| 摘要 |
PURPOSE:To contrive an improvement in a heat transmission coefficient, by a method wherein the external surface of a heat transfer tube is provided with a porous layer and as for the inner surface of the same, this side of a flowing direction of a fluid in the tube is provided with a rising surface and the opposite side of the rising surface is provided with an annular portrusion in the circumferential direction having a gentle slop. CONSTITUTION:The external surface of a heat transfer tube 10 of a liquid-filled type heat exchanger to be used for low heat head for generation due to temperature variations of sea water is provided with a porous layer 11 through flame spray coating of metallic particles. An inner wall surface of the heat transfer tube 10 is provided with an annular protrusion 12 which is extending in a prulurality of circumferential directions at intervals in the longitudinal direction of the tube. The annular protrusion 12 is constituted with a rising surface 12a rising at right angles with the longitudinal direction of the tube on this side of a flowing direction of a fluid in the inside of the heat transfer tube 10 and a gentle slope 12b descending toward the front of the flowing direction of the fluid from the upper end of the rising surface 12a. As for the rising surface, a height (e) of 0.2-0.7mm. is favorable and as to a ratio p/c of a pitch (p) of the rising surface to the height (e) of the rising surface, 20-80 is good. As for a flame- spraying metal for providing the porous layer on the external surface of the heat transfer tube, copper and a copper alloy are good for the quality of the material and 325-200 meshes are desirable for its grain size. |
