality of flat tubes that connect two
header pipes together, a plurality of refrigerant passages with a
fluidic diameter of 0.015 inches (about 0.38 millimeters) to 0.07
inches (about 1.78 millimeters) are formed parallel to one another.
The outline of the cross section of those refrigerant passages is
so designed as to have two or more comparatively straight portions
that meet together and at least one dented portion formed where
they meet. This design helps reduce the air-side front-face area
obstructed by flat tubes, and thus makes it possible to increase
the air-side heat transfer surface without increasing the air-side
pressure drop.
[0018] In the parallel-flow heat exchanger described in Patent
Document 2, refrigerant passages inside flat tubes are given a
height of 0.35 millimeters to 0.8 millimeters. This helps reduce
the sum of the drop in heat emission due to draft resistance and
the drop in heat emission due to tube pressure loss, and thus helps
improve heat emission performance.
[0019] In the parallel-flow heat exchanger described in Patent
Document 3, a flow distribution parameter .gamma., i.e., the ratio
of the resistance parameter .beta. of flat tubes to the resistance
parameter .alpha. of the refrigerant inlet-side header pipe is set
at 0.5 or more. This helps prevent a concentrated flow of
refrigerant through flat tubes connected to a refrigerant-inlet
part of the header pipe where the pressure is higher. It is thus
possible to make the pressure applied to the respective flat tubes
even so that satisfactory flow distribution is achieved, and
thereby to obtain satisfactory heat exchange performance.
LIST OF CITATIONS
Patent Literature
[0020] Patent Document 1: JP-A-H5-87752
[0021] Patent Document 2: JP-A-2001-165532
[0022] Patent Document 3: JP-A-2000-111274
SUMMARY OF THE INVENTION
Technical Problem
[0023] In a case where a parallel-flow heat exchanger is used as an
evaporator, with respect to refrigerant passing through a
refrigerant path, it is preferable that no such condition arise
where more liquid refrigerant passes through some flat tubes and
more gaseous refrigerant passes through other flat tubes; that is,
it is preferable that no "uneven flow" occur. The present invention
aims to provide a parallel-flow heat exchanger of a side-flow type
that is designed optimally from the perspective of avoiding such an
uneven flow with respect to the number of flat tubes constituting a
refrigerant path. In particular, the present invention aims to
optimize the number of flat tubes constituting a refrigerant path
through which passes refrigerant with a large proportion of gaseous
refrigerant.
Means for Solving the Problem
[0024] According to one aspect of the present invention, a
parallel-flow heat exchanger of a side-flow type is provided with
two header pipes extending in the vertical direction, and a
plurality of flat tubes extending in the horizontal direction and
coupling together the header pipes with each other. Here, the
plurality of flat tubes are grouped such that each group comprises
a plurality of flat tubes, each group constituting a one-turn
refrigerant path through which refrigerant is passed from one to
the other of the two header pipes extending in the vertical
direction. Moreover, the upper limit of the number of flat tubes
constituting the one-turn refrigerant path is determined to be
within a range of .+-.2 of a value calculated using, when the
parallel-flow heat exchanger is used in an outdoor unit of an air
conditioner, the formula
n<3.0.times.10.sup.-4.times.Q+8.0, (A)
and when the parallel-flow heat exchanger is used in an indoor unit
of an air conditioner, the formula
n<4.2.times.10.sup.-4.times.Q+7.9, (A)
where
[0025] n represents the number of flat tubes constituting the
one-turn refrigerant path; and
[0026] Q represents rated capacity, given in watts (W). Used as Q
is, for an outdoor unit, rated heating capacity and, for an indoor
unit, rated cooling capacity.
[0027] When the parallel-flow heat exchanger configured as
described above is used in an outdoor unit of an air conditioner,
it is preferable that the lower limit of the number of flat tubes
constituting the one-turn refrigerant path be determined using the
formula
n>(.alpha.Q+.beta.).times.[(1.4.times.10.sup.-16).times.L/(d.times.A'-
.sup.2)].sup.0.5, (B)
where
[0028] .alpha.=0.0161;
[0029] .beta.=8.86;
[0030] d represents the hydraulic diameter, given in meters (m);
and
[0031] A' represents the refrigerant passage cross-sectional area
of one flat tube, given in square meters (m.sup.2).
