DRY 8: Radio Frequency and Microwave Drying
     Part 1: Feasibility of Dielectric Heating for Dryer Operations
         1 INTRODUCTION
             1.1 Introduction and Scope of Report
             1.2 Outline of the Report
         2. FEASIBILITY OF DIELECTRIC HEATING FOR DRYING OPERATIONS
             2.1 Introduction
             2.2 Preliminary Feasibility Study Based on Process and Final Product Requirements
             2.3 Technical Feasibility - Power Absorption and Drying Characteristics
             2.4 Advantages and Limitations of Dielectric Heating Techniques
             2.5 Design of Dryer, Drying Tests and Choice Between Radio or Microwave Frequencies
             2.6 Recent Developments in Dielectric Dryers
     Part 2: State of the Science
         1 VOLUMETRIC POWER ABSORPTION
             1.1 Introduction
             1.2 Frequency of Operation
             1.3 Dielectric Loss Factor
                 1.3.1 Mechanisms for energy absorption in liquids
                 1.3.2 Representation of loss mechanisms for dipolar and conductive losses in liquids
                 1.3.3 Loss mechanisms in dry solids
                 1.3.4 Dielectric properties of wet materials
                 1.3.5 Mixture theories for dielectric properties
                 1.3.6 Measurement of dielectric properties
                 1.3.7 Dielectric Data
             1.4 Electric Field Strength
                 1.4.1 Practicable electric field strengths - Electrical breakdown in air
                 1.4.2 Uniform heating in practice - limitations due to electric field penetration
                 1.4.3 Changes in the electric field at the interface of two dielectrics
             1.5 Power absorption by Human Beings - Safety Limits for Exposure to Electromagnetic fields
             1.6 Typical Values for Dielectric Heating
             1.7 Principal Symbols for Section Three
         2. HEAT AND MASS TRANSFER
             2.1 Introduction
             2.2 Physical Mechanisms for Internal Heat and Mass Transfer
             2.3 Simplified View of Drying Behaviour
                 2.3.1 Modified wet bulb temperature
                 2.3.2 Modified adiabatic saturation temperature
             2.4 Drying Characteristics - Basis of Modelling
             2.5 Drying Characteristics - Experimental and Theoretical Results
                 2.5.1 Webs and sheets - large power density
                 2.5.2 Webs and sheets - low power densities
                 2.5.3 Drying of blocks and slabs - large power densities
                 2.5.4 Combinational Drying of blocks and slabs.
                 2.5.5 Drying of particulate beds - drying with dielectric heating.
                 2.5.6 Combinational drying of particulate beds - throughflow of air.
             2.6 Modelling of Freeze Drying
             2.7 Vacuum Drying
             2.8 Overview of Modelling and the Use of Drying Tests
             2.9 Principal Symbols Section Two
     Part 3: State of the Technology
         1. INDUSTRIAL RADIO FREQUENCY DRYERS
             1.1 Introduction
                 1.1.1 Classification of dryers
                 1.1.2 Applicator ovens
                 1.1.3 Industrial systems
             1.2 RF Generators
             1.3 Drying of web and sheet material- - Strayfield Electrodes
                 1.3.1 Large power output dryers 200-900 kW rf power
                 1.3.2 Small power output dryers < 20 kW's rf power
             1.4 Drying of slabs - through field and staggered through field rod electrodes
             1.5 Drying of blocks and stab - plate electrodes
             1.6 Drying of Particulates
             1.7 Power Requirements, Efficiencies and Costs
                 1.7.1 Energy for drying
                 1.7.2 Efficiency of energy usage
                 1.7.3 Capital costs
             1.8 Operating Characteristics
                 1.8.1 Dryer controls and monitoring for abnormal behaviour
                 1.8.2 Safety measures for operating personnel
                 1.8.3 Maintenance
                 1.8.4 Fire and explosion hazards
                 1.8.5 Operating experience
                 1.8.6 Design
         2. RADIO FREQUENCY COMPONENTS
             2.1 Introduction
             2.2 RF Power Generators
             2.3 The Heating Oven (Applicator) - Types of Capacitor
                 2.3.1 Introduction
                 2.3.2 Parallel plate electrodes
                 2.3.3 Strayfield electrodes
                 2.3.4 Staggered through-field and through-field rod electrodes
             2.4 Other Applicator Electrode Configurations
             2.5 Tuning Capacitors
             2.6 Construction of Electrodes
             2.7 Tuning Inductors
             2.8 Leads and Earth Straps
             2.9 Auxiliary Wiring
             2.10 Combined Inductance and Capacitance for the Tank Circuit
             2.11 Frequency Filters
             2.12 Transportation of the Product - Belting Material
             2.13 Sensors For Electromagnetic Environments
                 2.13.1 Temperature measurement
                 2.13.2 Humidity measurement
                 2.13.3 Electric field measurements
                 2.13.4 Monitoring of leakage power from dryers
             2.14 Principal Symbols for Section Six
         3. INDUSTRIAL MICROWAVE SYSTEM OPERATING AT ATMOSPHERIC PRESSURE
             3.1 Introduction
             3.2 Microwave generators
             3.3 Drying of Webs and Sheets - Meander and Single Mode Resonant Devices
             3.4 Drying of Blocks, Slabs, and Beds of Particulates
                 3.4.1 Batch ovens
