Strona 2_redak - Instytut Agrofizyki im. Bohdana Dobrzańskiego ...

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Table 10.1. Measured (k s ) and calculated (k ϕ ) values of the pressure ratio of seeds and corresponding
values the angle of internal friction 3 (mean ± St.dev)
Seeds k s k 3 = 1.1(1 – sinϕ) 3 (deg)
Amaranthus
Pea
White mustard
Buckwheat
Soybean
Lentil
0.62 ± 0.02
0.53 ± 0.01
0.43 ± 0.01
0.59 ± 0.02
0.37 ± 0.02
0.74 ± 0.01
0.70 ± 0.02
0.59 ± 0.01
0.64 ± 0.01
0.68 ± 0.02
0.55 ± 0.01
0.80 ± 0.02
21.3 ± 0.8
27.3 ± 0.6
24.7 ± 0.4
22.0 ± 0.8
30.1 ± 0.9
15.5 ± 0.6
Table 10.2. Range of variability of the pressure ratio of grain and food powders [145] and values
recommended by Eurocode 1 [50]
Material
Barley
Corn
Oat
Wheat
Rye
Rape seeds
Soybens
Sugar
Wheat flour
Experimental Eurocode 1 [50]
k s k 3 = 1.1(1 – sinϕ) K
0.30-0.47
0.30-0.67
0.40-0.49
0.31-0.44
0.32-0.52
0.24-0.46
0.35-0.40
0.31-0.47
0.26-0.37
0.50-0.59
0.49-0.60
0.63-0.68
0.46-0.62
0.58-0.67
0.56-0.64
0.54-0.55
0.44-0.50
0.50-0.52
0.59
0.53
–
0.54
–
–
0.63
0.50
0.36
11. AIRFLOW RESISTANCE
11.1. Effects of density, moisture and packing
The main task of the design of a drying or aeration system is to define the
operating airflow that in match with the pressure-drop-air-velocity relationship will
assure the desired course of designed process. Apart from air velocity, other factors
were found to influence the resistance of the bedding to airflow and, consequently,
the pressure drop.
Theoretical modelling of static-bed-drying of grain employs four variables [23]:
mass flow rate of air, air humidity ratio, air temperature, and kernel temperature.
In developing the mathematical model several simplifying assumptions have to be
introduced, one of those being that airflow through the grain is uniform and one
dimensional, with no transfer the in transverse direction. However, moisture and
temperature distribution in a silo is generally non-uniform in practical storage
conditions. Thus for aeration control, location of humidity and temperature probe