[0032] When the parallel-flow heat exchanger configured as
described above is used in an indoor unit of an air conditioner, it
is preferable that the lower limit of the number of flat tubes
constituting the one-turn refrigerant path is determined using the
formula
n>(.alpha.Q+.beta.).times.[(1.4.times.10.sup.-16).times.L/(d.times.A'-
.sup.2)].sup.0.5, (B)
where
[0033] .alpha.=0.0228;
[0034] .beta.=6.62;
[0035] d represents the hydraulic diameter, given in meters (m);
and
[0036] A' represents the refrigerant passage cross-sectional area
of one flat tube, given in square meters (m.sup.2).
[0037] According to another aspect of the present invention, an air
conditioner is provided with a parallel-flow heat exchanger
configured as described above in an outdoor unit or in an indoor
unit.
Advantageous Effects of the Invention
[0038] According to the present invention, it is possible to obtain
a parallel-flow heat exchanger of a side-flow type that is free
from an uneven flow depending on refrigerant circulation rate.
BRIEF DESCRIPTION OF DRAWINGS
[0039] FIG. 1 An outline configuration diagrams of a parallel-flow
heat exchanger of a side-flow type;
[0040] FIG. 2 A sectional view along line II-II in FIG. 1;
[0041] FIG. 3 A table listing the specifications of flat tube
samples;
[0042] FIG. 4 A table showing the correlation between refrigerant
circulation rate and the uneven-flow-free number of flat tubes;
[0043] FIG. 5 A plot showing the correlation between refrigerant
circulation rate and the number of flat tubes;
[0044] FIG. 6 A plot showing the correlation between cooling
capacity and refrigerant circulation rate;
[0045] FIG. 7 A plot showing the correlation between heating
capacity and refrigerant circulation rate;
[0046] FIG. 8 A plot showing the optimal range of the number of
flat tubes for an outdoor unit of an air conditioner;
[0047] FIG. 9 A plot showing the optimal range of the number of
flat tubes for an indoor unit of an air conditioner;
[0048] FIG. 10 A plot showing the correlation between refrigerant
circulation rate and suction pressure;
[0049] FIG. 11 A plot showing the correlation between refrigerant
circulation rate and the number of flat tubes;
[0050] FIG. 12 A plot showing the correlation between the number of
flat tubes in an outdoor-unit heat exchanger and rated heating
capacity;
[0051] FIG. 13 A plot showing the correlation between the number of
flat tubes in an indoor-unit heat exchanger and rated cooling
capacity;
[0052] FIG. 14 An outline configuration diagram of an air
conditioner incorporating a parallel-flow heat exchanger according
to the present invention, in heating operation; and
[0053] FIG. 15 An outline configuration diagram of an air
conditioner incorporating a parallel-flow heat exchanger according
to the present invention, in cooling operation.
DESCRIPTION OF EMBODIMENTS
[0054] A parallel-flow heat exchanger 1 of a side-flow type as
shown in FIG. 1 wherein the number of flat tubes constituting a
refrigerant path is set according to a method as described below is
assumed to be a parallel-flow heat exchanger according to the
present invention. The number of refrigerant paths, however, is not
limited to four; more than four or less than four refrigerant paths
may be provided.
[0055] First, the upper limit of the number of flat tubes 4
constituting a one-turn refrigerant path is determined; it is
calculated, in a case where the parallel-flow heat exchanger is
used in an outdoor unit of an air conditioner, using the
formula
n<3.0.times.10.sup.-4.times.Q+8.0, (A)
and in a case where the parallel-flow heat exchanger is used in an
indoor unit of an air conditioner, using the formula
n<4.2.times.10.sup.-4.times.Q+7.9, (A)
where n represents the number of flat tubes constituting a one-turn
refrigerant path; and Q represents the rated capacity, given in
watts (W).
[0056] Formula (A) was derived through experiments. The table in
FIG. 3 lists the specifications of the flat tubes examined in the
experiments. Sample a had a width of 16.2 mm, a thickness of 1.9
mm, and a refrigerant passage cross-sectional area of 13 mm.sup.2.
Sample b had a width of 13.9 mm, a thickness of 1.9 mm, and a
refrigerant passage cross-sectional area of 11 mm.sup.2 Sample c
had a width of 16.2 mm, a thickness of 1.6 mm, and a refrigerant
passage cross-sectional area of 11 mm.sup.2 Sample d had a width of
19.2 mm, a thickness of 1.9 mm, and a refrigerant passage
cross-sectional area of 14 mm.sup.2.
[0057] The experiments were conducted in the following manner.
Refrigerant was circulated through different numbers of flat tubes,
and whether an uneven flow occurred was checked visually by
thermography. For each of the four samples shown in FIG. 3, the
refrigerant was circulated through it at varying circulation rates.
