TECHNICAL FIELD
[001] The present invention relates to heat exchangers suitable for automotive air conditioning system. Specifically relates to multiple bank tube fin heat exchangers used as evaporators in an automotive air conditioning system with optimized design for more compact packaging and enhanced capacity.
BACKGROUND
[002] Heat exchangers have long been used as evaporators in an automotive air conditioning system. Typically, these heat exchangers have been round tube and plate fin heat exchangers. However, flat tube and louver fin heat exchangers are predominantly employed due to their lower weight, compactness, structural rigidity, and reduced refrigerant charge requirement, in comparison to conventional round tube and plate fin heat exchangers.
[003] Flat tube and louver fin heat exchangers typically include a first header, a second header, and a plurality of flat, hollow tubes forming a tube bank, disposed in spaced parallel relationship and connected between the first header and the second header. Each of the flat hollow tubes provides a flow path for a first fluid, commonly refrigerant in the auto air conditioning system, which communicates between the first header and the second header. Additionally, a plurality of fins are disposed and brazed to the adjacent flat, hollow tubes to increase the heat transfer area. As the air flows across the plurality of fins, heat in the refrigerant flowing inside the flat hollow tubes is conducted through the walls of the flat hollow tubes into the plurality of fins and transferred to the air passing through the inter-tube spacing and plurality of fins.
[004] It is also very common for the flat tube and louver fin heat exchangers to include more than one tube bank. These types of multiple bank tube fin heat exchangers, such as double bank tube fin heat exchangers are typically formed of two conventional tube banks, one disposed behind the other.
[005] However in recent years, more stringent heat rejection requirements of tube fin heat exchangers along with overall packaging compactness has enforced component manufacturers to further down size the component, whereas keeping the similar or enhanced performance. A
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known or benchmark tube fin heat exchanger which fulfills these requirements includes a heat exchanger core configured in such a way that, the two tube banks are arranged in the direction of air flow path, where each tube bank consists of a plurality of flat tubes arranged at predetermined intervals. A first header which is disposed on one end of the flat tubes in such a way that front and rear tube banks are aligned perpendicular to air flow direction. A second header is disposed on the other end of the flat tubes such that both the tube banks enter the header parallel and both headers are perpendicular to tube length and parallel to each other.
[006] Numerous efforts have been made to the benchmark flat tube, louver fin heat exchangers in order to achieve foregoing objectives by modifying various design parameters of the tube fin heat exchanger, including but not limited to the following: tube bank spacing, tube width, tube height, fin pitch, fin height, number of tube ports etc. However, such benchmark tube fin heat exchangers fail to provide compact tube fin heat exchangers with improved or comparable heat rejection capacity. Also another major concern associated with the tube fin heat exchangers is the poor drainage of condensed water from the surface of the flat hollow tubes caused from close tube spacing.
[007] In view of the foregoing, at least one object is to provide a multiple bank tube fin heat exchanger for an automotive air-conditioning system with reduced weight, packaging compactness and enhanced heat rejection rate. Another object is to provide a multiple bank tube fin heat exchanger which is capable of more easily draining condensed water generated in the tube fin heat exchanger. Other objects such as desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.
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SUMMARY
[008] It is therefore an object of the invention to provide a multiple bank tube fin heat exchanger which is compact, light weight and exhibits enhanced heat rejection rate.
[009] Another object of the invention is to provide a multiple bank flat tube louver fin heat exchanger, that has substantially free draining of condensed water, which also enhance heat exchange capacity.
[010] The present invention discloses, in one aspect, a multiple bank tube fin heat exchanger in the form of evaporator for an automotive application, comprising a first tube bank including a first plurality of flat tubes extending longitudinally and arranged in spaced parallel rows between a first pair of headers and a second tube bank including a second plurality of flat tubes extending longitudinally and arranged in spaced parallel rows between a second pair of headers. The first and second tube banks defining a flow path for a first fluid between the first and second pair of headers and the second tube bank is disposed behind the first tube bank. A plurality of corrugated, louver fins disposed between adjacent pairs of the first and second plurality of flat tubes and extending between the first and second plurality of flat tubes of both first and second tube banks and are arranged parallel to the direction of a flow of a second fluid.
[011] In an embodiment of the invention, the multiple bank tube fin heat exchanger is in the form of evaporator for the automotive application comprises a unique tube fin configuration and inter-bank spacing to exhibit enhanced heat rejection rate along with weight reduction and packaging compactness. The design parameters of the multiple bank tube fin heat exchanger such as tube width, number of tube ports, fin height and space between the tube banks are optimized in such a way that, significant improvement on overall heat rejection and overall compactness and/or reduction in weight is achieved.
