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Research Papers: Radiative Heat Transfer

A Model of Transient Heat and Mass Transfer in a Heterogeneous Medium of Ceria Undergoing Nonstoichiometric Reduction

[+] Author and Article Information
Wojciech Lipiński

e-mail: lipinski@umn.edu
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55455

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received March 28, 2012; final manuscript received January 22, 2013; published online April 11, 2013. Assoc. Editor: Oronzio Manca.

J. Heat Transfer 135(5), 052701 (Apr 11, 2013) (9 pages) Paper No: HT-12-1134; doi: 10.1115/1.4023494 History: Received March 28, 2012; Revised January 22, 2013

The redox chemistry of nonstoichiometric metal oxides can be used to produce chemical fuels by harnessing concentrated solar energy to split water and/or carbon dioxide. In such a process, it is desirable to use a porous reactive substrate for increased surface area and improved gas transport. The present study develops a macroscopic-scale model of porous ceria undergoing thermal reduction. The model captures the coupled interactions between the heat and mass transfer and the heterogeneous chemistry using a local thermal nonequilibrium (LTNE) formulation of the volume-averaged conservation of mass and energy equations in an axisymmetric cylindrical domain. The results of a representative test case simulation demonstrate strong coupling between gas phase mass transfer and the chemical kinetics as well as the pronounced impact of optical thickness on the temperature distribution and thus global solar-to-chemical energy conversion.

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Figures

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Fig. 1

Schematic of the axisymmetric cylindrical two-phase solid–gas reacting medium under direct irradiation

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Fig. 2

Boundary conditions for mass and energy Eqs. (22), (23), (25), and (27)

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Fig. 3

Time evolution of the terms identified in the global energy balance described by Eq. (37)

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Fig. 4

The axial distributions of (a) solid temperature, (b) fluid temperature, (c) nonstoichiometry, (d) oxygen partial pressure, and (e) reaction rate are plotted at r = 0 for selected times

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