Onset of Convection Cells Within Insulated Building Walls

Stefano Lazzari (), Michele Celli, Antonio Barletta and Pedro Vayssière Brandão
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Stefano Lazzari: Department of Architecture and Design, University of Genoa, Stradone S. Agostino 37, 16123 Genova, Italy
Michele Celli: Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy
Antonio Barletta: Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy
Pedro Vayssière Brandão: Department of Industrial Engineering, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy

Energies, 2025, vol. 18, issue 21, 1-14

Abstract: The linear stability of convection in a vertical two-layer porous structure representing a building external wall is studied. The wall is confined by two open vertical boundaries kept at different but uniform temperatures and is composed of two homogeneous porous layers, characterized by different values of permeability and thermal conductivity. The aim of this paper is investigating whether the wall can undergo the transition to thermal instability, namely, the onset of a multicellular convective pattern. The basic stationary state, given by the fully developed buoyant flow in the vertical direction, is perturbed by means of small-amplitude disturbances, and the resulting eigenvalue problem for neutrally stable modes is studied numerically. The solution of the perturbed governing equations shows that, for suitable values of the governing parameters, thermal instability can arise. The results highlight that the ratio of the permeabilities of the two layers as well as the ratio of their thermal conductivities, together with the aspect ratio between their thicknesses, are key parameters for the possible onset of instability. The temperature difference between the two open boundaries that can trigger instability is determined with reference to practical cases, namely, insulated walls that fulfill the Italian requirements in terms of overall thermal transmittance.

Keywords: buoyant flow; linear stability; thermal convection in building walls; two-layer porous vertical wall (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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