喷嘴射流特征对连铸二冷区蒸汽膜穿透行为的影响

 连铸二冷区铸坯表面温度通常高于900 ℃,此时喷淋液滴接触高温铸坯时不会湿润铸坯表面,仅在其上形成一层蒸汽膜,阻碍了液滴与铸坯表面接触传热。针对以上问题,以国内某钢厂连铸二冷区的扁平型水喷嘴为原型,建立了喷嘴射流仿真计算模型,并对所建模型进行了理论和实验室验证;采用数值模拟的方法研究了喷嘴自由射流区的流场分布,运用连铸喷嘴冷却检测系统测量获得了射流液滴粒径演变规律;结合数值模拟和实验室测定结果,定量分析了喷嘴在不同水流量下射流液滴冲击铸坯表面蒸汽膜深度的变化规律。结果表明,该喷嘴的最大射流速度在喷嘴出口处,射流在喷嘴出口附近出能维持较大的射流速度,且随着水量的增加,射流保持高射流速度的距离也增长;整体射流的轴向速度占比均在80%以上。当喷淋水量越大时,射流液滴粒径变得越小;随着距喷嘴出口距离的增加,射流中心处的液滴粒径逐渐增大并达到最大值;当水流量为9和12 L/min时,液滴粒径基本相同,这表明当水流量增加到一定值时,冷却水量的增加不影响液滴粒径分布。在不同水流量下,随着喷淋距离的增加,液滴穿透铸坯表面蒸汽膜深度呈先增大后略微减小的变化规律,在喷射距离为100~200 mm范围内时,液滴穿透深度最大,这表明喷射高度在该范围时,喷淋冷却效果最好。

Influence of jet characteristics nozzle on penetration behavior to vapor film in secondary cooling zones of continuous casting

The surface temperature of the slab in the second cooling zone of continuous casting is usually higher than 900 ℃. At this temperature,the spraying droplets will not wet the surface of the slab when they contact the high-temperature slab,but only form a vapor film on it,which prevents the subsequent heat transfer between the droplets and the slab surface. In view of the above problems,a nozzle jet simulation calculation model is established based on the flat water nozzle in the secondary cooling zone of continuous casting in a domestic steel plant. The model is verified by theoretical calculation and laboratory experiments. The flow field distribution in the free jet area of the nozzle is studied by numerical simulation and the evolution law of the jet droplet size is measured by the continuous casting nozzle cooling detection system. Combined with the numerical simulation results and laboratory measurement results,the variation law of the depth of the vapor film on the surface of the billet by the jet droplets impacted by the nozzle under different working conditions is quantitatively analyzed. The results show that the maximum jet velocity of the nozzle is at the nozzle outlet. The jet can maintain a large jet velocity near the nozzle outlet. With the increase of water volume,the distance of the jet to maintain a high jet velocity also increases. The axial velocity of the whole jet accounts for more than 80%. When the amount of water is larger, the particle size of jet droplets becomes smaller. As the distance from the nozzle outlet increases,the droplet size at the center of the jet increases gradually and reaches the maximum value. When the water flow rate is 9 and 12 L/min,respectively,the droplet size is basically the same,indicating that the increase of the cooling water does not affect the droplet size distribution when the water flow rate increases to a certain amount. Under different initial flow rates,the depth of droplet penetration through the steam film on the billet surface increases firstly and then decreases slightly with the increase of spray distance. When the spray distance is between 100-200 mm,the penetration depth of droplet is the largest,which indicates that the spray cooling effect is the best when the nozzle spray height is within this range.