Abstract
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) 
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Keywords
 aerosols
 aerosol dynamics
 electrical agglomeration
 agglomerates
 particle collisions
 coalescence
 nanomaterials
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Theoretical studies on aerosol agglomeration processes : Dissertation. / Lehtinen, Kari.
Espoo : VTT Technical Research Centre of Finland, 1997. 45 p.Research output: Thesis › Dissertation › Collection of Articles
TY  THES
T1  Theoretical studies on aerosol agglomeration processes
T2  Dissertation
AU  Lehtinen, Kari
N1  Project code: N7SU00189
PY  1997
Y1  1997
N2  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.
AB  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.
KW  aerosols
KW  aerosol dynamics
KW  electrical agglomeration
KW  agglomerates
KW  particle collisions
KW  coalescence
KW  nanomaterials
M3  Dissertation
SN  9513850471
T3  VTT Publications
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 