Mass transfer measurements on periodic roughness in a circular pipe and downstream of orifice
Mass transfer measurements on periodic roughness in a circular pipe and downstream of orifice
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DOI：
10.1016/j.ijheatmasstransfer.2016.10.002
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发表时间：
2017-02
影响因子：
5.2
通讯作者：
N. Fujisawa;Kazuya Uchiyama;T. Yamagata
中科院分区：
文献类型：
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作者：
N. Fujisawa;Kazuya Uchiyama;T. Yamagata
本文研究了周期性粗糙度下圆管内及孔板下游的传质特性。采用石膏溶解法测定了不同粗糙度和周期性粗糙度波长组合下粗糙管相对于光滑管的传质强化比，并对粗糙度对传质强化的影响进行了实验研究。周期性粗糙度对传质的增强作用随着粗糙度参数的增大而显著增强，粗糙度参数由粗糙度高度与波长的比值定义。结果表明，粗糙管的传质强化效果是光滑管的2倍以上，这是由于周期性粗糙表面形成了局部回流区。另一方面，观察到较小的传质增强上的流下游的孔。采用低雷诺数k-ε模型对周期性粗糙面及孔口下游的流动和传质进行了数值模拟。结果表明，周期性粗糙度上局部回流区的形成是粗糙管上传质强化的主要来源，而孔板下游较小的传质强化则是源于孔板边缘的壁面分离剪切层的作用，其作用大于孔板下游周期性粗糙度上局部回流区的作用.
This paper describes the mass transfer characteristics on periodic roughness in a circular pipe and that downstream of an orifice. The mass transfer enhancement ratio of the rough pipe with respect to the smooth pipe are measured by the plaster dissolution method for various combinations of roughness height and wavelength of the periodic roughness, and the influence of roughness on the mass transfer enhancement is examined experimentally. The mass transfer enhancement on periodic roughness is highly increased with increasing the roughness parameter, defined by the roughness height to the wavelength. It is found that the mass transfer enhancement of rough pipe is more than 2 times larger than that of the smooth pipe, which is due to the formation of the local recirculating region over the periodic roughness. On the other hand, minor mass transfer enhancement is observed on the flow downstream of an orifice. The examination of the flow and mass transfer over the periodic roughness and that downstream of orifice is carried out by the numerical simulation with low-Reynolds numberk–εmodel. The result indicates that the formation of local recirculating region on the periodic roughness is the major source of mass transfer enhancement on the rough pipe, while the minor mass transfer enhancement downstream of the orifice is attributed to the effect of separating shear layer originating from the orifice edge on the wall, which is dominant over the local effect of recirculating flow on the periodic roughness downstream of the orifice.