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Research Papers: Porous Media

Tomography-Based Determination of Effective Transport Properties for Reacting Porous Media

[+] Author and Article Information
Sophia Haussener1

Department of Mechanical Engineering, EPFL, 1015 Lausanne, SwitzerlandSophia.haussener@epfl.ch

Iwan Jerjen, Peter Wyss

Department of Electronics/Metrology,   EMPA Material Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland

Aldo Steinfeld

Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland; Solar Technology Laboratory,  Paul Scherrer Institute, 5232 Villigen, Switzerland

1

Corresponding author.

J. Heat Transfer 134(1), 012601 (Oct 27, 2011) (8 pages) doi:10.1115/1.4004842 History: Received April 16, 2011; Accepted July 30, 2011; Published October 27, 2011; Online October 27, 2011

The effective heat and mass transport properties of a porous packed bed of particles undergoing a high-temperature solid–gas thermochemical transformation are determined. The exact 3D geometry of the reacting porous media is obtained by high-resolution computed tomography. Finite volume techniques are applied to solve the governing conservation equations at the pore-level scale and to determine the effective transport properties as a function of the reaction extent, namely, the convective heat transfer coefficient, permeability, Dupuit–Forchheimer coefficient, tortuosity, and residence time distributions. These exhibit strong dependence on the bed morphological properties (e.g., porosity, specific surface area, particle size) and, consequently, vary with time as the reaction progresses.

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References

Figures

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Figure 1

CT scans of samples of the packed bed of tire shreds at three reaction extents: (a) initially at XC  = 0; (b) after pyrolysis at XC  = 0.68 (char); and (c) after gasification at XC  = 1 (ash). The edge length is 5.2 mm.

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Figure 2

Schematic of the DPLS domain, consisting of a square duct containing a sample of the packed bed, and inlet and outlet regions

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Figure 3

Mesh cutting plane of the computational domain of the initial packed bed. The packed bed region is enlarged. Parts of the inlet and outlet regions are visible at the top and bottom.

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Figure 4

Re dependent Nu numbers for the packed bed at XC  = 0, 0.68, and 1 (initial, char, and ash) and at Pr = 0.1, 1, and 1. The symbols indicate numerically calculated Nu numbers and the solid line the fits given by Eq. 8 and Table 2.

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Figure 5

Nu correlations for packed beds given by Gnielinski (ɛ = 0.61 and 0.74) [5], Wakao [6], Gunn (ɛ   = 0.61 and 0.74) [7], Saidi [8], and of present study for Pr   = 0.1 (a) and for Pr   = 1 (b)

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Figure 6

Dimensionless pressure drop, Πpg , as a function of Re for the three samples of the packed bed at XC  = 0, 0.68, and 1 (initial, char, and ash)

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Figure 7

K and FDP numerically determined by DPLS with those calculated by models for packed beds with Kinner  = 10−10 m2 and for (a): ɛ = 0.61, d = 1.14 mm; (b): ɛ = 0.74, d = 0.97 mm; and (c): ɛ = 0.65, d = 0.42 mm. FDP is calculated by MacDonald (grey, Eq. 28) and by Ward (black, Eq. 29)

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Figure 8

Residence time distribution at Re = 1 for the reacting packed bed at XC  = 0, 0.68, and 1 (initial, char, and ash)

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Figure 9

Tortuosity distribution at Re = 1 for the reacting packed bed at at XC  = 0, 0.68, and 1 (initial, char, and ash)

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