| 摘要 |
PURPOSE:To exceedingly facilitate generation of air bubbles and remarkably heightening the evaporating heat transfer coefficient by forming build-up portions on the tip end sides of outer fins to narrow the interval between the fins and to form an opening interval easy for generation of air bubbles, and forming inner cavities widened toward the inner parts at the lower parts of the build-up portions to stably hold air bubble nucleuses. CONSTITUTION:Spiral fins 2 are formed around the outer periphery of a heat transfer tube material 1, and metal build up portions 3 made up of aluminum or the like are formed on the tip end sides of the fins 2. The thickness (f) on the tip end side is made larger than the thickness T on the root side [as a result, the interval (l) between the tip end sides of adjacent build-up fins is narrower than interval L on the root side]. As a result, spiral cavities widened toward the inner part, having fine spiral openings 4 are formed on the surfaces of the heat transfer tube material 1. The heat transfer tube having the above described structure is designed so that the interval (l) of the spiral opening 4 is in a range of from 20-100mum in which generation of air bubbles is easiest. Consequently, air bubbles are generated smoothly by the heat transfer tube by being stimulated by air bubble nucleuses within the inner cavities. |
