Abstract
In this thesis, theoretical modeling of certain aerosol
systems has been presented. At first, the aerosol general
dynamic equation is introduced, along with a
discretization routine for its numerical solution. Of the
various possible phenomena affecting aerosol behaviour,
this work is mostly focused on aerosol agglomeration. The
fundamentals of aerosol agglomeration theory are thus
briefly reviewed. The two practical applications of
agglomeration studied in this thesis are flue gas
cleaning using an electrical agglomerator and
nanomaterial synthesis with a free jet reactor.
In an electrical agglomerator the aerosol particles are
charged and brought into an alternating electric field.
The aim is to remove submicron particles from flue gases
by collisions with larger particles before conventional
gas cleaning devices that have a clear penetration window
in the problematic 0.1  1 mm size range. A mathematical
model was constructed to find out the effects of the
different system parameters on the agglomerator s
performance. A crucial part of this task was finding out
the collision efficiencies of particles of varying size
and charge. The original idea was to use unipolar
charging of the particles, and a laboratory scale
apparatus was constructed for this purpose. Both theory
and experiments clearly show that significant removal of
submicron particles can not be achieved by such an
arrangement. The theoretical analysis further shows that
if the submicron particles and the large collector
particles were charged with opposite polarity,
significant removal of the submicron particles could be
obtained.
The second application of agglomeration considered in
this thesis is predicting/controlling nanoparticle size
in the gastoparticle aerosol route to material
synthesis. In a typical material reactor, a precursor
vapor reacts to form molecules of the desired material.
In a cooling environment, a particulate phase forms, the
dynamics of which are determined by the rates of
collisions and coalescence. In the thesis, it is first
theoretically demonstrated how the onset of dendrite
formation and primary particle size can be predicted by
studying the characteristic time scales of collision and
coalescence. Then it is shown how the linear rate law for
coalescence can be approximately applied to agglomerate
structures by dividing the agglomerates into sections.
The developed models are then applied to a free jet
material reactor. From the comparisons between theory and
experiment it is obvious that such a model is able to
capture the effects of the system parameters
(temperature, velocity, volume loading of material and
location of collection) on the primary particle size of
the produced material.
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  26 Apr 1997 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9513850471 
Electronic ISBNs  951385048X 
Publication status  Published  1997 
MoE publication type  G5 Doctoral dissertation (article) 
Keywords
 aerosols
 aerosol dynamics
 electrical agglomeration
 agglomerates
 particle collisions
 coalescence
 nanomaterials
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Lehtinen, K. (1997). Theoretical studies on aerosol agglomeration processes: Dissertation. VTT Technical Research Centre of Finland. http://www.vtt.fi/inf/pdf/publications/1997/p304.pdf