| 摘要 |
PROBLEM TO BE SOLVED: To improve heat radiation characteristics from a fin by applying black-colored coating having low light reflectivity on each fin. SOLUTION: A hydrophilic coating film of 5 to 10μm is formed on the outside of a rust-proof layer. The hydrophilic coating film is formed in order to prevent water droplets acting as vent resistance from being formed on the surface of a fin 23. The hydrophilic coating film is a black colored pigment such as a carbon black pigment mixed and added to a composite comprising hydrophilic organic resin and silica, and is formed by cleaning the fin 23 with triethane and thereafter dipping it in a black colored coating, pulling, drying, and baking it. The surface of the hydrophilic coating film is made a fine rough surface by mixing-in of such a black colored pigment, and contributes to reduction of light reflectivity, in and an improvement of heat exchange efficiency can therefore be achieved. Piping insertion holes are previously formed in the fin 23, and the fins 23 are successively inserted into a straight pipe 26A. After the straight pipe 26A is expanded, a bend piping 26B is welded for communication with the straight pipe 26A.
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