TED-AJ03-382 AN ANALYTICAL APPROACH TO BUBBLY/SLUG FLOW REGIME MODELING USING A MULTI-FIELD, TWO-FLUID MODEL :

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The prediction of flow character and heat transfer properties in gas/liquid (either air/water or vapor/liquid) flow is difficult. Early approaches used the concept of a flow regime map, essentially an empirical rule for determining whether the flow will consist of small spherical bubbles, larger deformed bubbles (either spherical caps or elliptical), Taylor bubbles, or a droplet-laden gas core surrounded by liquid annulus (i.e., annular flow). Two theoretical approaches in the literature which are concerned with flow regimes are instability theory and the interfacial area density transport theory. In this paper, we shall present and analyze a model that predicts some of the most important features of the bubbly/slug flow regime transition. In this transition, small spherical bubbles in sufficient concentration cause coalescence to occur. Subsequently, the coalesced bubbles may be broken into smaller bubbles by turbulence or interfacial instabilities. We model this process by describing three fields : the dispersed vapor, or small bubbles; the continuous liquid carrying the small bubbles; the continuous liquid carrying the small bubbles, and the continuous vapor, which here refers to Taylor bubbles or large bubble clusters. We restrict this model to fully developed flow in a channel, and solve the resulting system of equations describing the velocity and volume fraction profiles. By requiring that the overall production of continuous vapor by coalescence balance the overall production of small bubbles by breakup, we obtain volume fraction profiles that result from the distribution of total vapor into the continuous and dispersed vapor fields.

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