[012] In an another embodiment, a gap between two tube banks is set more than a tube width of first or second plurality of flat tubes, the tube width of each of the first and second plurality of flat tubes are substantially equal.
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[013] In another embodiment, the gap between the first and second tube banks is 1.2 to 2.3 times more than the tube width of the first or second plurality of flat tubes and the tube width of each of the first or second plurality of flat tubes is set below 10 mm.
[014] In yet another embodiment, the plurality of corrugated louver fins disposed between the adjacent flat tubes, which runs transversely from one outside edge of the tube of one tube bank to the other outside edge of the tube, hence filling the gap between tube banks in continuation. Further, the plurality of corrugated louver fins extend on both sides of the flat tubes of each of the first and second plurality of flat tubes.
[015] In yet another embodiment, a fin height of the plurality of corrugated louver fins lies between 2.5 mm and 3.5 mm and a fin pitch of the plurality of corrugated louver fins is set no less than 2.4 mm.
[016] In yet another embodiment, a number of ports in individual tube has been kept well below 5 numbers to meet pressure drop and refrigerant side heat transfer coefficient requirements as the selection of number of ports is subjected to overall refrigerant side pressure drop.
[017] In yet another embodiment, a heat exchange core section of the multiple bank tube fin heat exchanger has a width of 32 mm and each of the first and the second plurality of flat tubes has a tube height of 0.9 mm to 1.2 mm.
[018] Additional aspects, advantages, features, and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative embodiments, construed in conjunction with the appended claims.
[019] It will be appreciated that the features of the present disclosure are susceptible to being combined in various combinations without departing from the spirit and the scope of the disclosure, as defined by the appended claims.
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BRIEF DESCRIPTION OF THE DRAWINGS
[020] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those skilled in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.
[021] Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
[022] FIGURE 1 illustrates an isometric view of a multiple bank tube fin heat exchanger in accordance with an embodiment of the disclosure showing the tube banks with tube configuration;
[023] FIGURE 2A illustrates a sectional view of a multiple bank tube fin heat exchanger and FIGURE 2B is a side view of corrugated louvered fins illustrated in FIGURE 2A in accordance with an embodiment of the disclosure;
[024] FIGURE 3A illustrates a sectional view of a known or benchmark multiple bank heat exchanger and FIG.FIGURE 3B is a side view of corrugated louvered fins illustrated in FIGURE 3A;
DETAILED DESCRIPTION OF EMBODIMENTS
[025] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.
[026] In accordance with a preferred embodiment of the present invention, a multiple bank tube fin heat exchanger is provided where a refrigerant flow path is reduced in the same proportion as free flow area is reduced so as to have same level of refrigeration side pressure drop. The optimization of tube spacing and number of tube ports in each flat tube has resulted into reduction in a refrigerant side path length, which actually helps in controlling the increased
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refrigerant side pressure drop resulted due to reduced refrigerant side free flow area caused by downsizing of tube width and tube height in proposed multiple bank tube fin heat exchanger. Further reduced refrigerant side pressure drop has a positive impact on refrigerant side heat transfer characteristics.
[027] FIGURE 1 illustrates an isometric view of a multiple bank tube fin heat exchanger 100 in accordance with an embodiment of the disclosure showing the tube banks with tube configuration. The multiple bank tube fin heat exchanger 100 comprising a first tube bank 101 including a first plurality of flat tubes 106 extending longitudinally and arranged in spaced parallel rows between a first pair of headers 102, 104 and a second tube bank 201 including a second plurality of flat tubes 206 extending longitudinally and arranged in spaced parallel rows between a second pair of headers 202, 204. The second tube bank 201 is disposed behind the first tube bank 101.
[028] The first and second tube banks 101, 201 define a flow path for a first fluid between the first pair of headers 102, 104 and between the second pair of headers 202, 204, the first fluid is generally refrigerant in auto air conditioning system. The flow path of the refrigerant is configured such that, the refrigerant enters into the second pair of headers 202, 204 first, where it is collected in the header 202 and flows through the second plurality of flat tubes 206 before entering into the header 204. From the header 204, the refrigerant transferred to the header 104 by means of micros channels embedded at the bottom of the second pair of headers 202, 204, participating in fluid communication. Thereafter it flows through the first plurality of flat tubes 106 arranged in first tube bank 101, where it is finally being collected by the header 102, before leaving the multiple bank tube fin heat exchanger 100. Thus, the header 202 has an inlet and the header 102 has an outlet for the flow of the refrigerant.
[029] A plurality of corrugated louver fins 115 disposed between adjacent pairs of the first and the second plurality of flat tubes 106, 206 and extending between the first and second plurality of flat tubes 106, 206 of both the first tube bank 101 and the second tube bank 201 and are arranged parallel to the direction of flow of a second fluid. The second fluid which is air in auto air
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conditioning system flows over the outer surface of the first and second plurality of flat tubes 106, 206 and along the surfaces of the plurality of corrugated louver fins 115.
