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(11) | EP 0 138 435 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Tube and fin heat exchanger |
| (57) A tube and fin heat exchanger is disclosed having a plurality of U-shaped tubes (14),
each comprising two substantially parallel legs (24) interconnected by a U-shaped
bight portion (26), and being arranged within the heat exchanger so that each leg
(24) thereof lies in a respective one of two separate banks of tube legs with the
banks being staggered relative to one another so that each U-shaped tube (14) lies
in a plane inclined at an acute angle to the longitudinal axes (32, 34) of the banks,
and the ends of the legs (24) are interconnected by manifolds (28, 30) having separate
plenum chambers (48, 50, 52, 54, 56, 58) so as to convey fluid back and forth across
the heat exchanger in a plurality of passes of several legs each. |
[0001] This invention relates to tube and fin heat exchangers and more particularly to manifold arrangements therefor.
[0002] In tube and fin heat exchangers such as those used as a condenser in an automotive air conditioning system, the function is to reject heat from the refrigerant inside the tubes to the ambient air passing over the condenser exterior with the resistance to heat transfer kept as balanced as possible by adding fins to the condenser exterior (i.e. in contact with the tubes). In such an application, the main mechanism for heat transfer on the refrigerant side is condensing where the thermal energy of the phase change is rejected to the cooling air. It is a characteristic of all condensing fluids that only one condensing temperature exists for a given condensing pressure. And therefore, it is a good idea to reduce the refrigerant side pressure drop as much as possible without reducing refrigerant velocity to the point where the film resistance to heat transfer increases. Typically, the conventional automotive air conditioning condenser employs U-shaped tubes commonly referred to as "hairpins" which are inter-connected at their ends so as to form a plurality of fluid passes of two hairpin legs or tube lengths each. These condensers exhibit good refrigerant pressure drop characteristics so long as the depth or core thickness allows for a large enough tube diameter. For example, there are 33 mm (1.3") and 44.5 mm (1.75") deep production condensers with 9.5 mm (3/8") outside diameter(O.D.) tubes that have been manufactured for many years by the assignee of the present invention which provide good refrigerant pressure drop characteristics. But with advancing car design calling for shallower and lighter weight condensers having a depth of 25.4 mm (1.0") or less, a smaller tube diameter of, for example, 6.35 mm (1/4") O.D. is needed but without the normally accompanying higher pressure drop and loss of heat transfer when interconnected in conventional manner.
[0003] The present invention is an improved manifold arrangement characterized by separate multi-pass manifolds which interconnect the ends of the hairpins when the latter are arranged diagonally so that the fluid is caused to flow in several passes of several hairpin legs or tube lengths each across the heat exchanger. Various embodiments will be disclosed with the pass pattern effected by the improved manifolds in each case providing a substantially reduced pressure drop as compared with conventional manifolding having many passes but with just two hairpin legs or tube lengths each. The resulting improvement can be measured in heat transfer rate per pound of heat exchanger material and on a comparison basis of equal heat transfer and pressure drop performance of acceptable levels at certain vehicle speeds was found to provide as much as about 65% increase in BTU/MIN. LB. METAL.
[0004] These and other objects, features and advantages.of the present invention will become more apparent from the following description and the accompanying drawings, in which:
Figure.1 is a front view of a heat exchanger with one embodiment of the manifold arrangement according to the present invention.
Figure 2 is a sectional view taken along the line 2-2 in Figure 1.
Figure 3 is a top view taken along the line 3-3 in Figure 1.
Figure 4 is a view similar to Figure 2 but reduced and showing another embodiment of the manifold arrangement according to the present invention.
Figure 5 is a view similar to Figure 2 but showing still another embodiment of the manifold arrangement according to the present invention.
Figure 6 is a view similar to Figure 2 but showing still another embodiment of the manifold arrangement according to the present invention.
