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delay between the initiation of the dust dispersion and activation of the ignition source (ignition delay t v ) was 60 ms. The pressure was recorded as a function of time. From the pressure/time curve, the explosion pressure ( p ex ) was determined by taking the arithmetic mean of the values measured by the pressure sensors. The testing procedure was started from a concentration of 250 g/m 3 , and the concentration was increased by steps of 250 g/m 3 , which is shown as 250 g/m 3 , 500 g/m 3 , 750 g/m 3 , 1000 g/m 3 , 1250 g/m 3 , and 1500 g/m 3 for each kind of wood dust with different particle size. Then researchers determined the explosion pressure ( p ex ) under each concentration and found a maximum value P max .
Fig. 1. 20 dm 3 sphere explosion testing system
RESULTS AND DISCUSSION Particle Size and Surface Morphology of Dust
Tables 1 through 3 show the D 10 , D 50 , D 90 and specific surface area for each fraction of wood dust samples. For all dust samples, the values of D 10 , D 50 , and D 90 gradually increased with increasing particle size, yet the values of specific surface area presented an opposite trend. Generally speaking, the median diameter of dust (D 50 ) should be smaller than the corresponding upper bound value of the particle size, as shown by the particle size of 0 to 63 μm, 63 to 125 μm , 125 to 250 μm , and 250 to 500 μm . P. massoniana dust had median diameters of 34 μm, 57 μm, 120 μm , and 219 μm , respectively, and P. massoniana dust showed a median diameter of 30 μm, 66 μm, 16 2 μm , and 303 μm. However, for P. alba dust, the median diameters were 38 μm, 89 μm , 180 μm , and 566 μm , respectively. Herein a median diameter of 566 μm was larger than the corresponding upper bound value of the particle size, 250 to 500 μm . This phenomenon can be explained from the morphology of wood dust samples, as shown in Figs. 2 through 4. Dust from P. alba had a higher length to diameter ratio, and the long needle shapes can pass through the lengthwise portion of the sieve. In addition, in the same particle size, the D 10 , D 50 , and D 90 values of P. alba dust were greater than those of P. massoniana and C. camphora dust. This is mainly attributed to P. alba dust’ s slender
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Guo et al . (2019 ). “Explosion of wood d usts,” B io R esources 14(2), 3182-3199.
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