DRY 10: Product Quality and Solids Properties
     Part 2: Powder Stickiness
         1 INTRODUCTION
         2 MECHANISMS OF INTERPARTICLE AND PARTICLE-SURFACE ATTRACTION
             2.1 Intermolecular Forces
             2.2 Mobile Liquid Bridges
                 2.2.1 Pendular State
                 2.2.2 Funicular and Capillary States
                 2.2.3 Conclusions
             2.3 Immobile Liquid Bridges
                 2.3.1 Viscous Binders
                 2.3.2 Bridges of the Same Material as the Particles
             2.4 Solid Bridges
             2.5 Mechanical Interlocking
         3 CHARACTERISATION OF POWDERS
             3.1 Flow Properties of Powders
                 3.1.1 Introduction
                 3.1.2 Shear Testing of Powders
                 3.1.3 Effect of Moisture Content on Shear Properties
                 3.1.4 Effect of Storage Time on Shear Properties
                 3.1.5 The Use of the Material Yield Locus Curve
                 3.1.6 Measurement of Powder Flow Properties and Cohesive Forces
             3.2 Wall Friction and Adhesion
                 3.2.1 Theory
                 3.2.2 The Measurement of Wall Friction and Adhesion
                 3.2.3 Relationship of Cohesion and Adhesion
         4 POWDER STICKINESS AND DRYING
             4.1 Powder Characterisation in the Drying Industry
                 4.1.1 Introduction
                 4.1.2 Measurement of the Sticky-Point Temperature
                 4.1.3 Tilting Hot Plate Test
             4.2 Powder Stickiness in Spray Dryers
             4.3 Powder Stickiness in Pneumatic Conveying Dryers
             4.4 Powder Stickiness in Contact Dryers
             4.5 Powder Stickiness in Fluidised Bed Dryers
             4.6 Powder Stickiness in Cascading Rotary Dryers
         5 POWDER COHESION AND ADHESION AS RELATED TO THE PERFORMANCE OF PNEUMATIC CONVEYING DRYERS
             5.1 Feed Rate
             5.2 Agglomerate Size
         6 CAKING IN STORAGE
         7 CONCLUSIONS AND RECOMMENDATIONS
             7.1 Overview
             7.2 Further Work
         8 REFERENCES
         9 NOMENCLATURE
         10 APPENDIX: Definition and look-up tables for flowability and floodability
             10.1 Flowability
             10.2 Floodability
     Part 3: Heat-Sensitive and Non-Newtonian Materials
         1. INTRODUCTION
             1.1 Objective
             1.2 Summary of contents
         2. HEAT-SENSITIVITY
             2.1 Introduction
             2.2 Factors affecting heat-sensitivity
             2.3 Physical changes
                 2.3.1 Softening and melting
                 2.3.2 Case hardening
                 2.3.3 Collapse during freeze drying
                 2.3.4 Loss of secondary volatile components
             2.4 Chemical changes
                 2.4.1 Introduction
                 2.4.2 Reaction kinetics and the effect of temperature
             2.5 Biological changes
                 2.5.1 Introduction
                 2.5.2 Lipid autoxidation
                 2.5.3 Non-enzymatic browning
                 2.5.4 Denaturation
                 2.5.5 Enzyme reactions
             2.6 Measurement of heat-sensitivity
                 2.6.1 Test procedures
                 2.6.2 Theoretical models
             2.7 Effect of degree and type of heat-sensitivity on dryer selection
             2.8 Safety margins
         3. RHEOLOGICAL CONSIDERATIONS
             3.1 Classification of rheological behaviour
                 3.1.1 Time-independent non-Newtonian behaviour
                 3.1.2 Thixotropic behaviour
                 3.1.3 Viscoelastic behaviour
                 3.1.4 Granulo-viscous behaviour
             3.2 Feeders for non-Newtonian materials
             3.3 Effect of feedstock characteristics on dryer selection
             3.4 Modification of feedstock characteristics
             3.5 Rheological changes during drying
             3.6 Mixing effectiveness of agitators with non-Newtonian materials
             3.7 Effect of temperature on apparent viscosity
             3.8 Power consumption of vertical agitators handling non-Newtonlan materials
                 3.8.1 Introduction
                 3.8.2 Pseudoplastic materials
                 3.8.3 Bingham plastic materials
                 3.8.4 Determination of apparent viscosity from power consumption data
                 3.8.5 Scale-up of power consumption
             3.9 Heat transfer to non-Newtonian materials in vessels with vertical agitators
                 3.9.1 Introduction
                 3.9.2 Anchor agitators
                 3.9.3 Helical ribbon agitators
                 3.9.4 Screw agitators
                 3.9.5 Heated agitators
                 3.9.6 Effect of wall clearance on heat transfer
                 3.9.7 Scale-up of heat transfer requirements
                 3.9.8 Utility of the correlations
             3.10 Horizontal agitators and agitators of special design
         4. FREEZE DRYERS
             4.1 Introduction
             4.2 Freezing
             4.3 Sublimation
             4.4 Water vapour removal systems
             4.5 Optimisation
             4.6 Costs
             4.7 Limited freeze drying
             4.8 Theoretical models of freeze drying
                 4.8.1 Heat transfer through the frozen layer
                 4.8.2 Heat transfer through the dry layer
             4.9 Types of freeze dryer
                 4.9.1 Tray freeze dryers
                 4.9.2 Band freeze dryers
                 4.9.3 Spray freeze dryers
                 4.9.4 Rotary freeze dryers
                 4.9.5 Fluid bed dryers
         5. VACUUM DRYERS
             5.1 Introduction
             5.2 Selection of operating pressure
             5.3 Evaporation
             5.4 Condensers
             5.5 Vacuum equipment
             5.6 Vapour filtration
             5.7 Common types of vacuum dryer
                 5.7.1 Batch vacuum dryers
                 5.7.2 Continuous vacuum dryers
             5.8 Less common vacuum dryers
                 5.8.1 Vacuum-puff dryers
         6. ATMOSPHERIC DRYERS
             6.1 Introduction
             6.2 Spray dryers
             6.3 Pneumatic conveying dryers
             6.4 Fluid bed granulators
             6.5 Band dryers
             6.6 Foam-mat dryers
         7. DIELECTRIC DRYERS
         8. RECOMMENDATIONS FOR RESEARCH
         9. NOMENCLATURE
         10. REFERENCES
     Terms and Conditions of Use

