Geometric mean dimensions GMD) of particle length, as calculated directly using sieve opening sizes and mass fraction on ASABE forage sieves depended on biomass selection (Table 1). Ratio of GMD to knife mill screen size ranged from 0.21 to 0.36.
Table 1 Effect of biomass selection and knife mill screen size on overall geometric mean dimensions (GMD) of particle length calculated directly using sieve opening sizes and mass fraction on ASABE forage sieves, for various mass input rates and rotor speeds of knife mill.
Biomass |
Knife mill Screen size |
Geometric Mean Dimensions (GMD) of Particle Length |
Ratio of GMD to Knife mill Screen Size |
Mean |
(mm) |
(mm) |
Corn Stover |
12.7 |
3.62 |
0.28 |
Corn Stover |
19.1 |
5.77 |
0.30 |
Corn Stover |
25.4 |
7.68 |
0.30 |
Corn Stover |
50.8 |
14.01 |
0.28 |
Switchgrass |
12.7 |
3.05 |
0.24 |
Switchgrass |
19.1 |
5.10 |
0.27 |
Switchgrass |
25.4 |
9.27 |
0.36 |
Switchgrass |
50.8 |
13.04 |
0.26 |
Wheat Straw |
12.7 |
3.46 |
0.27 |
Wheat Straw |
19.1 |
4.58 |
0.24 |
Wheat Straw |
25.4 |
6.91 |
0.27 |
Wheat Straw |
50.8 |
10.87 |
0.21 |
GMD values based on image analysis (Fig 7) of actual switchgrass particles retained by ASABE sieves and mass fractions revealed interesting trends (Figs 8 – 9). GMD of switchgrass particle length was about 5 times greater than the GMD calculated using ASABE sieve opening sizes and mass fraction on sieves (Fig 8). GMD of switchgrass particle width was about one-third of the GMD calculated using ASABE sieve opening sizes and mass fraction on sieves (Fig 9).
These results emphasize that sieve analyses of irregular shaped particles provide relative comparisons, and that actual dimensions of particles residing on sieves differ and are not necessarily represented by sieve sizes above and below the sample.
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