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Effects of 90-deg Vertical Elbows on the Distribution of Local Two-Phase Flow Parameters

Mohan S. Yadav, Seungjin Kim

Nuclear Technology / Volume 181 / Number 1 / January 2013 / Pages 94-105

Technical Paper / Special Issue on the 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14) / Thermal Hydraulics /

The present study focuses on developing a database to investigate the effects of 90-deg vertical elbows on the transport and distribution of local two-phase flow parameters in air-water bubbly flows. The experimental facility consists of both vertical and horizontal sections made out of 50.8-mm inner diameter pipes and interconnected via 90-deg glass elbows. Six different flow conditions within or near the bubbly flow regime at the inlet are investigated in the current study. A multisensor conductivity probe is employed to measure detailed local two-phase flow parameters at ten axial locations along the test section, within which 90-deg elbows are installed at L/D = 63 and 244.7 from the inlet. The data show that the elbow makes a significant impact on the two-phase pressure drop, bubble distribution, and bubble velocity. The bubbles moving across the vertical-upward elbow are entrained along the secondary flow streamlines leading to a bimodal distribution. For the test conditions investigated in the present study, this bimodal distribution is independent of the bubble distribution upstream of the vertical-upward elbow. In the case of the vertical-downward elbow, on the other hand, the large inertia of the axial liquid flow results in the bubbles migrating toward the inside of the elbow curvature.

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