| 摘要 |
PURPOSE:To obtain a heat exhanger small in size, securely provided with a stable high efficiency, excellent in durability and capable of being manufactured inexpensively, by a method wherein the inside surface of a main body of a heat exchanger provided integrally with internal fins in the axial direction on the inside surface thereof by extrusion is subjected to a blackening suface treatment such as a black heat-resistant coating. CONSTITUTION:A high-temperature combustion gas generated in a combustion chamber 17 flows as indicated by arrows 28, whereby heat is effectively transferred at a plurality of internal fins 10 and the inside surface of the main body 9 of the heat exchanger 6, and heat is exchanged between the gas and a countercurrent airflow 27 passing at the outside peripheral part of the heat exchanger 6. By subjecting the inside surface of the main body 9 to a blackening surface treatment such as a heat-resistant coating, absorptivity for radiant heat from a flame 18 or the combustion gas is enhanced, a stable high thermal efficiency is obtained, while local abnormal heating of the heat exchanger is prevented from occurring, and can be contrived to reduce material cost and facilitate mechanical workability. |
