Heat exchange – Side-by-side tubular structures or tube sections – With manifold type header or header plate
Reexamination Certificate
2002-03-29
2004-01-13
Zimmerman, John J. (Department: 1775)
Heat exchange
Side-by-side tubular structures or tube sections
With manifold type header or header plate
C029S890052
Reexamination Certificate
active
06675882
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a one-piece flat-sided extrusion for use in multiple applications, such as heat exchanger headers or other high pressure vessels, and methods of making the same.
BACKGROUND OF THE INVENTION
Extruded products are used in a variety of applications. A primary use of extruded products is to provide structural strength or stiffness to various structural shapes, such as beams, angles, channels, and tubing. In manufacturing steel extruded products or extruded products made out of heavy material, the material is heated and pressure is applied to force the material through a diehead. As the flow of material is forced through the diehead, the material tends to conform to the shape of the cutout or opening in the die, producing an extruded product with a cross-section that matches the shape of the opening in the die. As the extrudate exits the diehead, it is cooled (usually with water) to harden the extrudate into the shaped article intended from the process.
When an extruded product is being produced for use in a high pressure environment, strong materials, such as steel or a form of steel having additives intended to strengthen or provide other enhanced structural or physical properties, need to be used. For example, cogeneration facilities employing heat exchangers commonly have cylindrical header pipes made of steel. They are manufactured with round, heavy-walled steel tubing and must comply with American Society for Testing and Materials (ASTM) standards for high pressure vessels.
Heat exchangers in general are used in a variety of applications to heat or cool gases or liquids. Heat exchangers typically include two parallel header units with a plurality of tubes connected between the two headers. Such flow designs are referred to as parallel-flow, because the tubes are parallel to each other, but the process is in actuality more of a “cross-flow” pattern. Liquids or gases flow through the tubes (side-to-side or up and down), from one header to the other, and forced outside air runs perpendicular to the tubes, i.e., crossed with the liquid or gaseous flow. The headers act to collect the cooling or heating medium being used in the application and direct the medium through the tubes.
A variety of different header shapes have been used for different applications. For applications involving high pressure within a heat exchanger, such as in cogeneration facilities, the headers are typically extruded into a cylindrical shape. Cogeneration heat exchanger headers have also been formed having a rectangular shape, but these headers have joints where individual portions of the header are attached or welded together. Rectangular headers have also been criticized as not being as good pressure vessels as are cylinders.
FIG. 1
shows one cylindrical header pipe
10
of the type currently in use. Header
10
has tube receiving apertures
12
drilled at various angles to surface
14
. Tubes
16
are inserted into apertures
12
.
Cylindrical header pipes
10
with this structure present some problems due to their shape. The fabrication process is costly and difficult due to the odd angles at which apertures
12
need to be machined in the continuous curving surface
14
of the header
10
to allow for the incorporation of tubes
16
into the header
10
. The apertures
12
are drilled on a contoured surface
14
, commonly called hillside boring. In manufacturing apertures
12
, deformation may occur around the edges of the apertures
12
. Furthermore, structural integrity is jeopardized by the removal of material in a concentrated area
17
, resulting in deformation caused by lack of structural support. The contact thickness of the area
17
where the header
10
and the tubes
16
are to be connected becomes less than the thickness of the remainder of the header
10
since the aperture
12
is formed on a curved surface
14
rather than a flat plane. As a result, the aperture
12
is angled. Accordingly, the coupling of the end of the tube
16
to the tube receiving aperture
12
of the header
10
becomes unstable.
For example, the welding process to attach tubes
16
is extremely difficult because of the contoured areas encountered with a curved connection surface
14
. Thus, the junction between the header
10
and the tube
16
is rendered incomplete, causing leakage of the heat exchange medium.
Additionally, an unnecessary space
18
is formed around the tube
16
when it is inserted into the area
17
inside of the header
10
so that the flow efficiency of the heat exchange medium is lowered, and the necessary amount of charge of the heat exchange medium is increased. It is also difficult to adjust the depth to which the tube
16
is inserted into the header
10
during manufacturing.
Moreover, when tube receiving apertures
12
are manufactured in cylindrical headers
10
, a second stage of machining is required to machine chamfers
13
around each aperture
12
drilled for the tubes
16
to accommodate the welding process. This second stage of machining is time consuming and adds additional cost to the production of the header
10
.
An additional header is discussed in U.S. Pat. No. 5,246,066, which discloses an extruded tank that has four solid longitudinal side walls. Three of the walls are generally flat-sided and a fourth side, into which flat sided extruded tubes are inserted, is formed as an arc or a curvature bowing outwardly from the fluid-containing space. This curved shape also presents the above-discussed problems.
A one-piece header with a flat side is disclosed in U.S. Pat. No. 5,842,515. However, this header is not extruded to form one continuous piece, but is formed by bending a malleable aluminum sheet with both sides of the sheet coming into contact with each other to form a hollow passage inside the header, and then brazing the sides of the sheet together to seal the opening. This type of header would not be appropriate for use in a high pressure environment, as the thickness of steel required when using high pressures would not allow the manufacture of the header through bending.
An extruded aluminum header pipe with a flat side is disclosed in U.S. Pat. No. 5,622,220. Similar to other aluminum headers, this header would not be suitable for use in a high pressure environment. The header pipe has a D-shaped cross-section with a flat side and is manufactured by extrusion. This header, however, is manufactured for use in an automobile air conditioning system and accordingly, is made out of aluminum. Additionally, this header has a flat section with a rounded section extending from opposed sides of the flat section. A header for use in a cogeneration facility or other high pressure vessel needs side walls that are substantially perpendicular to the flat section and that provide more structural support and integrity than the minimal support provided by the rounded section defining the D-shaped header in U.S. Pat. No. 5,622,220.
Furthermore, there are distinct differences in the manufacturing requirements, and thus the components used, in an air-conditioning heat exchanger unit as opposed to a cogeneration facility heat exchanger unit. For example, the size of a cogeneration facility heat exchanger unit is several hundred times larger than an automobile (or other similar-type use) heat exchanger unit. Because of this, the construction materials used in a cogeneration facility heat exchanger are entirely different. The extreme pressures and temperatures reached during normal operation of a cogeneration facility would render the processes and materials used to manufacture an automobile (or other similar-type use) heat exchanger unit inadequate for use in cogeneration facilities. For example, the stresses accruing during operation of a cogeneration facility are greatly increased. Accordingly, the construction materials for a heat exchanger unit for use with a cogeneration facility must be able to withstand extreme pressures, for example, those up to 3600 psig. The thickness of the material used in a cogeneration fac
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