Abstract: A method for making a heat exchanger includes providing a first outer tube, and an inner tube disposed in the first outer tube; placing a first coiled heat-transfer tube in a space defined between the inner tube and the first outer tube without being fixed to either one of an outer peripheral surface of the inner tube and an inner peripheral surface of the first outer tube, the first coiled heat-transfer tube including a plurality of coiled sections, an inside space of the heat-transfer tube defining a first flow path, a coiled space defined between coiled sections of the heat-transfer tube in the space, defined between the inner tube and the first outer tube, defining a second flow path, wherein heat is exchanged between two fluids.

Abstract: A small heat exchanger can efficiently exchange heat, and can be produced at low cost in comparison with a conventional heat exchanger. In the heat exchanger, a heat-transfer tube can be easily replaced so that the heat exchanger can be used for a treatment which requires a low flow rate. A heat-transfer tube produced in the form of a coil is attached to, for example, a lower closing portion and an inner tube, which are integrally produced. The heat-transfer tube is pulled in the U-direction to reduce the diameter of the coiled portions and, thus, is closely bonded or welded to the inner tube. An outer tube and an upper closing portion are attached so that there is a slight gap between the outer tube and the outer diameter of the heat-transfer tube.