Boiling heat transfer behavior of lead–bismuth–steam–water direct contact two-phase flow

The boiling heat transfer behavior of lead–bismuth (Pb–Bi)–steam–water direct contact two-phase flow was experimentally investigated. Experimental study was performed using Pb–Bi–steam–water direct contact boiling two-phase flow loop. The heat transfer rate was estimated from data of one-dimensional flow direct contact boiling of water in Pb–Bi. It is assumed in the analysis that film boiling occurs at the surfaces of a small water droplet after water is injected into hot Pb–Bi flow, because of the large temperature difference between water and Pb–Bi (i.e. 493 K and 733 K for injection water and Pb–Bi temperature, respectively). The heat transfer occurs between Pb–Bi and steam without phase change after all water completely evaporates. The overall heat transfer coefficient decreased with the superheat at low injection flow rate and was nearly constant for high injection flow rate. The local heat transfer coefficient was higher than average one in the whole tube, which means that the direct contact boiling heat transfer coefficient was high and it decreased in the downstream direction. Almost all the water vaporized in the test tube at high pressure according to the local and total heat transfer rate.