带钢保护气氛循环喷射冷却热工过程的数值模拟

Numerical simulation on thermal process of recycling jet cooling in heat treatment of strip steel in protective hydrogen atmosphere

对带钢保护气氛循环喷射冷却热工过程建立了一维非稳态传热模型,采用有限差分计算方法计算了带钢的温度场,确定了带钢在不同厚度、初始温度及运行速度下所需的综合换热系数,考察了喷箱的结构参数和循环环冷却介质的物性参数对带钢出口温度的影响。结果表明,不同厚度的带钢在满足性能能要求及安全的条件下,存在最大运行速度,厚度超过3mm的带钢的断面温差对带钢性能的影响不能忽略;带钢出口温度会随带钢至喷孔板距离(Η)与喷孔直径(D)的比值增大而增大,但增大速率随Η/D增加逐渐变小。喷孔间距(Χn)与喷孔直径的比值存在最佳范围,且与Η有关,因此在实际设计喷箱结构时,不仅需考虑Χn/D的最佳值,还需结合Η综合考虑;冷却介质质(H2+N2)的温度度每升高10℃,,带钢出口温度度增加约3℃。带钢出口温度随冷却介质中氢气含量及流速增加而减小,但减小速率随随二者增加而逐渐减小。现场应用结果表明,带钢出口温度的模拟值与实测值吻合较好,误差约为3.4%,满足应用要求。

A one-dimensional unsteady heat transfer model was established for the cyclic spray cooling heat transfer of strip steel protective atmosphere. The temperature field of strip steel was calculated by finite difference numerical calculation method. The comprehensive heat transfer coefficient required of the strip steel at different thicknesses, different initial temperatures and operating speeds were determined. The effects of structural parameters of the spray box and the parameters of the circulating cooling medium on strip steel outlet temperature were studied. The results showed that there was a maximum operating velocity for strip steel with different thicknesses on the premise of meeting the performance requirements and safety. For strip steel with thickness of more than 3 mm, the influence of the section temperature difference on the strip steel properties could not be ignored. The temperature of strip steel outlet increased with the increase of the ratio(H/D) of distance between strip and orifice(H) to orifice diameter(D),but increase rate gradually decreased as Η/D increased. There was an optimal range of the ratio(Χn/D) of the orifice spacing(Χn) to the orifice diameter(D) which was related to H. Therefore, when actually designing the spray box structure, it is necessary to consider not only the optimal value of D, but also the H.As the temperature of the cooling medium increased by 10 ℃, strip steel outlet temperature increased by about 3℃. When the volume percentage of hydrogen in the cooling medium and the flow rate of the cooling medium increased, the temperature of strip steel outlet decreased,however, the decrease rate gradually decreased as the volume percentage of hydrogen in the cooling medium and its flow rate increased. The industrial application resultsshowed that the calculated value of the outlet temperature of strip steel was in good agreement with the measured value, and the error was about 3.4% which meant that the model met the application requirements.