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The growth of the global population is accompanied by an increase in energy demand, which promotes the use of biomass for cooking. Given the scarcity of this resource and its often inefficient use, optimizing the thermal efficiency of improved biomass-fueled cookstoves and furnaces appears essential. While many studies are limited to comparing the performance of existing stove models using the Water Boiling Test (WBT) protocol [1–2], a meaningful improvement also requires optimization of the materials from which these devices are made.
The present study focuses on the characterization of the structural and thermal properties of a geopolymer foam produced from Bangeli clay, a local material from Togo used as a primary component in the manufacture of cookstoves and furnaces.
First, an experimental characterization is carried out on geopolymer samples (sample C2.75: apparent porosity of 65%, apparent thermal conductivity of 0.16 ± 9% W·m⁻¹·K⁻¹, and true density of 2429 ± 1% kg·m⁻³). The geometric properties (porosity ranging from 33 to 42%, specific surface area ranging from 3212.69 to 5400,95 m-1 and Average aperture radius 175.47 to 204.67 µm ) are determined from three-dimensional reconstructions of real porous media (cf. Figure 1), obtained by X-ray micro-computed tomography and analyzed using the iMorph software [3].
In a second step, a Monte Carlo approach is used to model steady-state coupled conduction–radiation heat transfer, based on a probabilistic formulation of the heat equation. The coupling between the two heat transfer modes occurs at the solid–fluid interface. The algorithm relies on a unique path space composed of random sub-paths alternating between conduction (in the solid phase) and radiation (in the fluid phase) — cf. Figure 2 — according to probability laws applied at the interfaces. The solid phase is assumed to be opaque to radiation, while the fluid phase is considered transparent. Temperature is computed as the average of the weights assigned to the endpoints of the simulated trajectories.
The Monte Carlo method is implemented using the open-source software Stardis (https://www.meso-star.com/projects/stardis/stardis.html). This method is particularly well suited to complex geometries, as it is a probe-based approach that does not require volumetric meshing. Moreover, surface mesh refinement has no impact on the computational cost, making it an efficient tool for the analysis of complex porous structures [4–7].
The originality of this work lies in the investigation of conduction–radiation coupling within a multiscale porous geopolymer, carried out on different samples (Figure 1) using a path-space Monte Carlo approach. This method belongs to the class of comparative approaches used to solve conduction–radiation coupling in heterogeneous semi-transparent media, particularly for the analysis and comparison of temperature profiles [8]. Finally, the apparent thermal conductivity of the material is determined using Fourier’s law.
| References | [1] T. Abasiryu et al. Performance evaluation of some locally fabricated cookstoves in Mubi, AdamawaState, Nigeria, Nigerian Journal of Technology, 48-53 (2016), 10.4314/njt.351.1047 [2] Anjorin, Malahimi et al. Étude économique des foyers domestiques par la technique d’ébullition de l’eau : cas du Bénin, Afrique Science 10(2014) http://www.afriquescience.info [3]L. Ibarrart, et al. Combined conductive-convective-radiative heat transfer in complex geometry usingthe monte carlo method, Begel House Inc. (2018) doi10.1615/IHTC16.pma.023662 [4] Brun, E. et al., “De l’imagerie 3D Des Structures à l’étude Des Mécanismes de Transport En Milieux Cellulaires”, https://theses.fr/2009AIX11014. [5] M. Bati et al., Coupling Conduction, Convection and Radiative Transfer in a Single Path- Space :Application to Infrared Rendering, ACM Trans. Graph., 42, 1-79, (2023) 10.1145/3592121[6] G. L.Vignoles et al. Computation of the Conducto-Radiative Effective Heat Conductivity of PorousMedia Defined by TPMS, I.J.T.S., (2021) 10.1016/j.ijthermalsci.2020.106598 [7] M. Sans et al. Exp. Charac. of the Coupled Conductive and Radiative Heat Transfer in CeramicFoams with a Flash Method at High Temp., IJHMT, (2020) 10.1016/j.ijheatmasstransfer.2019.119077 [8] L. Penazzi et al. Analyse comparative de méthodes de résolution du couplage conduction- rayonnement dans des matériaux hétérogènes semi-transparents, SFT, (2025) |
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| Country | FRANCE |
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