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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

The effect of magnetic field and compressibility on the Rayleigh - Taylor instability

Vijayalakshmi A. R.

International Journal of Applied Mechanics and Engineering

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2011

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Vol. 16, no 3

899-910

EN

The Rayleigh-Taylor instability of inviscid electrically conducting compressible fluid layer of finite thickness in the presence of magnetic field has been investigated. The linear growth rate for the instability that occurs when the density in the region above the interface is greater than that of fluid below is calculated by solving the linear eigenvalue problem obtained using the normal mode analysis. This problem has been solved separately in both the regions which are filled with constant temperature ideal polytrope exponentially stratified electrically conducting fluids and the eigenfrequencies are obtained by using the kinematic and dynamic pressure matching conditions at the interface. Thus we have obtained the solution of the eigenvalue problem for the frequencies and investigated its dependence on the wave number k and other parameters. We have also obtained various limiting cases viz when the wave number k - 0 and the adiabatic index [...]. For finite y i.e., compressible fluids, it is observed that the growth rates are greater than that for the incompressible fluids. It is also observed that the growth rate decreases with magnetic field. Numerical results are obtained and the limiting cases are deduced which illustrate the importance of the general nature of the problem and the conclusions.

3

Stability of superposed viscous - viscoelastic (couple-stress) fluids in the presence of variable magnetic field through porous medium

Kumar P., Sharma P.

International Journal of Applied Mechanics and Engineering

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2008

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Vol. 13, no 3

837-845

EN

The Rayleigh-Taylor instability of a Newtonian viscous fluid overlying a couple-stress viscoelastic fluid through a porous medium is considered in the presence of a variable horizontal magnetic field. The stability analysis is carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities. For the stable configuration, the system is found to be stable or unstable under certain conditions. However, for the unstable configuration, the magnetic field has got stabilizing effects.

4

Rozpad kropel etanolu w dwutlenku węgla w stanie nadkrytycznym

Bałdyga J., Kubicki D., Smith K.

Inżynieria Chemiczna i Procesowa

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2004

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T. 25, z. 3/1

635-640

PL

Badano rozpad kropel etanolu w dwutlenku węgla w stanie nadkrytycznym w dyszy koncentrycznej wykorzystywanej do produkcji proszków metodą wytrącania. W pracy rozpatruje się dwa mechanizmy rozpadu kropel: pierwszy wynika z różnicy pomiędzy prędkościami kropel i fazy ciągłej (na granicy faz powstają niestabilności Rayleigha-Taylora), drugi - z występowania naprężeń generowanych przez fluktuacje burzliwe prędkości płynu. Wyniki obliczeń zostały porównane z wynikami doświadczeń.

EN

Breakup of ethanol droplets in the supercriticaI carbon dioxide by a twin-fluid nozzle is considered in relation to powder production. Two mechanisms of drop breakup are considered: the first resulting from the volocity difference between the drop and the continuous phase (Rayleigh-Taylor instability) and the second one resulting from the stress generated by velocity fluctuations. Model predictions are compared with experimental results.

5

Laser-produced copper plasmas

Henc-Bartolic V., Kovacevic E., Kunze H.-J., Stubicar M.

Journal of Technical Physics

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2003

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Vol. 44, no 2

153-158

EN

The Cu plasmas were produced by a ruby laser (~ 5 J, 694.3 nm, ~ 18 ns, ~140 GWcm^-2). Time-resolved spectra of the plasmas were observed in the region of 8-24 nm. The electron temperature was estimated to be about 40 eV. A small depth of the crater (~ 3 [my]m) and the surrounding ripples were observed at the Cu target surface. The trace of deposited plasma was explained as the Rayleigh-Taylor instability. Plasma was transparent to the laser beam.