Abstract
In this study, a series of experiments were carried out on thermal insulation properties of charred woods, using a cone calorimeter under steady radiative heat fluxes. Specimens of Japanese cedar, Douglas fir, hinoki cypress, and larch were tested. A thin steel plate was attached onto the unexposed side of the specimens to measure heat flux through the specimens. Incident heat flux and specimen thickness were the main experimental parameters in this study. The results of the experiments showed that heat flux through char layers decreased to 10–25 % of the incident heat flux onto the specimen surface as the thickness of charred wood increased. The ratio \( {\overset{.}{q}}_{char}^{"}/{\overset{.}{q}}_{in}^{"} \) was approximated by the following equation \( {\overset{.}{q}}_{char}^{"}/{\overset{.}{q}}_{in}^{"}= \exp \left(-{\delta}_{eff}^a\right) \) as the regression equation of the experimental data.
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Abbreviations
- \( {\overset{.}{q}}_{char}^{{\prime\prime} } \) :
-
Transmitted heat flux (kW/m2)
- \( {\overset{.}{q}}_{wood}^{{\prime\prime} } \) :
-
Heat flux into uncharred wood (kW/m2)
- \( {\overset{.}{q}}_{r,t}^{"} \) :
-
Radiative heat flux of trestle (kW/m2)
- \( {\overset{.}{q}}_{r,s}^{"} \) :
-
Radiative heat flux of steel plate (kW/m2)
- \( {\overset{.}{q}}_{c,s}^{"} \) :
-
Convective heat flux (kW/m2)
- \( {\overset{.}{q}}_{in}^{\prime \prime } \) :
-
External heat flux (kW/m2)
- a :
-
Charring characteristic coefficient (−)
- c s :
-
Heat capacity of steel plate (kJ/kg/K)
- D :
-
Characteristic length (=0.01) (m)
- d :
-
Specimen thickness (mm)
- F :
-
Radiation shape factor with steel plate and trestle (−)
- g :
-
Acceleration of gravity (m/s2)
- Gr :
-
Grashof number (−)
- h :
-
Convective heat transfer coefficient (kW/m2/K)
- h′:
-
Convective heat transfer coefficient between specimen and gas in furnace (kW/m2/K)
- k w :
-
Thermal conductivity of wood (kW/m/K)
- L :
-
Heat of pyrolysis (kJ/kg)
- m″:
-
Mass loss rate per unit area (g/s/m2)
- Pr :
-
Prandtl number (=0.72) (−)
- t :
-
Time (s)
- T ∞ :
-
Ambient temperature (K)
- T f :
-
Heating temperature (K)
- t ig :
-
Ignition time (s)
- T s :
-
Temperature of steel plate (K)
- T t :
-
Temperature of trestle surface (K)
- T v :
-
Pyrolysis temperature (K)
- ΔH :
-
Heat of combustion (kJ/kg)
- δ s :
-
Steel plate thickness (=0.003) (m)
- α w :
-
Thermal diffusivity of wood (kW/m/K)
- δ b :
-
Constriction/burn-out depth (mm)
- δ eff :
-
Char thickness (= δ ϕ − δ b ) (mm)
- δ ϕ :
-
Char depth (mm)
- ε s :
-
Emissivity of steel plate (=0.78) (−)
- ε t :
-
Emissivity of trestle (=0.9) (−)
- ϕ :
-
Residue ratio (kg/kg)
- λ :
-
Thermal conductivity of air (kW/m/K)
- v :
-
Coefficient of kinematic viscosity of air (m2/s)
- ρ :
-
Density of wood (kg/m3)
- ρ s :
-
Density of steel plate (kg/m3)
- σ :
-
Stefan-Boltzmann constant (kW/m2/K4)
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Acknowledgments
The authors thank Mr. Ryo Sekiya, Mr. Ryo Yamanaka, and Mr. Jun Makino (at the time, a Tokyo University of Science graduate student) for their assistance in performing the experiments.
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Noaki, M., Suzuki, Ji., Ohmiya, Y., Delichatsios, M.A. (2017). Experimental Study on Thermal Insulation Properties of Charred Woods Under Radiative Heating. In: Harada, K., Matsuyama, K., Himoto, K., Nakamura, Y., Wakatsuki, K. (eds) Fire Science and Technology 2015. Springer, Singapore. https://doi.org/10.1007/978-981-10-0376-9_71
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DOI: https://doi.org/10.1007/978-981-10-0376-9_71
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