Effective interfacial tension induced convection (EITIC) in miscible fluids

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Conference Proceeding

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Using spinning drop tensiometry, we confirmed that an effective interfacial tension (EIT) exists between miscible fluids, which is necessarily transient. We studied glycerin and water and found that the value depends on how the drop of water is introduced into the glycerin. We developed a procedure in which the less dense fluid was introduced into the more dense fluid and then the capillary was rapidly spun up to its working value. We also studied dodecyl acrylate in poly(dodecyl acrylate) at high temperature. Using the concept of the Korteweg stress induced by concentration and temperature gradients, we show with numerical simulations that convection should occur in miscible systems with sharp but nonuniform concentration and/or temperature gradients, analogous to surface-tension induced convection in immiscible fluid layers. The parameter for the stress was estimated by comparing the Cahn-Hilliard formula for the interfacial tension to experimental data from the spinning drop tensiometer. Steady-state simulations with a variation in the width of the concentration gradient were compared to simulations for a standard immiscible interface in which the variation of interfacial tension was equivalent to the variation in EIT. The maximum velocity was within 20%. Because concentration and temperature gradients also cause buoyancy-induced convection, experiments must be performed in weightlessness. We attempted to observe convection in low g caused by a temperature gradient imposed along the interface between glycerin and water but because of the short time of low g available in our free-floating experiment, our results were inconclusive. Therefore, long term, high quality weightlessness is required to test the predictions of the modeling. © 2001 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Publication Source (Journal or Book title)

39th Aerospace Sciences Meeting and Exhibit

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