Heat exchanger

An automotive condenser (10) includes spaced manifold assemblies (18) comprised of semicylindrical tanks (20), matching semicylindrical headers (22) and simple, circular disks (38) serving as manifold separators. The disks (38) are sandwiched between the tank (20) and header (22) with no need for orientation, and with no slots or through notches to pierce the surface of the tank (20) or header (22). The disks (38) sit within matching pairs of common diameter grooves (30, 36) which provide complete, continuous pockets therefore.

This invention relates to heat exchangers in general and specifically to an 
improved design for the header and tank assembly of a heat exchanger. 
BACKGROUND OF THE INVENTION 
Automotive air conditioning systems use a heat exchanger called a condenser 
that cools the compressed system refrigerant, and which experiences high 
pressures. To resist such pressures, it has been known for decades to use 
cylindrical tubes as the main structural component for the condenser, both 
for the flow tubes that carry the cooling refrigerant and for the 
manifolds that inlet flow to and outlet it from the flow tubes. This 
venerable design has come to be called a tube and fin condenser, and was a 
preferred design for a long time, both because of its structural 
simplicity and ability to easily withstand internal pressures of ten 
atmospheres or more. An improvement to this basic design, shown in 
co-assigned European Patent 0138435, involved the use of axially inserted 
plugs, sometimes referred to as separators or baffles, within the 
cylindrical manifolds to segregate the flow tubes into multiple passes. 
This improves thermal efficiency while leaving the manifolds uninterrupted 
at any point along their length, apart from the flow tube slots. Only the 
ends of the tanks, and the flow tube to tank interfaces, needed to be 
sealed. Such a design would be difficult to scale up to larger diameters, 
however, as it would be difficult to axially insert a larger diameter plug 
deep into a long cylinder without cocking or deformation. 
While representing the simplest design, cylindrical tubes were not the most 
thermally efficient flow tube design, nor were cylindrical tanks the most 
spatially efficient manifold shape, despite their obvious high internal 
pressure resistance. Flat flow tubes were known to be more thermally 
efficient, since they present more surface area to be cooled for a given 
internal volume and, with suitable internal webbing, could be made 
sufficiently resistant to internal pressures. Flat tubes cannot be 
practically bent around into the hair pin shape often found in tube and 
fin condensers, however, so the manifold tanks are simply placed at 
opposite sides of the heat exchanger, as in a typical radiator. Likewise, 
manifold tanks with a rectangular cross section were known to be more 
space efficient, for the same reason that rectangular boxes stack more 
efficiently on a shelf than do cylindrical cans of a comparable size. 
Furthermore, by making such a rectangular cross section tank from a three 
sided extruded unit enclosed by a stamped and slotted tube header, and by 
providing sufficient material thickness and adequate brazing seams, enough 
internal pressure resistance could be provided. A two piece, brazed 
manifold assembly also provides the capability of stamping shallow 
separator grooves into the inner surfaces of the two pieces and accurately 
and easily inserting flow pass separators as the two pieces are assembled 
together. An example of such a condenser incorporating all of these 
features may be seen in co-assigned U.S. Pat. No. 5,062,476. 
Despite the availability of rectangular tank designs with easy to install 
separators, designers have continued to work on designs that incorporate 
cylindrical (or nearly cylindrical) manifolds, while retaining the flat 
flow tubes, because of the inherently better pressure resistance (for a 
given material thickness and weight) that a cylindrical pressure vessel 
gives. Two design directions have been followed, one piece cylindrical 
tubes with plugged ends and two piece cylindrical manifold assemblies. One 
piece cylindrical manifolds simply scale up the diameter of a tube and fin 
condenser manifold, but face the difficulty of how to install the 
necessarily larger flow pass separators, as noted above. Since the larger 
flow pass separators cannot be simply axially rammed into place, they are 
typically inserted radially into the back of the tank through slots. An 
example may be seen in U.S. Pat. No. 4,825,941. This presents the real 
disadvantage of creating another potential leak path through the surface 
of the tank. Another problem is that the separator cannot be a simple 
circle, but must have a step in its outer edge in order be able to both 
seal against the inner surface of the tank and fill the slot in the back 
of the tank. Not being a simple circle, the separator has to be properly 
oriented during installation. A later design with a one piece cylindrical 
tank, U.S. Pat. No. 5,348,083, notes this deficiency, and does provide a 
separator that is a simple circle. However, the slot in the back of the 
tank must be more complex, including a pair of side barbs that are 
initially straight, and which are then bent in and around the circular 
separator after it is inserted. This adds an additional assembly step, and 
still represents a potential leak path. 
