Bending Vibration of a Heated Rod in Quenching Process

当垂直加热的棒材被向上流动的过冷水冷却时，在一定条件下观察到了棒材的弯曲振动。这种振动是由棒周围淬火前沿的扭曲分布和由此产生的热应力引起的。但淬火前沿周期性变形的机理以及水温过冷对振动的贡献还不是很清楚。在本研究中，考虑到冷却水中的热分层，研究了弯曲振动与温度不同的两层界面上重力波的关系，并对水中热分层的形成进行了流体力学研究。由数值模拟可知，汽膜沸腾的蒸汽流动在淬火锋面上方产生循环流动，而从棒体传递到水中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。界面通常位于激冷前沿附近，理论分析了同心环形管道中两层界面上重力波的频率。为了证实界面波引起猝灭波阵面扭曲分布的假设，进行了各种实验。测量了水温、水流量和杆的初始温度对频率的影响。重力波的计算频率与弯曲振动的频率基本一致。通过实验得到了弯曲振动开始的边界。

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.