| 摘要 |
PROBLEM TO BE SOLVED: To provide a heat exchanger, in which safety as drinking water of supply hot-water and corrosion resistance to condensate in a brazed part are made compatible by preventing contamination of different kinds of brazing-filler metals. SOLUTION: A tube is constituted of two heat-transfer plates. A to-be-seamed part 4a of a first heat-transfer plate 4A is folded back from the inside of a second heat-transfer plate 4B to be seamed together so that the end of the plate 4B is sandwiched on both sides, and contact faces of the plates 4A, 4B are brazed. In this case, the first joint 9 made inside (supply hot-water side) relative to the bent part of the plate 4A and the second joint 10 made outside (combustion gas side) are brazed with brazing-filler metals different from each other. That is, in the first joint 9 copper brazing filler is used. In the second joint 10, Ni-brazing-filler is used, which has a melting point (liquidus temperature) close to that of the copper brazing-filler.
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