Two piece cylindrical manifold assemblies, of which there are numerous 
examples, are basically the cylindrical structural equivalent of the two 
piece rectangular tank design noted above, with all the same inherent 
assembly advantages, but with the potential for greater pressure 
resistance for a given material thickness. Known two piece cylindrical 
tank designs have not, however, provided a simple separator or baffle 
design. U.S. Pat. No. 5,125,454 shows a separator that is not only very 
complex in shape, with numerous steps and notches, but which also, despite 
the two piece design, is inserted from the back through a separate slot, 
combining the worst features of one and two piece designs. U.S. Pat. No. 
5,127,466 shows a two piece design in which one half cylinder slide fits 
down lengthwise into heavy, continuous internal flanges within the other 
half cylinder. While the design does not disclose separators per se, they 
would have to be of a notched or stepped design, as well, because of the 
internal discontinuity created by the extruded internal flanges. U.S. Pat. 
No. 5,036,914 shows a two piece manifold design with at least some 
embodiments that are free of internal discontinuities, though these 
embodiments do not have a circular cross section. Again, separators are 
not disclosed per se. The design intent for the separators can instead be 
seen in published European application EP-450-619-A, which has the same 
assignee, in FIGS. 8 and 9. The separators also have locating notches that 
pierce both the header and the tank. There appears to be a near consensus 
in the art, therefore, that separators in two piece cylindrical manifolds 
should have locating notches that pierce the wall of one or both pieces of 
the manifold. An exception is U.S. Pat. No. 5,341,872, which avoids 
separator locating notches by instead incorporating an additional 
component in the form of an internal locating rail that holds the 
separators. Besides the additional expense and bother of a separate 
component, the separators disclosed are still not simple circular disks, 
but also have notches that interfit with the locating rail, and which 
would require careful orientation at installation. 
SUMMARY OF THE INVENTION 
A heat exchanger in accordance with the present invention is characterized 
by the features specified in Claim 1. Specifically, the invention provides 
what the various known designs described above fail to provide, a two 
piece, manifold assembly of circular internal cross section in which 
simple, circular separators may be installed in any orientation and 
location, and without piercing or jeopardizing the seal of either the 
header or tank. 
In the embodiment disclosed, an automotive air conditioning system 
condenser includes two spaced manifold assemblies, each comprised of a 
semi cylindrical tank and semi cylindrical header that mate along their 
longitudinal edges. The mating inner surfaces of each tank and header pair 
lie on substantially a common circle, and each mating inner surface has at 
least one pair of matching grooves formed therein which lie exactly on a 
common circle. The matching pairs of grooves allow a separator in the form 
of a simple circular disk to be installed therein, sandwiched between the 
tank and header, before the two are joined and brazed together. The 
uniform, simple separators can be installed in any location and 
orientation, with no slots or notches to create potential leak paths. 
Preferably, all components may be made of suitable, brazable aluminum 
alloy, and produced as simple extrusions and stampings.

Referring first to FIGS. 1, 2 and 5, a preferred embodiment of a heat 
exchanger made according to the invention, being a condenser indicated 
generally at 10, includes a central core comprised of a plurality of flat 
flow tubes 12 brazed to the peaks of intermediate corrugated cooling fins 
14. Side rails 16 protect the top and bottom tubes 12, and have their ends 
fixed to corresponding ends of a spaced pair of manifold assemblies, 
indicated generally at 18. This creates a basic four sided structural 
frame surrounding the flow tubes 12. Each manifold assembly 18 is 
basically an elongated cylinder, comprised of two half cylinders, a tank, 
indicated generally at 20, and header indicated generally at 22. 