• Part 1 Introduction
• Part 2 Powder stickiness
• Part 3 Drying of heat-sensitive and non-Newtonian materials
• Part 9 Troubleshooting

Volume DRY X  Part 1 Introduction.

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Volume DRY X  Part 2 Powder stickiness.

Stickiness, cohesion and adhesion can have a major effect not only on the performance of a dryer but also on the upstream and downstream handling processes. This Part acts as a state-of-the-art report exploring current knowledge on the subject. The various kinds of cohesive forces are distinguished: intermolecular forces, surface tension and liquid bridges, solid bridges and mechanical interlocking. Existing types of test apparatus for determining cohesive and adhesive forces are reviewed. The sticky-point and its relationship to the glass transition temperature are explained. Finally, effects of powder stickiness in various kinds of dryers are reported.

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Volume DRY X  Part 3 Product quality and heat sensitivity.

The drying of heat-sensitive non-Newtonian materials is frequently a problem since they are often difficult to handle and are easily damaged by quite moderate temperatures. Only by thoroughly characterising the feedstock from the viewpoints of heat-sensitivity and flow behaviour can the choice of the most appropriate dryer be narrowed down to one or two types. There is a great deal of useful information on topics such as power consumption of agitators, heat transfer in agitated vessels and the phenomena responsible for product degradation which have not hitherto been condensed into a single document and presented in a form useful to the intending dryer user or designer. The main types of physical, chemical and biological change which can impair product quality as a result of heating are described. The rheological transitions that can occur as a material dries are considered and their effects on agitator power consumption and heat transfer coefficient are discussed. Published scale-up rules and correlations for agitator power consumption and heat transfer coefficients are presented and recommendations made on their usefulness. The remainder of the report surveys the main types of dryer which are best suited to drying these grades of materials. These include freeze dryers and short residence time and specialised atmospheric dryers.

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Volume DRY X  Part 9 Troubleshooting

Sections of this manual part will include :-

1. Introduction
2. Particulate Gas Problems
3. Equipment Failure Modes
4. Recommended Procedures