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

对热交换器用偏置翅片阵列放大模型进行了实验研究，结果表明，在自持振荡流态下，单点二阶速度互相关函数-uv^^-取正值翅片的尾流，其符号在下游翅片表面周围变为负值。这意味着在尾流中引起的不稳定流动在下游翅片周围稳定，并且动量传递在那里被抑制，这与在相同位置处发生的热传递增强相反。因此，产生了动量传递和热传递之间的差异。将二维非定常数值计算应用到同类型的流动中，分析了翅片传热增强的机理以及动量与传热过程的相异性。尾流中出现的每个反向旋转涡流将主流中的新鲜流体夹带到尾流中，并将尾流中心部分的热低速流体泵出到外部。这些可以有效加速尾流中速度缺陷和温度过高的恢复。每个涡流冲击下游翅片并对翅片表面施加“清洗作用”。这些导致翅片传热的增强。每个漩涡的洗涤作用产生了不同性。相同的数值计算适用于不同几何形状的其他类型的流动。在通道流被插入的方杆阻碍的情况下，发现了卡门涡旋的十字形运动。通过流动可视化证实这实际上发生了。杆下游产生的不稳定流动增强了壁面传热。这种传热增强的机理还与壁面附近产生的孤立涡流的冲洗作用有关。所有这些研究表明，实现间歇性涡流冲洗作用的新想法对于联合国的建模非常重要。