                 3.4.2 Continuous ovens
             3.5 Power Requirements, Efficiency and Costs.
             3.6 Operating characteristics
                 3.6.1 Dryer controls and monitoring for abnormal behaviour
                 3.6.2 Safety measures for operating personnel
                 3.6.3 Maintenance
                 3.6.4 Fire and explosion hazards
                 3.6.5 Operating experience
                 3.6.6 Design
         4. MICROWAVE VACUUM DRYERS
             4.1 Introduction
             4.2 Continuous Vacuum Dryers
             4.3 Batch Vacuum Dryer
             4.4 Power Requirements, Efficiencies and Running Costs
                 4.4.1 Energy for drying
                 4.4.2 Efficiency of energy usage
                 4.4.3 Capital costs
             4.5 Design and Operating Experience with Batch Vacuum Microwave Dryers
                 4.5.1 Introduction
                 4.5.2 Design
                 4.5.3 Operation
             4.6 Freeze Drying
             4.7 Combined Microwave Heating and Vacuum Drying
         5. MICROWAVE COMPONENTS
             5.1 Introduction
             5.2 Power Generation - Tubes for Microwave Heating
             5.3 Isolating the Power Supply from Reflected Energy - Circulators and Isolators
             5.4 Transmitting Microwave Energy to the Oven Cavity - Waveguides and Flanges
             5.5 Transmitting Microwave Energy - Bends, Twists and Corners
             5.6 Transmitting Microwave Energy - Power Splitters, T Junctions and Magic Tees
             5.7 Transmitting Microwave Energy - Mounting of the Magnetron
             5.8 Dissipating Unused Microwave Energy - Water Loads
             5.9 Power Transfer - Stub Tuners, Matching Irises and Posts
             5.10 Launching of Microwave Power into the Heating Oven Horns and Lossy Waveguide Antennas
             5.11 Waveguide Windows which Permit Microwave Propagation
             5.12 Apertures, Inlet and Outlet Product Ports - Containment of Microwave Energy
             5.13 Viewing Windows and Perforated Plates for Shielding
             5.14 Transportation of the Product - Belting Material
             5.15 Drying Ovens - Microwave Applicators
             5.16 Uniform Heating - Mode Stirrers
             5.17 Uniform Heating - Turntables
             5.18 Sensors For Electromagnetic Environments
                 5.18.1 Temperature measurement
                 5.18.2 Humidity measurement
                 5.18.3 Electric field measurements
                 5.18.4 Monitoring of leakage power from dryers
             5.19 Principal Symbols Section 5
         6 COMBINATIONAL DRYERS
             6.1 Introduction
             6.2 Convective Dryer Assisted by Radio Frequency Heating (ARFA)
             6.3 Power Requirements, Efficiencies and Costs for the ARFA Dryer
                 6.3.1 Power requirements
                 6.3.2 Efficiency of energy usage
                 6.3.3 Capital costs
             6.4 Combinational Microwave and Hot Air Dryer - Microdry System
             6.5 Operating Characteristics
             6.6 Other Forms of Combinational Dryer
     Part 4: Electromagnetic Fundamentals
         1 RESONANT CIRCUITS
             1.1 Introduction
             1.2 Voltage and Current Relationships for Discrete Circuits
                 1.2.1 Direct current circuits
                 1.2.2 Alternating current circuits
                 1.2.3 Use of complex numbers in circuit theory
                 1.2.4 Power dissipation and storage
             1.3 Oscillatory Circuits
             1.4 Resonant Circuits
                 1.4.1 Series resonance
                 1.4.2 Parallel resonance
                 1.4.3 Inductively coupled circuits
                 1.4.4 Criteria for power transfer and frequency of operation
                 1.4.5 Self-excited oscillators
                 1.4.6 Summary of formulae and some numerical values for Chapter 1
             1.5 Principal Symbols for Chapter 1
         2 CIRCUITS AT RADIO AND MICROWAVE FRFOUENCIES
             2.1 Introduction
             2.2 Wave Propagation
             2.3 Ideal Conductors
             2.4 Transmission Line Theory
                 2.4.1 Ideal Line- circuit approach
                 2.4.2 Ideal transmission line terminated in an arbitrary impedance
                 2.4.3 Reflections on a line terminated in an arbitrary impedance
                 2.4.4 Smith chart
                 2.4.5 Electromagnetic approach to transmission lines
                 2.4.6 Losses in transmission lines
                 2.4.7 Radiation from an open ended transmission line
             2.5 Principal Symbols Chapter 2
         3 WAVE GUIDE THEORY
             3.1 Introduction
             3.2 Basic characteristics and nomenclature
             3.3 Rectangular waveguides
             3.4 Cylindrical waveguides
             3.5 Wave impedance, reflections and matching
             3.6 Principle of matching techniques
             3.7 Excitation of waveguide modes
             3.8 Microwave resonant cavities
                 3.8.1 Single mode cavities
                 3.8.2 Multimode resonance cavities
             3.9 Principal Symbols for Chapter 3
         4 CONCLUSIONS AND RECOMMENDATIONS
             4.1 Conclusions
             4.2 Recommendations
     Part 5: References and Appendices
         1 ACKNOWLEDGEMENTS
         2 BIBLIOGRAPHY
         3 REFERENCES
         4 APPENDIX 1 LIST OF EQUIPMENT MANUFACTURERS
         5 APPENDIX 2 Glossary of radio-frequency and microwave heating terms
     Terms and Conditions of Use

