Mechanism of Solid-Liquid Contact During Rapid Quenching of Thin Wires in Liquids

快速浸没冷却技术的发展是熔体纺丝法生产新型高性能材料如非晶态合金、纳米晶合金等纤维的重要基础。此外，了解浸没冷却过程中固液接触启动的机理也是非常重要的，因为它与蒸汽爆炸现象密切相关。本文通过实验研究了铂丝(直径分别为0.3 mm和0.5 mm)在过冷液体(水、CaCl2/水溶液和乙醇)中快速淬火时的流动和换热特性。试验丝落速为0.1~1.5m/S，淬火液过冷度为20~80K，CaCl2浓度为0~40%。对于水和CaCl2/水溶液，用一种电导p…测量了淬火过程中的固液接触更多的睡袍。研究结果表明：(1)由冷却曲线得到的瞬时沸腾曲线存在两个最小热流点。(2)当管壁温度高于最低热流密度上限(M1点)时，钢丝表面覆盖有汽膜，很少发生固液接触。当壁面过热度降低到M1点以下时，固液信号和热流密度迅速增大。(3)在壁面过热度超过最低热流点下限的区域(M2点)，M1点处的壁面过热度和热流密度随液体过冷度、下降速度和CaCl2浓度的增大而增大。(4)M2点处的壁面过热度与液体过冷度和下降速度无关。它随CaCl2浓度的增加而增大。(5)在对非晶态合金产生重要影响的壁面过热区，CaCl2溶液使平均热流密度提高了140%。从金属丝表面形成的薄汽膜的流体动力稳定性的角度，从理论上研究了固-液接触的机理。该理论考虑了叠加在汽膜上的扰动的线性稳定性。假设运动由液体侧的波动方程和蒸汽侧的层流方程所控制。对于水和乙醇，中性稳定点的传热系数的理论预测值与M1点的结果吻合较好。较少

Development of a rapid immersion cooling technique is very important as a basis of the production of fibers of a new class of high performance materials, such as amorphous alloys, nanocrystalline alloys etc., by melt spinning process. Also, understanding of the mechanism of the incipience of solid-liquid contact during the immersion cooling process is very important because it is closely connected with the vapor explosion phenomena. In this study, experiments were conducted to investigate the fluid flow and heat transfer characteristics during the rapid quenching of thin horizontal platinum wires (0.3 and 0.5 mm in diameter) in a pool of subcooled liquids (water, CaCl_2/water solution and ethanol). The falling speed of the test wire ranged from 0.1 to 1.5m/s, the subcooling of quenching liquid from 20 to 80K,and the concentration of CaCl_2 from 0 to 40%. For water and CaCl_2/water solution, the solid-liquid contact during the quenching process was measured using a kind of conductance p … More robe. The results are summarized as follows : (1) The transient boiling curve obtained from the cooling curve has two minimum-heat-flux points. (2) At a wall temperature higher than the upper minimum-heat flux point(named the M1 point), the wire is covered with vapor film and the occurrence of solid-liquid contact is very rare. When the wall superheat decreases below the M1 point, both the solid-liquid signal and the heat flux increase rapidly. (3) In the region of wall superheat exceeding the lower minimun-heat-flux point (named the M2 point) , the wall superheat at the M1 point and the heat flux increases with increasing liquid subcooling, falling velocity and CaCl_2 concentration. (4) The wall superheat at the M2 point is constant irrespective of the liquid subcooling and falling velocity. It increases with increasing CaCl_2 concentration. (5) In the region of wall superheat important for the production of amorphous alloys, the average heat flux increases as much as 140% by use of the CaCl_2 solution. The mechanism of solid-liquid contact was studied theoretically from the viewpoint of hydrodynamic stability of thin vapor film formed on the wire surface. The theory considered the linear stability of disturbance superimposed on the vapor film. The motion was assumed to be governed by the wave equation on the liquid side and by the laminar flow equation on the vapor side. The theoretical prediction of the heat transfer coefficient at the neutral stability point compared well with that at the M1 point for water and ethanol. Less