Systematic Research on the Characteristics of Impingement Heat Transfer in Comparatively Narrow Space

撞击流已越来越多地被用于强化换热介质的传热传质强度。在工程装置中会遇到与这种流动相对应的条件，以从电气设备中带走热量，烘干薄膜或纸张，并使高温钢板的温度分布变平。本文通过改变喷嘴的种类(狭缝式喷嘴和圆形喷嘴)、喷嘴的数量(单个喷嘴和多个喷嘴)、喷嘴与撞击表面的距离、撞击表面的尺寸、喷嘴的流量和喷嘴的节距进行了实验和分析。此外，还对层流冲击射流进行了数值分析。在第一步中，数值考察了加热板坯的尺寸效应对c…的影响层流射流引起的流动状况和冲击换热的更多特点。结果表明，加热板坯和上约束板侧表面附近回流的产生依赖于加热板坯尺寸与喷嘴宽度之比(W&gT；L，W&lt；1)，下壁局部Nusselt数的展向变化呈现一个或两个极大值。第二步，对三种缝隙射流的冲击换热特性进行了实验研究。对于层流射流，将实验值与数值结果进行了比较。对于湍流射流，在第二喷嘴后面出现了两个局部Nusselt数峰值。随着喷嘴与撞击表面间距的减小，第二峰的位置向喷嘴靠近。中心喷管和第二喷管之间的平均努塞尔数由比率P/H和基于喷嘴节距的雷诺数决定。第三步，研究了单股圆形射流和四股湍流圆形射流的冲击换热。对于单个圆形射流，在R=0.5时会产生两个局部Nusselt数峰值，其位置与雷诺数有关。对于四个圆形射流，在无因次喷嘴冲击表面间距H=1.5-2时，平均努塞尔数达到最大值。这些结果将作为基础数据应用于实际设备中。较少

The impingement flow has been increasingly utilized for enhancing the intensity of heat and mass transfer of heat transfer media. Conditions corresponding to such flows are encountered in engineering device to remove the heat from the electric device, to dry the film or the paper and to flatten the temperature distribution of high temperature steel slab. So, we should study on the beat transfer of impinging flow in the narrow space between the nozzle and the impinged surface.In the present study, we experimented and analyzed by changing the kind of the nozzle ( slit-type nozzle and the circular nozzle ), the number of the nozzles ( a single nozzle and array of the nozzles ), the distance between the nozzle and the impinged surface, the size of the impinged surface, the flow rate and the pitch of the nozzles. Additionally, numerical analysis was performed in the laminar impinging jet flow.In the first step, the effect of the size effect of a heated slab was examined numerically on the c … More haracteristics of flow situation and impingement heat transfer caused by a laminar jet. It was found that the generation of recirculating flows near the side surface of a heated slab and the upper confined plate depends on the ratio of the size of a heated slab and the nozzle width (W>l, W<1) and the spanwise variation of the local Nusselt number on the lower wall exhibits one or two maxima. In the second step, experiments were performed on the characteristics of impingement heat transfer by three slot jets. For laminar jet, experimental values were compared with numerical results. For turbulent jet, two peaks of the local Nusselt number were obtained behind the second nozzle. The position of the second peak approached the nozzle with the decrease of the space between nozzle and impinged surface. The average Nusselt number between the central and the second nozzle was determined by the ratio was determined by the ratio P/H and tile Reynolds number based on the pitch of the nozzles. In the third step, the impingement heat transfer caused by a single circular jet and four-turbulent circular jets. For a single circular jet, two peaks of the local Nusselt number were produced at R=0.5 and the position depended on Reynolds number. For four circular jets, the maximum value of mean Nusselt number was obtained at the dimensionless nozzle-impinged surface spacing H=1.5-2.These results will be applied in the practical facility as the basic data. Less