| Closed gravity heat pipe has a good application prospect, and the research on heat transfer enhancement for it has received wide concerns at present. In this paper, the three-phase flow heat transfer enhancement technique is applied to closed gravity heat pipe and a set of three-phase flow gravity heat pipe system is set up. With water as working fluid and the heating power, filling rate, solid holdup and the size of built-in pipe as operating parameters, the investigations and analyses are made for the heat transfer performance of two-phase flow gravity heat pipe and three-phase flow gravity heat pipe with and without built-in pipe. The equivalent convective heat transfer coefficient is used to assess the heat transfer performance.The research results indicate that for the two-phase flow gravity heat pipe, the equivalent convective heat transfer coefficient increases as the heating power increases and decreases as the filling rate increases. For the three-phase flow gravity heat pipe without built-in pipe, the equivalent convective heat transfer coefficient increases as the heating power increases. For being not well fluidized, the solid holdup has no obvious effect on the equivalent convective heat transfer coefficient for theΦ5.5 mm polyformaldehyde; but for the better fluidizedΦ3.15 mm polyformaldehyde and resin particles, as the solid holdup increases, the equivalent convective heat transfer coefficient first increases, then begin to fluctuate after reaching some value. For the three-phase flow gravity heat pipe with built-in pipe, the researches show the existence of built-in pipe can increase the equivalent convective heat transfer coefficient, and the diameter of built-in pipe can influence the heat transfer. The equivalent convective heat transfer coffecient forФ20 mm×1.5 built-in pipe is higher than that forФ26 mm×2 mm built-in pipe. When the solid holdup of sand is above 2%, the equivalent convective heat transfer coffecient is obvious higher than the two-phase flow, and the maximum increase is 30.7%. As the heating power increases, the equivalent convective heat transfer coffcient also increases. The research results in this paper preliminarily prove the three-phase flow closed gravity heat pipe can enhance the heat transfer under some conditions. |
