INAUGURAL–DISSERTATION zur Erlangung der Doktorwürde der ...

5. Conclusions and Future Work
The objective of the present work is modeling and simulation of polymer or sugar solution
spray drying until the solid layer formation at the droplet surface, and dispersion
in bi-component evaporating spray flows in an Eulerian framework.
In order to understand the behavior of droplet distribution under various drying
conditions, the direct quadrature method of moments (DQMOM) is implemented, for
the first time, in two dimensions to study the bi-component evaporating spray flows. In
DQMOM, the droplet size and velocity distribution of the spray is modeled by approximating
the number density function in terms of joint radius and velocity. The DQMOM
has been extended to accommodate gas–liquid interactions such as convective droplet
evaporation, drag force and gravity as well as droplet–droplet interactions by including
coalescence. The effect of these physical processes on the evolution of droplet size
distribution and kinetic properties is analyzed and validated with the experiments.
The DQMOM simulation results are also compared with the quadrature method of
moments (QMOM) in one-dimensional configuration whereas in two-dimensional axisymmetric
configuration DQMOM is compared with discrete droplet model (DDM),
which is a well known Euler – Lagrangian approach.
First, evaporating water spray in nitrogen is modeled using DQMOM in one physical
dimension, and the simulation results are compared with QMOM. The water evaporation
is accounted through convective evaporation model of Abramzon and Sirignano,
which accounts for variable liquid and film properties. The drag and droplet coalescence
are included through appropriate sub-models. The gas phase is not yet fully coupled
with DQMOM but its inlet flow properties are used to compute droplet evaporation
and drag. The initial data to start simulations is generated from the experimental data,
which were provided by Dr. R. Wengeler, BASF Ludwigshafen. The simulation results
are validated with experiment at various cross sections. The influence of individual
physical processes is analyzed. It is demonstrated that the model reflects the evaporation
to have a pronounced effect on the parameters pertaining to droplet size. More
importantly, when evaporation is considered in combination with droplet coalescence,
the numerical results are improved significantly and show excellent agreement with
experiments. The droplet velocity is largely influenced by the drag force and gravity.
Based on the successful of implementation of DQMOM, it is then extended to model
evaporating water in air in two-dimensional, axisymmetric configuration. The same