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Figure 9: Parametric sensitivity of mass and heat transfer coef- ficients values on conversion. Holmgren and Andersson (1998) case.

Figure 9 Parametric sensitivity of mass and heat transfer coef- ficients values on conversion. Holmgren and Andersson (1998) case.

Related Figures (13)

where B, is the Prater number. and L, the global characteristic length defined as the
where B, is the Prater number. and L, the global characteristic length defined as the
The subscript “0” is used for parameters calculated at the bulk fluid phase conditions. The intrinsic effec- tiveness factor was calculated using the following ex- pression (Gottifredi et al., 1986): R’(1) is the first derivative of R(C) respect of C evaluate at C=1. Therefore, besides effectiveness factors, n and 10, temperature and reactant concentrations on the wash- coat-fluid interphase are calculated at each point of the axial reactor position by a trial and error algebraic pro- cedure.
The subscript “0” is used for parameters calculated at the bulk fluid phase conditions. The intrinsic effec- tiveness factor was calculated using the following ex- pression (Gottifredi et al., 1986): R’(1) is the first derivative of R(C) respect of C evaluate at C=1. Therefore, besides effectiveness factors, n and 10, temperature and reactant concentrations on the wash- coat-fluid interphase are calculated at each point of the axial reactor position by a trial and error algebraic pro- cedure.
Let us consider a square monolith channel of side (L) covered by a non uniform washcoat layer. It is charac- terized by the minimum washcoat thickness (5) and the radius of washcoat in the corner (R,). For this type of geometrical configuration, symmetry allows to consider (1/8)" of the total washcoat cross section (see Fig. 1). Figure 1: A quarter square channel normalized cross-section. In grey a washcoat slice.
Let us consider a square monolith channel of side (L) covered by a non uniform washcoat layer. It is charac- terized by the minimum washcoat thickness (5) and the radius of washcoat in the corner (R,). For this type of geometrical configuration, symmetry allows to consider (1/8)" of the total washcoat cross section (see Fig. 1). Figure 1: A quarter square channel normalized cross-section. In grey a washcoat slice.
Provided the values of the radius of washcoat in the corner (R,), the minimum washcoat thickness (5) and the side of a particular monolith sample (L); parameters A, Ry and 6y can be calculated.
Provided the values of the radius of washcoat in the corner (R,), the minimum washcoat thickness (5) and the side of a particular monolith sample (L); parameters A, Ry and 6y can be calculated.
Kinetic expression and parameter values for CO oxida- tion over Pt supported catalyst were taken from Oh and Cavendish, (1985): Where k;, also depends upon platinum surface concen- tration. To estimate its value, in terms of unit washcoat volume, a surface site density of 1.25 10'° Pt surface atoms per metal area and a washcoat density of 1.3 g/cm* were assumed. In each experimental case studied, the corresponding washcoat platinum loading and dis- persion was utilized.
Kinetic expression and parameter values for CO oxida- tion over Pt supported catalyst were taken from Oh and Cavendish, (1985): Where k;, also depends upon platinum surface concen- tration. To estimate its value, in terms of unit washcoat volume, a surface site density of 1.25 10'° Pt surface atoms per metal area and a washcoat density of 1.3 g/cm* were assumed. In each experimental case studied, the corresponding washcoat platinum loading and dis- persion was utilized.
Thus, the intrinsic effectiveness factor was calculated using the expression (13) with:
Thus, the intrinsic effectiveness factor was calculated using the expression (13) with:
Figure 2: CO bulk concentration estimated (our procedure), considering uniform washcoat (L.g); experimental results observed by Ullah et al.(1992). The global effectiveness factor changes from 0.621 at the entrance to 0.872 at the outlet, with a minimum of 0.585 at z = 0.9 cm from the reactor entrance. In this case the calculated Reynolds number was 172 and the Sherwood number 3.64. Consequently, the CO and O, mean mass transfer coefficients were 0.259 and 0.262 m/s, respectively.
