1. Field of the Invention
The present invention relates generally to heat exchangers, such as condensers for automotive vehicles. More particularly, the present invention relates to a condenser and a method for making the condenser wherein the internal diameter of the condenser tubing is deformed to a predetermined limit during the manufacture of the condenser.
2. Disclosure Information
Fin and tube type heat exchangers are commonly used in vehicle, industrial and residential environments for heating and cooling purposes. Typically, these heat exchangers utilize a plurality of hairpin-shaped tubes to form a condenser or the like wherein the fluid passes through the plurality of tubes. The number of tubes depends upon the thermal capacity requirements of the fin and tube heat exchanger. Interleaved between the plurality of tubes are a plurality of stacked fin members which aid in dissipating the heat from the condenser as is well known in the art. A manifold interconnects the tubes so that fluid can flow therethrough.
To ensure good heat transfer between the tubes and the fins, there must be significant contact between the outer diameter of the tubes and the fins. In order to accomplish this, it is well known in the art to insert a bullet-like tool or expander plug into the heat transfer tube and displace the tool axially with respect to the tube to effect radial expansion of the tube into gripping engagement with the surrounding fins. It is also well known that one method to increase the thermal transfer coefficient of the tubing is to increase its internal surface area by providing surface irregularities therein. Typically, these irregularities are in the forms of grooves which, as shown in U.S. Pat. No. 3,517,536, are formed by inserting a bullet-like tool having cutting edges thereon which form grooves along the inner diameter of tube. Typically, the tool is rotated along the axial length of the tubing to form spiral grooves therein. However, because of tool wear during repeated expanding operations, the uniformity of the spiral grooves often changes and the efficiency of the heat exchanger decreases. It would, therefore, be advantageous to provide a method for making a heat exchanger wherein the internal surface irregularities of the tubing remains more uniform during the manufacturing process.
In most known manufacturing operations, the internal surface of the tubing is smooth prior to the insertion of the expander plug and the forming of the helical grooves therein. Prior to the present invention, it has not been known to expand the tubing wherein the surface irregularities are formed integral with the tube prior to the expansion process, and where the height of the surface irregularities are maintained to a specific height after expansion of the tubing to retain heat transfer characteristics.
The present invention overcomes the disadvantages associated with the prior art by providing a method of making an automotive heat exchanger comprising the steps of:
assembling a plurality of spaced, stacked fin members on a first endsheet member, each of the fin members having a plurality of apertures extending longitudinally therethrough;
providing a plurality of tubes, each of the tubes having an integrally-formed, corrugated internal surface comprising a plurality of alternating projections and recesses;
lacing each of the tubes through the apertures in respective stacked fin members;
placing a second endsheet member over the opposite end of the tube and fin assembly to thereby form a heat exchanger core. The method further comprises steps of fixing the heat exchanger core in a station so that the open ends of the tubes are proximate an expander tool having a predetermined diameter;
expanding the diameter of the tubes a predetermined distance by forcing the tool therethrough so that the height of the projections within the tubes remains within 75% of its original height;
removing the expander tool from the tubes and connecting the open ends of the tubes to a fluid conduit, such as a manifold assembly via brazing or soldering the heat exchanger core.
The present invention also includes a heat exchanger, such as an automotive condenser for liquefying gaseous coolant manufactured according to the above method.
It is an advantage of the present invention to improve the thermal transfer coefficient and characteristics of the heat exchanger by providing an extruded tube having a corrugated cross-section comprising a plurality of projections and recesses which are deformed a predetermined amount during the expansion of the tube process. These and other objects, features and advantages of the present invention will become apparent from the drawings, detailed description and claims which follow.