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

More documents

Recommendations

Info

86 conventional engineering analyses that consider resistance to be isotropic overestimate the pressure drop across aerated grain bulks. Experiments and theoretical investigations of Endo et al. [48] showed that particle polydispersity and and/or nonspherical particle shape significantly influenced permeation resistance of either gas or liquid through a particle layer. 11.2. Laboratory testing Typical system used for measuring airflow resistance is shown in 11.1. A cylindrical PVC pipe with a diameter of 0.25 m and a height of 0.49 m was used to hold grain sample during the testing procedures. Air was introduced through a plenum in the bottom of the cylinder. The differential static pressure was measured at depths of 0.05 m and 0.45 m above the bottom of the cylinder. The static pressure was measured using a variable reluctance differential pressure transducer (Validyne DP103, Northridge, CA) with a diaphragm (maximum pressure rating of 1370 Pa (5.5 in H 2 O) and an accuracy of ±0.25% full scale. The flow rate was measured using a multiple nozzle outlet chamber according to ANSI/ASHRAE 51-1985 standard and a hot wire anemometer (Alnor Model 2106, Shoreview, MN) [37]. ∆p Y Fig. 11.1. Schematic of apparatus for measuring airflow resistance in grains as a function of bulk density [112]
87 Experimental airflow resistance as a function of air velocity for three types of seeds and centric filling is shown in figure 11.2. The lowest was airflow resistance of soybeans and the highest – that of wheat. This order does not correspond exactly to the determined porosities that were 0.37, 0.40 and 0.39 for wheat, corn and soybeans, respectively. Higher airflow resistance of corn despite its higher porosity in respect to soybeans may be the result of more complex geometry of pore space due to more irregular shape of corn kernels as compared to the roughly spherical shape of soybeans. Fig. 11.2. Airflow resistance as a function of airflow velocity for centric filling of grain column with: red soft wheat, corn and soybeans 11.3. Ergun’s equation Pressure drop data for airflow through agricultural products are usually presented as curves or equations [5, 23, 121]. These formulations imply that pressure drop per unit of height is independent of the depth of the grain. This assumption is not correct, because the density and porosity of grain in the silo changes along the height due to compaction from grain load. Fluctuations of filling stream may introduce additional non-homogeneity of the bedding. Li and Sokhansanj [95] concluded that Ergun’s equation could be the basis for a generalized model of airflow resistance through agricultural products. Ergun [49] hypothesized that the pressure drop was the summation of viscous and kinetic energy loses. The general equation takes a form as [95]: û3 L ⎛ 2 2 2 1 − % !90 k1 1 − % !90 = aV0 + bV0 = 2fE = 2⎜ + k ⎟ 3 2 , 3 % D p ( Re) (11.1) dp % dp where: û3 – pressure drop, L – length, ⎝ ⎞ ⎠
Page 2 and 3:
EC Centre of Excellence AGROPHYSICS
Page 4 and 5:
4 9.3. Factors influencing the coef
Page 6 and 7:
6 BASIC NOTATION c - cohesion [kPa]
Page 8 and 9:
8 Numerous granular materials when
Page 10 and 11:
10 the tensor of plastic strain inc
Page 12 and 13:
12 Fig. 2.1. Yield curves with comp
Page 14 and 15:
14 Stable or unstable behaviour of
Page 16 and 17:
16 In turn, the model of Lade, also
Page 18 and 19:
18 same porosity need not have iden
Page 20 and 21:
20 where: A = ∫ E( β) sin βdβ
Page 22 and 23:
22 (β = 0 o ), positioning the out
Page 24 and 25:
24 grain was poured into the mould
Page 26 and 27:
26 axes of the ellipse characterizi
Page 28 and 29:
28 [176] for the determination of p
Page 30 and 31:
30 A different approach to the desc
Page 32 and 33:
32 where: I - moment of inertia, k
Page 34 and 35:
34 a) b) f s f s m M f n f n Contac
Page 36 and 37: 36 The micropolar model yields resu
Page 38 and 39: 38 Fig. 3.17. Model of shear band f
Page 40 and 41: 40 In the case of agricultural mate
Page 42 and 43: 42 5.2. Density of consolidated mat
Page 44 and 45: 44 (cereal grain, sand, soil), the
Page 46 and 47: 46 Multiple wetting and drying of g
Page 48 and 49: 48 vertical pressure within the ran
Page 50 and 51: 50 of the curve defined by A, where
Page 52 and 53: 52 6. Vertical consolidation refere
Page 54 and 55: 54 poured into the box without vibr
Page 56 and 57: 56 7.2.2. Bulk density Stress-strai
Page 58 and 59: 58 near the box wall and lifted alo
Page 60 and 61: 60 and the upper boundary was 18.5
Page 62 and 63: 62 A -1 5 -1 0 -5 1 0 5 -5 5 1 0 1
Page 64 and 65: 64 Fig. 8.2. Yield locus and effect
Page 66 and 67: 66 in such a way that friction woul
Page 68 and 69: 68 a) b) µ = tg ϕw ϕ w c) d) e)
Page 70 and 71: 70 9.3. Factors influencing the coe
Page 72 and 73: 72 galvanized steel received from d
Page 74 and 75: 74 9.3.4. Velocity of sliding Becau
Page 76 and 77: 76 1+ sinϕ k = . 1 − sinϕ (10.3
Page 78 and 79: 78 N ϕ VLQϕ 3UHVVXUHUDWLRN
Page 80 and 81: 80 10.4.1. Friction force mobilizat
Page 82 and 83: 82 10.4.3. Moisture content With in
Page 84 and 85: 84 Table 10.1. Measured (k s ) and
Page 88 and 89: 88 a, b - product-dependent coeffic
Page 90 and 91: 90 also be performed as a function
Page 92 and 93: 92 reliable processing and stable v
Page 94 and 95: 94 unconfined yield strength to pow
Page 96 and 97: 96 The Chute Index (CI) is recommen
Page 98 and 99: 98 obtained the maximum deviation o
Page 100 and 101: 100 efficient flow control using op
Page 102 and 103: 102 In the field of experimental in
Page 104 and 105: 104 22. Britton M.G., Moysey E.B.:
Page 106 and 107: 106 69. Horabik J., Rusinek R.: Pre
Page 108 and 109: 108 114. Morland L.W., Sawicki A.,
Page 110 and 111: 110 158. 6WSQLHZVNL$ Influence of m
Page 112 and 113: 112 16. APPENDIX - Physical Propert
Page 114 and 115: 114 16.2. Density and porosity Tabl
Page 116 and 117: 116 Table 16.7. Mean values (±St.
Page 126 and 127: 126 Table 16.16. Cont. 1 2 3 4 Icin
Page 136 and 137:
136 Table 16.25. Cont. 1 2 3 4 Icin
Page 138 and 139:
138 Table 16.27. Mean values (±St.
Page 140 and 141:
140 Table 16.29. Cont. Table sugar
Page 142 and 143:
142 Table 16.31. Mean values (±St.
Page 144 and 145:
144 Table 16.35. Mean values (± St
show all

Strona 2_redak - Instytut Agrofizyki im. Bohdana DobrzaÅskiego ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?

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