Liquid Jet Impingement Cooling of Strip Metals

拟议研究的一个主要目标是解决与液体射流冲击冷却高温、高热流密度表面有关的基本问题。这些问题涉及与单相强迫对流、强迫对流核沸腾和受热平板上暴露于单一或一系列射流的薄膜沸腾相关的区域的划定。从一个区域到另一个区域的转变受喷流水动力条件(湍流强度和速度分布)的强烈影响，通过平板上的流动从层流到湍流边界层的转变，以及一系列喷流的这种流动的相互作用。摄影将被用来识别成核、转变和薄膜沸腾，而局部换热测量将被用来确定单相流和两相流区的对流系数。要研究的参数包括射流和射流阵列的流体力学和几何特征，板速和表面条件，以及液体中是否存在不可冷凝物质。在可能的情况下，将对过渡和对流换热系数数据进行关联。为了预测单相强迫对流和膜沸腾区域的换热数据，将建立守恒方程的有限差分解和积分解。为了评估实验室研究得出的基本结果的适用性，还将在内陆钢铁公司的热轧厂进行流动可视化实验，并将通过对比实验室和磨机获得的结果来解决缩尺问题。将建立一个模型，利用实验室生成的数据来预测带钢在轧制条件下的热响应，并将预测结果与现有数据进行比较。近年来，低湍流度液体射流冷却在钢、铝等原金属加工中得到了广泛的应用。然而，目前支持建立最佳设计和运行条件所需的知识库有限，必须求助于试错程序。在单一应用中，铁水的冷却同时涉及单相强迫对流、强迫对流成核沸腾和膜沸腾区域，金属的温度历史强烈地影响其最终的机械和冶金性能。为了开发工具来确定最佳的设计和操作条件，很重要的一点是要很好地了解与射流冲击相关的流动和换热过程。这个研究项目应该提供这样的知识基础。

A major objective of the proposed investigation is to address fundamental issues related to the cooling of high temperature, high heat flux surfaces by liquid jet impingement. Such issues concern the delineation of regions associated with single phase forced convections, forced convection nucleate boiling, and film boiling on a heated plate exposed to a single jet or an array of jets. Transitions from one region to another are strongly influenced by jet hydrodynamic condition (turbulence intensity and velocity profile), by the transition from a laminar to turbulent boundary layer for flow on the plate, and by the interactions of such flows for an array of jets. Photography will be used to identify nucleate, transition and film boiling, while local heat transfer measurements will be used to determine convection coefficients in single and two-phase flow regimes. Parameters to be studied include hydrodynamic and geometrical features of the jet and jet arrays, plate speed and surface conditions, and the presence of noncondensibles in the liquid. Where possible transition and convection heat transfer coefficient data will be correlated. In an attempt to predict heat transfer data for the single phase forced convection and film boiling regions, finite-difference and integral solutions of the conservation equations will be developed. To assess the applicability of basic results inferred from laboratory studies, flow visualization experiments will also be performed at Inland Steel Corporation's hot rolling mill, and scaling considerations will be addressed by contrasting results obtained in the laboratory and the mill. A model which uses laboratory generated data to predict the thermal response of strip steel under mill conditions will be developed, and predictions will be compared with available data. In recent years, cooling by means of low turbulence, liquid jets has become widely used in the processing of primary metals such as steel and aluminum. However, currently the knowledge base required to support the establishment of optimal design and operating conditions is limited, and recourse must be made to trial-and-error procedures. In a single application, cooling of hot metals simultaneously involve regions of single phase forced convection, forced convection nucleate boiling, and film boiling, and the attendant temperature history of the metal strongly influences its final mechnical and metallurical properties. To develop tools for establishing optimal design and operating conditions, it is essential that flow and heat transfer processes associated with jet impingement be well understood. This research program should provide such a knowledge base.