To provide a water tube boiler that ensures high stability and high energy efficiency by increasing the durability of water tubes and increasing the heat transfer efficiency of water tube heating surfaces.
Heat exchanger tubes D with a plurality of dimples arrayed in one side or both sides of a heating surface are provided, and heat exchange is utilized between a low temperature fluid flowing in the heat exchanger tubes D and a high temperature gas. The rim of the dimples preferably has a curve of a predetermined radius. Further preferably, the heat exchanger tubes D are arranged for heat exchange in a high temperature gas section in the boiler, and heat exchanger tubes F with fins on a heating surface are arranged for heat exchange in a low temperature gas section. The tube-to-tube spacing of the heat exchanger tubes D or heat exchanger tubes F is preferably changed according to the gas temperature. In a hot water boiler, the heating surface of the heat exchanger tubes D with the array of the plurality of dimples preferably faces a gas side of a fire bridge.
NOGAMI HARUO
Koichi Kajisaki
Yuzo Ozaki
Toshihiko Taniguchi
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