Abstract

The effect of the entrance geometry conditions on the local and average heat transfer coefficient in a rectangular channel with 45° angled ribs has been investigated. Ribs were deployed on one side only, the remaining walls of the channel being assumed smooth and unheated. The influence of entrance conditions was addressed by considering either a long ribbed unheated section or a smooth channel upstream of the ribbed heated section. As known, channels with 45° angled ribs are characterized by spanwise variations of heat transfer coefficient due to secondary flows, with high heat transfer levels close to one side and low heat transfer levels on the opposite side. Numerical results, checked against experimental data, showed that heat transfer coefficients of first modules are affected by entrance conditions, especially in the most effective heat transfer region. Regardless of entrance condition, a quasi-periodically fully developed heat transfer condition is attained only in the low heat transfer region, while elsewhere heat transfer coefficient distributions are periodic in shape but values tend to increase with the streamwise coordinate. These findings indicate that heat transfer experiments on ribbed channels should be generally accompanied by a careful description of the entrance conditions assumed in the experiments.

摘要

已经研究了入口几何条件对具有 45° 角肋的矩形通道中局部和平均传热系数的影响。肋骨仅部署在一侧，通道的其余壁被假定为光滑且未加热。通过考虑长肋未加热部分或肋加热部分上游的光滑通道来解决入口条件的影响。众所周知，具有 45° 角肋的通道的特点是由于二次流引起的传热系数在翼展方向上的变化，靠近一侧的传热水平高，而另一侧的传热水平低。与实验数据核对的数值结果表明，第一个模块的传热系数受入口条件的影响，特别是在最有效的传热区域。无论入口条件如何，仅在低传热区域达到准周期性充分发展的传热条件，而其他地方的传热系数分布在形状上是周期性的，但值倾向于随着流向坐标而增加。这些发现表明，肋状通道上的传热实验通常应该伴随着对实验中假设的入口条件的仔细描述。