In the recent years, researchers have discovered a multitude of applications
using nanofibers in fields like composites, biotechnology, environmental engineering,
defense, optics and electronics. This increase in nanofiber applications needs
a higher rate of nanofiber production. Electrospinning has proven to be the best
nanofiber manufacturing process because of simplicity and material compatibility.
Study of effects of various electrospinning parameters is important to improve the
rate of nanofiber processing. In addition, several applications demand well-oriented
nanofibers. Researchers have experimentally tried to control the nanofibers using
secondary external electric field. In the first study, the electrospinning process is
modeled and the bending instability of a viscoelastic jet is simulated. For this, the
existing discrete bead model is modified and the results are compared, qualitatively,
with previous works in literature. In this study, an attempt is also made to simulate
the effect of secondary electric field on electrospinning process and whipping instability.
It is observed that the external secondary field unwinds the jet spirals, reduces
the whipping instability and increases the tension in the fiber. Lattice Boltzmann method (LBM) has gained popularity in the past decade as
the method is easy implement and can also be parallelized. In the second part of this
thesis, a hybrid numerical scheme which couples lattice Boltzmann method with finite
difference method for a Oldroyd-B viscoelastic solution is proposed. In this scheme,
the polymer viscoelastic stress tensor is included in the equilibrium distribution function
and the distribution function is updated using SRT-LBE model. Then, the local
velocities from the distribution function are evaluated. These local velocities are used
to evaluate local velocity gradients using a central difference method in space. Next,
a forward difference scheme in time is used on the Maxwell Upper Convected model
and the viscoelastic stress tensor is updated. Finally, using the proposed numerical
method start-up Couette flow problem for Re = 0.5 and We = 1.1, is simulated. The
velocity and stress results from these simulations agree very well with the analytical
solutions.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1347 |
| Date | 15 May 2009 |
| Creators | Karra, Satish |
| Contributors | Girimaji, Sharath, Srinivasa, Arun R. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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