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

发展快速浸没冷却技术是生产新型高性能材料纤维的基础，如非晶合金、纳米晶合金等，通过熔融纺丝工艺。此外，在浸没冷却过程中的固-液接触的初始机制的理解是非常重要的，因为它是密切相关的蒸汽爆炸现象。本文对水平铂丝（直径为0.3和0.5mm）在过冷液池（水、CaCl_2/水溶液和乙醇）中快速淬火时的流动和传热特性进行了实验研究。试验丝的下落速度为0.1 ~ 1.5m/s，淬火液的过冷度为20 ~ 80 K，CaCl_2的浓度为0 ~ 40%。对于水和CaCl_2/水溶液，用电导法测量了淬火过程中的固液接触 关于我们 长袍结果表明：（1）由冷却曲线得到的瞬态沸腾曲线存在两个最小热流密度点。(2)当壁温高于最小热流点（M1点）时，金属丝表面被蒸汽膜覆盖，固液接触现象很少发生。当壁面温度降低到M1点以下时，固液信号和热通量都迅速增加。(3)在壁面温度超过最小热流密度下点（M2点）的区域内，随着液体过冷度、下降速度和CaCl_2浓度的增加，M1点处的壁面温度和热流密度均增加。(4)在M2点处的壁厚是恒定的，与液体过冷度和下降速度无关。随着CaCl_2浓度的增加，其电导率增加。(5)在对非晶态合金生产至关重要的壁面区域，使用CaCl_2溶液可使平均热流密度提高140%。从金属丝表面形成的薄蒸汽膜的流体动力学稳定性的观点出发，对固液接触机理进行了理论研究。该理论考虑了附加在汽膜上的扰动的线性稳定性。该运动被假定为在液体侧由波动方程和在蒸气侧由层流方程支配。中性稳定点处的传热系数的理论预测相比，以及在M1点的水和乙醇。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