MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
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Task and Methodology<br />
Task<br />
One of the tasks of this aspect of the study was to find a correction function to<br />
improve the accuracy of the general asymptotic solution method in the intermediate range<br />
of M T for both the Langmuir and m-th order rate equations;<br />
Since catalytic pellets and solid fuel particles usually have shapes that can be<br />
approximated more or less by spheres, rather than by semi-infinite flat-slabs or infinite<br />
cylinders, this study focuses on analytical and numerical solutions in spherical<br />
coordinates. For simplicity, this study is limited to the following conditions:<br />
a) Isothermal conditions (no temperature gradients in the particle).<br />
b) No volume-change resulting from reactions (equi-molar counter-diffusion in the pores<br />
of the particle).<br />
c) Irreversible reactions.<br />
d) Two intrinsic reaction rate forms (m-th order and Langmuir rate equations).<br />
e) Limits of zero and unity for the reaction order in the m-th order rate form.<br />
Numerical Methods<br />
A numerical model of diffusion of oxidizer through the particle interior was<br />
developed in order to test the accuracy of the Thiele modulus approaches. The<br />
concentration of oxidizer in the particle interior can be described by an ordinary<br />
differential equation and two boundary conditions. The generalized steady-state<br />
continuity equation in a spherical particle (a catalytic pellet or a solid fuel particle) may<br />
be expressed as (Smith, 1981):<br />
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