Patent Application
20150168072
The present invention relates to a parallel-flow heat exchanger of a side-flow type, and to an air conditioner incorporating it.
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.
An example of the structure of a parallel-flow heat exchanger is shown in
The flat tubes 4 are elongate moldings of metal formed by extrusion and, as shown in
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
In parallel-flow heat exchangers, elaborate designs have been made for improved performance. Examples are seen in Patent Documents 1 to 3 identified below.
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.
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.
In the parallel-flow heat exchanger described in Patent Document 3, a flow distribution parameter γ, i.e., the ratio of the resistance parameter β of flat tubes to the resistance parameter α 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.
Patent Document 1: JP-A-H5-87752
Patent Document 2: JP-A-2001-165532
Patent Document 3: JP-A-2000-111274
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.
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<3.0×10−4×Q+8.0, (A)
and when the parallel-flow heat exchanger is used in an indoor unit of an air conditioner, the formula
n<4.2×10−4×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). Used as Q is, for an outdoor unit, rated heating capacity and, for an indoor unit, rated cooling capacity.
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>(αQ+β)×[(1.4×10−16)×L/(d×A′2)]0.5, (B)
where
α=0.0161;
β=8.86;
d represents the hydraulic diameter, given in meters (m); and
A′ represents the refrigerant passage cross-sectional area of one flat tube, given in square meters (m2).
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>(αQ+β)×[(1.4×10−16)×L/(d×A′2)]0.5, (B)
where
α=0.0228;
β=6.62;
d represents the hydraulic diameter, given in meters (m); and
A′ represents the refrigerant passage cross-sectional area of one flat tube, given in square meters (m2).
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.
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.
A parallel-flow heat exchanger 1 of a side-flow type as shown in
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<3.0×10−4×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<4.2×10−4×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).
Formula (A) was derived through experiments. The table in
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
As will be seen from the table in
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.
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.
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.
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.
n=1.9×10−2 m+7.8. (a)
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
Using a rated heating capacity Q (in watts (W)), the refrigerant circulation rate m is given by
m=0.0161 Q+8.86. (b)
Using a rated cooling capacity Q (in watts (W)), the refrigerant circulation rate m is given by
m=0.0228 Q+6.621. (c)
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)×(Suction Pressure Density)×(Compressor Volume).
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.
Accordingly, as shown in
n=3.0×10−4 Q+8.0.
As shown in
n=4.2×10−4 Q+7.9.
This makes it possible to suppress an uneven flow.
Next, the lower limit of the number of flat tubes constituting each refrigerant path is determined As shown in
Tout<0° 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° C.
Let the temperature drop due to a pressure loss ΔP be TDp, then
TRin−TDp<0° C.,
where TRin represents the inlet evaporation temperature of the refrigerant. The pressure loss ΔP is given in pascals (Pa).
That is,
PRin−ΔP>Plim,
where PRin represents the inlet evaporation temperature, and Plim represents the saturation pressure of the refrigerant at 0° C.
Here,
ΔP=λ×L/d×ρ×u2/2,
where λ 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); ρ represents the refrigerant density, given in kilograms per cubic meter (kg/m3); and u represents the flow speed of the refrigerant, given in meters per second (m/s).
The flow speed is given by
u=M/ρA,
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 (m2).
Thus,
ΔP=λ/2 ρ×L/dA2×M2.
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.
Here,
ΔP<PRin−Plim.
λ/2 ρ×L/(dn2×A′2)×M2<PRin−Plim
Here,
n2>M2×λ/2 ρ×L/dA′2×1/ (PRin−Plim).
The above formula gives
n>M [λ/2 ρ×L/dA′2×1/(PRin−Plim)]0.5. (d)
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=αQ+β.
How the refrigerant circulation rate correlates with capacity is shown in
m=0.0161 Q+8.86.
Using a rated cooling capacity Q (in watts (W)), the refrigerant circulation rate m is given by
m=0.0228 Q+6.62.
For an outdoor-unit heat exchanger, rated heating capacity can be used; for an indoor-unit heat exchanger, rated cooling capacity can be used.
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)×(Suction Pressure Density)×(Compressor Volume).
On the other hand, it is common to keep the pressure loss below 200 kPa. Thus,
PRin−Plim<200×103.
The coefficient of friction λ 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/m3 with a gaseous refrigerant.
Thus, performing unit conversion from M to m gives
n>(αQ+β)×[π+L/(d×A′2)]0.5.
Here, π is given by
1.4×10−16<π<4.8×10−15.
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.
Here, considering that the pressure loss should be as low as possible, it is preferable to set II at its lowest value, namely 1.4×1016. Hence
n≧(αQ+β)×[(1.4×10−16)×L/(d×A′2)]0.5. (B)
Thus, using formula (B), it is possible to determine the lower limit of the number of flat tubes constituting a one-turn path.
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.
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.
The parallel-flow heat exchanger 1 according to the present invention can also be used as the heat exchanger 104 in the outdoor unit.
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.
The present invention finds wide application in parallel-flow heat exchangers of a side-flow type.
1 heat exchanger
2, 3 header pipe
4 flat tube
5 refrigerant passage
6 fin
7 side plate
A, B, C, D refrigerant path
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-194111 | Sep 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/071301 | 8/7/2013 | WO | 00 |
