Corrosion-resistant heat exchanger

Abstract

A corrosion-resistant, copper-finned heat exchanger for a water heater is provided. The heat exchanger includes a conduit through which water runs, heat-transfer fins extending from the conduit and an anti-corrosive coating containing electroless nickel. The heat-transfer fins contain copper, and the coating is deposited directly onto at least one of the copper heat-transfer fins.

We claim:  
     
         1 . A copper-finned heat exchanger for a water heater, the heat exchanger comprising: 
 a conduit through which water runs;    heat-transfer fins extending from the conduit, the heat-transfer fins comprising copper; and    an anti-corrosive coating comprising electroless nickel, the coating being deposited directly onto at least one of the copper heat-transfer fins.    
     
     
         2 . The heat exchanger of  claim 1 , wherein the anti-corrosive coating is about 0.05 mils to about 10 mils in thickness.  
     
     
         3 . The heat exchanger of  claim 2 , wherein the anti-corrosive coating is about is 0.1 mil to about 1.5 mils.  
     
     
         4 . The heat exchanger of  claim 3 , wherein the anti-corrosive coating is about 0.25 to about 1.0 mils in thickness.  
     
     
         5 . The heat exchanger of  claim 1 , wherein the anti-corrosive coating is applied directly to at least one of the copper heat-transfer fins by an electroless-chemical-deposition process.  
     
     
         6 . The heat exchanger of  claim 1 , wherein the anti-corrosive coating further comprises phosphorus.  
     
     
         7 . The heat exchanger of  claim 1 , wherein the coating is thermally conductive and does not hinder heat transfer.  
     
     
         8 . The heat exchanger of  claim 1 , wherein the heat-transfer fins comprise pure copper to enhance the thermal conductivity thereof.  
     
     
         9 . The heat exchanger of  claim 1 , wherein the conduit comprises a copper alloy and has an electroless-nickel-coating deposited onto at least a portion thereof.  
     
     
         10 . A water heater comprising: 
 a housing;    a combustor positioned within the housing;    a flue positioned above the combustor in the housing; and    a copper-coiled heat exchanger positioned within the housing, the heat exchanger having a conduit through which water runs, heat-transfer fins extending therefrom and an anti-corrosive coating chemically deposited directly onto a portion of the copper heat exchanger, the anti-corrosive coating including electroless nickel.    
     
     
         11 . The water heater of  claim 10 , wherein the anti-corrosive coating is about 0.05 mils to about 10 mils in thickness.  
     
     
         12 . The water heater of  claim 11 , wherein the anti-corrosive coating is about 0.10 mils to about 1.50 mils in thickness.  
     
     
         13 . The water heater of  claim 12 , wherein the anti-corrosive coating is about 0.25 to about 1.0 mils in thickness.  
     
     
         14 . The water heater of  claim 10 , wherein the portion of the heat exchanger onto which the electroless nickel is directly deposited is a heat-transfer fin.  
     
     
         15 . The water heater of  claim 14 , wherein the heat-transfer fins comprise pure copper in order to enhance thermal conductivity thereof.  
     
     
         16 . The water heater of  claim 10 , wherein the conduit comprises a copper alloy and the conduit is the portion of the heat exchanger onto which the coating is directly deposited.  
     
     
         17 . The water heater of  claim 10 , wherein the coating further comprises phosphorus.  
     
     
         18 . A method of preventing corrosion of a copper heat exchanger for a water heater, the method comprising: 
 immersing a copper heat exchanger into an aqueous-chemical-deposition bath comprising at least one of nickel, cobalt, palladium or platinum; and    electroless-chemically depositing an electroless coating selected from the group consisting of nickel, cobalt, palladium, platinum or a combination thereof onto at least a portion of the heat exchanger, whereby the electroless coating prevents corrosion of the heat exchanger when the heat exchanger is used in conjunction with a functioning water heater.    
     
     
         19 . The method of  claim 18 , wherein the electroless coating is about 0.05 mils to about 10 mils in thickness.  
     
     
         20 . The method of  claim 19 , wherein the electroless coating is about 0.1 mils to about 1.5 mils in thickness  
     
     
         21 . The method of  claim 20 , wherein the electroless coating is about 0.25 to about 1.0 mils in thickness.  
     
     
         22 . The method of  claim 18 , wherein the chemical-deposition bath further comprises phosphorus.  
     
     
         23 . The method of  claim 22 , wherein the electroless coating is an electroless nickel-phosphorus network.  
     
     
         24 . The method of  claim 23 , wherein the heat exchanger is a copper-coiled heat exchanger having heat-transfer fins, the heat-transfer fins having the electroless coating applied thereon.  
     
     
         25 . The method of  claim 24 , wherein the electroless nickel-phosphorus network comprises about 0.01 to about 16 percent phosphorus.  
     
     
         26 . The method of  claim 25 , wherein the electroless nickel-phosphorus network comprises about 6 to about 9 percent phosphorus.  
     
     
         27 . The method of  claim 18 , wherein the chemical-deposition bath further comprises sodium hypophosphite, an acid, a boron derivative and water.  
     
     
         28 . The method of  claim 27 , wherein the bath comprises about 20 to about 100 grams of nickel per liter of solution, about 10 to 40 grams of sodium hypophosphite per liter of solution, and about 20 to about 40 grams of acid per liter of solution.  
     
     
         29 . The method of  claim 28 , wherein the bath comprises about 80 to about 90 grams of nickel per liter of solution, about 15 to about 20 grams of sodium hypophosphite per liter of solution and about 25 to about 35 grams of acid per liter of solution.  
     
     
         30 . The method of  claim 18 , whereby no electrical current is used during the chemical deposition process.  
     
     
         31 . The method of  claim 18 , whereby an electrical current is used initially after the heat exchanger is immersed in the bath, but for no more than thirty seconds.  
     
     
         32 . The method of  claim 18 , whereby the electroless coating can withstand high temperatures associated with products of combustion.  
     
     
         33 . The method of  claim 18 , wherein the electroless coating comprises nickel, boron or phosphorus and at least one other metal selected from the group consisting of cobalt, iron, tungsten and molybdenum.