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Fundamental Physics and Chemistry Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988) / Chapter Skim
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5. Scaling and Acceptable Acceleration Level
Pages 86-89

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From page 86...
... But it is also due to the fact that our current detailed understanding of the scaling laws and dynamic response pertains primarily, but not exclusively, to the case of a constant, spatially homogeneous acceleration. The task group recognizes, however, that the microgravity environment is characterized by both a steady background and transient excursions in both the magnitude and orientation of the acceleration vector, and that these excursions are not necessariTy small and are potentially rich in spectral content.
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From page 87...
... The unportance of such fluid motion is measured by the magnitude of the dimensionless Grashof number, Or = ~ppl3/p~2 Thus, for sedimentation to be negligible, we must have Gr << I In this sunple example we see that lowering 9 from its normal value 90 has the identical dynamical effect as lowering the density mismatch, up between the phases, reducing the characteristic length scale, i, or raising the fluid kinematic viscosity, L,.
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From page 88...
... Sedimentation, however slow, will exert a hydrodynamic force on the particles, which, for a loose flee, will scale in the following way: F~ a,uV where a is a typical particle size, ~ is the fluid viscosity, and V is the sedimentation velocity. Furthermore, V ~ (^p/p~gl2/p so that Fin supple Knowledge of the strength of the attractive force holding the aggregate together may be used with the above estunates to set acceptable gravitational levels in order that the aggregate not be torn apart by the hydrodynamic forces.
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From page 89...
... 89 matches, levels of 10~6 to 1~6 g would allow experiments of reasonable scale to be relatively free of buoyancy-driven flows. However, the task group emphasizes that each experiment implies a separate set of requirements, and that many of them may well involve gravitational levels of substantially lower magnitude.
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Key Terms

  • acceptable acceleration
  • gravitational levels
  • fluid viscosity
  • density mismatch
  • acceleration levels

  • acceptable gravitational
  • spatial extent
  • acceleration level
  • spatially homogeneous
  • dynamic response

  • scaling laws
  • upper length
  • sedanentation velocity
  • hydrodynamic forces
  • aggregate composed

  • typical particle
  • single value
  • steady background
  • alter fluid
  • scaling behavior

  • sunple example
  • nearly neutrally
  • fin supple
  • identical dynamical
  • microgravity experiments

  • wid lead
  • dynamical effect
  • normal value
  • fractal scaling
  • neutrally buoyant


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