螺旋管蒸汽发生器的瞬态流动与传热特性

Transient Flow and Heat Transfer in Helical Coil Steam Generator

针对快速和安全启动的要求 ,实验研究了螺旋管蒸汽发生器在同步启动过程中的流动和传热特性 ,并分析了各种参数对启动安全和启动时间的影响 .螺旋管的管圈直径和管道直径分别为2 5 6mm和 0 0 11mm .启动的参数范围是 :最大加热流密度 6 0 0kW /m2 ,最大质量流速 12 0 0kg/(m2 ·s) ,最大实验压力 3 0MPa .由实验得到了启动过程的单相湍流、沸腾传热规律 ,以及瞬态临界热负荷 .瞬态单相湍流传热和临界热负荷的规律与稳态的有明显不同 .瞬态湍流传热特性符合直管的Dittus Boelter公式 ,瞬态临界热负荷远远低于稳态的值 。

The behaviors of flow and heat transfer in helical coil steam generator during the start-up processes were experimentally investigated. The coil diameter and the inner diameter of the tube are 256 mm and 0.011 mm respectively. The ranges of test parameters were as follows: the maximum heat flux was 600 kW/m2, the maximum mass flux was 1200 kg/(m2&middots), and the maximum pressure was 3.0 MPa. The transient processes, namely the synchro-start-up processes, were investigated in a closed cycle loop with deionized water, which was referred to because the pump load and the heat load were increased synchronously from zero. The influences of different factors on the start-ups were investigated to determine the optimized start-up operation for fast start-up and safety. The experimental results show that the transient single-phase heat transfer is less than that in the stable state because of the weakened enhancement of heat transfer resulting from a secondary flow, and that it can be estimated with the Dittus-Boelter correlation which is used for the straight tube flow. The transient boiling heat transfer can be predicted by correlation for the steady state case. The critical heat transfer phenomena during synchro-start-up processes were analyzed and a criterion for safety evaluations was proposed. It is found that the critical heat flux is much lower than that on the stable condition.