[0005] Referring to Figures 1-3, there is shown a tube and fin heat exchanger constructed according to the present invention and adapted for use as a condenser in an automotive air conditioning system. The condenser basically comprises a pair of headers 10 and 12, a plurality of U-shaped tubes or hairpins 14, each comprising two substantially parallel legs 24 interconnected by a U-shaped bight portion 26, a plurality of fins 16 and a manifold arrangement generally designated as 18 having an inlet fitting 20 and an outlet fitting 22 by which the condenser is connected in the refrigerant system.
[0006] Both the headers 10 and 12 and the fins 16 are stamped sheet metal pieces and are each perforated in identical patterns with two parallel rows of equally spaced holes to receive the parallel legs 24 of the hairpins 14. The hairpin legs 24 extend through the holes in the header 12 such that the bight portions 26 are at one end of the heat exchanger (the righthand end as viewed in Figure 1). The two legs 24 of the hairpins then extend through the holes in the fins 16 and on through those in the other header 10 with the hairpins all angled diagonally in the same direction as best shown in Figure 2 such that one leg of each hairpin extends through a hole in one of the rows and the other hairpin leg extends through a hole in the other and adjacent row. With the open ends of the hairpins extending through the header 10, long expander pins or rods (not shown) are then forced therethrough to expand the tubes radially outward and affect a forced fit with the headers and fins to retain these pieces together. Thereafter, the manifold arrangement 18 which is also formed of metal is joined, such as by soldering or brazing, to the open ends of the hairpin legs to complete the heat exchanger assembly.
[0007] According to the present invention, the manifold arrangement 18 is formed so as to effect by connection with the hairpins a multi-pass circuit of several hairpin legs or tube lengths each across the heat exchanger that produces only a small refrigerant pressure drop between the inlet and outlet when the condenser is formed with hairpins of 6.35 mm (1/4") O.D. that allow a shallow depth X (see Figure 3) of about 25.4 mm (1.0").
[0008] In the embodiment of the manifold arrangement 18 in Figures 1-3, this is accomplished with a pair of tubular manifolds 28 and 30 of 12.7 mm (1/2")O.D. metal tube which extend parallel to the header plate 10 and directly opposite to the respective rows 32 and 34 of tube ends, as best seen in Figure 2. Both ends of each of the manifold tubes 28 and 30 are closed with the manifold tube 28 connected adjacent one of its ends with the condenser inlet fitting 20 by an inlet pipe 36 and the other manifold tube 30 connected adjacent one of its ends with the condenser outlet fitting 22 by an outlet pipe 38; these connections being located at the opposite ends of the manifold arrangement 18 as seen in Figures 1 and 2. In the particular construction shown, a total of twenty-one hairpins are used and the manifold arrangement is compartmentized so as to interconnect them such that there are two passes across the heat exchanger of five hairpin legs or tube lengths 24 each and eight passes of four hairpin legs or tube lengths 24 each. To this end, the manifold tubes 28 and 30 are each perforated with a row of equally spaced holes along their length which receive and are joined, such as by soldering or brazing, to the open ends of the hairpin legs. The manifold tube 28 is thus joined with one leg of each of the hairpins in the tube row 32 while the other manifold tube 30 is joined with the other leg of each of the hairpins in the tube row 34. The multipass arrangement is completed by two plugs 40, 42 inserted in the manifold tube 28 and two plugs 44 and 46 inserted in the other manifold tube 30 with these plugs axially spaced in relation to each other so as to define three plenum chambers 48, 50 and 52 in the manifold tube 28 and three plenum chambers 54, 56 and 58 in the other manifold tube 30. The plenum chamber 48 in the manifold tube 28 is directly joined with the inlet pipe and also with one leg each of five of the hairpins 24 in the row 32. The other leg of these hairpins in the row 34 are in turn directly connected to the adjacent plenum chamber 54 in the other manifold tube 30 to thus complete two passes of five tube lengths each across the condenser. The latter manifold plenum chamber 54 also directly joins with one leg each of four other hairpins in the row 34 with the other leg of these hairpins in the other row 32 in turn connected to the adjacent manifold plenum chamber 50 in the manifold tube 28 to thus complete two passes but of four tube lengths each. Then in continuing zig-zag fashion, the manifold plenum chamber 50 directly joins with one leg of four other hairpins whose other leg is connected to the manifold plenum chamber 56 to make two more passes of four tube lengths each. The latter manifold plenum chamber 56 in the manifold tube 30 also joins directly with the leg of four more hairpins in the row 34 with other leg of these hairpins in turn joined to the remaining plenum 52 in the manifold tube 28 to complete two more passes of four tube lengths each across the condenser. The latter manifold plenum 52 also directly joins with the leg of the four remaining hairpins in the row 32 with the other leg of these hairpins in turn connected to the last manifold plenum chamber 58 in the manifold tube which leads directly to the outlet pipe and completes the last of two passes of four tube lengths each across the condenser. It has been found that the above manifold arrangement, which will be referred to as the 5-5-4-4-4-4-4-4-4-4 manifold arrangement with its passes of many hairpin legs or tube lengths, significantly reduces the refrigerant pressure drop so as to effect significant increase in the heat transfer performance as do the other embodiments of the invention, as will be shown later.
