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Experimental investigation of air–water two-phase flow through vertical 90° bend

Saidj, Faiza; Kibboua, Rachid; Azzi, Abdelwahid; Ababou, Noureddine; Azzopardi, Barry J.

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Faiza Saidj

Rachid Kibboua

Abdelwahid Azzi

Noureddine Ababou

Barry J. Azzopardi


The behaviour of two-phase air–water mixture flowing from the horizontal to the vertical through a 90° bend has been investigated experimentally. Cross sectional void fraction at nine positions, three upstream and six downstream of the bend have been measured using a conductance probe technique. The bend, manufactured from transparent acrylic resin has a diameter of 34 mm and a curvature (R/D) equal to 5. The superficial velocity of the air was varied between 0.3 and 4 m/s and that for the water between 0.21 and 0.91 m/s. The characteristics signatures of Probability Density Function (PDF), the Power Spectral Density (PSD) of the time series of cross sectionally average void fraction and visual observations have been used to characterise the flow behaviour. For the experimental conditions, plug, slug and stratified wavy flow pattern occurred in the horizontal pipe while slug and churn flow patterns were present in the vertical pipe. The void fraction increased with the gas superficial velocity. The correlation of Nicklin et al. predicted the structure velocity for the slug flow in both horizontal and vertical pipes reasonably accurately. With regards to the frequency of the periodic structures present, some conditions showed little change from upstream to downstream the bend whilst others showed an increasing in the structure frequency from horizontal to vertical pipe. The slug length increased by passing through the vertical bend.


Saidj, F., Kibboua, R., Azzi, A., Ababou, N., & Azzopardi, B. J. (2014). Experimental investigation of air–water two-phase flow through vertical 90° bend. Experimental Thermal and Fluid Science, 57,

Journal Article Type Article
Acceptance Date Apr 25, 2014
Online Publication Date May 9, 2014
Publication Date Sep 3, 2014
Deposit Date Jul 29, 2016
Publicly Available Date Jul 29, 2016
Journal Experimental Thermal and Fluid Science
Print ISSN 0894-1777
Electronic ISSN 0894-1777
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 57
Keywords 90° Bend; Two-phase flow; Void fraction; Air–water; Conductance probe; Flow pattern
Public URL
Publisher URL
Contract Date Jul 29, 2016


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