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Particle shape effects on gas-solid reactions

Citation

Choi, Moon Kyu (1992) Particle shape effects on gas-solid reactions. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-07232007-152302

Abstract

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A theoretical study of the reaction of nonspherical particles is carried out in the shrinking core regime to determine the effect of particle shape on total reaction rate, particle temperature, and to characterize the evolution of shape with consumption of particle. This problem involves the solution of the external diffusion and heat conduction equations with the reaction entering as a boundary condition over the particle surface. Firstly, the problem is treated isothermally by a domain perturbation technique to give analytical results for a slightly nonspherical particle and by the boundary integral technique for spheroids of arbitrary aspect ratio. Secondly, the nonisothermal problem is solved to give the pseudosteady and dynamic behaviors of nonspherical particles taking char combustion as an example. For the dynamic problem the diffusion and heat conduction in the gas phase are assumed to be at pseudosteady state with respect to the evolving particle temperature and particle size and shape. Lastly, the effect of surface roughness on the gas-solid reaction is similarly examined by representing the particle surface as a series in Legendre polynomials superimposed on an underlying spherical surface.

For nonspherical particles of equal volume but varying shape reacting under isothermal or nonisothermal conditions, the total reaction rate increases with the aspect ratio and is approximately equal to that of the sphere of equal surface area, and the local reaction rate increases with the distance from the particle center. The pseudosteady particle temperature under nonisothermal conditions is essentially the same for various spheroidal particles of equal volume. The particle temperature approaches quickly and remains close to its pseudosteady trajectory with conversion. During reaction a particle becomes more and more nonspherical. As for the effect of roughness, from the method of domain perturbation the nth mode decreases if the Damkohler number Q > Qcr [...], and vice versa. For highly irregular particles, too, this criterion applies overall, but they do not have sharp critical values of Q showing mixed behavior in a certain range around Qcr.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Gavalas, George R.
Thesis Committee:
  • Unknown, Unknown
Defense Date:30 December 1991
Record Number:CaltechETD:etd-07232007-152302
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-07232007-152302
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2972
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:01 Aug 2007
Last Modified:26 Dec 2012 02:55

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