The desire to improve product quality and drying efficiency has led to the development of new techniques and dryers to replace traditional equipment. One such technique utilises the volumetric absorption of radiofrequency and microwave (collectively called dielectric) radiation throughout the entire body of the wet material. The novelty of this technology both in terms of electrical equipment and of drying characteristics led to the writing of this major reference volume on the topic. The report is divided into four parts:

• Part 1 Feasibility of dielectric heating for dryer operations
• Part 2 State of the science
• Part 3 State of the technology
• Part 4 Electromagnetic fundamentals

Volume DRY VIII   Part 1 Feasibility of dielectric heating for dryer operations.

The volume begins with a guide to aid readers in assessing the feasibility of dielectric drying for their application.

Volume DRY VIII   Part 2 State of the science.

This includes volumetric heating (operating frequency, dielectric loss factor, electric field strength, power absorption by human beings, typical values) and heat and mass transfer (mechanisms, simplified view, drying characteristics, basis for modelling, experimental and theoretical results, freeze drying, vacuum drying, use of drying tests).

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Volume DRY VIII   Part 3 State of the technology.

This includes radiofrequency dryers, radiofrequency components, atmospheric microwave dryers, vacuum microwave dryers, microwave components and combinational dryers.

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Volume DRY VIII   Part 4  Electromagnetic Fundamentals.

Including resonant circuits, circuits at radio and microwave frequencies and wave guide theory.