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|Title:||FLOW ACCELERATED CORROSION IN SINGLE AND DUAL S-SHAPE BENDS UNDER SINGLE AND TWO PHASE ANNULAR FLOW CONDITIONS|
|Authors:||Mazhar, Mohamed Mohamed Ahmed|
|Advisor:||Ching, C. Y.|
Cotton, J. S.
|Keywords:||flow;corrosion;erosion;mass transfer;bends;dual bends;PIV;FAC;Mechanical Engineering;Mechanical Engineering|
|Abstract:||<p>Flow Accelerated Corrosion (<em>FAC</em>) is defined as a flow enhanced mass transfer phenomenon that results in pipe wall thinning of the piping system and results in abrupt failure in some cases. <em>FAC</em> is controlled by the transport of corrosion species from the wall to the bulk fluid and is determined by the local distribution of the mass transfer coefficient. The overall objective of this research is to investigate the mass transfer in pipe bends arranged in single and dual S- shape configurations under single and annular two phase flow conditions. A novel wall dissolving mass transfer technique was developed to measure the local mass transfer distribution under a Schmidt number (<em>Sc</em>) of 1280, which mimics the level of carbon steel in water in industrial applications. Flow field measurements using Particle Image Velocimetry (<em>PIV</em>) and flow visualizations using laser induced fluorescence were performed to understand the causal relation between the mass transfer and the flow dynamics.</p> <p>The mass transfer in single 90<sup>o</sup> bends under single phase flow was measured for a range of <em>Re</em> from 40,000 to 130,000. Three regions of elevated mass transfer rates were determined in the single bend, (i) near the inlet to the bend inner wall, (ii) midway on the bend inner wall sides and (iii) near the outlet of the bend outer wall. The maximum mass transfer enhancement relative to the upstream pipe was found to occur near the outlet of the single bend outer wall and spans over the first part of the downstream pipe with a magnitude of approximately 1.8. The surface roughness of the test sections were determined at the end of each experiment and found to be in the fully rough wall region. The mass transfer coefficient at the high mass transfer locations was found to scale as <em>Re</em><sup>0.92</sup>. The maximum enhancement was found to be independent of <em>Re</em> for the range of <em>Re</em> studied here.</p> <p>For the dual S- shape bends, tests were performed for different separation distances <em>L/D</em> of 0, 1 and 5. The <em>L/D</em>=0 case were tested for a range of <em>Re</em> from 40,000 to 130,000. The maximum mass transfer enhancement relative to the upstream pipe was found to occur when there was no separation distance between the bends. This maximum occurred at the transition from the first bend outer wall to the second bend inner wall with a magnitude of approximately 3.2. The mass transfer enhancement was found to decrease when the separation distance between the two bends was increased. A second region of high mass transfer enhancement was found to occur midway on the second bend inner wall in the form of two symmetric regions shifted from the centerline with a magnitude of 2.8.</p> <p>The effect of air and water superficial velocities for annular flow in the range of <em>J<sub>v</sub></em>= 22- 29.5 m/s, and <em>J<sub>L</sub></em>= 0.17- 0.41 m/s on the mass trasnfer in single and dual S- shape bends was determined. The maximum mass transfer was found to occur midway on the centerline of the bend outer wall for the single bend case. This location corresponded to the entrained liquid droplet impingment and anticipated high velocity region due to liquid film thining. A second high mass transfer region was observed on the latter part of the bend outer wall. The effect of the air superficial velocity on the mass transfer enhancement was more significant than the effect of the water superficial velocity.</p> <p>The maximum mass transfer enhancement in the S- shape bend geometry under annular two phase flow was found to always occur on the first bend outer wall at a similar location to the single bend case. The mass transfer in the second bend was lowest for the zero separation distance between the bends, and increased with an increase in the separation distance. The maximum mass transfer in the second bend occurred near the outlet of the second bend outer wall with a magnitude of approximately 60% of that in the first bend when the separation distance was zero. The maximum mass transfer in the second bend was found to increase with an increase in separation distance to reach approximately 85% of that in the first bend for <em>L/D</em>=40. The location of the maximum region was observed to shift in the upstream direction as the separation distance was increased to approach the location of the single bend maximum near <em>L/D</em>=40.</p> <p>Flow field measurements showed matching of the areas with high mean flow velocity on the inlet portion of the single bend inner wall. The high velocity stream was observed to shift toward the outer wall near the bend outlet. Similar features were observed in the first bend of the S- shape configuration. The flow velocity increased significantly near the transition from the first bend outer wall to the second bend inner wall of the dual S-shape bend. High turbulent kinetic energy was measured near the outlet of the single bend outer wall and inner wall. Similar kinetic energy distribution was observed on the first bend of the S- shape. The turbulent kinetic energy downstream of the first bend increased to approximately twice that in the first bend and was observed to travel from the outlet of the first bend inner wall to the second bend inner wall. For two phase annular flow, the phase redistribution visualization showed liquid separation from the core flow and deposition on the bend wall. Three locations of deposition were observed (a) on the first bend outer wall near <em>ϕ</em><sub>1</sub> of 50<sup>o</sup>, (b) between the 50<sup>o</sup> and the outlet of the first bend (c) on the latter part of the second bend outer wall.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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