6. AnnularFlow_web

6. AnnularFlow_web - ENU 4134 Annular Flow D. Schubring...

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Unformatted text preview: ENU 4134 Annular Flow D. Schubring July 28, 2010 Learning Objectives I 1-f-i Characterize the various regimes of two-phase flow I 1-f-iii Identify the importance of coherent structures (waves, droplets, bubbles, etc.) in two-phase flow and in the differentiation among regimes I 1-f-v Use and critically evaluate the traditional modeling paradigm for annular flow (triangular relationship, etc.) Annular Flow Topics I Description of the flow regime. I Traditional modeling approach. I Modeling of disturbance waves. I Pressure drop modeling. I Film thickness I Film behavior (including laminar vs. turbulent). Description of Annular Flow Liquid film (base film and waves), entrained droplets Gas gas core (dominant) and entrained bubbles. Traditional Modeling Approach Triangular Relationship A relation among three parameters is asserted: I (Average) film thickness I Film flow rate (entrained fraction) I Interfacial shear stress (pressure gradient) Given any two, the third can be computed (film flow rate comes from integral y = 0 to y = in terms of shear). The link between film thickness and shear stress is termed the film roughness concept . This asserts that interfacial shear is enhanced by the film, which acts as a rough surface. Often ignored: the velocity profile within the film is not known. (Laminar vs. turbulent, unsteady vs. steady.) This an exceptionally challenging measurement. Traditional Modeling Approach Excess Liquid Concept Liquid is divided between film and entrainment. By simple mass conservation, this is zero sum more film flow rate means less entrainment.entrainment....
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6. AnnularFlow_web - ENU 4134 Annular Flow D. Schubring...

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