复合多孔表面管竖直管束在液氮中的沸腾传热

NUCLEATE POOL BOILING HEAT TRANSFER OF LIQUID NITROGEN IN COMBINATIVE SURFACE TUBE BUNDLE

复合Gewa T多孔表面管是在机械加工Gewa T表面上再覆盖一层烧结多孔层而形成的强化传热管 ,针对复合Gewa T多孔表面管竖直单管和管束在液氮池中的核态沸腾进行了实验研究 ,通过改变管束管间距、热负荷等得到了不同情况下的管束沸腾传热特性 .沸腾的最佳管间距与管外径比为 1 2 ,此时管束沸腾特性优于单管 .

A combinative surface tube is a new kind of enhanced heat transfer tube, which is machined to Gewa-T surface and then is coated with sintered porous material on the Gewa-T surface. Experimental study on the nucleate pool boiling heat transfer of liquid nitrogen in combinative surface tube bundle at atmosphere pressure was carried out. A glass Dewar vacuum vessel with an inner diameter of 270 mm and a height of 700 mm was used to contain liquid nitrogen. Heat isolation was made except two windows with an area of 150 mm × 150 mm, which were used for flow visualization. A combinative surface tube has an outer diameter of 20 mm and a height of 430 mm, and the height with porous surface is 400 mm. Single combinative surface tube and tube bundles with 12 tubes were tested. Boiling heat transfer curves were obtained and flow characteristics were visualized. The results showed that the combinative surface tubes shared the features of both Gewa-T surface and sintered porous surface. Bubbles of a small diameter grew fast on the surface in a great amount, and the departure frequency was high. This was the reason why the combinative surface tubes could enhance heat transfer. With changing the tube pitch and heat flux, there was an optimal tube pitch at which the boiling heat transfer coefficient of liquid nitrogen inside combinative surface tube bundle reached a maximum. The optimal ratio of tube pitch to tube diameter was about 1.2. At this tube pitch, the boiling performance of the tube bundle was higher than that of a single tube.