Flow regime transition criteria for upward two-phase flow in vertical rod bundles
Flow regime transition criteria for upward two-phase flow in vertical rod bundles
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DOI：
10.1016/j.ijheatmasstransfer.2016.12.029
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发表时间：
2017-05
影响因子：
5.2
通讯作者：
Hang Liu;T. Hibiki
中科院分区：
文献类型：
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作者：
Hang Liu;T. Hibiki
为了准确预测由燃料棒束组成的核反应堆堆芯或由换热管束组成的热交换器的两相流动特性，需要对流态、空隙率、传热和压降有全面的了解。相对于管道、环空和矩形通道等简单几何形状的两相流流型过渡准则的研究取得了巨大成功，垂直杆束中向上两相流流型过渡准则的研究还很有限。在垂直杆束中，由于其表面不稳定，不能存在跨越管束套管的段塞气泡，并且垂直杆束中的两相流动特征与管道、环空或矩形通道中的两相流动特征不同，后者的通道尺寸小于表面不稳定的长度尺度。本文在分析垂向杆束上向两相流动基本物理特性的基础上，提出了一种新的流型转换准则模型。最近开发的一种预测垂直杆束空隙率的可靠漂移通量相关性方法已被用于模拟流型转换准则。本研究将流型划分为气泡流、细分散气泡流、帽状气泡流、帽状湍流流、搅拌流和环空流6种不同的流型。将新开发的流型转换准则与现有的4个垂直杆束流型图进行了比较。流体系统包括空气-水和蒸汽-水。新开发的过渡准则与实测的流型图之间存在一些差异，但有相当好的一致性。
The demand of accurate prediction for two-phase flow behavior in a nuclear reactor core composed of fuel rod bundles or a heat exchanger composed of heat transfer tube bundles requires comprehensive understanding of flow regime, void fraction, heat transfer and pressure drop. In comparison with the great success in developing the two-phase flow regime transition criteria for simple geometries such as pipes, annulus and rectangular channels, limited researches have been performed for developing the flow regime transition criteria of upward two-phase flow in vertical rod bundles. In the vertical rod bundles, slug bubbles spanning the bundle casing cannot exist due to their surface instability and the two-phase flow characteristics in the vertical rod bundles are different from those in pipes, annulus or rectangular channels whose channel size are smaller than the length scale of the surface instability. This study has proposed a new flow regime transition criteria model based on the analysis on the underlying physics of the upward two-phase flow behavior in the vertical rod bundles. A reliable drift-flux correlation to predict void fraction in the vertical rod bundle developed recently has been used in modeling the flow regime transition criteria. This study has classified the flow regime into 6 distinct flow regime such as bubbly, finely dispersed bubbly, cap-bubbly, cap-turbulent, churn and annular flows. The newly developed flow regime transition criteria have been compared with existing 4 flow regime maps obtained in vertical rod bundles. The fluid systems include air-water and steam-water. A fairly good agreement with some discrepancies has been obtained between the newly developed transition criteria and the measured flow regime maps.