[0009] The embodiment of the manifold arrangement shown in Figure 4 has parts similar to those in Figures 1-3 designated by the same numbers but with the suffix A and added parts identified by new numbers and provides fourteen passes with three hairpin legs each, using the twenty-one hairpins 14A. These additional passes, but with less tube lengths each, are formed by retaining the plugs 40A,42A,44A and 4.6A but now in different locations and adding one more plug 60 and 62 in the respective manifold tubes 28A and 30A which remain connected at their one end to the respective inlet pipe 36A and outlet pipe 38A as before. This adds another plenum 64 and 66 to the respective manifold tubes 28A and 30A while the other manifold plenum chambers 48A,5OA,52A,54A,56A and 58A remain but with all the plenum chambers now located so as to be connected with three hairpin legs 24A each rather than to four or five as in the previous embodiment.
[0010] The embodiment of the manifold arrangement shown in Figure 5 has parts similar to those in Figures 1-3 designated by the same numbers but with the suffix B and added parts identified by new numbers and provides six passes with five hairpin legs each, two passes with four hairpin legs each and two passes with two hairpin legs each using the twenty-one hairpins 14B. These three descending numbers of passes are formed by retaining the same number of plugs as in the Figure 1-3 embodiment but.in different relative axial locations with the plug 40B remaining in the same location as the plug 40 in Figure 2 but the other plugs 42B,44B and 46B relocated to effect the different number passes. The manifold plenum chamber 48B which is connected to the inlet pipe 36B thus remains directly connected with one leg each of five of the hairpins 14B as does the plenum chamber 54B with the other leg of these hairpins. However, the plenum chamber 54B as well as plenum chambers SOB and 56B are also similarly connected with one leg of five of the hairpins while the manifold plenum chamber 56B is also now connected with one leg each of four of the hairpins as is the plenum chamber 52B while the manifold plenum chamber 52B is also now connected as is the plenum chamber 58B with one leg each of the two remaining hairpins. The last plenum chamber 58B remains connected to the outlet pipe 38B to complete the circuit which will be referred to as the 5-5-5-5-5-5-4-4-2-2 manifold arrangement.
[0011] The embodiment of the manifold arrangement shown in Figure 6 has parts similar to those in Figures 1-4 designated by the same numbers but with the suffix C and provides two passes with five hairpin legs each, four passes with four hairpin legs each, four passes with three hairpin legs each and two passes with two hairpin legs each using the twenty-one hairpins 14C. These passes are provided with the same number of plugs in the manifold pipe 28C as in the Figure 4 embodiment; namely three and designated as 40C, 42C and 60C while, in the other manifold pipe 30C they are provided with only two plugs like in the Figure 1-3 embodiment and designated as 44C and 46C. In this case, the plugs are located in their respective manifold pipes and relative to those in the other manifold pipe such that the manifold plenum chamber 48C which remains connected to the inlet pipe 36C is connected to one leg each of five hairpins as is the manifold plenum chamber 54C to the other legs and to one leg each of four more hairpins, each of whose other leg is connected to the manifold plenum chamber 50C. The latter plenum chamber 50C is similarly connected to one leg each of four more hairpins as is the plenum chamber 56C to the other legs and to one leg of three more hairpins,each of whose other leg is connected to the plenum chamber 52C. The latter plenum chamber is in turn open to one leg of still three more hairpins, each of whose other leg is connected to the plenum chamber 58C. The latter plenum chamber connects with one leg each of the two remaining hairpins, the other legs of which are connected with the remaining plenum 64C which is now connected directly to the outlet tube 38C, i.e. both the inlet pipe 36C and outlet pipe 38C being thus connected to the one manifold pipe 28C as compared with the previous embodiments wherein the outlet pipe was connected with the other manifold pipe 30,30A and 30B. This manifold arrangement following the previous manner of description will thus be referred to as the 5-5-4-4-4-4-3-3-3-3-2-2 manifold arrangement.
