MECHANISM OF HEAT REMOVAL BY HEAT TRANSPORT VORTEX

在这种情况下，热输送涡由撞击射流形成的更新涡和混合对流形成的固定涡组成。通过对碰撞换热和混合对流特性的考察，研究了涡旋如何传递热量和增强换热。第一阶段研究了单圆射流和瞬态过程中撞击射流的传热特性。实验采用热敏液晶和（r,g,b）法进行。研究了喷嘴形状和喷嘴姿态对局部换热的影响。将冲击射流实验扩展到四个方形布置的圆形喷嘴。局部努塞尔数的二维行为与油膜法在撞击表面的流动显示相对应。平均努塞尔数用几何函数和Re^<2/3>表示。用二维图捕捉了环形喷嘴的碰撞换热过程。用幂律表达式r/r_p （r_p：局部努塞尔数的位置）给出了主流区和小流区局部努塞尔数的实验公式。在第二阶段，采用数值和实验方法研究了具有三个换热壁的水平方形管道内混合对流的传热和流动特性。流动特性取决于壁面和入口流体之间的相对温差。靠近壁面的流体向后流动以补偿浮力引起的流动。随着理查德森数的增加，回流的大小增大。在侧壁加热和冷却过程中，纵向上产生一个旋流，在截面上可以发现几个涡。这些流动行为传递热量并影响壁面的局部换热。最后的报告由两章组成，分别讨论了碰撞射流和混合对流。

In the present case, heat transport vortexes are composed of the renewal vortex by impinging jet and fixed vortex by the mixed convection. We studied on how vortex transports heat and contributes to heat transfer enhancement by examining the characteristics of the impingement heat transfer and the mixed convection.In the first stage, the heat transfer characteristics on impinging jet were studied on a single circular jet and in transient process. Experiment was performed using thermosensitive liquid crystal and (r,g,b) method. Effects of the shape and the attitude of the nozzle were investigated on the local heat transfer. Experiments on impinging jet were expanded to four circular nozzles arranged in square-type. The two-dimensional behavior of the local Nusselt number was corresponded to the flow visualization by oil film method on the impingement surface. The average Nusselt number was expressed by the geometric function and Re^<2/3>. Impingement heat transfer by annular nozzle was also captured in two-dimensional map. Experimental formulas of the local Nusselt number were obtained in power-law expressions of r/r_p (r_p : position of local Nusselt number)for the major and minor flow regions.In the second stage, the heat transfer and flow characteristics of mixed convection in a horizontal square duct with three heat transfer walls were examined numerically and experimentally. The flow behavior depends on the relative temperature difference between wall and inlet fluid. The fluid near the wall flows backward to compensate the buoyancy induced flow. The size of the flow reversal increases with increase of Richardson number. In side wall heating and cooling, a swirl flow is generated longitudinally and at the cross section, several vortexes can be found. These flow behavior transports heat and affects the local heat transfer on the walls.The final report is composed of two chapters on impinging jet and mixed convection.