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Flammability Limits of Flat Materials with Moderate Thickness in Microgravity

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Abstract

The flammability limits of flat materials with different moderate thickness in opposed flow were investigated to clarify the effect of sample thickness on flammability limit. Thin poly-methyl methacrylate (PMMA) sheets and polycarbonate (PC) sheets were used as samples. The thickness was varied as 0.2 mm, 0.5 mm and 1.0 mm for PMMA, and 0.1 mm, 0.2 mm, 0.5 mm and 1.0 mm for PC. The limiting oxygen concentration (LOC) of each sample was obtained by 20 s parabolic flight experiments in mild and low flow velocity condition, and by blow-off tests on ground in high flow velocity condition. The flight experiments showed that there existed significant difference in LOC according to the sample thickness especially in mild flow condition; the thicker the sample was, the larger the LOC became. We applied a hypothesis of heat penetration zone shape into the heat balance equation around the preheat zone to account the effect of sample thickness on quenching phenomena. Although the hypothesis was not confirmed by experimentally, the obtained empirical model based on the hypothesis well represented the trend of the change of LOC when the sample thickness varied not only for the PMMA and PC samples, but also for low-density polyethylene (LDPE) and high-density polyethylene (HDPE) samples with relatively thick thickness. The modified model states that increase in the sample thickness has equivalent effect to increase in the radiative heat loss and such thickness effect is amplified when the pyrolysis temperature of the material is high.

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Abbreviations

A* :

Empirical pre-exponential factor by blow-off test

B 2 :

Empirical constant for RradB2 = 4.2

a abs :

Absorption coefficient of gas, aabs = 1

c g :

Specific heat of gas

c s :

Specific heat of solid

Da :

Damkohler number

E* :

Empirical activation energy by blow-off test

Pr :

Prandtl number

R :

Gas constant

R rad :

Radiative heat loss number

T f :

Characteristic flame temperature

T v :

Pyrolysis temperature

T ∞ :

Ambient temperature

t :

Sample thickness

t con :

Characteristic time for heat conduction

t pen :

Characteristic time for heat penetration

V g :

Opposed flow velocity

V g,cr :

Critical opposed flow velocity

V f :

Flame spread rate

V f,th :

Flame spread rate in thermal regime

x d :

Location for blow-off, xd = 0.04 [m]

Y 0 :

Oxygen mass fraction

α g :

Thermal diffusivity of gas, evaluated at Tv

α s :

Thermal diffusivity of solid, evaluated at Tv

β :

Non-dimensional sample thickness

ε :

Surface emissivity

η :

Non-dimensional spread rate, η = Vf /Vf,th

λ g :

Thermal conductivity of gas

λ s :

Thermal conductivity of solid

ρ g :

Gas density evaluated at Tv

ρ s :

Solid density

σ :

Stefan-Boltzmann constant

τ :

Sample half-thickness, τ = t/2

τ crit :

Critical sample half-thickness

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Acknowledgments

This study was conducted as a part of the FLARE project supported by Japan Aerospace Exploration Agency (JAXA) under the third phase utilization of JEM/ISS, titled “Evaluation of gravity impact on combustion phenomenon of solid material towards higher fire safety.” We are also thankful to the members of Diamond Air Service for their excellent technical support to parabolic flight experiments and to all team members of FLARE project for their helpful suggestions.

Funding

A part of this research was conducted in the support of Japan Aerospace Exploration Agency (JAXA) under the third phase utilization of JEM/ISS, titled “Evaluation of gravity impact on combustion phenomenon of solid material towards higher fire safety.”

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Authors and Affiliations

  1. Department of Mechanical Engineering, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu, 501-1193, Japan

    Shuhei Takahashi, Rikiya Oiwa, Misuzu Tokoro & Yoshinari Kobayashi

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  1. Shuhei Takahashi
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  2. Rikiya Oiwa
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  3. Misuzu Tokoro
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  4. Yoshinari Kobayashi
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Correspondence to Shuhei Takahashi.

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Takahashi, S., Oiwa, R., Tokoro, M. et al. Flammability Limits of Flat Materials with Moderate Thickness in Microgravity. Fire Technol 57, 2387–2406 (2021). https://doi.org/10.1007/s10694-021-01121-1

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  • DOI: https://doi.org/10.1007/s10694-021-01121-1

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