[0012] The improvement provided by the above embodiments is demonstrated by comparison with a typical conventional manifold arrangement having a core depth of 33 mm (1.30") and 16 passes with two hairpin legs each. The comparison was made on the basis of equal heat transfer and pressure drop performance of acceptable levels at vehicle speeds of 25 MPH and 50 MPH and appears in the following table:
1. A tube and fin heat exchanger having a plurality of U-shaped tubes (14), each comprising
two substantially parallel legs (24) interconnected by a U-shaped bight portion (26),
the free ends of the legs (24) of the tubes (14) being interconnected so as to convey
a fluid back and forth across the heat exchanger in a plurality of passes between
an inlet (20) and an outlet (22), characterised in that each U-shaped tube (14) is
arranged within the heat exchanger so that each leg (24) thereof lies in a respective
one of two separate banks of tube legs with the banks being staggered relative to
one another so that each U-shaped tube (14) lies in a plane inclined at an acute angle
to the longitudinal axes (32,34) of the banks, and there are separate multi-pass manifold
means (28,30) interconnecting the ends of the legs (24) so that the fluid is caused
to flow in several passes, each comprising several legs (24), across the heat exchanger
between the inlet (20) and the outlet (22)
2. A tube and fin heat exchanger according to claim 1, characterised in that-the multi-pass
manifold means comprise two substantially parallel manifold tubes (28,30) each of
which is subdivided into plenum chambers (48,50,52,54,56,58), each of which plenum
chambers (48,50,52,54,56,58) is interconnected with several ends of the legs (24)
in a respective bank of tube legs.
3. A tube and fin heat exchanger according to claim 2, characterised in that each
manifold tube (28,30) is subdivided into plenum chambers (48,50,52,54,56,58) by means
of plug means (40,42,44,46)inserted into predetermined positions within the manifold
tube (28,30).
4. A tube and fin heat exchanger according to claim 2 or 3, characterised in that
there are twenty-one U-shaped tubes (14), the ends of which are interconnected to
respective plenum chambers (48,50,52,54,56,58) in a 5-5-4-4-4-4-4-4-4-4 arrangement
as hereinbefore defined.
5. A tube and fin heat exchanger according to claim 2 or 3, characterised in that
there are twenty-one U-shaped tubes (14), the ends of which are interconnected to
respective plenum chambers (48A,50A,52A,54A,56A,58A,64,66) in a 3-3-3-3-3-3-3-3-3-3-3-3-3-3
arrangement as hereinbefore defined.
6. A tube and fin heat exchanger according to.claim 2 or 3, characterised in that
there are twenty-one U-shaped tubes (14), the ends of which are interconnected to
respective plenum chambers (48B,50B,52B,54B,56B,58B) in a 5-5-5-5-5-5-4-4-2-2 arrangement
as hereinbefore defined.
7. A tube and fin heat exchanger according to claim 2 or 3, characterised in that
there are twenty-one U-shaped tubes (14), the ends of which are interconnected to
respective plenum chambers (48C,50C,52C,54C,56C,58C,64C) in a 5-5-4-4-4-4-3-3-3-3-2-2
arrangement as hereinbefore defined.