倾斜射流条件下的热轧板带钢高强度均匀化冷却换热机理和模型研究

The ultra fast cooling technology has been widely accepted by the iron and steel production enterprises, which can prompt the product performance by fine grain, precipitation and phase transformation strengthening. The jet impingement heat transfer method was adopted to achieve extraordinary cooling capacity. However, there are many problems to be solved to improve the heat transfer efficiency, achieve homogenous cooling under large heat transfer coefficient, and precisely adjust the cooling technical parameters during industrial application process. Therefore, the research of jet impingement heat transfer mechanism and theoretical model must be carried out to improve the ultra fast cooling technology immediately. The inclined jet impingement heat transfer mechanism with the significant anisotropy property will be researched in this research project. The flow characteristics of single jet, the local heat transfer coefficient distribution and the coupled thermal-fluid heat transfer mechanism will be explored and revealed. Furthermore, the characteristics of flow interaction among multiple jets will be investigated by using numerical simulation and experiment. Meanwhile, the heat transfer zone distribution and heat transfer uniformity will be analyzed under the influence of geometrical and physical parameters such as array mode, flow velocity et al. The theoretical results will be used to optimize the nozzle structure to improve the heat transfer efficiency between cooling water and hot strip, and realize homogenous cooling for cooling product especially the one with big width-to-thickness ratio. Furthermore, the heat transfer coefficient mathematic mode and the coupled thermal-fluid heat transfer FEM analytical model will be established under big heat transfer coefficient boundary condition to realize cooling technology parameters high precise control. Finally, these research results will enrich the inclined jet impingement heat transfer theory, and have significant effect on promoting ultra fast cooling technology with independent intellectual property rights, and even propping up the progress of the TMCP technology.

热轧板带钢超快速冷却技术能够充分发挥细晶、析出和相变综合强化作用，显著提升产品性能，正逐步得到行业普遍认可和使用。该技术采用射流冲击换热方式，获得超常规的冷却能力。但如何提升冷却水换热效率，实现高强度均匀化冷却以及工艺参数高精度控制仍是工业应用中的难点问题，迫切需要对射流冲击换热机理和理论模型进行深入研究。为此，本课题针对性研究具有各向异性特征的倾斜射流换热机理，探索单束流体流动特性、沸腾换热及热流耦合作用机理；通过模拟与实验相结合，研究多束流体冲击换热规律，分析阵列形式、流速等参数变化对流体间交互作用规律、热交换区域分布以及换热均匀性的影响。进而优化喷嘴结构，提高冷却水换热效率，实现大宽厚比产品高强度均匀化冷却。并建立换热系数模型及热流耦合有限元解析模型，满足冷却工艺参数大范围高精度控制需求。上述研究成果对丰富射流冲击换热理论，完善超快速冷却技术乃至推动TMCP技术进步具有重要意义。

射流冲击换热方式具有换热能力强的优点，被广泛应用于热轧板带钢超快速冷却技术，在提升产品性能，改善产品质量方面发挥着重要作用。然而，如何提升冷却水换热效率，实现高强度均匀化冷却以及工艺参数高精度控制仍是工业应用中的难点问题。本研究项目采用数值分析与实验研究相结合的方式，针对圆形/狭缝倾斜射流换热机理开展研究，探索其流动特性、沸腾行为和换热规律。研究结果表明：①运动状态下采用倾斜射流冲击换热方式，可以提高再润湿同步性，再润湿前沿呈一条直线，热流密度曲线间距均匀分布，可满足板带钢高强度均匀冷却的需求。在0~45°范围内，倾角增大有利于换热能力提升，热流密度峰值增幅12.8~13.2%。②倾斜角度对单束圆形喷嘴射流冲击换热能力有着显著影响，顺向流区域内的热流密度、换热系数以及再润湿速度均有所增加。在此基础上，研究获得了喷嘴结构、开冷温度、水温、射流方向等参数变化均对换热特性的影响规律。③研究获得了多束流体射流冲击冷却过程的流体结构和换热区域分布。喷嘴间平行流相互冲击飞溅，形成干涉区和液滴飞溅区，促进热流密度和换热系数增强。增加流速有助于提高冷却强度，改善冷却均匀性。④在实验室和现场条件下开展多束射流实验研究，随流速的增加平均换热系数有所增加，但增幅逐渐减小。这对于丰富和完善高温金属快速冷却过程中的射流冲击冷却沸腾换热理论具有重要价值。相关成果为热轧板带钢超快冷工艺技术装备改进、控制系统模型优化以及冷却工艺调优提供理论支持，已在多个超快冷和淬火机项目中得到应用。