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Investigation of Two-Phase Flow Through Single- and Multi-Stage Orifices

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Title: Investigation of Two-Phase Flow Through Single- and Multi-Stage Orifices
Author: Almalki, Naief
Department: School of Engineering
Program: Engineering
Advisor: Ahmed, Wael
Abstract: The intent of this research is to determine the effect of single- versus two-stage orifices installed in a horizontal piping structure. A multi-channel void fraction sensor was developed to measure the instantaneous void fraction simultaneously at multiple locations to investigate the effect of orifices on the flow pattern development. Additionally, pressure measurements and flow visualizations were carried out. For a single-stage orifice, the results revealed that as the gas superficial velocity increased, the flow pattern downstream of the restriction changed to a dispersed bubbly or a liquid jet and annular-dispersed liquid for an intermittent flow upstream of the orifice. The flow pattern development along the test section was affected significantly in the region close to the orifice (1-5 Diameters), especially at a lower area ratio. An analysis of the statistical characteristics of the slug flow pattern, such as the slug velocity, the elongated bubble length, and the slug frequency, was determined from the void fraction data and then presented for different upstream flow conditions. For multi-stage orifice, the experiments suggested that restricting the flow over multiple stages, with the smaller area of the restriction in the final stage, reduced the flow separation and enhance the mixing and improve flow development downstream if the distance between orifices is optimized. Also, the total pressure drop of the two-stage orifice found to decrease as the spacing between the stages decreased especially at low gas superficial velocity. This is attributed to the ability in reducing phases defragmentation that create drastic changes in the two-phase flow pattern. Based on the present analysis, a new approach to correlate the total pressure drop was proposed and successfully implemented in order to determine the pressure drop multiplier of two-stage orifice with different spacing. The Chisholm correlation [1] was modified to account for single- and multi-stage orifices to predict the pressure drop and found to predict the experimental data within ±20%. Finally, a machine learning algorithm was also used to predict the flow pattern change downstream of the orifice that can be used for engineering design purposes.
Date: 2020-12
Rights: Attribution-NonCommercial-NoDerivatives 4.0 International
Related Publications: N. Almalki and W. H. Ahmed, "Evaluating the two-phase flow development through orifices using a synchronised multi-channel void fraction sensor," Experimental Thermal and Fluid Science, vol. 118, p. 110165.
Embargoed Until: 2021-12-08

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