High Density Array of Tubes in Horizontal Tube-Bundle Evaporator

点击翻译按钮获取中文摘要

An experimental study on nucleate boiling heat transfer was performed to investigate various effects on heat transfer characteristics in horizontal tube bundle and to gain useful information for developing an evaporator with horizontal tubes more densely arrayd. Experiments were done for in-line and ataggered tube arrangement under the conditions of natural circulation and forced circulation of fluid within a tube bundle. Findings are as follows.(1) Compared with the performance of a single horizontal tube in pool boiling, heat transfer coefficient of tube bundle shows the same level at higher heat flux where nucleate boiling is fully established, while at lower heat flux the boiling heat transfer is highly enhanced in a bundle.(2) The above mentioned difference in performance between a single tube and a tube bundle is true for both bundles of in-line and staggered arrangement.(3) Under the condition of natural circulation a rise of heat transfer coefficient at lower heat flux is more enhanced as the location of tube is higher in a bundle.(4) In the case of forced circulation, heat transfer coefficient at lower heat flux increases with an increase of circulating flow velocity. Heat transfer coefficient increases vertically at first for lower tubes, then decreases for higher tubes.(5) As for an effect of tube pitch, a pitch to diameter ratio P/D of 1.5 shows better performance under the natural circulation, while a P/D of 1.3 is preferable for the forced circulation.