Theoretical studies on aerosol agglomeration processes

Dissertation

Kari Lehtinen

Research output: ThesisDissertationCollection of Articles

2 Citations (Scopus)

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 gas-to-particle 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 agglo-merates 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 languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Jokiniemi, Jorma, Supervisor, External person
  • Friedlander, Sheldon, Supervisor, External person
Award date26 Apr 1997
Place of PublicationEspoo
Publisher
Print ISBNs951-38-5047-1
Electronic ISBNs951-38-5048-X
Publication statusPublished - 1997
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

agglomeration
aerosols
theses
reactor materials
coalescing
flue gases
collisions
free jets
cleaning
charged particles
dendrites
synthesis
gases
accumulators
particulates
charging
mathematical models
polarity
penetration
reactors

Keywords

  • aerosols
  • aerosol dynamics
  • electrical agglomeration
  • agglomerates
  • particle collisions
  • coalescence
  • nanomaterials

Cite this

Lehtinen, K. (1997). Theoretical studies on aerosol agglomeration processes: Dissertation. Espoo: VTT Technical Research Centre of Finland.
Lehtinen, Kari. / Theoretical studies on aerosol agglomeration processes : Dissertation. Espoo : VTT Technical Research Centre of Finland, 1997. 45 p.
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keywords = "aerosols, aerosol dynamics, electrical agglomeration, agglomerates, particle collisions, coalescence, nanomaterials",
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note = "Project code: N7SU00189",
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Lehtinen, K 1997, 'Theoretical studies on aerosol agglomeration processes: Dissertation', Doctor Degree, Aalto University, Espoo.

Theoretical studies on aerosol agglomeration processes : Dissertation. / Lehtinen, Kari.

Espoo : VTT Technical Research Centre of Finland, 1997. 45 p.

Research output: ThesisDissertationCollection 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 gas-to-particle 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 agglo-merates 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 gas-to-particle 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 agglo-merates 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 - 951-38-5047-1

T3 - VTT Publications

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Lehtinen K. Theoretical studies on aerosol agglomeration processes: Dissertation. Espoo: VTT Technical Research Centre of Finland, 1997. 45 p.