Events
Colloquium 01/31/2014 -The First Measurement of Spatially-Localized Viscous Heating |
| Time: Jan 31, 2014 (03:00 PM) |
| Location: Parker Hall Room 236 Snacks provided Allison Lab 200 @ 2:45 |
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Details: Viscous heating is ubiquitous. It is the way energy is lost by flowing liquids, for example blood flowing through a body's vessels. Viscous heating happens most intensely where there is a large gradient or shear in the fluid's velocity. While it is easy enough to heat a fluid by causing a shear flow, it is surprisingly difficult to detect a temperature increase that is localized where the shear is greatest. It is so difficult; in fact, that it seems nobody had ever reported such an experiment, according to our literature search. The reason is that most fluid substances have such a high thermal conductivity that heat is carried away too rapidly to leave a hot spot. By using an extreme substance, we have now observed such a localized heating. The substance is a strongly-coupled dusty plasma. Dusty plasmas are common in interstellar nebulae; they are a mixture of small solid particles, electrons, ions and gas. They can also be made in the laboratory by introducing polymer microspheres into a low-pressure gas that is partially ionized. The polymer microspheres are electrically levitated. Under laboratory conditions, the collection of microspheres behaves like molecules in a liquid, but with an extraordinarily low density. The radiation pressure force from a laser is used to drive a flow of the polymer microspheres, which are imaged using a high-speed video camera. |