[030] As the air flows, heat in the refrigerant flowing inside the first and second plurality of flat tubes 106, 206 is conducted through the walls of the first and second plurality of flat tubes 106, 206 into the plurality of corrugated louver fins 115 and transferred into the airflow. As it can be seen from FIGURE 1, the air passes first transversely across the first plurality of flat tubes 106 of the first tube bank 101 and then passes transversely across the second plurality of flat tubes 206 of the second tube bank 201, and the refrigerant flows first through the second plurality of flat tubes 206 of the second tube bank 201 and then through the first plurality of flat tubes 106 of said first tube bank 101.
[031] FIGURE 2A illustrates a sectional view of a multiple bank tube fin heat exchanger 100 and FIGURE 2B is a side view of the corrugated louvered fins illustrated in FIGURE 2A and is in accordance with the new tube fin configuration corresponding to an optimum design. Series of iterations has been done by varying fin height, tube width, number of ports and tube bank spacing etc. According to the results of the present invention, a gap “G” between the first tube bank 101 and the second tube bank 201 is more than a tube width “Tw” of the first or second plurality of flat tubes 106, 206, the tube width “Tw” of the first plurality of flat tubes 106 and the tube width “Tw” of the second plurality of flat tubes 206 are substantially equal.
[032] In comparison to a known or benchmark multiple bank heat exchanger 300 as shown in FIGS. 3A and 3B, the gap “G” between the first and second tube banks 101, 201 is increased and kept 1.2 to 2.3 times more than the tube width “Tw” of the first or second plurality of flat tubes 106, 206 and the tube width “Tw” of each of first and second plurality of flat tubes 106, 206 is set below 10 mm. In the benchmark multiple bank heat exchanger 300 of FIGURE 3A, the gap “G” between the first and second tube banks 101, 201 is always less than the tube width “Tw” of the first and second plurality of flat tubes 106, 206.
[033] In one embodiment of the invention, the multiple bank tube fin heat exchanger 100 of the FIGURE 2A has the gap “G” of 17 mm between the first and second tube banks 101, 201 and the
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tube width “Tw” of 7.5 mm for each of the first and second plurality of flat tubes 106, 206. Also, a number of ports 204 of each of the first and second plurality of flat tubes 106, 206 are set below 5. The increased gap “G” between the first and second tube banks 101, 201, the reduced tube width “Tw” and the reduced number of tube ports 204 of each of the first and second plurality of flat tubes 106, 206 results into reduced refrigerant side pressure drop caused by reduced flow path length and increased air side heat transfer coefficient, leading to enhanced heat exchange capacity along with improved condensate drainage from the surface of the first and second plurality of flat tubes 106, 206.
[034] According to the present invention, overall compactness and/or reduction in weight of the multiple bank tube fin heat exchanger 100 is achieved by reducing a width “W” of a heat exchange core section 108, tube height “Th”, tube pitch “Tp” and fin height “Fh”. As shown in FIGURE 2A, the width “W” of the heat exchange core section 108 is preferably set to 32 mm. Each of the first and second plurality of flat tubes 106, 206 has a tube height “Th” of 0.9 mm to 1.2 mm. The tube pitch “Tp” which is a distance between each of the adjacent first and second plurality of flat tubes 106, 206 is preferably set to 3.7 mm.
[035] For overall heat rejection rate, an air side heat transfer coefficient becomes a controlling parameter. Therefore, a secondary heat transfer area (fin area) is optimized to achieve the weight reduction and overall compactness, while keeping the same or improved heat rejection rate. Accordingly, the fin height “Fh” of the multiple bank tube fin heat exchanger 100 is reduced in comparison to the benchmark multiple bank heat exchanger 300. Referring to FIGURE 2B, a fin height “Fh” of the plurality of corrugated louver fins 115 lies between 2.5 mm and 3.5 mm and a fin pitch defined by a distance between adjacent fins of the plurality of corrugated louver fins 115 is preferably not less than 2.4 mm which helps in downsizing the multiple bank tube fin heat exchanger 100.
[036] FIGS 3A and 3B illustrate the benchmark multiple bank heat exchanger 300. In the benchmark multiple bank heat exchanger 300, the gap “G” is always less than the tube width “Tw”. This result in requirement of higher value of “Tw”, which further increases the width
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“W”. Thus, the benchmark multiple bank heat exchanger 300 has the drawbacks of being relatively large, bulky with limited heat rejection rate.
[037] The below table 1 shows the results of the multiple bank tube fin heat exchanger 100 of the present invention compared with the benchmark multiple bank heat exchanger 300.