The maximum numbers of flat tubes with which no uneven flow was
observed at different circulation rates (in the present
description, such a state is often referred to as uneven-flow-free)
are listed in FIG. 4.
[0058] As will be seen from the table in FIG. 4, Sample a was used
in Experiment 1. A refrigerant circulation rate of 27.3 kg/h gave a
maximum uneven-flow-free number of 8. A refrigerant circulation
rate of 42.5 kg/h gave a maximum uneven-flow-free number of 9. A
refrigerant circulation rate of 64.3 kg/h gave a maximum
uneven-flow-free number of 10. A refrigerant circulation rate of
63.2 kg/h gave a maximum uneven-flow-free number of 10.
[0059] Sample b was used in Experiment 2. A refrigerant circulation
rate of 20.9 kg/h gave a maximum uneven-flow-free number of 9. A
refrigerant circulation rate of 22.1 kg/h gave a maximum
uneven-flow-free number of 8.
[0060] Sample c was used in Experiment 3. A refrigerant circulation
rate of 59.2 kg/h gave a maximum uneven-flow-free number of 10. A
refrigerant circulation rate of 48.8 kg/h gave a maximum
uneven-flow-free number of 9. A refrigerant circulation rate of
26.4 kg/h gave a maximum uneven-flow-free number of 8.
[0061] Sample b was used in Experiment 4. A refrigerant circulation
rate of 54.8 kg/h gave a maximum uneven-flow-free number of 8. A
refrigerant circulation rate of 89.2 kg/h gave a maximum
uneven-flow-free number of 8.
[0062] Sample d was used in Experiment 5. A refrigerant circulation
rate of 26.6 kg/h gave a maximum uneven-flow-free number of 6. A
refrigerant circulation rate of 44.3 kg/h gave a maximum
uneven-flow-free number of 9. A refrigerant circulation rate of
67.3 kg/h gave a maximum uneven-flow-free number of 9.
[0063] FIG. 5 is a plot of the results of the experiments shown in
FIG. 4. An approximation straight line is drawn, and from the
approximation formula, the number of flat tubes is determined to be
within a range of .+-.2 of the value given by
n=1.9.times.10.sup.-2 m+7.8. (a)
[0064] The refrigerant circulation rate m (kg/h) is typically set
as a value proportional to the rated capacity of a product. How the
refrigerant circulation rate correlates with the rated capacity is
shown in FIGS. 6 and 7.
[0065] Using a rated heating capacity Q (in watts (W)), the
refrigerant circulation rate m is given by
m=0.0161 Q+8.86. (b)
[0066] Using a rated cooling capacity Q (in watts (W)), the
refrigerant circulation rate m is given by
m=0.0228 Q+6.621. (c)
[0067] The correlation between rated capacity and refrigerant
circulation rate varies slightly from one product to another.
Incidentally, the refrigerant circulation rate here is calculated
in a simplified manner using the following formula:
(Refrigerant Circulation Rate m)=(Compressor Rotation
Rate).times.(Suction Pressure Density).times.(Compressor
Volume).
[0068] A parallel-flow heat exchanger, when used as an outdoor-unit
heat exchanger of an air conditioner, functions as an evaporator in
heating operation and, when used as a an indoor-unit heat exchanger
of an air conditioner, functions as an evaporator in cooling
operation.
[0069] Accordingly, as shown in FIG. 8, in a case where a
parallel-flow heat exchanger is used as an outdoor-unit heat
exchanger, using formulae (a) and (b) above, the upper limit of the
number of flat tubes constituting a one-turn refrigerant path is
determined to be
n=3.0.times.10.sup.-4 Q+8.0.
[0070] As shown in FIG. 9, in a case where a parallel-flow heat
exchanger is used as an indoor-unit heat exchanger, using formulae
(a) and (c) above, the upper limit of the number of flat tubes
constituting a one-turn refrigerant path is determined to be within
a range of .+-.2 of the value given by
n=4.2.times.10.sup.-4 Q+7.9.
This makes it possible to suppress an uneven flow.
[0071] Next, the lower limit of the number of flat tubes
constituting each refrigerant path is determined As shown in FIG.
10, as the temperature at the outlet of the heat exchanger falls
into the range
T.sub.out<0.degree. C.,
the suction pressure drops greatly; that is, the suction pressure
drops sharply with respect to the refrigerant circulation rate.
This is due to frost formation resulting from the outlet
temperature falling below 0.degree. C.
[0072] Let the temperature drop due to a pressure loss .DELTA.P be
T.sub.Dp, then
T.sub.Rin-T.sub.Dp<0.degree. C.,
where T.sub.Rin represents the inlet evaporation temperature of the
refrigerant. The pressure loss .DELTA.P is given in pascals
(Pa).
