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

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4 9.3. Factors influencing the coefficient of friction ……………………………….. 70 9.3.1. Moisture content ………………………………………………………. 70 9.3.2. Surface roughness ……………………………………………………... 71 9.3.3. Normal pressure ……………………………………………………….. 73 9.3.4. Velocity of sliding …………………………………………………….. 74 9.3.5. Wear in ………………………………………………………………... 74 9.3.6. Frictional vibrations, slip-stick effect …………………………………. 74 10. PRESSURE RATIO ……………………………………………………………... 75 10.1. Yielding at the silo center ………………………………………………….. 75 10.2. Yielding at the silo wall ……………………………………………………. 76 10.3. Experimental procedures …………………………………………………… 78 10.4. Factors influencing the pressure ratio ………………………………………. 79 10.4.1. Friction force mobilization …………………………………………... 80 10.4.2. Packing structure …………………………………………………….. 81 10.4.3. Moisture content ……………………………………………………... 82 10.4.4. Grain shape and surface roughness ………………………………….. 82 10.5. Concluding remarks ………………………………………………………… 83 11. AIRFLOW RESISTANCE ………………………………………………………. 84 11.1. Effects of density, moisture and packing ………………………………. 84 11.2. Laboratory testing ……………………………………………………… 86 11.3. Ergun’s equation ……………………………………………………….. 87 12. FLOW RATE THROUGH ORIFICES ………………………………………….. 88 13. INDICES OF STRENGTH AND FLOWABILITY USED BY PROCESS TECHNOLOGY………………………………………………………………….. 89 13.1. Quality determination ………………………………………………………. 90 13.1.1. Peschl rotational split level shear tester ……………………………… 91 13.1.2. Johanson’s apparatus and indices ……………………………………. 92 13.1.3. Jenike & Johanson powder quality tester ……………………………. 96 13.1.4. Uniaxial tester of POSTEC ………………………………………….. 97 13.2. Carr Indices …………………………………………………………………. 98 13.3. In-line control of structure of granular products ……………………………. 99 13.4. Tendencies in development of applications ………………………………… 101 14. REFERENCES …………………………………………………………………... 103 15. SUMMARY ……………………………………………………………………… 111 16. APPENDIX – Physical Properties of Grain and Food Powders ………………… 112
5 PREFACE In recent decades granular materials have gained great interest of both industrial specialists and researchers. Growing competition on the global market, combined with an increase in the scale of operations, enforced producers to use raw materials and final products in granular form that is relatively easy for storage, handling and processing. On the other hand, after fairly complete description of solid, liquid and gaseous states of matter, scientists turned their attention to granular materials. With their unique behaviour, some researchers postulate to consider this group of materials as a separate state of matter. Research and technology developments made from the sixties of the twentieth century resulted in a substantial progress in science and technology in the field. This work deals with some aspects of the mechanics of granular materials. It is focused on the materials of biological origin used in agro and food technology. The main features of agro and food materials that make them different from mineral materials are strong influence of moisture content on mechanical behaviour and high deformability of granules. These differences bring about certain peculiar behaviours and necessity of adjustments of models of material, experimental techniques and technological solutions. While presenting this book, our purpose was to focus attention of the reader on what we believe is important for understanding of the mechanical behaviour of granular materials of biological origin. Selection of the presented material was based on direct professional experience of the authors. The main theoretical approaches – from the origins of soil mechanics to micropolar theory and DEM modelling have been addressed. A review of commonly applied experimental methods and material parameters has been presented. Finally, a catalogue of material parameters drawn from laboratory testing of the authors was attached for reference as well as for comparison with results of other laboratories. This “Mechanical Properties of Granular Agro- Materials and Food Powders for Industrial Practice” is composed of two volumes. Part I presents mainly issues relevant for storage and handling, while Part II addresses questions of grinding and agglomeration. We kindly acknowledge support given by the European Commission that made this publication possible. Authors
Page 2 and 3: EC Centre of Excellence AGROPHYSICS
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
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54 poured into the box without vibr
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56 7.2.2. Bulk density Stress-strai
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58 near the box wall and lifted alo
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60 and the upper boundary was 18.5
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62 A -1 5 -1 0 -5 1 0 5 -5 5 1 0 1
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64 Fig. 8.2. Yield locus and effect
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66 in such a way that friction woul
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68 a) b) µ = tg ϕw ϕ w c) d) e)
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70 9.3. Factors influencing the coe
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72 galvanized steel received from d
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74 9.3.4. Velocity of sliding Becau
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76 1+ sinϕ k = . 1 − sinϕ (10.3
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78 N ϕ VLQϕ 3UHVVXUHUDWLRN
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80 10.4.1. Friction force mobilizat
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82 10.4.3. Moisture content With in
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84 Table 10.1. Measured (k s ) and
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86 conventional engineering analyse
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88 a, b - product-dependent coeffic
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90 also be performed as a function
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92 reliable processing and stable v
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94 unconfined yield strength to pow
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96 The Chute Index (CI) is recommen
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98 obtained the maximum deviation o
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100 efficient flow control using op
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102 In the field of experimental in
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104 22. Britton M.G., Moysey E.B.:
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106 69. Horabik J., Rusinek R.: Pre
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108 114. Morland L.W., Sawicki A.,
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110 158. 6WSQLHZVNL$ Influence of m
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112 16. APPENDIX - Physical Propert
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114 16.2. Density and porosity Tabl
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116 Table 16.7. Mean values (±St.
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126 Table 16.16. Cont. 1 2 3 4 Icin
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136 Table 16.25. Cont. 1 2 3 4 Icin
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140 Table 16.29. Cont. Table sugar
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Page 144 and 145:
144 Table 16.35. Mean values (± St
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