#multiphase

In many geophysical and metallurgical processes, there is a stage with a porous layer of liquid-infused solid known as a mushy layer. Such layers form in sea ice, in cooling metals, and even in the depths of our mantle.  (Image credit: J. Kyselica; via Physics Today) Read the full article

Pattern formation is extremely common in nature, from the dendritic growth of trees and snowflakes to the stripes of a tiger. A new paper describes how a thin layer of ice in a liquid can form labyrinthine patterns when illuminated with near-infrared light. Both the liquid and ice are maintained at a constant temperature below the melting point, but the ice absorbs the near-infrared light more effectively than the water. This means that parts of the ice that are far from the liquid warm and melt faster, creating holes that can then allow a pocket of liquid to seep in and reduce the absorption rate. The ice crystals themselves thin and expand across the surface at the expense of more holes, which eventually create larger channels that pock the ice. (Image and research credit: S. Preis et al.; via Nature; submitted by Kam-Yung Soh)

This is a bubble absorber. It’s formed from an array of three springs, seen end-on in the upper center, each of which is coated to make it superhydrophobic. The hollow interior of the springs is filled with air and ventilated to the atmosphere. As bubbles rise through the water, they contact the springs and readily coalesce with the interior gas. In the blink of an eye, the large bubble is almost completely absorbed into the thin air film that clings to the springs. Superhydrophobic arrays like these may be useful in power and life support systems that need to separate liquid and gas phases under low-gravity conditions. (Image credit: N. Pour and D. Thiessen, source)

Recently, however, scientists have begun observing these multiphase flows inside sandstone pores using x-ray imaging. They’re only able to take an image every 45 seconds or so, but even that is frequent enough to show that the flow is surprisingly unsteady. An example image is shown above. The colored areas show pores filled with nitrogen inside the rock. Brine is also being injected into the rock but not being shown. The colors indicate how connected the nitrogen-filled pores are to other pores nearby. Red areas are highly connected; blue have moderate connections; and green areas are smaller and have fewer connections. The network connections inside the rock change relatively rapidly, even with steady-state injection conditions. That varying connectivity implies that some of the injection energy is going into shifting interfaces around rather than actually moving the fluids through the pores. More work will be needed to unravel what’s really happening inside the porous network, but the results have far-reaching implications for understanding groundwater filtration, fossil fuel extraction, and, in the future, the possibility of carbon sequestration. (Image credit: C. Reynolds et al., source; submitted by Simon D.)

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