Coffee-making continues to be a rich source for physics insight. The roasting and brewing processes are fertile ground for chemistry, physics, and engineering. Recently, one research group has focused on the phenomenon of channeling, where water follows a preferred path through the coffee grounds rather than seeping uniformly through the grounds. Channeling reduces the amount of coffee extracted in the brew, which is both wasteful and results in a less flavorful cup. By uncovering what mechanics go into channeling, the group hopes to help baristas mitigate the undesirable process, creating a repeatable, efficient, and tasty espresso every time. (Image credit: E. Yavuz; via Ars Technica)
Tag: porous media
Engineering Our Landfills
We create a lot of waste and, at least for now, much of that waste goes into landfills. Properly managing garbage requires much more than digging a hole in the ground, as Grady from Practical Engineering shows in this video. Maintaining a landfill requires careful management of water, soil, landfill strata, and even gas buildup. And these challenges don’t end once the trucks stop arriving. Landfills require decades of care even after their closure. Check out the video to learn more about how these artificial structures are built, managed, and maintained. (Video and image credit: Practical Engineering)
Origins of Salt Polygons
Around the world, dry salt lakes are crisscrossed by thousands of meter-wide salt polygons. Although they resemble crack patterns, these structures are actually the result of convection occurring in the salty groundwater beneath the soil. I have covered the physics previously, but this new article by several of the researchers gives a behind-the-scenes glimpse of the investigation itself and how they uncovered the true explanation. (Image credit: S. Liu, see also: Physics Today)
Washing By Vortex Ring
Spraying a surface clean with a jet of fluid can be an energy-intensive operation. But a recent experiment shows that pulsed flow — which creates vortex rings — could be a viable cleaning alternative. Here we see vortex rings impacting a porous, beaded surface that’s covered in oil. Vortex rings with lots of rotation actually pass through the beads, knocking oil off both the front and back surfaces (Image 1). Even with a lower rotation rate, a vortex ring can still help clean the upper surface (Image 2). (Image and research credit: S. Jain et al.; via APS Physics)
Vietnam’s Emerald Isles
Vietnam’s HαΊ‘ Long Bay is home to more than 1,600 islands, many of them made up of mountainous limestone. The area is famous for its karst features, a type of terrain formed from highly porous, water-soluble rock. Over time, water dissolves and fractures the limestone, creating karst landscapes full of caves, springs, sinkholes, and fluted rock outcroppings. The area’s erosion also produces highly fertile soil, leading to a verdant ecosystem with many unique and endemic species. (Image credit: N. Kuring/NASA/USGS; via NASA Earth Observatory)
Groundwater-Structure Interactions
Groundwater can sometimes wind up in unexpected places, given the way it interacts with subsurface structures. In this Practical Engineering video, Grady discusses the paths that groundwater takes around structures and how civil engineers account for groundwater-related forces on dams and other buildings. As always, he illustrates with excellent model demos, allowing viewers to see groundwater interactions for themselves. (Image and video credit: Practical Engineering)
How Wells and Aquifers Work
When rain falls, some of that water turns into run-off in storm systems but much of it seeps into the ground. What happens to that water? In most places, it joins the local aquifer, infusing the spaces between soil particles underground. In this video, Grady takes us through some of the interactions between surface water, aquifers, and the wells we use to access water underground. He’s even built some great demonstrations to show how aquifers and surface water like rivers pass water back and forth. (Image and video credit: Practical Engineering)
Beijing 2022: Sliding on Snow
Skiing and snowboarding events rely on the peculiar physics of sliding on snow. According to classical lubrication theory, that sliding shouldn’t be nearly as low in friction as what we observe. The key here is that snow is soft and porous; it’s compressible, but it can also trap air (or water) in the pores between flakes. Because the passage of a skier or snowboarder is so fast, the air doesn’t have the time to slip out of the pores. Instead, it gets pressurized, providing lift that keeps the slider’s friction low. In the end, it isn’t the snow holding the slider up, it’s the air trapped in the snow beneath them! (Image credit: skier in powder – J. Andersson, snowboarder – Visit Almaty, halfpipe – P. T’Kindt; research credit: Z. Zhu et al.)
Modelling Volcanic Bombs
When magma meets water on its journey to the surface, the two form a large, partially molten chunk known as a volcanic bomb. As you would expect from their name, these bombs can often be explosive, either in the air or upon impact. But a surprising number of these bombs never explode. Since catching volcanic bombs in action is far too dangerous, researchers modeled them instead to determine what makes a dud.
The type of volcanic bomb they were most interested in comes from Surtseyan eruptions, where the bombs travel through shallow sea or lake water, collecting moisture along the way. When the water reaches the molten interior of the volcanic bomb, it flashes into steam. That’s where the pressure to explode the bombs comes from. But the team found that the bombs are also extremely porous, thanks to bubbles created as the magma depressurizes on its trip to the surface. If the bomb is porous enough, steam escapes the rock before it can build to explosive pressures. (Image credit: top – NASA, others – E. Greenbank et al.; research credit: E. Greenbank et al.; via NYTimes; submitted by Kam-Yung Soh)
Sandsculpting Bees
Building sandcastles is more than a pastime for the bumblebee-mimic digger bee. This species of bee collects water into an abdominal pouch, then uses it to wet sand to help her sculpt her nest. She’ll use the material she digs out to create a protective turret over the nest’s entrance, and once her eggs are laid and stocked with food, she’ll deconstruct the turret to rebury the nest and keep her brood safely hidden. (Image and video credit: Deep Look)
