Lubricated pipelining. Part 3 Stability of core-annular flow in vertical pipes

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Abstract
The stability of core-annular flow in vertical pipes is analysed using the linearized theory of stability. In previous studies instabilities due to interfacial friction, interfacial tension and Reynolds stresses in the bulk fluid were identified and associated with observed instabilities. In this study we include and analyse the effects of gravity. In one case gravity opposes and in the other aids the applied pressure gradient. Some preliminary results from our experiments are also presented. The prediction of stability for perfect core-annular flow in a carefully selected window of parameters is verified for the case of free fall in which the applied pressure gradient vanishes.