THEORETICAL AND NUMERICAL STUDY OF THERMOMAGNETIC CONVECTION IN MAGNETIC FLUIDS

摘要: Tero Tynjala Theoretical and numerical study of thermomagnetic convection in magnetic fluids Lappeenranta 2005 95 pages Acta Universitatis Lappeenrantaensis 220 Diss. University Technology ISBN 952-214-109-7, ISSN 1456-4491 Magnetic consist particles suspended an appropriate carrier liquid. The novelty the is that fluid flow apparent properties may be controlled by external field. Since discovery unique fluids, several applications for have been considered. variety diverse, ranging from technical biomedical to scientific applications. physics a highly multi-disciplinary topic, which combines statistical mechanics magnetism with hydrodynamics. size stable varies few tens nanometers. particle range only about order magnitude larger than molecular scale. Therefore, are potential candidate currently intensively studied microfluidic nanotechnology In this thesis, field control instabilities heat mass transfer processes investigated simulations theoretical considerations. Simulation models based on finite element volume methods developed. addition standard conservation equations, inside simulation domain calculated Maxwell equations necessary terms take into account body force dissipation added governing motion. effect non-homogeneous distribution convection, carried out using both single phase two-phase mixture models. tested against available experimental results qualitatively good achieved. Detailed quantitative comparison experiments often problematic because lack information properties. Even if synthesized analyzed laboratory where performed, not monodisperse averaged mean values. Based simulations, drop aggregates, could lead experimentally observed sedimentation, was found 100 nm or larger, clearly more commonly accepted value quality. Numerical near threshold supported observations qualitatively. Near onset competitive action thermal concentration density gradients leads mostly spatiotemporally chaotic oscillatory travelling wave regimes, previously binary mixtures nematic liquid crystals. Oscillatory entire temperature region different such as spirals, targets, rolls cross-rolls, were discovered. existence large small periods typical convection. Experimentally hysteresis strong dependence measured flux prehistory alludes non-newtonian nature fluids. many including effects fields great importance. concepts used applied also studies convective ordinary well other complex