Scientific and Technical Aerospace Reports Volume 39 April 6, 2001

from an isolated bubble regime to a coalesced bubble regime in boiling occurs at a superheat of about 14 C on Cu-Gr surface and
19 C on Al-Gr surface.
Author (revised)
Heat Transfer; Nucleate Boiling; Mathematical Models; Microgravity; Metal Matrix Composites; Metal Surfaces
20010024997 Michigan Univ., Dept. of Mechanical Engineering and Applied Mechanics, Ann Arbor, MI USA
Thermocapillary Migration of Bubbles
Esmaeeli, Asghar, Michigan Univ., USA; Arpaci, Vedat, Michigan Univ., USA; Proceedings of the Fifth Microgravity Fluid Physics
and Transport Phenomena Conference; December 2000, pp. 1462-1474; In English; See also 20010024890; No Copyright;
Avail: CASI; A03, Hardcopy; A10, Microfiche
We use direct numerical simulation to investigate motion of a few two- and three-dimensional bubbles at O Reynolds and
Marangoni numbers due to thermocapillarity. The full Navier-Stokes and energy equations for the flows inside and outside the
bubbles are solved using a front tracking/finite difference technique which accounts for the bubble deformation. The nondimensional
parameters that govern the problem are Marangoni number; Ma, Reynolds number; Re, Capillary number; Ca, volume fraction;
alpha, and the ratios of the material properties of the fluid inside the bubbles and the ambient fluid. Our goal is to investigate
the collective behavior of large systems of bubbles. We are primarily concerned with the effect of the microstructural mechanics
on the macroscopic properties of the flow. However, the computations are limited by the high expenses of the three-dimensional
simulations as the grid resolution increases. As a compromise between our goal and the expenses, we have chosen to reduce one
of the dimensions of the system in most of our computations, therefore, to study large two-dimensional systems (up to 120
bubbles). Although this reduction in dimensions seems to raise some questions on relevance of the results, comparison of motion
of solitary bubbles in two and three dimensions at the same volume fractions (keeping all the other nondimensional numbers the
same) reveals that the migration velocities have small differences during the relaxation period and are very close at steady state.
As the bubbles migrate, they interact with each other and the flow. Interesting phenomena such as pairing and tripling of the
bubbles and formation of horizontal layers of bubbles are observed.
Author (revised)
Bubbles; Direct Numerical Simulation; Thermocapillary Migration; Three Dimensional Models; Microstructure
20010024998 DynaFlow, Inc., Fulton, MD USA
Determination of the Accommodation Coefficient Using Vapor-Gas Bubble Dynamics in an Acoustic Field
Gumerov, N., DynaFlow, Inc., USA; Hsiao, C.-T., DynaFlow, Inc., USA; Goumilevski, A., DynaFlow, Inc., USA; Proceedings
of the Fifth Microgravity Fluid Physics and Transport Phenomena Conference; December 2000, pp. 1475-1477; In English; See
also 20010024890; No Copyright; Abstract Only; Available from CASI only as part of the entire parent document
Nonequilibrium liquid/vapor phase transformations can occur in superheated or subcooled liquids in fast processes such as
in evaporation in a vacuum, in processing of molten metals, and in vapor explosions. The rate (xi) at which such a phase transformation
occurs can be described by the Hertz-Knudsen-Langmuir formula. Our preliminary study showed that in certain range
of parameters the dynamics of the bubble in an acoustic field strongly depends on the value of the accommodation coefficient.
It is known that at temperatures close to the saturation temperature small vapor bubbles grow in a liquid under the action of an
acoustic field due to nonlinear effects called ”rectified heat transfer”. This is particularly true of the bubble average radius in isotropic
acoustic fields and of the bubble motion in standing waves. This finding can be used as the basis for an effective measurement
technique of this coefficient. During the current effort the model and theory were substantially extended. We developed a
theory of vapor bubble behavior in an isotropic acoustic wave and in a plane standing acoustic wave including physical effects
such as liquid inertia, heat transfer inside and outside the bubble, surface tension, diffusion of the inert gas inside and outside the
bubble, the Soret and Dufour effects in the gas phase, liquid viscosity and compressibility, and nonequilibrium phase transitions
in two-component systems. A numerical code was developed which enables simulation of a variety of experimental situations
and accurately takes into account slowly evolving temperature. Using the theory and computational tools developed we performed
a parametric study, which showed that the measurement of beta can be made over a much broader range of frequencies and bubble
sizes than it is commonly thought. We found several interesting regimes and conditions that can be efficiently used for measurements
of beta, including steady fast oscillations of the bubble radius, low frequency oscillations of the mean bubble size/position
and bubble growth/shrinkage near threshold and resonance values. Our results show that measurements of beta can be performed
both in a reduced gravity environment and in a normal gravity environment.
Author (revised)
Accommodation Coefficient; Bubbles; Liquid-Vapor Interfaces; Acoustics; Sound Fields; Fluid Dynamics
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