Panta Rei (#4) comes Down to Earth

Welcome to the fourth installment of Panta Rei, the blog carnival that's all about heat and fluid flow. The posts we have this round take us from outer space, down to earth, and inside our kitchen. They conclude with a simple participatory experiment, whose results you can leave in the comments.

In his series on space applications of heat transfer, Subrahmanya Katte provides Panta Rei two posts on protecting spacecraft from excess temperatures. In one, he explains why spacecraft re-entering Earth’s atmosphere do so not with a pointy, aerodynamic nose facing the Earth but with a flatter, bluff surface. This is so that the shock wave produced, which heats the air, is further away from the spacecraft itself. In the other post Katte explains why the space shuttle employs reusable tiles to protect it from the heat produced during re-entry, while spacecraft like the Apollo capsule can not.

Arunn Narasimhan, writing at TechBizMedia, proposes a scheme to increase the flow of money using a device that controls the flow of thermal energy. The composite heat sink he presents may be useful to cool on-board electronics in Indian space vehicles, among other things.

Arunn, this time writing at Nonoscience, traces the evolution of models of porous media flow from Henry Darcy, back in 1856, to the present day.

Looking a fluid flow inside porous media, like sand, is one thing. Adding macropores and plant roots is a whole new ball game. Yours Truly, here at Down to Earth, describes a phenomenon known as hydraulic lift, in which plant roots act as low-resistance tubes to allow soil water to move from wet to dry zones, without the need to move through the porous soil medium.

Alex Liberzon, of Alex’s Blog fame, uses particle image velocimetry (PIV) to illustrate the effect surfactants have on reducing drag. He also has a nice compilation of interesting flow patterns, that inspire poet and scientist alike.

The physics of fluid flow is most comprehensively embodied in the Navier-Stokes equations, but solving them can prove challenging. For anything but simple problems of fluid flow, there is no analytical solution available, and numerical solutions must be developed using computers. Working out how to solve the equations analytically, though, is a prized goal, so much so that the Clay Mathematics Institute has offered US$1 million to whoever sufficiently advances the ability to do so. About a month ago, a mathematician almost did, and blogs carried the story with gusto. Seed Magazine provides coverage of this coverage.

Gavin Schmidt, at RealClimate, draws upon an editorial by Carl Wunsch on the Gulf Stream – the oceanic current that moves northeast off the eastern coast of North America. He raises the issue because of confusion between the Gulf Stream and the Meridional Overturning Circulation (which is often conflated with the Thermohaline Circulation).

Javier Pazos, The Science Pundit, reports on a Nature article about volcanic eruptions. The focus is a curious series of events that lead to particularly explosive eruptions.

In a similar neck of the woods, an old post at Interesting Thing of the Day provides us with the basics of mantle convection.

Lastly, for the experimentalists among you lacking a personal volcano or tectonic plate, let me bring some research from Corgilabs out of the freezer. Eric brings us into his lab with a series of experiments on freezing coke in a sarcophagus. Experiments I, II, III, IV, IV-followup.

An easier kitchen-based experiment, relating to mantle convection, calls for a pot of water (copper-based pot is better), cooking oil, and a gas burner. Heat the water so convection starts, but not so much that the water starts to boil. Add oil at any time (don’t add so much as to cover even a quarter of the water surface), and watch how the convection moves the hydrophobic oil around the pot. I just tried the experiment with my electric element on my stove, but I can’t control the heat well enough – hence the gas burner. Does the oil aggregate? Do the size and number of oil aggregates fluctuate over time? How does water depth (and hence size of convective cells) affect oil dynamics? How does the temperature affect these dynamics? What happens when you add more oil? Leave results in the comments.