Mechanism of Unsteady Flow Heat Transfer and Its Modelling

非定常流动传热机理及其建模

基本信息

批准号：
03452129
负责人：
SUZUKI Kenjiro
金额：
$ 4.42万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1993
项目状态：
已结题

项目摘要

Experimental study was made for an enlarged model of offset fin array to be used in heat exchagers and it reveals that, under self-sustained oscillation flow regime, one-point second-order velocity cross-correlation -uv^^- takes positive value in the wakes of fins and that its sign becomes negative around the downstream fin surface. This means that unstable flow induced in the wake is stabilized around the downstream fin and that momentum transfer is suppressed there in contranst with the heat transfer enchancement occuring at the same positions. Therefore, dissimilarity between momentum transfer and heat transfer is generated. Two-dimensional unsteady numerical computation was applied to the same type of flow of and was used to analyze the mechanism of the enchancement of fin heat transfer and of the dissimilarity between momentum and heat transfer processes. Each of counter-rotating vortices appearing in the wake entrains fresh fluid from main stream into the wake and pumps out the hot and low-speed fluid from the central part of the wake to the outside. These are effective to accelerate the recovery of the velocity defect and temperature excess int the wake. Each vortex hits the downstream fin and exerts "washing action" to the fin surface. These result in the enhancement of fin heat transfer. The washing action of each vortex produces the dissimilarity. The same numerical computation was applied to other types of flows of different geometries. In the case of channel flow obstructed by an inserted square rod, crisscross motion of Karman vortex was found. This was confirmed to actually occur through flow visualization. Unsteady flow incurred downstream of the rod enhances the wall heat transfer. The mechanism of this heat transfer enhancement is also related to the washing action of an isolated vortex produced near the wall. All these studies suggest that new idea of implementing the intermittent, washing action of vortex is important in the modelling of un

进行了实验研究，用于用于热交换器中的偏移鳍阵列的扩大模型，它揭示，在自我维持的振荡流程下，一分二阶速度交叉相交-UV ^^ - 在鳍片中呈正值，并且其符号在下游鳍片周围是负的。这意味着在尾流中引起的不稳定流动在下游鳍周围稳定，并且这种动量转移在那里被抑制在同一位置上发生的传热增强剂。因此，产生动量转移和传热之间的差异。将二维不稳定的数值计算应用于相同类型的流量，并用于分析鳍传热的结合和动量和热传递过程之间的差异。每个反向旋转的涡流都出现在尾流中的新鲜流体中，从主流进入尾流，并从尾流的中部到外部将热和低速流体抽出。这些是有效的，可以加速速度缺陷和温度过高的唤醒的恢复。每个涡流都击中下游鳍，并将“洗涤动作”施加到鳍片表面。这些导致鳍传热的增强。每个涡流的洗涤作用会产生差异。将相同的数值计算应用于不同几何形状的其他类型的流。在被插入的方杆阻塞的通道流动的情况下，发现了卡尔曼涡流的纵横运动。这是通过流动可视化实际发生的。杆下游产生的不稳定流量增强了壁热。这种传热增强的机制也与墙附近产生的孤立涡流的洗涤作用有关。所有这些研究表明，实施间歇性，涡流的洗涤作用的新想法在联合国建模中很重要