Scientific and Technical Aerospace Reports Volume 39 April 6, 2001

we concluded that this too fast kinetics was a result of a breakdown of the SE as the system became concentrated, i.e., as the gel
point was approached. The goal of our present work is to understand aggregation kinetics when a particulate system becomes concentrated.
Aerosols are the ideal system for such a study because, unlike colloids, there are no solvent mediate effects influencing
the particles. Moreover, this allows us to make direct comparison between experiment and simulation. We are currently advancing
our work on three fronts: (1) further studies of acetylene soot formation, (2) aggregation in dense TiO2 aerosols, and (3) large-scale
simulation of diffusion-limited cluster aggregation in both two and three dimensional systems. Our preliminary simulations suggest
that a fast aggregation kinetics takes place for concentrated systems, while for dilute system the aggregation kinetics is consistent
with a mean-field kinetic theory. Understanding this fast kinetics in dense systems and the corresponding breakdown of the
mean-field theory is the main motivation for the theoretical research.
Author (revised)
Aerosols; Soot; Gelation; Kinetics
20010024948 Georgia Inst. of Tech., School of Mechanical Engineering, Atlanta, GA USA
Novel Optical Diagnostic Techniques for Studying Particle Deposition Upon Large Cylinders in a Sheared Suspension
Yoda, M., Georgia Inst. of Tech., USA; Bailey, B. C., Georgia Inst. of Tech., USA; Proceedings of the Fifth Microgravity Fluid
Physics and Transport Phenomena Conference; December 2000, pp. 1148-1158; In English; See also 20010024890; No Copyright;
Avail: CASI; A03, Hardcopy; A10, Microfiche
On a twelve-month voyage to Mars, one astronaut will require at least two tons of potable water and two tons of pure oxygen.
Efficient, reliable fluid reclamation is therefore necessary for manned space exploration. Space habitats require a compact, flexible,
and robust apparatus capable of solid-fluid mechanical separation over a wide range of fluid and particle densities and particle
sizes. In space, centrifugal filtration, where particles suspended in fluid are captured by rotating fixed-fiber mat filters, is a logical
candidate for mechanical separation. Non-colloidal particles are deposited on the fibers due to inertial impaction or direct interception.
Since rotation rates are easily adjustable, inertial effects are the most practical way to control separation rates for a wide variety
of multiphase mixtures in variable gravity environments. Understanding how fluid inertia and differential fluid-particle inertia,
characterized by the Reynolds and Stokes numbers, respectively, affect deposition is critical in optimizing filtration in a microgravity
environment. This work will develop non-intrusive optical diagnostic techniques for directly visualizing where and when
non-colloidal particles deposit upon, or contact, solid surfaces: ’particle proximity sensors’. to model particle deposition upon
a single filter fiber, these sensors will be used in ground-based experiments to study particle dynamics as in the vicinity of a large
(compared with the particles) cylinder in a simply sheared (i.e., linearly-varying, zero-mean velocity profile) neutrally-buoyant,
refractive-index matched solid-liquid suspension.
Author (revised)
Fluid-Solid Interactions; Filtration; Detection; Deposition
20010024949 Johns Hopkins Univ., Dept. of Chemical Engineering, Baltimore, MD USA
Effect of Pressure on Microstructure of C12E5/n-Octane-in-D2O Microemulsions
Ferdinand, S., Johns Hopkins Univ., USA; Bossev, D., Johns Hopkins Univ., USA; Paulaitis, M. E., Johns Hopkins Univ., USA;
Proceedings of the Fifth Microgravity Fluid Physics and Transport Phenomena Conference; December 2000, pp. 1159-1167; In
English; See also 20010024890; No Copyright; Avail: CASI; A02, Hardcopy; A10, Microfiche
Forced Rayleigh scattering was used to measure the self-diffusion coefficients of oil droplets dispersed in a water-continuous
phase of the C12E5/n-octane-in-D2O microemulsion at atmospheric pressure as a function of temperature from 17.34 to 24.55
C, and at 26.2 C as a function of pressure up to 534 bar. Droplet self-diffusion coefficients were found to decrease by a factor of
two with increasing temperature from the emulsification failure boundary to the phase boundary for this phase and the lamellar
phase. This decrease is attributed to a reduction in the spontaneous curvature of the oil/water interface, leading to a transition from
spherical to larger non-spherical oil droplets in water with increasing temperature. The effect of increasing pressure, like decreasing
temperature, leads to a comparable increase the oil droplet self-diffusion coefficients, which is attributed to an increase in the
spontaneous curvature of the oil/water interface, and a transition from non-spherical to smaller spherical oil droplets in water. We
conclude from these results that the spontaneous curvature of the oil/water interface is sensitive to pressure, with increasing curvature
corresponding to increasing pressure. This conclusion is consistent with the observed pressure-induced sequence of phase
transitions observed for mixtures of C(sub i)E(sub j) surfactants, liquid alkanes, and water. These results motivate further studies
to determine the extent to which pressure will stabilize certain morphologies that can be used as organic templates for inorganic
polymerizations in the aqueous phase. The use of oil-in-water microemulsions takes advantage of the fact that the oil phase is
compressible, and as such, pressure can control microstructure during the synthesis reaction. by uncoupling self-assembly from
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