| 摘要 |
PURPOSE:To improve boiling thermal conducting performance without giving any substantial mechanical and thermal influence on a surface of a base pipe by a method wherein a porous flame spray layer with a desired thickness as well as a desired void rate is formed at the surface of the base pipe. CONSTITUTION:Porous flame spray layer 12 is in close contact with a base pipe 11. Flame spray metallic powder particles 21 are melted and adhered to each other and have voids 22 at a substantial constant proportion. The voids 22 are combined in complex manner within the porous flame spray layer 12 to communicate with each other. These voids 22 may act as an effective reentrant cavity. With this arrangement, it is possible to improve boiling thermal conducting performance under a condition in which a rate of void is 0.1 or less, added power within the flame melting layer can not be removed even if they are immersed in melting medium. In case that a rate of void is more than 0.4, the flame spray layer itself becomes brittle. As the flame spray layer become thick, the voids communicate with each other to improve the performance. However, too thick flame spray layer may not remove completely the added powder, but become a thermal resistor.
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