Preferably, each tank 20 is an extruded aluminum part, with an inner 
surface 24 that lies on a cylindrical surface, departing therefrom only at 
a pair of radially inwardly projecting shelves 26 at the outer edges 
thereof. Shelves 26 serve a purpose described below. The outer surface of 
tank 20 may depart from a cylindrical surface wherever desired, most 
notably where a pair of initially flat longitudinal flanges 28 are offset 
outwardly from the tank inner surface 24 by a distance indicated at X. The 
shelves 26 and flanges 28 form a comer that is slightly obtuse, because of 
the fact that the tank inner surface 24 subtends a total angle that is 
slightly more than a half circle. At several axially spaced locations, a 
semi circular groove 30 is formed into tank inner surface 24, but only 
partially thereinto, and also locally through the shelves 26. At least two 
such grooves 30 would be formed, near the ends of tank 20, and as many 
other intermediate grooves 30 as needed to form the number of flow passes 
desired. Each header 22 is a simple semi cylindrical stamping, with a 
thickness T roughly equal to X and an inner surface 32 that substantially 
matches the diameter of tank inner surface 24. Edge to edge, header 22 
subtends the remainder of a complete circle not covered by tank 20, being 
just under a half circle here. Preferably, header 22 is stamped from 
aluminum clad on both sides with a suitable braze layer. Header 22 is 
slotted regularly at 34, to receive the ends of the flow tubes 12. The 
header inner surface 32 is also formed with the same number of semi 
cylindrical grooves 36 as is tank 20, and at the same axial locations, and 
of equal diameter. The remaining components comprise a number of simple, 
circular disks 38, stamped from the same material as header 22, which 
serve as separators or baffles. Each identical disk 38 has a diameter and 
axial thickness nearly equal to that of the grooves 30 and 36. 
Referring next to FIGS. 2 through 4, the installation of the disks 38 
within of manifold assembly 18 is illustrated. Since the grooves 30 and 36 
have exactly the same diameter, axial thickness, and axial location, they 
align in matching pairs, lying on a common circle, when the header 22 and 
tank 20 are aligned. A disk 38 is simply set into the grooves 30 or 36 of 
either tank 20 or header 22, without deliberate orientation. Then, the 
aligned header 22 and tank 20 may be simply pushed straight toward one 
another until the longitudinal edges of header 22 abut the tank shelves 
26, inboard of the flanges 28. The disks 38 are automatically captured and 
held within the aligned groove pairs 30, 36. Regardless of whether the 
respective inner surfaces 24 and 32 lie on exactly the same circle, the 
fact that the matching groove pairs 30 and 36 do lie on the same circle, 
and extend partially into and all the way across both of the respective 
inner surfaces 24 and 32, provides a complete and continuous pocket for a 
disk 38. Then, the flanges 28 are bent in and partially around the outer 
surface of header 22, crimping the two together. Since the flanges 28 do 
not have to be bent severely, a simple roller mechanism would suffice. The 
separator disks 38 are completely captured within the matching pairs of 
grooves 30 and 36. It will be appreciated that each disk 38 may be 
installed into any pair of grooves 30 and 36, and in any orientation, 
simplifying the assembly task greatly. Once the subassembly of header 22 
and tank 20 is complete, the tubes 12, fins 14 and side rails 16 are held 
in a suitable stacker and the ends of tubes 12 are inserted into the 
header slots 34. Finally, the entire unit is run though a conventional 
braze oven. Braze material from the fins 14, header 22 and disks 38 melts 
and runs into all intra part interfaces, eventually solidifying to form 
leak proof seams. Specifically, the edges of the disks 38 sit within the 
matching pairs of grooves 30 and 36 with a slight clearance, which draws 
in melted braze material by capillary action, providing a complete seam 
all the way round. 
In the completed condenser 10, shown in FIG. 5, the end most disks 38 seal 
the ends of the completed pair of spaced manifold assemblies 18, creating 
a complete, strong cylindrical pressure vessel. The integrity of the seams 
around the end most disks 38 may be easily visually checked. The 
intermediate disks 38 provide separate flow passes segregating specific 
groupings of flow tubes 12. While the seams around the intermediate disks 
38 cannot be visually checked, as with the end disks 38, a small crevice 
in their seams would not adversely affect operation of the condenser 10 
significantly. And, since no part of the disks 38 protrudes through the 
outer surfaces of either the header 22 or tank 20, any discontinuities in 
their braze seams would not jeopardize the overall seal of the pressure 
vessel. In conclusion, a manifold assembly 18 of high pressure resistance 
optimized simplicity of manufacture and assembly is provided, with a 
minimal amount of potential leak path from the assembly.