Combined Influence of Pore Diffusion and Intraparticle Heat Transport

2 Combined Influence of Pore Diffusion and Intraparticle Heat Transport 

The solution of the differential equations for internal heat and mass transfer (details in Emig and Klemm, 2005 Levenspiel, 1996, 1999) lead to the temperature difference between the center and the outer surface of a particle with an effective thermal conductivity X-p-. 

An estimation of the temperature gradient in a particle is given in Example 4.5.7, indicating that notable gradients can only occur for gas-phase reactions. For an exothermic reaction, overheating of the particle (to a certain mean temperature f Ts) leads to an increase in the intrinsic rate constant compared to the one reached at the temperature of the external surface of the particle. This effect can overcompensate for the lo ver concentration compared to the bulk phase caused by dif-fusional limitations, and the effectiveness factor may reach values above unity 

To calculate ripom, the mass and heat balances must be solved simultaneously. Analytical and numerical solutions are given by Petersen (1962), Tinkler and Pigford (1961), Carberry (1961), Tinkler and Metzner (1961), and Weisz and Hicks (1962). The behavior of a non-isothermal pellet in the regime of pore diffusion limitation is governed by the Thiele modulus (f (related to Tsurface) the Prater number and the Arrhenius number /int  

Example 4.5.7 Intraparticle T-gradients for gas and liquid phase reactions 

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