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Research Interests:
The
overall focus of our research is to further the fundamental understanding
of particulate flows.
Flows involving solid particles are used
extensively in industry including areas such as
pollution control,
pharmaceuticals, energy production, and materials synthesis, and are also
found in natural environments like
landslides, avalanches, and planetary rings. However, since the
fundamental flow behavior of such systems is not well understood, the
prediction, design and operation of
related systems are often based on experience rather than on scientific
principles. As a result, processes
employing particulate flows often operate below design capacity and
exhibit undesired flow behavior. These
challenges motivate our goal to better resolve the elusive particulate
phenomena.
Research Summary:
The overall aim of
our project is to develop a mathematical model for flows composed of
a distribution of
particle sizes, and to validate the model with both experimental and
simulation data.
Flows
found in both industry (mixers, fluidized beds) and natural settings
(avalanches, motion in planetary
rings) are typically not monodisperse. The presence of a nonuniform size
distribution gives rise to de-mixing, or
segregation. Although such a phenomenon may be beneficial
to operations involving separation, it may prove detrimental if a
well-mixed system is desired, as is
common in the pharmaceutical industry. For example, a tablet is made from
two powder substances – the
medication and the binder which holds the medication together. If these
two substances are not-well mixed prior to
tablet formation, a patient may be over- or under-medicated. A
better understanding of polydisperse flows will allow for an improvement
of such existing operations and an
efficient design of new operations.
Polydispersity is well-known to
have a strong impact on the performance of fluidized, gas-solid systems.
Empirical correlations for polydisperse, fluidized beds are highly
unreliable, with typical errors between predictions and experiments on the
order of 100%. As a result, computational fluid dynamics (CFD) tools have
been identified as crucial for the improved performance of coal-based
technologies. To date, continuum models for polydisperse systems have been
largely based on ad-hoc modifications of monodisperse theory. Not
surprisingly, recent comparisons between model predictions and
experimental data indicate that such ad-hoc approaches are
inadequate.
To address the aforementioned
shortcomings, the overall aim of our work is to develop a fully-specified,
continuum, gas-solid model targeted specifically at materials with
differences in size and/or density. In particular, balance equations and
closures for both solid-solid interactions (stress, etc) and gas-solid
interaction (drag force) will be rigorously derived for polydisperse
systems. Furthermore, the impact of polydisperse on both solid-phase
instabilities (clustering) and gas-phase instabilities (turbulence) will
be probed.
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