Bending Vibration of a Heated Rod in Quenching Process

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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.