This invention relates to a heat exchanger exhibiting resistance to galvanic corrosion and more specifically, to protecting copper-aluminum heat exchangers for use in air conditioners.
Galvanic corrosion occurs when two dissimilar metals make contact with one another in the presence of an electrolyte thereby forming a galvanic couple. The more noble metal (higher on the galvanic series) provides the surface area for die reduction reaction and the less noble metal (lower on the galvanic series) corrodes in an oxidation process. The oxidation occurs in the greatest amount at the interface of the two metals but may also occur at some distance away from the actual interface. In coastal regions, the most common electrolyte is salt water in the air. A fine salt water mist may be blown inland for up to fifty miles from the coast Sulfur dioxide from industrial pollution also creates an electrolyte when it combines with moisture in the air.
A common method of preventing galvanic corrosion has been to coat the exposed surfaces of the metals with various types of paint. These protective coatings have met with only limited success for a number of reasons. The main problem with coating is that their effectiveness at preventing corrosion is degraded by exposure to the environment such as ultraviolet light and acid rain. Another common problem is that the coating materials often do not adhere well to the metal substrates and eventually flake off or erode away exposing the metal substrates. Moreover, such protective coatings are somewhat porous and allow the electrolyte to penetrate the surface of the substrates and connect the galvanic couple. In addition, the application of protective coatings to the surfaces of certain articles can negatively affect their performance.
Attempts have been made, with varying degrees of success, to coat conventional copper-aluminum heat exchanges with various materials in an effort to extend the useful life of the unit. These coating materials often times reduce the heat transfer capability of the unit, exhibit poor adhesion properties and fail to penetrate into all the areas that might be exposed to a hostile environment.
In general the present invention provides an advanced galvanic corrosion protection method. In accordance with the present invention, in an article made of two metals, one being more noble man the other, the outer surface of the more noble metal is treated with a metal which is galvanically compatible with the less noble metal to form a protective layer between the two dissimilar metals which prevents the reduction reaction of the galvanic couple from occurring. The invention gready reduces the oxidation reduction process which occurs when two dissimilar metals are in contact with one another in the presence of an electrolyte.
The present invention therefore, provides a heat exchanger exhibiting resistance to galvanic corrosion comprising:
a fin collar formed from a first metal; and
a tube connected with said fin collar at a contact area said tube formed from copper, said copper more noble than said first metal, such that direct contact between said first metal and said copper in the presence of an electrolyte would lead to galvanic corrosion characterized in that said surface is treated with a contact material prior to the connection of said tube with said fin collar, said contact material being located at least in the location of said contact area and comprises a third metal galvanically compatible with said first metal,
said contact material contacts said fin collar and prevents contact between said surface of said tube and said fin collar for preventing galvanic corrosion of said fin collar relative to said tube.
FIG. 1 is a perspective view of a heat exchanger incorporating heat exchanger tubes treated in accordance with the present invention.
As will be described in detail below the present invention will be described in to providing for galvanic corrosion protection of a copper-aluminum heat exchanger. However, it should be evident to one skilled in the art that the present invention is not limited to this specific example and could be used in connection with a number of arrangements where dissimilar metals are in contact with one another in the presence of an electrolyte.
FIG. 1 illustrates a fin/tube heat exchanger 10 of the type typically used in air conditioning units. The heat exchanger includes one or more flow circuits for carrying refrigerant through the heat exchanger unit For the purposes of explanation, the heat exchanger 10 contains a single flow circuit tube 2 consisting of an inlet line 3 and an outlet line 4 which are connected at one end of the heat exchanger 10 by means of a 90° tube bend 5. It should be evident, however, that more circuits may be added to the unit depending upon the demands of the system. The unit further includes a series of fins 6 comprising radial disposed plate like elements spaced along the length of the flow circuit. The fins 6 are supported in the assembly between a pair of end
negative effect on the heat transfer of the unit, excessively thick protective layer should be avoided. The optimal range of thickness contemplated by the present invention is .1 mils to 2 mils.

We claim:
1. A heat exchanger exhibiting resistance to galvanic corrosion comprising:
a fin collar formed from a first metal; and
a tube connected with said fin collar at a contact area said tube formed from copper, said copper more noble than said first metal, such that direct contact between said first metal and said copper in the presence of an electrolyte would lead to galvanic corrosion characterized in that said surface is treated with a contact material prior to the connection of said tube with said fin collar, said contact material being located at least in the location of said contact area and comprises a third metal galvanically compatible with said first metal,
said contact material contacts said fin collar and prevents contact between said surface of said tube and said fin collar for preventing galvanic corrosion of said fin collar relative to said tube.
2. A heat exchanger exhibiting resistance to galvanic corrosion as claimed in
claim 1 comprising:
a fin collar formed from aluminum and
a tube connected with said fin collar at a contact area said tube formed from copper, said copper more noble than said aluminum, such that direct contact between said aluminum and said cooper in the presence of an electrolyte would lead to galvanic corrosion, and having a surface which is treated with a contact material prior to the connection of said tube with said fin collar, said contact material being located at least in the location of said aluminum metal, said contact material selected from the group consisting of aluminum, an aluminum alloy containing silicon, aluminum alloy containing zinc, zinc, tin, magnesium, gallium, cadmium, lead and combination thereof;
said contact material contacts said fin collar and prevents contact between said surface of said tube and said fin collar for preventing galvanic corrosion of said fin collar relative to said tube.
3. A heat exchanger exhibiting resistance to galvanic corrosion substantially as herein described with reference to the accompanying drawings.