陈听宽,贾岫庄
Chen Tingkuan and Jia Xiuzhuang (Xian Jiaotong University, Xian)According to the authors investigation on boiling heat transfer in vertical U-shaped tubes, the boiling heat transfer deterioration on the inner side of the bend occurring at lower mass velocities and lower steam qualities leads to elevated wall temperature on the inner side of the bend due to the stratification of the steam-water flow under the action of both centrifugal and gravitational forces. In order to improve the boiling heat transfer performance, modified U-shaped tubes with inclined upward bottom were tested in a high pressure electrically heated water loop under the conditions of p = 75- 14MPa, G = 500-1400kg/(m2·s) and q = 90-330kW/m2. This paper describes the experimental results on the boiling heat transfer deterioration in the bend of modified U-shaped tubes with R1/d=3, R2/d = 6 and R1/d=6, R2/d=6, and bottom straight tube inclination of 18? According to the tests the mass velocity at which the wall temperature begins to rise is much decreased than that in ordinary U-shaped tube. So the modified U-shaped tubes may be recommended tor waste heat boilers in synthetic ammonia plants for ensuring safe operation.
摘要： 本文针对垂直U型沸腾管弯管段由于汽水分层引起传热恶化,使壁温升高经常发生爆管事故的问题,提出用底边倾斜上升的改进型U型管来代替原普通型U型管,以改善其传热特性.文中阐述了压力7.5—14MPa、质量流速500—1400kg/(m~2·s)及热负荷90—330kW/m~2条件下改进型U型管的传热特性试验结果,得出了沿弯管段的壁温分布规律,与U型管的传热特性相比,具有明显的优越性.试验同时确定了改进型U型管的两相流阻力特性,较原U型管稍有增加.
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