Patent Application
20080185134
Not Applicable.
Not Applicable.
Not Applicable.
This invention relates to heat exchangers and more particularly to header/manifold constructions for heat exchangers having a core formed from flattened tubes, and in more particular applications such heat exchangers that are used in high pressure systems, such as CO2 refrigeration or air conditioning systems.
There are many ways to design a heat exchanger such as a gas cooler or condenser for air conditioning systems for automotive or vehicular applications. The counter flow configuration or CF design relies on flowing refrigerant through multiple rows of tubes in a counterflow direction to the air flow passing through the core of the heat exchanger. Accordingly, the CF design requires tubes to be bent in a special manor or to use multiple header/manifolds to redirect the refrigerant flow through the multiple rows of tubes. These multiple header/manifolds and/or tube bends can add cost to the heat exchanger. Another alternative is the parallel flow configuration or PF design which typically has one row or slab of flattened microchannel extruded tubes extending between two header/manifolds. To enhance heat transfer, the refrigerant may be directed through multiple passes by using baffles in the header/manifolds.
While PF designs such as described above are often used for condensers in conventional R134a refrigerant systems, it is challenging to design a header/manifold to accommodate wide microchannel extruded tubes while withstanding the high operating pressures required for CO2 or other transcritical refrigerant systems.
In accordance with one feature of the invention, a header/manifold construction is provided and is adapted to receive a plurality of flattened tube ends in a heat exchanger having a plurality of flattened tubes. The header/manifold construction includes first and second pieces extending along a longitudinal axis.
As one feature, the first piece has a transverse cross section defined by a tube receiving wall, a side wall spaced opposite from the tube receiving wall, and two nose walls that are spaced opposite from each other to connect the tube receiving wall and the side wall. The tube receiving wall has a plurality of tube slots spaced along the longitudinal axis to receive the tube ends, and the side wall is divided by an elongate opening extending along the longitudinal axis. The second piece has a transverse cross section defined by a center leg and a two side legs extending from opposite sides of the center leg. The center leg extends through the opening in the side wall and has an end surface bonded to an interior surface of the tube receiving wall, with the end surface being interrupted by a plurality of tube end clearance notches, each of the notches aligned with a corresponding one of the tube slots in the tube receiving wall. The two side legs are bonded to an exterior surface of the side wall on opposite sides of the opening.
In one feature, the first piece has a C-shaped transverse cross defined by an elongate opening extending along the longitudinal axis. The first piece has a plurality of tube slots spaced along the longitudinal axis opposite from the opening. The second piece has a T-shaped transverse cross section with two side legs extending from opposite sides of a center leg. The center leg extends through the elongate opening and has an end surface bonded to an interior surface of the first piece, with the end surface interrupted by a plurality of tube end clearance notches and each of the notches aligned with a corresponding one of the tube slots in the tube receiving wall. The two side legs are bonded to an exterior surface of the first piece on opposite sides of the opening.
According to one feature, the second piece has a mount flange extending away from the exterior surface of the side wall. As one further feature, the mount flange has an elongate slot extending along the longitudinal axis. As another further feature, the mount flange has a transverse opening extending therethrough.
In accordance with one feature, each of the tube end clearance notches is sized to provide a fluid flow gap between the center leg and a tube end received the corresponding one of the tube slots.
As one feature, the end surface of the center leg is further interrupted by a plurality of tabs, with each of the tabs extending through a tab receiving opening in the tube receiving wall and being deformed to engage the second piece with the first piece.
In one feature, the second piece is an extrusion.
According to one feature, at least one of the first and second pieces is braze clad.
In accordance with one feature, the first piece is braze clad.
In one feature, the first piece is a formed piece of braze clad sheet metal.
As one feature, the center leg is bonded to opposite side edges of the opening in the side wall.
According to one feature, the side legs are normal to the center leg.
In accordance with one feature, there is a port formed in the second piece, and the header/manifold construction further includes a fluid connection bonded in the port.
With reference to
The header/manifold 14 is a multi-piece construction formed from two elongate pieces 20 and 22 that extend along a longitudinal axis 24, with an pair of end baffles 26 (only one shown in
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Preferably, the piece 20 is formed from a metal sheet, and in a highly preferred form from a piece of braze clad sheet metal, such as braze clad aluminum. In this regard, it is preferred that the tube slots 40 be pierced or punched while the sheet is flat. However, in some applications it may be desirable to pierce or punch the tube slots 40 after the sheet has been formed into the C-shape. While a sheet is preferred, it should be understood that it is possible to form the piece 20 in other ways, such as by extrusion or by molding.
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The center leg 46 may also include a baffle slot 66 for receiving the end baffle 26 and holding the baffle 26 in its desired location during the brazing operation.
Preferably, the piece 22 is an extrusion, with the notches 58 and tabs 62 (if provided) being formed by a suitable technique, such as machining or die cutting, after the T-shaped cross section is extruded. However, it should be understood that in some applications it may be desirable to form the piece 22 using another suitable technique, such as by machining from a piece of bar stock or by molding.
Preferably, the piece 20 is clad with a suitable braze material, and the pieces 20, 22, and 26 of the header/manifold 14 and the tube ends 42 are brazed together in a single oven braze operation at the same time as the other components of the heat exchanger 10 are brazed together. In this regard, it is preferred that the clearance between mating parts, such as, for example, the tube slots 40 and the tube ends 42, and the tabs 62 and the openings 64, be designed such that a suitable sealed braze joint is formed between the mating parts. Further in this regard, it is preferred that the clearance between the opening 44 and the center leg 46 be such that a braze joint be formed between the center leg 46 and opposite side edges 70 of the opening 44. However, in some applications this may not be desired and/or required. While braze cladding is preferred on the piece 20, it should be understood that in some applications the braze material may be applied to the components of the header/manifold 14 in other suitable forms, such as by cladding some of the other components or by applying the braze material to the components after assembly.
It should be appreciated that the mating shapes of the two pieces can allow for a cost effective construction of the header/manifold 14, with the bonding of the legs 46 and 48 to the surfaces 56 and 52, respectively, allowing for the structure of the piece 22 to support the structure of the piece 34, and particularly the walls 30 and 32, so that the header/manifold can withstand the high pressure associated with CO2 and other transcritical refrigeration systems.
