Dependence of polyethylene combustion dynamics in a 1 m³ chamber on particle size

Introduction. The results of a standard study on the explosion hazard of polyethylene air suspensions (PES) can contribute to the theory of turbulent combustion. For example, analysis of polydispersity data and values of the PES lean combustion limit in a 1 m³ chamber helped to identify the maximum size of explosive particles d^*_m,t ≈ 100 µm (Poletaev, 2014). In this work, a relationship was obtained between the dynamics of PES combustion in a 1 m³ chamber and the average particle size of the suspension, which is understood as the average particle size of its explosive fraction d^*₅₀.

Initial data. Well-known findings of a study on the explosion of 28 polyethylene specimens in a 1 m³ chamber were used. Continuous functions of specimen particles distribution by size, necessary for calculating d^*₅₀, were represented using the Rosin-Rammler distribution.

Combustion dynamics. The dynamics of PES turbulent combustion in a 1 m³ chamber is described by the maximum rate of air suspension burnout U_b. U_b was calculated according to the formula (Kumar, 1992) intended for gas-air mixtures by substituting PES explosion parameters into this formula.

Results and its discussion. The graph, describing the dependence of the complex d^*₅₀U_b on d^*₅₀, is provided. The averaged value of the complex (≈ 45 µm · (m/s)) is constant in the range 40 µm < d^*₅₀ < 90 µm. The latter is typical for the product of the particle size and the normal velocity of laminar flame in liquid aerosols (Myers, 1986), which indicates similarity between the effect of particle dispersion and dynamics of turbulent and laminar combustion of the aforementioned heterogeneous mixtures.

Conclusions. The dispersive capacity of an explosive polydisperse polyethylene specimen is determined by the average particle size of the explosive fraction of the specimen d^*₅₀. The similarity of combustion patterns indicates the proximity of propagation mechanisms typical for turbulent flame, typical for PES, and laminar flame, typical for liquid aerosols.

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