Figure 2: CO bulk concentration estimated (our procedure), considering uniform washcoat (L.g); experimental results observed by Ullah et al.(1992). The global effectiveness factor changes from 0.621 at the entrance to 0.872 at the outlet, with a minimum of 0.585 at z = 0.9 cm from the reactor entrance. In this case the calculated Reynolds number was 172 and the Sherwood number 3.64. Consequently, the CO and O, mean mass transfer coefficients were 0.259 and 0.262 m/s, respectively.
Figure 3: Estimated intrinsic and global effectiveness factors along the reactor. Ullah et al.(1992) case.
Figure 3: Estimated intrinsic and global effectiveness factors along the reactor. Ullah et al.(1992) case.
In Fig. 5, differences between the bulk fluid and washcoat surface temperatures and percent relative dif- ference concentration [(Cp - Cs)/Co]%, along the reactor are presented. The bulk fluid and washcoat surface tem- peratures vary from 573K to 588.2K and from 660.4K to 662.4K, respectively. The relative concentration dif- ference [(Co - Cs)/Co] varies from 0.21, at the reactor entrance, to 0.36, at the reactor exit, with a maximum of 0.47 at z = 4.5 cm. This indicates a strong external mass transfer resistance. Fig. 6 presents global and intrinsic effectiveness factor values along the reactor. While no varies from 1.27 to 0.19 with a minimum of 0.172 at z= 7.2 cm, n changes from 0.7646 to 0.404, with a mini- mum of 0.347 at z = 5.76 cm. Figure 4: CO conversion along the reactor. (©) Exit conver- sion experimental value. Holmgren and Andersson (1998).
In Fig. 5, differences between the bulk fluid and washcoat surface temperatures and percent relative dif- ference concentration [(Cp - Cs)/Co]%, along the reactor are presented. The bulk fluid and washcoat surface tem- peratures vary from 573K to 588.2K and from 660.4K to 662.4K, respectively. The relative concentration dif- ference [(Co - Cs)/Co] varies from 0.21, at the reactor entrance, to 0.36, at the reactor exit, with a maximum of 0.47 at z = 4.5 cm. This indicates a strong external mass transfer resistance. Fig. 6 presents global and intrinsic effectiveness factor values along the reactor. While no varies from 1.27 to 0.19 with a minimum of 0.172 at z= 7.2 cm, n changes from 0.7646 to 0.404, with a mini- mum of 0.347 at z = 5.76 cm. Figure 4: CO conversion along the reactor. (©) Exit conver- sion experimental value. Holmgren and Andersson (1998).
Figure 5: Difference between the bulk fluid and washcoat surface temperature and percent relative difference concentra- tion [(Co - Cs)/Co]% along the reactor. Holmgren and Anders- son (1998) case. between external and internal resistances is produced which, as a whole, does not modify no and consequently conversion. In actual facts our numerical results shows that the maximum deviation in yo presents a maximum decrease of 6% at reactor entrance and after | cm from the entrance there is no sensible difference between no values although transfer coefficients have been in- creased up to 40%.
Figure 5: Difference between the bulk fluid and washcoat surface temperature and percent relative difference concentra- tion [(Co - Cs)/Co]% along the reactor. Holmgren and Anders- son (1998) case. between external and internal resistances is produced which, as a whole, does not modify no and consequently conversion. In actual facts our numerical results shows that the maximum deviation in yo presents a maximum decrease of 6% at reactor entrance and after | cm from the entrance there is no sensible difference between no values although transfer coefficients have been in- creased up to 40%.
Figure 6: Average global n, and intrinsic n effectiveness factor along the reactor.
Figure 6: Average global n, and intrinsic n effectiveness factor along the reactor.
Figure 7: Parametric sensitivity of heat and mass transfer coefficients values on concentration differences between bulk and interfacial values along the reactor. Holmgren and Andersson (1998) case.
Figure 7: Parametric sensitivity of heat and mass transfer coefficients values on concentration differences between bulk and interfacial values along the reactor. Holmgren and Andersson (1998) case.
Figure 8: Parametric sensitivity of heat and mass transfer coef- ficients values on temperature differences between bulk and interfacial values along the reactor. Holmgren and Andersson (1998) case.
Figure 8: Parametric sensitivity of heat and mass transfer coef- ficients values on temperature differences between bulk and interfacial values along the reactor. Holmgren and Andersson (1998) case.
Related topics:
Materials ScienceHeterogeneous CatalysisEffectiveness FactorReactor Engineering
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