Heat exchanger having tube support plate

0001This invention relates to a heat exchanger comprising the features of the preamble of claim 1. The support plate used in such a heat exchanger, which is, for example, known from DE-A-3 136 865, supports the tubes.

0002Another support plate is shown, for example, in Japanese Patent Document JP-P-HEI 4-292797 issued to Urabe. Generally, the Urabe heat exchanger is designed for use in an air conditioning system of a motor vehicle. As such, the tubes are typically subjected to vibration from the motor vehicle and from the flow of refrigerant fluid in the cooling circuit. This vibration may cause the tubes to shift, bend, break or otherwise become damaged. Damage to the tubes may, in turn, cause the space between adjacent tubes to be nonuniform and the air flow, which passes across the tubes, to become uneven. This can result in a decrease in the heat exchange efficiency of the heat exchanger. Also, the air resistance of the beat exchanger may increase. Because of these problems, a beat exchanger may be provided with a tube support system to inhibit lateral movement of the tubes.

0003Referring to Fig. 1 (Urabe) a tube support plate 32 for supporting closely packed heat transfer tubes 15 is typically transversely disposed with respect to heat transfer tubes 15 in the heat exchanger. Tube support plate 32 has a plurality of holes 33, which receive a plurality of heat transfer tubes 15. Holes 33 are circular in shape and are respectively identical to, or slightly larger in diameter than, heat transfer tubes 15 to support heat transfer tubes 15 against lateral movement. Referring also to Fig.2, each hole 34 includes a plurality of projection portions 34a extending from an edge thereof. Projection portions 34a contact with an outer surface of a heat transfer tube 15 so as to inhibit lateral movement of heat transfer tube 15. A relatively small gap 44 is created between the edges of holes 34 and heat transfer tubes 15.

0004Generally, the air flow contains moisture in a vapor state. Typically, the vapor is cooled to a temperature below the dew point as the air flow passes across the heat transfer tubes This temperature reduction changes the vapor into a condensate, which can form on and adhere to the outer surfaces of the heat transfer tubes.

0005In the Urabe heat exchanger, the condensate which forms on the outer surfaces of heat transfer tubes 15, can move to and collect on tube support plate 32 if the outer surfaces of heat transfer tubes 15 contact the inner edges of holes 33 as shown in Fig. 1. This is undesirable for a variety of reasons including the propagation of rust on plate 32. To solve this problem, the diameter of holes 33 may be enlarged. However, if the diameter of holes 33 is enlarged to avoid contact with tubes 15, support for tubes 15 may become greatly reduced. Alternatively, as shown in Fig. 2, projections 34a may be provided to create a gap 44 between the outer surface of beat transfer tube 15 and the edge of hole 34 as shown Fig. 2. However, this alternative solution might present similar problems already considered. For example, if gap 44 is too small, the condensate can encounter difficulty in flowing along the surface of tube 15 and past plate 32. Thus, condensate may move to and collect on plate 32. If projections 34a are elongated to enlarge gap 44, the strength of projection 34a might become weak and projections 34a may be more easily damaged.

0006Other problems also exist. For example, condensate which collects on tube support plate 32 can be carried to the outside of heat exchanger 10 by the air flow. Thus, engine parts in the vicinity of such a heat exchanger used in a motor vehicle are subject to problems such as corrosion or rust. Moreover, the air resistance of heat exchanger 10 might increase since condensate on plate 32 and tubes 15 disrupts the air flow passing across tubes 15. Because of these and other problems, the heat exchanger cannot maintain the high heat exchange efficiency over extended periods of use.

0007It is an object of the invention to provide a heat exchanger which maintain high heat exchange efficiency over extended periods of use by preventing the collection of condensate on a tube support plate of the heat exchanger.

0008DE 3136865 discloses a heat exchanger comprising a first tank; a second tank; at least one tube connected at one end to the first tank and at the other end to the second tank for circulation of a first medium between the tanks; a support plate disposed between the first tank and the second tank and having at least one hole formed therein, the at least one tube passing through the at least one hole in the plate, the edge of the hole contacting the tube at a plurality of regions around the tube to locate the tube against lateral movement relatively to the plate, and that part of the edge of the hole interconnecting at least one pair of adjacent contact regions consisting of two substantially straight portions which converge towards one another and extend from the contact regions at which they are substantially tangential to the tube to an apex remote from the tube to form a lobe-like aperture adjacent to the tube; and a flow path for a second medium around the tube to effect heat exchange between the first and second media; and the present invention is characterised in that the first and second tanks are upper and lower tanks which are connected by opposed side plates to define therebetween the flow path which is across the tube(s), the support plate being mounted substantially horizontally between the side plates; and in that the or at least one of the apices of the hole points downstream from the tube relative to the direction of flow of the second medium along the flow path whereby any condensation on the tube will tend to be drawn by the flow of the second medium around the tube and to drain through the lobe-like aperture rather than collect on the plate.

