Convection in Ferro-Nanofluids: Experiments and Theory by Aleksandra A. Bozhko & Sergey A. Suslov

Convection in Ferro-Nanofluids: Experiments and Theory by Aleksandra A. Bozhko & Sergey A. Suslov

Author:Aleksandra A. Bozhko & Sergey A. Suslov
Language: eng
Format: epub
ISBN: 9783319944272
Publisher: Springer International Publishing


5.2 Horizontal Layer

5.2.1 Temporal Behaviour of Convection Flows

The main distinction of behaviour of colloidal fluids from their single-component counterparts contained in a layer bounded by horizontal plates is that colloid remains an “active medium” even if it is isothermal and remains at rest at a macroscopic scale. Microscopically, the continuous action of gravity on the contained solid particles and their aggregates leads to their barometric redistribution, which breaks fluid’s homogeneity. If the fluid is kept in non-isothermal conditions, the effects of gravitational sedimentation can be enhanced by thermodiffusion. The overall degree of inhomogeneity depends on the time fluid remains at macroscopic rest. Therefore, the behaviour of a colloid becomes dependent on a pre-history of experiment. We discuss this feature of ferrofluid behaviour in detail below.

Experiments have been conducted in flat cylindrical cavities of diameter d = 75 mm and thicknesses d = 2. 0, 3.5 and 5.0 mm; see Figures 4.​4 and 4.​10. The solid-phase concentration of experimental fluids varied between ϕ = 4 and 12%. The properties of ferrofluids2 are listed in Table 5.1.

Table 5.1Properties of ferrofluids and the corresponding convection threshold temperatures.



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