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Huragan w filiżance, czyli ruch trochoidalny i efekty niestabilności podczas dyfuzji kawy z mlekiem

Cielica Nina, Szymańska-Markowska Barbara

Postępy Fizyki

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2022

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T. 73, z. 1

24--29

PL

W artykule przedstawiono zjawisko dyfuzji kawy z mlekiem rozpatrzone z perspektywy dynamiki formujących się w trakcie procesu wirów. Zilustrowano je przy wykorzystaniu danych uzyskanych za pomocą kamery termowizyjnej. Pomiary pokazały zależność właściwości utworzonych wirów od czynników takich jak temperatura płynów, stosunek objętości płynów, kierunek i prędkość obrotu tarczy, na której umieszczona jest filiżanka. Na podstawie rozpoznanych efektów niestabilności stworzono symulację pokazującą w przybliżony sposób przebieg zjawiska. Analiza wskazała także podobieństwa do zjawisk w większej skali np. mechanizmu formowania huraganów.

EN

The article presents the phenomenon of milk diffusion in coffee, considered from the perspective of the dynamic of vortices forming during the process. hey are illustrated using data obtained with a thermal imaging camera. The measurements showed the dependence of vortices’ properties on the factors such as the temperature of the fluids, the volume ratio or the direction and speed of rotation of the disc on which the cup is placed. On the basis of the identified instability effects, simulation, that shows the approximate course of the phenomenon, was created. he analysis also showed similarities to larger-scale phenomena, such as the mechanism of hurricane formation.

2

Effective interfacial tension effect on the instability of streaming Rivlin-Ericksen elastico-viscous fluid flow through a porous medium

Singh M.

International Journal of Applied Mechanics and Engineering

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2016

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Vol. 21, no. 1

221--229

EN

The instability of the plane interface between two uniform, superposed and streaming Rivlin-Ericksen elastico-viscous fluids through porous media, including the ‘effective interfacial tension’ effect, is considered. In the absence of the ‘effective interfacial tension’ stability/instability of the system as well as perturbations transverse to the direction of streaming are found to be unaffected by the presence of streaming if perturbations in the direction of streaming are ignored, whereas for perturbation in all other directions, there exists instability for a certain wave number range. The ‘effective interfacial tension’ is able to suppress this Kelvin-Helmholtz instability for small wavelength perturbations, the medium porosity reduces the stability range given in terms of a difference in streaming velocities.

3

The instability of streaming viscous-viscoelastic fluids in a porous medium

Kumar P., Singh G. J.

International Journal of Applied Mechanics and Engineering

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2012

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Vol. 17, no. 1

191-201

EN

The Kelvin-Helmholtz instability of a Newtonian viscous fluid overlying a viscoelastic fluid in a porous medium is considered separately for Walters B' and Rivlin-Ericksen viscoelastic fluids. It is found that for the special case when perturbations in the directions of streaming are ignored, the system is unstable for a potentially unstable configuration and the system is stable for a potentially stable configuration for Rivlin-Ericksen viscoelastic fluids, which is in contrast to the case of the Walters B' viscoelastic fluid, where the system can be stable or unstable depending upon kinematic viscoelasticity, medium porosity, relative density of the viscoelastic fluid and medium permeability, for both potentially unstable and potentially stable configurations. In every other direction, a minimum value of wave-number has been found. The system is unstable for all wave-numbers greater than this minimum wave number.

4

Kelvin - Helmholtz instability of two superposed Oldroydian viscoelastic fluid layers in a horizontal magnetic field

Khan A., Tak S. S., Patni P.

International Journal of Applied Mechanics and Engineering

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2010

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Vol. 15, no 4

1129-1142

EN

The Kelvin-Helmholtz instability of the plane interface separating two superposed viscous electrically conducting streaming Oldroydian fluids permeated with surface tension and magnetic field in a porous medium is considered. The stability motion is also assumed to have uniform two dimensional streaming velocity. The stability analysis has been carried out for two highly viscous fluids. By applying the normal mode technique to the linearized perturbation equations, the dispersion relation has been derived. As in the case of superposed Newtonian fluids, the system is stable in the potentially stable case and unstable in the potentially unstable case, that holds also for the present case. The behavior of growth rate with respect to kinematic viscosity, elasticity, permeability of porous medium, surface tension and streaming velocity are examined numerically and discussed in detail in section 5.