0009The holes may be of a variety of shapes. For instance, substantially rhombus, teardrop, triangle, or square-shaped holes may be used. In conjunction with these or other basic shapes, a portion of the peripheral surface of the bole may be curved so that it contacts a corresponding tube at least one interface defining a curve. This has the technical advantage of supporting the tubes with linear or arcuate contact as opposed to point contact support Alternatively, the basic shape of a hole may provide contact at three or more points to support the corresponding tube. This arrangement has the technical advantage of providing point contact without the need for projection portions extending from the peripheral surface of the hole.

0010Another technical advantage of the present invention is that the condensate may move along the outer surface of the tubes and through the gap without moving to the support plate. This may be achieved, in part, by forming relatively large gaps as compared to gaps used in the prior art. This advantage be achieved is due to the positioning of the gaps at the downstream sides of the tubes with respect to the now of air across the tubes. The air flow can thereby force the condensate to the downstream sides of the tubes where gravity can cause the condensate to flow down the tubes and through the gaps.

0011When used in a typical heat exchanger, these features facilitate flow of the condensate to a bottom portion of the heat exchanger. Thus, condensate is not carried away from the heat exchanger by the air flow. This can minimize rusting of parts in the vicinity of the heat exchanger (<u>e.g.</u>, motor vehicle engine parts). Further, the support plate can more firmly support the heat transfer tubes, thereby preventing damage to the tubes. Also, air resistance of the heat exchanger is minimized since the air flow smoothly passes across the heat transfer tubes without the resistance of the condensate. This maximizes the efficiency of the heat exchanger.

0012Further advantages of the present invention will be understood from the following detailed description of the preferred embodiments with reference to the appropriate figures.

0013In the accompanying drawings:

0014Fig. 1 is a partial cross-sectional view in accordance with the prior art.

0015Fig. 2 is a partial cross-sectional view in accordance with the prior art.

0016Fig. 3 is a perspective view of a heat exchanger in accordance with an embodiment of the present invention.

0017Fig. 4 is a side view of the heat exchanger depicted in Fig. 3.

0018Fig. 5 is a partial cross-sectional view of a heat exchanger taken along line 5-5 of Fig. 4 in accordance with an embodiment of the present invention.

0019Fig. 6 is a partial cross-sectional view of the heat exchanger of Fig. 4 in accordance with another embodiment of the present invention.

0020Fig. 7 is a partial cross-sectional view of the heat exchanger of Fig. 4 in accordance with yet another embodiment of the present invention.

0021Referring to Figs. 3 and 4, heat exchanger 10 comprises an upper tank 11 and a lower tank 12. A heat exchanger core 13 is disposed between upper tank 11 and lower tank 12. Heat exchanger core 13 comprises a plurality of heat transfer tubes 15 spaced apart and substantially parallel to one another. As shown in Fig. 3, upper tank 11 may be divided by an upper partition 11a into four chambers including first upper chamber 18, second upper chamber 19, third upper chamber 20 and fourth upper chamber 21. Chambers 18, 19, 20 and 21 all preferably have the same capacity. Lower tank 12 may be divided by a lower partition 12a into two chambers including first lower chamber 22 and second lower chamber 23.

0022Upper partition 11a preferably has a plurality of holes 11b formed therein to link second upper chamber 19 and third upper chamber 20 so as to permit fluid communication between chamber 19 and chamber 20. First upper chamber 18 and fourth upper chamber 21 are respectively provided with inlet pipe 16 and outlet pipe 17. Inlet pipe 16 and outlet pipe 17 preferably connect heat exchanger 10 to the remainder of a vehicle air conditioning system (not shown).

0023Heat exchanger core 13 comprises a plurality of heat transfer tubes, each of which is connected at a first end to upper tank 11 and at a second end to lower tank 12. A first side plate 30 is connected at a first end to upper tank 11 and at a second end to lower tank 12. Similarly, a second side plate 31 is connected at a first end to upper tank 11 and at a second end to lower tank 12. Support plate 32 is disposed within core 13 between upper tank 11 and lower tank 12 and is preferably connected at a first end to first side plate 30 and at a second end to second side plate 31. Support plate 32 is preferably substantially parallel to both upper and lower tanks 11 and 12. Support plate 32 has a plurality of holes 32a. Heat transfer tubes 15 penetrate holes 32a and are thereby supported so that lateral movement of tubes 15 is inhibited.