[038] Modifications to embodiments of the present disclosure described above are possible without deviating from the spirit and the scope of the disclosure as defined in the accompanying claims. Expressions such as “comprise” and “include”, and variations such as “comprises”, “comprising”, “includes”, and including are intended to be construed in a non-exclusive manner, namely allowing for items, components, or elements not explicitly described (or recited) also to be present. Reference to the singular is also to be construed to relate to the plural, except where explicitly stated.
Controlling Parameter
Units
Baseline
Proposed
Refrigerant Side Area
m
2
100%
43%
Refrigerant Side Free Flow
Area
m
2
100%
57%
Refrigerant Side Path Length
m
100%
50%
Primary Air side Area (Tube)
m
2
100%
81%
Secondary Air side Area (Fin)
m
2
100%
84%
Total Air side Area (A)
m
2
100%
84%
Air side heat transfer
coefficient (h)
W/m2-K
100%
120%
h x A
W/K
100%
100%
Q (Evaporator)/Core weight

WE CLAIM:
1. A multiple bank tube fin heat exchanger (100) for use in an automotive air conditioning system comprising:
a first tube bank (101) including a first plurality of flat tubes (106) extending longitudinally and arranged in spaced parallel rows between a first pair of headers (102, 104) and defining a flow path for a first fluid between the first pair of headers (102, 104); and
a second tube bank (201) including a second plurality of flat tubes (206) extending longitudinally and arranged in spaced parallel rows between a second pair of headers (202, 204) and defining a flow path for the first fluid between the second pair of headers (202, 204), wherein the second tube bank (201) is disposed behind the first tube bank (101);
a plurality of corrugated louver fins (115) disposed between adjacent pairs of the first and second plurality of flat tubes (106, 206) and extending between the first and second plurality of flat tubes (106, 206) of both of the first tube bank (101) and the second tube bank (201) and arranged parallel to the direction of flow of a second fluid;
wherein a gap (G) between the first tube bank (101) and the second tube bank (201) is more than a tube width (Tw) of the first or second plurality of flat tubes (106, 206), the tube width (Tw) of the first plurality of flat tubes (106) and the tube width (Tw) of the second plurality of flat tubes (206) are substantially equal.
2. The multiple bank tube fin heat exchanger (100) as claimed in claim 1, wherein the gap (G) between the first and second tube banks (101, 201) is 1.2 to 2.3 times more than the tube width (Tw) of the first or second plurality of flat tubes (106, 206).
3. The multiple bank tube fin heat exchanger (100) as claimed in claim 2, wherein each of the first plurality of flat tubes (106) and each of the second plurality of flat tubes (206) has the tube width (Tw) which is set below 10 mm.
4. The multiple bank tube fin heat exchanger (100) as claimed in claim 1, wherein a fin height (Fh) of the plurality of corrugated louver fins (115) lies between 2.5 mm and 3.5 mm.
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5. The multiple bank tube fin heat exchanger (100) as claimed in claim 4, wherein a fin pitch (Fp) of the plurality of corrugated louver fins (115) is set no less than 2.4 mm.
6. The multiple bank tube fin heat exchanger (100) as claimed in claim 5, wherein the plurality of corrugated louver fins (115) extend on both sides of the first and second plurality of flat tubes (106, 206).
7. The multiple bank tube fin heat exchanger (100) as claimed in claim 1, wherein a heat exchange core section (108) has a width (W) of 32 mm and each of the first and second plurality of flat tubes (106, 206) has a tube height (Th) of 0.9 mm to 1.2 mm and a tube pitch “Tp” of 3.7 mm respectively.
8. The multiple bank tube fin heat exchanger (100) as claimed in claim 7, wherein a number of ports (204) of each of the first and second plurality of flat tubes (106, 206) are set below 5.
9. The multiple bank tube fin heat exchanger (100) as claimed in claim 1, wherein the first fluid is refrigerant and the second fluid is air.
10. The multiple bank tube fin heat exchanger (100) as claimed in claim 9, wherein the air flows first transversely across the first plurality of flat tubes (106) of said first tube bank (101) and then passes transversely across the second plurality of flat tubes (206) of said second tube bank (201), and the refrigerant flows first through the second plurality of flat tubes (206) of said second tube bank (201) and then through the first plurality of flat tubes (106) of said first tube bank (101).
11. The multiple bank tube fin heat exchanger (100) as claimed in claim 10, wherein an inlet and an outlet for a flow of the refrigerant are provided on one of the header (202) of the second pair of headers (202, 204) and on one of the header (102) of the first pair of headers (102, 104) respectively.
12. The multiple bank tube fin heat exchanger (100) as claimed in claim 11, wherein the multiple bank tub fin heat exchanger (100) used as an evaporator in an automotive air conditioning system.