et al. . "> The convection in the right column is much stronger than the one on the left. The…
The convection in the right column is much stronger than the one on the left. The experiments (top) show that the convective pattern is rough in larger grain size (right), while the classical studies (middle) generally predict the opposite. After considering the effect of mechanical dispersion, the new simulation results (bottom) match the experimental observations. Credit: Liang et al. .
When Yu “Alex” Liang started at elementary school at the University of Texas in Austin, he was tasked to drive a straightforward attempt to gather data on a well-understood phenomenon in fluid mechanics: how density differences affect fluid flow in a porous medium.
It is a scenario that spans a wide range of scientific issues. In fact, Liang planned to apply experimental data to a major project on carbon dioxide binding. However, the experiment revealed that the physique that controls the flow was not as determined as scientists thought.
The findings showed that the primary driver of this type of fluid flow-called solutic convection ̵
1; had been overlooked. What’s more, when this driver is ready for it, it fully meets the expected flow results.
“To a degree, it’s a game exchange,” said Liang, who received his doctoral dissertation. in petroleum engineering 2017 and is now working for Hilcorp, a Houston-based energy company. “Our experiments and simulations show that the convective pattern is governed by a process other than the one who previously believed. People will realize that there are much more in-depth theories to explore around solar convection in porous media.”
The results of Liang’s research were published in the journal Geophysical Researcher Letters in September. His co-author includes Marc Hesse, Associate Professor at UT Jackson School of Geosciences and Institute of Computational Engineering and Sciences (ICES), David DiCarlo, Associate Professor at UT Hildebrands Department of Oil and Geosystem Engineering, and Baole Wen, a postdoctor at Jackson School and ICES. DiCarlo and Hesse are Liang’s Ph.D. advisor.
For decades, it has been the scientific consensus that the balance between density driven currents and diffusion was the primary factor controlling solar convection in porous media. Thinking went: areas of dense fluid move downward until diffusion eliminates the density difference that drives the flow and creates dense fingers that fall to the bottom. In general, the fingers must be far enough away so that diffusion can not melt them when the fluid drops. Therefore, the fingers were generally taken farther apart in slow flow and closer to each other in fast flow driven by greater density differences.
Although the pattern was well established in computer simulations, Hesse said the research team could not find experimental results showing this basic behavior. Then they developed a simple table top – a transparent tank filled with glass beads and water – to observe solut convection in real time. To start the convection process, the water was toppled with a layer of methanol and ethylene glycol – a mixture that is generally less dense than water, but gradually becomes denser and decreases as it undergoes convection with the water at the liquid interface.  The team expected the classic slim finger pattern to appear in experiments using larger diameter beads. Instead, the complete opposite pattern emerged. Finger distance increased with pearl size.
“Here are the basic phenomena that occur in all sorts of applications, a classic example of pattern formation – and you do the experiments and you literally oppose what everyone expects,” said Hesse. “This shows that something is completely gone in our basic understanding of this process.”
A deeper analysis showed that the dispersion created from larger diameter beads had a greater impact on the convective environment than diffusion. While earlier theories of solutal convection emphasize diffusion, the dispersion of the material in the water in their experiments was shown to be controlled by mechanical dispersion, which leads to further mixing of the fluids at the pore scale.
“In other words, what you’re streaming through is really important,” he said. “The dispersion gets bigger with increasing grain size, and that’s why your fingers grow wider as you do with larger pearls.”
Based on their observations of the table experiment, researchers were able to replicate their findings with a computational model.
“The most important point is that we analyze the effect of the underground convection effect based on our experimental data, then use high-resolution numerical simulations to verify our analysis,” said Wen.
Of course, the natural world is much more complex than a tank filled with beads or a simplified model. The researchers said that researchers have many factors to consider when investigating complex phenomena that involve soluting convection, such as carbon dioxide evolution. But DiCarlo said that these results show that researchers studying the process’s basic processes have some new factors to consider.
“The work shows that if you want to predict how carbon dioxide dissolves in the underground or similar dissolution process, the study needs to include dispersion correctly,” he said. “All previous studies have ignored dispersion.”
Hesse added that the experimental results can help to increase a reality dose to calculation models that have been wrong for decades.
“If your numerical simulation can not even simulate this simple experiment I do, what confidence do you think will make it right in an even more complicated environment,” he says.
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Yu Liang et al. Effect of dispersion on solute convection in porous media, Geophysical Research Letter (2018). DOI: 10,1029 / 2018GL079849