0024In operation, a heat exchanger medium (not shown) is introduced through inlet pipe 16 into first upper chamber 18. The medium flows down through one or more tubes 15 and reaches first lower chamber 22 of lower tank 12. From this location, the medium flows back up through tubes 15 to second upper chamber 19. Then, the medium flows to upper chamber 20 through holes 11b of upper partition 11a, down one or more of tubes 15 and into second lower chamber 23. Continuing, the medium flows back up tubes 15 into fourth upper chamber 21. Finally, the medium exits chamber 21 through outlet pipe 17.

0025Holes 32a are each defined by a peripheral surface which contacts a corresponding heat transfer tube 15 at one or more interfaces which define points, lines or curves. Holes 32a are formed to have shapes according to various embodiments of the present invention depicted in Figs. 5-8.

0026According to an embodiment shown in Fig. 5, hole 35 of tube support plate 32 is formed to be generally rhombus shaped. The vertices of rhombus holes 35 are preferably modified to be arc-shaped as depicted in Fig. 5. A first pair of arc-shaped vertices 35a and 35b are formed opposite each other and are defined by the respective pairs of sides which form acute angles. The radii of arc-shaped vertices 35a and 35b are unequal to, and preferably smaller than, the radius of the corresponding heat transfer tube 15. A second pair of arc-shaped vertices 35c and 35d are formed opposite each other and are defined by the respective pairs of sides which form obtuse angles. The radii of arc-shaped portion 35c and 35d are generally equal to, or slightly larger than, the radius of the corresponding heat transfer tube 15. Linear portions 35e, 35f, 35g and 35h join arc-shaped portions 35a, 35b, 35c and 35d.

0027Heat transfer tube 15 penetrates, and is laterally supported by, rhombus hole 35. This support is provided, at least partially, by arcuate contact between the peripheral surface of rhombus hole 35 and heat transfer tube 15. This arcuate contact is generally made at the second pair of arc-shaped portions 35c and 35d. First and second gaps 45a and 45b, which are generally triangle-shaped, are formed adjacent tube 15 on the upstream and downstream sides of tube 15 with respect to an air flow indicated by arrow A. Gap 45a is partially defined by arc-shaped portion 35a and gap 45b is partially defined by arc-shaped portion 35b. Although gaps 45a and 45b are preferably positioned as depicted in Fig. 5, with respect to air flow A, this positioning may be modified.

0028During operation, air flow A may contain moisture in vapor state. Typically, the vapor is cooled to a temperature below the dew point as the air flow passes across heat transfer tubes 15. This temperature reduction can change the vapor into a condensate, which can form on and adhere to the outer surfaces of heat transfer tubes 15. As discussed above in connection with Figs. 3 and 4, holes 32a are formed to have shapes according to various embodiments of the present invention depicted in Figs. 5-8. These shapes are different than the cross-sectional shape of tube 15 in the axial direction (<u>i.e.</u>, circular in Figs. 5-8). This difference in shape causes gaps to be formed between the peripheral surface of a hole and the outer surface of a corresponding heat transfer rube. The flow of condensate through the holes to a bottom portion of the heat exchanger is enhanced at least partially due to these gaps. Condensate is thereby prevented from moving to and collecting on the support plate.

0029In connection with the embodiment shown in Fig. 5, for example, rhombus holes 35 facilitate the flow of condensate through gaps 45a and 45b, thereby avoiding the movement of condensate from heat transfer tubes 15 to support plate 32. The majority of the condensate flows through gap 45b to the bottom of heat exchanger 10 because air flow A tends to force the condensate downstream laterally around the outer surface of heat transfer tube 15. Further, as described above, support plate 32 firmly supports heat transfer tubes 15 with linear or arcuate contact as opposed to the point contact support provide by conventional support plates (<u>e.g.</u>, Fig. 2).

0030The flow of condensate along the outer surface of tubes 15 without moving to support plate 32 is improved over that of conventional structures in part because the cross-sectional area of gaps 45a and 45b can be made larger than that of conventional gaps (<u>e.g.</u>, gap 44 of Fig. 2). At the same time, the tube support provided by the structure described above in connection with Fig. 5 will be at least as great as that provided by conventional tube support structures. Further, the strength of the support structure itself is improved over conventional structures such as that shown in Fig. 2. This is at least partially due to the use of linear or arcuate contact between the support plate and the heat transfer tubes.

