proprietary phenolic coating, the service life is over 8 years and the 

 cost increase is one-third. Some doubt exists concerning the integrity 

 of the bond when this material is applied to copper tube/aluminum fin 

 units. Patrick AFB also tried sticky oil as a corrosion preventive, but 

 this material collects dirt. 



The Long Beach Naval Shipyard (Ref 6) reported that aluminum tube/ 

 aluminum fin condenser coils on window air conditioners in a marine 

 environment lasted 3-4 years. Application of a chromium- chromate con- 

 version coating by the Iridite process increased the life to 7 or 8 

 years. Copper tube/copper fin units performed very well but were much 

 more expensive than the all aluminum units. 



For its study, CEL also decided to investigate nonf errous , finned 

 tube, liquid-to-gas heat exchangers of the type found on air conditioning 

 or refrigeration equipment which use air condensers. 



The approach was to record the temperature drop across each heat 

 exchanger because this would indicate heat loss and, therefore, cooling 

 efficiency. This drop would be recorded as a function of time over a 

 long enough period to attain severe deterioration of uncoated exchangers. 

 The long-term effects of the coatings selected could then be determined 

 based on their thermal behavior, and compared with the results for both 

 coated and uncoated exchangers. Information could also be obtained on 

 relative service lives of the different types of heat exchangers. 



EXPERIMENT DESIGN 



Heat Exchangers 



The twelve heat exchangers were purchased from The Vulcan Radiator 

 Company, Hartford, Conn. All of the heat exchangers had the following 

 characteristics : 



1. Tube - 1 in. (2.54 cm) ID nominal and 1-1/8 in. (2.86 cm) 

 OD with a wall thickness of 0.025 in. (0.064 cm) and 



a length of 6 ft (1.83 m) 



2. Fins - hard-tempered plate type embedded in the tube, 

 which is mechanically expanded to the diameter of the 

 hole in the fins; nominal 3-1/4 in. (8.26 cm) square; 

 0.020 in. (0.051 cm) thick; and spaced 33/ft (108/m) 



The materials or material combinations were: 



1. Copper tube with copper fins. 



2. Copper tube with aluminum fins coated with a synthetic 

 enamel.* 



3. Aluminum tube with aluminum fins. 



"This coating was removed before the cleaning process described in the 

 next section was done. 



