Bending Vibration of a Heated Rod in Quenching Process

在一定条件下，用过冷水对垂直加热的棒进行冷却，观察到棒的弯曲振动。这种振动是由杆周围淬火锋的畸变分布和由此产生的热应力引起的。但对淬火锋周期性畸变的机理和水温过冷对振动的贡献尚不清楚。本文以冷却水中的热分层层为研究对象，研究了不同温度的两层界面上的重力波与弯曲振动的关系。对水中热分层层的形成进行了流体动力学研究。数值模拟结果表明，气膜沸腾时的蒸汽流在淬灭锋上方引起循环流动，而从棒向水传递的热量被限制在循环流动中。因此，上部区域的温度变得饱和，而下部区域的温度保持过冷。界面通常位于淬火前附近。从理论上分析了同心环形管道两层界面处重力波的频率。为了证实界面波引起淬火锋畸变分布的假设，进行了各种实验。测量了水温、水流速率和初始杆温对频率的影响。计算得到的重力波频率与弯曲振动频率基本一致。实验得到了弯曲振动起始的边缘边界。

When a vertical heated rod is cooled by subcooled water flowing upward, bending vibration of the rod has been observed under certain conditions. This vibration is caused by the distorted distribution of quench front around the rod and the resultant thermal stress. But the mechanism of the periodical distortion of quench front and the contribution of subcooling of the water temperature to the vibration are not understood. In this study, paying attention to the thermally stratified layers in the cooling water, the relation between the bending vibration and the gravity waves on the interface separating two layers with different temperatures was investigated.The formation of the thermally stratified layers in the water was hydrodynamically investigated. From a numerical simulation, circulation flow is induced above the quench front by the steam flow of film boiling, and heat transmitted from the rod to the water is confined in the circulation flow. Consequently, the temperature of the upper region becomes saturated, and that of the lower region is kept subcooled. The interface usually locates near the quench front.Frequency of the gravity waves on the interface of two layers in a concentric annular conduit was theoretically analyzed. To confirm the hypothesis that the waves on the interface induce the distorted distribution of quench front, various experiments were performed. Influences of the water temperature, water flow rate, and initial rod temperature on the frequencies were measured. The calculated frequencies of gravity waves reasonably agree with those of bending vibration. The marginal boundaries of the onset of bending vibration were obtained experimentally.