PURPOSE: A dual type heat exchanger is provided to improve the thermal exchanging efficiency by increasing a heating surface area. CONSTITUTION: A dual type heat exchanger comprises an inner pipe(110) and an outer pipe(120). The first fluid flows in the inner pipe. The second fluid flows between the inner pipe and outer pipe. The inner pipe is included of a bellows pipe(111) and core pipe(112) of coil type. The core tube is arranged along the inner center of the bellows pipe. A second fluid flows through a corrugated surface or a curved surface.
