Fundamental Physics and Chemistry Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988) / Chapter Skim
Currently Skimming:
4. Systems Far from Equilibrium
4. Systems Far from Equilibrium
Pages 77-85
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 77... ...
ICATION PATTERNS ~ dendritic crystal growth, extraneous gravitational effects obscure the underlying physics of a pattern-forrn~ng process. The term "dendrite" refers here to tree-like patterns, which are most familiar in the form of snowflakes, and which are of special technological importance because of the role they play in determining metallurgical microstructures.
|
From page 78... ...
A basic feature of dendritic solidification as it occurs under the conditions described above is that at the speed, v, at which the leading tip of the tree-like structure grows, the Julius of curvature, p, of this tip, and the spacing, A, of the first side branches that appear behind it are all well-defined, reproducible functions of only the undercooling of the fluid. Thus, the classic experunents of Glicksman and his colleagues have been aimed at measuring v, p, and A
|
From page 79... ...
SURFACE TENSION AND CONVECTION EFFECTS Surface-tension-driven phenomena arise whenever a free surface interacts with a field (temperature, magnetic, electric fields) that influences surface tension.
|
From page 80... ...
Furthermore, most measurements at such length scales are limited to global properties (average surface temperature, average heat flux, etc.~. Field information (e.g., velocimetry or thermal profiling)
|
From page 81... ...
E[ECTllOlLINETICS The subject known as electrokinetics lies at an intersection between fluid mechanics and colloid chemistry since charged interfaces with diffuse layers of space charge produce phenomena different from those encountered in traditional fluid mechanics. Motion can arise in response to an unposed electric field, as in electrophoresm and electroosmosm, or from purely mechanical forces, as in the electroviscous effects.
|
From page 82... ...
From these simple arguments we see that buoyancy-driven motion makes it difficult to observe the electrokinetic phenomena in fundamental studies, and certainly influences benefits from practical applications. Microgravity experiments enable one to avoid, or at least suppress, effects of nonelectrokinetic motions.
|
From page 83... ...
COMBUSTIBLE MEDIA The central scientific issues in combustion are: flame initiation, the characteristic temperature-composition structures of flames, flame morphology, propagation speeds, and flame existence limits. The coupling of complex chemical kinetics with fluid mechanics is a general characteristic of flames.
|
From page 84... ...
For both single- and twophase flame structures, characteristic buoyancy-~nduced flow rates of flame gases are comparable to exper~rnentally observed flame propagation rates in the neighborhood of flame extinction Innits. This results in strikingly different limiting fuel concentrations for upward and downward flame propagation in normal gravity.
|
From page 85... ...
Flame theories have been constructed for gravity-free environments, but the ingredients require careful testing even without the complication of gravity. Inasmuch as buoyancy effects at ~ g have been shows to substantiaIly distort counterflow diffusion flame structures, experiments in microgravity are needed to support these studies.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.