1. Field of the Invention
The present invention generally relates to heat exchangers, such as those of the type used in air-conditioning systems. More particularly, this invention relates to a heat exchanger tube configuration that incorporates integral fins for transferring heat to and from the tube.
2. Description of the Related Art
Heat exchangers are employed within the automotive industry as condensers and evaporators for use in air conditioning systems, radiators for cooling engine coolant, heater cores for internal climate control, etc. One type of heat exchanger construction used in the automotive industry for condensers and evaporators comprises a number of parallel tubes that are joined to and between a pair of manifolds, creating a parallel flow arrangement. The ends of the tubes are typically metallurgically joined (brazed, soldered or welded) to tube ports, generally in the form of holes or slots formed in a wall of each manifold. In order to maximize the amount of surface area available for transferring heat between the environment and a fluid flowing through the heat exchanger, automotive heat exchangers often have a tube-and-fin construction in which numerous tubes thermally communicate with high surface area fins. The fins are typically in the form of flat panels having apertures through which tubes with circular cross-sections are inserted, or in the form of sinusoidal centers that are positioned between adjacent pairs of “flat” tubes with oblong cross-sections. In either case, the resulting tube-and-fin assembly is oriented so that the edges of the fins face the fluid (e.g., air) flowing between the tubes, i.e., the fins are normal to the plane defined by the tubes of the heat exchanger.
Alternative forms of fins have been suggested, examples of which include U.S. Pat. No. 4,546,819 to O'Connor, U.S. Pat. No. 4,951,742 to Keyes, and U.S. Pat. No. 5,353,868 to Abbott. Each of these patents discloses a cooling tube whose outer surface undergoes a second forming operation to have integral fins. Abbott discloses fin strips formed by lancing a conduit, while O'Connor and Keyes disclose integral fins formed by rolling the exterior of a tube. An approach to forming integral fins on round plastic tubing is taught in U.S. Pat. No. 4,926,933 to Gray, in which integral helical fins are defined on the exterior of a round plastic tube during injection molding or extrusion of the tube.
The present invention provides a method for forming tubing with integral fins, and to a heat exchanger tube produced by such a method. The method generally involves extruding the tube through a die so that the tube has at least one internal passage extending in a longitudinal direction parallel to the longitudinal direction in which the tube was extruded, an external surface having a cross-sectional shape in a plane transverse to the extrusion direction, and at least one integral fin parallel to the extrusion direction and extending in a direction away from the external surface of the tube. As such, the one or more fins are parallel to the longitudinal axis of the tube. The tube can be one of a plurality of identical tubes assembled in parallel to a pair of manifolds, and such tubes are preferably oriented so that their integral fins are substantially parallel, with the fin(s) of a given tube extending toward an adjacent one of the tubes. In this arrangement, the fins are oriented substantially parallel to the plane in which the tubes lie, contrary to conventional practice.
Significant advantages of the integral tube-and-fin construction of this invention include the elimination of separate fin stock and the costly manufacturing equipment associated with producing and brazing fins for heat exchanger tubing. Another feature of the invention is the potential for reducing the size of a heat exchanger for a given application as a result of the ability to more densely pack the tubes. Heat exchangers incorporating the integral tube-and-fin construction of this invention can find use in a variety of applications, including automotive and beverage cooling applications. For example, the integral tube-and-fin construction of this invention is suitable for use in conventional automotive cooling and air-conditioning units, as well as condensers and evaporators for CO2-based air-conditioning systems. For beverage cooling applications, the integral tube-and-fin construction has the potential to exhibit improved water shedding characteristics and greater resistance to clogging by dirt, dust and other debris commonly encountered by beverage coolers.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
As disclosed and defined herein, the fins 22 are “integral fins” with the tube portion 12 in that they are features formed of material continuous with the material that forms the tube portion 12, and not formed of material subsequently attached or otherwise added to the tube portion 12. In a preferred embodiment, the fins 22 are formed simultaneously with the tube portion 12, i.e., during the extrusion process, though integral fins 22 could also be defined following the operation by which the tube portion 12 is formed by deforming the surface of the tube portion 12 to create the fins 22.
The tube 10 (and therefore the tubes 20) is preferably formed from a suitable aluminum alloy, though other alloys could be used. The tubes 20 are attached, such as by brazing or soldering, to a pair of manifolds so that the tubes 20 are fluidically connected to the manifolds to allow fluid flow to and from the manifolds. The manifolds can be of any suitable configuration for the intended application.
While the invention has been described in terms of particular embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the processing steps could be modified, and materials and tube and manifold configurations other than those noted above could be adopted in order to yield a heat exchanger suitable for a wide variety of applications. Accordingly, the scope of the invention is to be limited only by the following claims.
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