[0073] That is,
P.sub.Rin-.DELTA.P>P.sub.lim,
where P.sub.Rin represents the inlet evaporation temperature, and
P.sub.lim represents the saturation pressure of the refrigerant at
0.degree. C.
[0074] Here,
.DELTA.P=.lamda..times.L/d.times..rho..times.u.sup.2/2,
where .lamda. represents the coefficient of friction between the
inner wall of the flat tubes 4 and the refrigerant; L represents a
tube path length, given in meters (m); d represents the hydraulic
diameter, given in meters (m); .rho. represents the refrigerant
density, given in kilograms per cubic meter (kg/m.sup.3); and u
represents the flow speed of the refrigerant, given in meters per
second (m/s).
[0075] The flow speed is given by
u=M/.rho.A,
where M represents the refrigerant circulation rate, given in
kilograms per second (kg/s); and A represents the sum of the
refrigerant passage cross-sectional areas of the plurality of flat
tubes constituting a one-turn refrigerant path, given in square
meters (m.sup.2).
[0076] Thus,
.DELTA.P=.lamda./2 .rho..times.L/dA.sup.2.times.M.sup.2.
[0077] Here, let the refrigerant passage cross-sectional area of
one flat tube 4 be A', then
A=nA',
where n represents the number of flat tubes 4 constituting a
one-turn refrigerant path.
[0078] Here,
.DELTA.P<P.sub.Rin-P.sub.lim.
Hence
[0079] .lamda./2
.rho..times.L/(dn.sup.2.times.A'.sup.2).times.M.sup.2<P.sub.Rin-P.sub.-
lim
[0080] Here,
n.sup.2>M.sup.2.times..lamda./2 .rho..times.L/dA'.sup.2.times.1/
(P.sub.Rin-P.sub.lim).
[0081] The above formula gives
n>M [.lamda./2
.rho..times.L/dA'.sup.2.times.1/(P.sub.Rin-P.sub.lim)].sup.0.5.
(d)
[0082] The refrigerant circulation rate m (kg/h), which is M as
given in a different unit, is typically set as a value proportional
to the rated capacity of a product; hence it can be expressed
as
m=.alpha.Q+.beta..
[0083] How the refrigerant circulation rate correlates with
capacity is shown in FIGS. 6 and 7. Using a rated heating capacity
Q (in watts (W)), the refrigerant circulation rate m is given
by
m=0.0161 Q+8.86.
That is, .alpha.=0.0161, and .beta.=8.86.
[0084] Using a rated cooling capacity Q (in watts (W)), the
refrigerant circulation rate m is given by
m=0.0228 Q+6.62.
That is, .alpha.=0.0228, and .beta.=6.62.
[0085] For an outdoor-unit heat exchanger, rated heating capacity
can be used; for an indoor-unit heat exchanger, rated cooling
capacity can be used.
[0086] The correlation between rated capacity and refrigerant
circulation rate varies slightly from one product to another.
Incidentally, the refrigerant circulation rate here is calculated
in a simplified manner using the following formula:
(Refrigerant Circulation Rate m)=(Compressor Rotation
Rate).times.(Suction Pressure Density).times.(Compressor
Volume).
[0087] On the other hand, it is common to keep the pressure loss
below 200 kPa. Thus,
P.sub.Rin-P.sub.lim<200.times.10.sup.3.
[0088] The coefficient of friction .lamda. varies with refrigerant
circulation rate, refrigerant pressure, the shape of flat tubes,
etc.; it is typically in the range of about 0.5 to about 0.05 in
air conditioners for household use. The density p varies with
refrigerant pressure and dryness; it is typically in the range of
20 to 70 kg/m.sup.3 with a gaseous refrigerant.
[0089] Thus, performing unit conversion from M to m gives
n>(.alpha.Q+.beta.).times.[.pi.+L/(d.times.A'.sup.2)].sup.0.5.
Here, .pi. is given by
1.4.times.10.sup.-16<.pi.<4.8.times.10.sup.-15.
[0090] In a case where the upper limit of the number of flat tubes
calculated using formula (A) is exceeded by the lower limit of the
number of flat tubes, it is preferable that the flat tubes be
branched at the inlet or in the middle of the heat exchanger.
[0091] Here, considering that the pressure loss should be as low as
possible, it is preferable to set II at its lowest value, namely
1.4.times.10.sup.16. Hence
n.gtoreq.(.alpha.Q+.beta.).times.[(1.4.times.10.sup.-16).times.L/(d.time-
s.A'.sup.2)].sup.0.5. (B)
[0092] Thus, using formula (B), it is possible to determine the
lower limit of the number of flat tubes constituting a one-turn
path.
