Combined Heat Transfer Mechanisms in the Porous Char Layer Formed from the Intumescent Coatings under Fire

Lingyun Zhang,Yupeng Hu,Minghai Li

doi:10.3390/coatings11020200

Lingyun Zhang, Yupeng Hu + Show 1 more

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https://doi.org/10.3390/coatings11020200

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Abstract

This study examines the combined heat transfer by thermal conduction, natural convection and surface radiation in the porous char layer that is formed from the intumescent coating under fire. The results show that some factors, such as the Rayleigh number, conductivity ratio, emissivity, radiation–conduction number, void fraction and heating mode have a certain effect on the total heat transfer. In addition, the natural convection of the air in the cavity always inhibits surface radiation among the solid walls and thermal conduction, and the character of the total heat transfer is the competition result of the three heat transfer mechanisms.

Highlights

In the field of steel structure, the improvement of fire resistance is always a key problem
The inherent weakness of steel structures that cannot maintain their strength and stiffness at high temperatures is often addressed by applying insulation to their exposed surfaces, which delays the transfer of heat to the internal structure and, increases the time required for the critical temperature of the steel structure to be reached [1]
The results are obtained in the following ranges of the associated dimensionless groups: the Rayleigh number, the thermal conductivity ratio of solid to air (10−1 –103 ), the emissivity (0.2–1), the radiation to conduction number (10−1 –103 ), the void fraction (0.1–0.9) and the heating mode, heating from the bottom or the top

Summary

Introduction

In the field of steel structure, the improvement of fire resistance is always a key problem. The char layer can often act as an efficient thermal barrier between the heat source and the steel structure [3]. One type is based on the improvement of the chemical components This kind of research mainly considers the effect of the main components of the intumescent coating in order to find their best chemical composition. Gottfried et al [7] found that the refractory fibers, such as alumina- and silica-based fibers, were able to improve thermal insulation performance when added to intumescent coatings. Research by Bourbigot et al [8] showed that adding boric acid to an APP–epoxy-based intumescent coating led to more efficient thermal protection, and to better mechanical resistance. Wang et al [9] compared the performance of classical intumescent coatings and EG-based intumescent coatings

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