Effective Thermal Conductivity of Monolithic and Porous Catalyst Supports by the Moment Technique

Abstract

The axial and radial effective thermal conductivities of a monolithic ceramic catalyst support and of porous alumina pellets were measured using the moment technique. At 180 °C, radial and axial thermal diffusivities were determined as 9.3 x 10-3 and 11.1 x 10~3 cm2is-1, respectively. Having pores being filled with hydrogen, the corresponding thermal conductivity values are 0.43 and 0.52 Wm_1'K_1, respectively. Experimental results obtained between 110 and 180 °C indicated a negligibly small dependence of effective thermal conductivities on temperature. A proposed model which included the geometrical parameters of the monolith and the thermal conductivity ratio of the ceramic catalyst support to gas was shown to give excellent agreement with experimental results. Thermal conductivities of alumina pellets having bidisperse pore structures were also measured using this dynamic procedure. Experimental effective thermal conductivity values ranged between 0.043 and 0.120 W-m^K"1 for pellets having porosities between 0.79 and 0.57, respectively.

Porous Medium Modeling of Catalytic Monoliths Using Volume Averaging

“…In the literature, most of the studies neglect the tortuosity and dispersion terms and evaluate the effective thermal conductivity and diffusivity using volume fraction of gas and solid. Several correlations exist to evaluate the effective thermal conductivity in monolithic channels, such as the electric circuit analogy and the moment technique . The effective diffusion coefficient is commonly evaluated as scriptD i ε f τ , where ε f and τ are porosity and tortuosity, respectively.…”

“…Several correlations exist to evaluate the effective thermal conductivity in monolithic channels, such as the electric circuit analogy 51 and the moment technique. 52 The effective diffusion coefficient is commonly evaluated as i f , where ε f and τ are porosity and tortuosity, respectively. Several efforts have been made to evaluate tortuosity based on porosity; Bruggeman model 53 and Millington-Quirk model 54 being the most commonly used.…”