Flame Extinction of Spherical PMMA in Microgravity: Effect of Fuel Diameter and Conduction
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ORIGINAL ARTICLE
Flame Extinction of Spherical PMMA in Microgravity: Effect of Fuel Diameter and Conduction Chuanjia Wu 1,2 & Peiyi Sun 3 & Xiuzhen Wang 1,2 & Xinyan Huang 3
&
Shuangfeng Wang 1,2
Received: 20 April 2020 / Accepted: 30 August 2020 # Springer Nature B.V. 2020
Abstract A series of experiments were conducted in the 3.6-s microgravity drop tower and normal gravity to investigate the effect of solid fuel curvature, conduction, and reradiation on the flame extinction of spherical polymethyl methacrylate (PMMA). In the semi-quiescent microgravity environment, flame extinction was observed if the PMMA diameter was larger than 40 mm, because of a smaller flame conductive heating in larger diameter (i.e., the curvature effect). Compared to the droplet combustion with a low evaporation point and fast heat convection in the liquid phase, the solid fuel has a high pyrolysis point and large transient heat conduction. Thus, the large surface reradiation effectively cools down the fuel surface to promote extinction. Also, as the initial burning duration increases, the conductive cooling into the solid fuel decreases, which delays or prevents the flame extinction in microgravity. The extinction criterion for microgravity flame is explained by the critical mass flux and mass-transfer number. This work helps to understand the curvature effect of solid fuel on flame extinction and the material fire safety in the microgravity spacecraft environment. Keywords Spacecraft fire . Plastic fuel . Drop tower . Curvature effect . Heat conduction
NomenclatureSymbols A B cg cp d deq
area (mm2) mass-transfer number (−). specific heat of gas (J/kg/K). specific heat of solid (J/kg/K). diameter (mm). equivalent diameter (mm).
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12217-020-09829-5) contains supplementary material, which is available to authorized users. * Xinyan Huang [email protected] * Shuangfeng Wang [email protected] 1
Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China
2
School of Engineering Science, University of Chinese Academy of Sciences, Beijing, China
3
Research Center for Fire Engineering, Department of Building Services Engineering, The Hong Kong Polytechnic University, Hong Kong, China
FSR Δhc Δhpy L m m⋅″ k q⋅″ r t t0 T V Xr Y O2
flame stand-off ratio (df/ds). heat combustion (J/kg). enthalpy of pyrolysis (J/kg). characteristic length (mm). mass (g). mass flux (g/m2/s). heat conductivity (W/m-K). conductive heat flux (kW/m2). sphere radius (mm). time (s). initial burning duration (s). temperature (K). Volume (mm3) fraction of flame radiation (−). mass fraction of oxygen (−).
Greeks δ depth (mm). ε radiative emittance (−). η ratio coefficient (−) κ fuel curvature, 1/r (mm−1). υ air to fuel stoichiometric mass ratio. ρ density (kg/m3). σ Stefan-Boltzmann constant (W/m2/K4). Φ thermocouple diameter (mm).
Microgravity Sci. Technol.
Subscripts ∞ ambient. cond conduction. crt critical value f flam
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