Category: turbulence

Chemical Turbulence : Belousov Zhabotinsky reaction Typically…

Chemical Turbulence : Belousov Zhabotinsky reaction

Typically one thinks about chemical reactions as walking down a straight path from home to destination.

A + B —-> C ( A reacts with B to give C). 

But this necessarily need not be true:

In a class of reactions known as Belousov–Zhabotinsky reaction, or BZ reaction. the reactions undergo a chaotic oscillating behavior for a substantial amount of time before they end up at the final product C .

Oxidation waves

It was observed in 1970 by Zaikin and Zhabotinsky that by using a thin
layer of unstirred solution with the ferroin-catalyzed BZ
reaction one could observe periodic propagation of
concentric chemical waves from point sources.

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The Belousov-Zhabotinsky oscillator reaction is known for the striking oxidation
waves that it produces.

In the above animation you can see symmetrical circular wave fronts being generated, but when the concentration parameters are tweaked it is possible to observe spiral waves as well.

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And when one propagating wave meets another, they mutually annihilate each other.

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One important note concerning this reaction is that this chaotic oscillating behavior that one observes does not last forever and dies out eventually.       

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                                     Source Video by nater06      

Another reaction that is analogous to the BZ reaction is the Briggs–Rauscher reaction (see below)

Simulating the BZ reaction

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Some of the  essential features of this reaction can be captured in a simple reaction model
involving three chemical substrate.

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The simulations are able to go so far as to predict the spirals and waves that one observes during the reaction.

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But the complete model for this nonlinear chemical oscillator is not entirely known and still remains a mystery..

References:

[1] The Belousov-Zhabotinsky Oscillator: An overview

[2] Ways in which the BZ reaction is studied

[3] Belousov-Zhabotinsky reaction on Scholarpedia

[4] A simple model of the BZ reaction from first principles.

The Earliest Galaxies Spin Just Like Our Milky…

The Earliest Galaxies Spin Just Like Our Milky Way, Defying Expectations

“As our data sets improve, we should begin to measure the internal motions of large numbers of galaxies like this, which will answer many questions and raise others. Do most/all galaxies at these early stages rotate in a whirlpool-like plane? Is there a variety and multiple sets of populations that exhibit different behaviors? What are the actual effects of gas infall, supernovae, and small-scale motions? What is the velocity profile of these rotation curves, and can they teach us anything about the interplay of radiation, normal matter, and dark matter?

While we hope to learn these answers, we can now ask these questions sensibly in the aftermath of having measured the movement and internal motions of a galaxy so far away. At least for the first two, they rotate very similarly to their much older cousins, a quite unexpected result. Thanks to ALMA, we’re taking those coveted next steps into the final frontier.”

It wasn’t supposed to be this way. When you form galaxies in the very young Universe, it’s supposed to be a chaotic, turbulent place. Sure, you have gravitation, pulling matter in and creating a pancake-like shape. But then you form stars, and everything goes haywire. Supernovae go off, gas falls in, protogalaxies merge and get swallowed, motions get stirred up, and turbulence should permeate the galaxy. It ought to take billions of years for them to quiet down into a Milky Way-like whirlpool. Well, for the first time, owing to ALMA and Renske Smit’s team, the internal motions of galaxies less than a billion years old were measured, and – surprise! – their movement is smooth and not chaotic at all.

They’re less than a billion years old. And, thanks to ALMA observing them, they might finally pave the way to understand how galaxies form altogether.

The meeting of land and sea often creates a rich and colorful…

The meeting of land and sea often creates a rich and colorful environment. This satellite image shows Mexico’s Laguna de Términos, a coastal lagoon off the Gulf of Mexico. A skinny barrier island forms the lagoon’s two connections to the ocean; the eastern side is the usual inlet (right), while the western side forms an outlet. Rivers feed freshwater into the lagoon from the south and southwest. These introduce sediments that cause some of the lighter swirls in the image. Winds and tides also contribute to this turbidity. The sheltered nature of the lagoon allows fresh and salt water to mix gradually, providing harbor for many forms of life. Oyster beds thrive in the river mouths; seagrasses prefer the calmer, saltier waters, and mangrove trees line the shore, slowly desalinating water for themselves as their roots shelter young fish and shrimp. (Image credit: NASA Earth Observatory)

Two-phase flows involve more than one state of matter – in…

Two-phase flows involve more than one state of matter – in this case, both gas and liquid phases. Flows like this are common, especially in applications involving heat transfer. In some heat exchangers, bubbles will rise and then slide along an inclined surface, as shown above. The motion of these bubbles is a complicated interplay between the surface, the bubble, and the surrounding fluid. The bubble’s wake, visualized here using schlieren imaging, is unsteady and turbulent. Although the bubble oscillates in its path, the wake spreads even wider, and its turbulence stirs up the liquid nearby, increasing the heat transfer. (Image and research credit: R. O’Reilly Meehan et al., source)

Combustion is complicated. You’ve ideally got turbulent flow,…

Combustion is complicated. You’ve ideally got turbulent flow, acoustic waves, and chemistry all happening at once. With so much going on, it’s a challenge to sort out the physics that makes one ignition attempt work while another fails. The animations here show a numerical simulation of combustion in a turbulent mixing layer. The grayscale indicates density contours of a hydrogen-air mixture. The top layer is moving left to right, and the lower layer moves right to left. This sets up some very turbulent mixing, visible in middle as multi-scale eddies turning over on one another. 

Ignition starts near the center in each simulation, sending out a blast wave due to the sudden energy release. Flames are shown in yellow and red. As the flow catches fire, more blast waves appear and reflect. But while the combustion is sustained in the upper simulation, the flame is extinguished by turbulence in the lower one. This illustrates another challenge engineers face: turbulence is necessary to mix the fuel and oxidizer, but turbulence in the wrong place at the wrong time can put out an engine. (Image, research, and submission credit: J. Capecelatro, sources 1, 2)

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