Development of water heater using tubular flame - Heat transfer characteristics on the coiled tube and the inserted tube heat exchangers - oleh Ryosuke MATSUMOTO, Tatsuro TANIKAWA, Tatsuya SUGIMOTO, Mamoru OZAWA, Yoshinori HISAZUMI, Tsukasa HORI, Noriko KAWAI, Akeshi KEGASA, Yosuke SHIRAGA, Toshikazu TAKEMORI, Masashi KATSUKI