[0093] FIGS. 12 and 13 are plots of examples of the results of
calculation using formula (B). FIG. 12 shows how the number of flat
tubes in an outdoor-unit heat exchanger correlates with rated
heating capacity. FIG. 13 shows how the number of flat tubes in an
indoor-unit heat exchanger correlates with rated cooling capacity.
These plots show the lower-limit values of the number of flat tubes
constituting a one-turn refrigerant path as optimized according to
rated capacity.
[0094] The parallel-flow heat exchanger 1 can be incorporated in a
separate-type air conditioner. A separate-type air conditioner is
composed of an outdoor unit and an indoor unit. The outdoor unit
includes a compressor, a four-way value, an expansion value, an
outdoor heat exchanger, an outdoor blower, etc. The indoor unit
includes an indoor heat exchanger, an indoor blower, etc. The
outdoor heat exchanger functions as an evaporator in heating
operation, and functions as a condenser in cooling operation. The
indoor heat exchanger functions as a condenser in heating
operation, and functions as an evaporator in cooling operation.
[0095] FIG. 14 shows a basic configuration of a separate-type air
conditioner that employs a heat pump cycle as a refrigerating
cycle. The heat pump cycle 101 is composed of a compressor 102, a
four-way value 103, an outdoor heat exchanger 104, a
decompression-expansion device 105, and an indoor heat exchanger
106 connected in a loop. The compressor 102, the four-way value
103, the heat exchanger 104, and the decompression-expansion device
105 are housed in the cabinet of an outdoor unit. The heat
exchanger 106 is housed in the cabinet of an indoor unit. The heat
exchanger 104 is combined with an outdoor blower 107. The heat
exchanger 106 is combined with an indoor blower 108. The blower 107
includes a propeller fan. The blower 108 includes a cross-flow
fan.
[0096] The parallel-flow heat exchanger 1 according to the present
invention can be used as a component of the heat exchanger 106 in
the indoor unit. The heat exchanger 106 comprises three heat
exchangers 106A, 106B, and 106C combined together like a roof
covering the blower 108. The parallel-flow heat exchanger 1 can be
used as any of the heat exchangers 106A, 106B, and 106C.
[0097] The parallel-flow heat exchanger 1 according to the present
invention can also be used as the heat exchanger 104 in the outdoor
unit.
[0098] FIG. 14 shows how heating operation proceeds. In this
operation, high-temperature, high-pressure refrigerant is
discharged from the compressor 102, and enters the indoor heat
exchanger 106, where the refrigerant emits heat and condenses. The
refrigerant then exits from the indoor heat exchanger 106, passes
through the decompression-expansion device 105, and enters the
outdoor heat exchanger 104, where the refrigerant expands as it
absorbs heat from the outdoor air, before returning to the
compressor 102. A current of air produced by the indoor blower 108
promotes heat emission by the indoor heat exchanger 106, and a
current of air produced by the outdoor blower 107 promotes heat
absorption by the outdoor heat exchanger 104
[0099] FIG. 15 shows how cooling operation or frost removal
operation proceeds. In this operation, the four-way value 103 is so
switched that the refrigerant circulates in the opposite direction
compared with in heating operation. Specifically, high-temperature,
high-pressure refrigerant is discharged from the compressor 102,
and enters the outdoor heat exchanger 104, where the refrigerant
emits heat and condenses. The refrigerant then exits from the
outdoor heat exchanger 104, passes through the
decompression-expansion device 105, and enters the indoor heat
exchanger 106, where the refrigerant expands as it absorbs heat
from the indoor air, before returning to the compressor 102. A
current of air produced by the outdoor blower 107 promotes heat
emission by the outdoor heat exchanger 104, and a current of air
produced by the indoor blower 108 promotes heat absorption by the
indoor heat exchanger 106.
[0100] It should be understood that the embodiment by way of which
the present invention is described above is in no way meant to
limit the present invention, which can thus be implemented with any
modifications or variations made within the spirit of the present
invention.
INDUSTRIAL APPLICABILITY
[0101] The present invention finds wide application in
parallel-flow heat exchangers of a side-flow type.
LIST OF REFERENCE SIGNS
[0102] 1 heat exchanger
[0103] 2, 3 header pipe
[0104] 4 flat tube
[0105] 5 refrigerant passage
[0106] 6 fin
[0107] 7 side plate
[0108] A, B, C, D refrigerant path
* * * * *