0031Also, the enhanced flow provided by the structure shown in Fig. 5 reduces the scattering of condensate to areas outside of heat exchanger 10. As a result, components in the vicinity of heat exchanger 10 (<u>e.g.</u>, engine parts of a motor vehicle) are not subjected to adverse effects, such as corrosion or rust, which can be caused by the condensate. Further, the air resistance of heat exchanger 10 is minimized because air smoothly passes across adjacent heat transfer tubes 15 without the resistance of the condensate. Moreover, the improved support reduces damage to heat transfer tubes 15, thereby promoting more uniform air flow. This further minimizes air resistance of heat exchanger 10. Thus, heat exchanger 10 can maintain a high heat exchange efficiency.

0032Fig. 6 illustrates another embodiment of the present invention in which each hole 36 of support plate 32 is generally teardrop-shaped Tear drop hole 36 is similar to rhombus hole 35 of Fig. 5 except that teardrop hole 36 has only one vertex 36a which is modified to be arc-shaped as shown in Fig. 6. The radius of arc-shaped vertex 36a is unequal to, and preferably smaller than, the radius of the corresponding heat transfer tube 15. Further, hole 36 includes a partially circular portion 36b which has a radius generally equal to, or slightly larger than, the radius of the corresponding heat transfer tube 15. Teardrop hole 36 has two linear portions 36c and 36d, which joins arc-shaped vertex 36a partially-circular portion 36b.

0033Heat transfer tube 15 penetrates, and is laterally supported by, teardrop hole 36. Support is provided, at least in part, by arcuate contact between the peripheral surface of teardrop hole 36 and heat transfer tube 15. This arcuate contact is generally made at partially circular portion 36b. Gap 46, which is generally triangle-shaped, is formed adjacent tube 15 on the downstream side of tube 15 with respect to air flow A. Gap 46 is partially defined by arc-shaped vertex 36a. The positioning of gap 46 with respect to air flow A may be modified.

0034Teardrop holes 36 facilitate the flow of condensate through gap 46, thereby avoiding the movement of condensate from heat transfer tubes 15 to support plate 32. The condensate flows through gap 46 to the bottom of heat exchanger 10 because air flow A tends to force the condensate downstream laterally around the outer surface of heat transfer tube 15. Further, as described above, support plate 32 firmly supports heat transfer tubes 15 with linear or arcuate contact as opposed to the point contact support provide by conventional support plates (<u>e.g.</u>, Fig. 2). The advantages of this embodiment are similar to those described above in connection with the structure depicted in Fig. 5.

0035Fig. 7 illustrates yet another embodiment of the present invention in which boles 37 of support plate 32 are generally triangle-shaped. Triangle holes 37 have three vertices 37a, 37b and 37c which are modified to be arc-shaped. Arc-shaped vertices have radii which are unequal to, and preferably smaller than, the radius of the corresponding heat transfer tube 15. Hole 37 also has three linear portions 37d, 37e and 37f, which are preferably equal in length and which join arc-sbaped vertices 37a, 37b and 37c.

0036Preferably, the diameter of a circle inscribed in triangle bole 37 and which contacts linear portions 37d, 37e and 37f, is identical to or slightly larger than that of the corresponding heat transfer tube 15. Thereby, heat transfer tube 15 contacts the peripheral surface of triangle bole 37 essentially at the midpoints of the three linear portions 37d, 37e and 37f of hole 37. As with the other embodiments, tube 15 is preferably firmly supported by hole 37 in a lateral direction.

0037Gaps 47a, 47b and 47c are formed adjacent tube 15 and are partially defined by arc-shaped vertices 37a, 37b and 37c. Preferably, at least one gap (<u>e.g</u>., gap 47c in Fig. 7) is formed on side of tube 15 which is downstream with respect to air flow A. However, the positioning of gaps 47a, 47b and 47c may be different from that shown in Fig. 7. In operation of heat exchanger 10, these gaps function similar to the gaps described in the previous embodiments and the details, therefore, are omitted.

0038Although similar advantages are achieved, the structure of this embodiment provides point contact support against the lateral movement of heat transfer tubes 15. However, this embodiment is different than conventional structures in that it avoids the use of projection portions which extend inward from the peripheral surface of the hole. Thus, firm point contact-type support is provided together with relatively large gaps without the danger of weakening the projection portions of conventional structures by elongating them to increase the size of the gaps.

0039An important aspect of the present invention is. an assembly for use in a heat exchanger and comprising a perforated support plate and at least one tube passing through a respective hole in the plate, the edge of the hole contacting the tube at a plurality of regions around the tube to locate the tube against lateral movement relatively to the plate, and that part of the edge of the hole interconnecting at least one pair of adjacent contact regions consisting of two substantially straight portions which converge towards one another and extend from the contact regions at which they are substantially tangential to the tube to an apex remote from the tube to form a lobe-like drainage aperture adjacent to the tube.