Flashcards in Drying Deck (24):
During manufacturing, drying is essential to guarantee process performances e.g. granulation and compaction. True or false?
What is moisture content defined as?
The amount of water contained in a material
What is % moisture by volume defined as?
The molecules of water per unit volume
Moisture content and relative humidity are the same thing. True or false?
What is humidity defined as?
The amount of water vapour present in the air
Relative humidity indicates the amount of moisture in the air as a percentage of the maximum amount of moisture that the air can hold. True or false?
Water content in the air increases as temperature increases. True or false?
An increase in temperature results in an increase in relative humidity. True or false?
False - a decrease in relative humidity because the air can hold a greater amount of water vapour
What is the dew point?
The temperature to which moisture condenses and evaporates at the same rate
During drying, only moisture content can change. True or false?
False - temperature also changes
Paper is non-hygroscopic. True or false?
False - it is hygroscopic
When there is less moisture in the air, paper releases moisture. True or false?
When there is more moisture in the air, water absorbs moisture. True or false?
What is meant by total moisture?
The total amount of water associated with a wet solid
Free moisture content is the amount of water that can be easily removed. True or false?
True - also known as unbound water
What is meant by equilibrium moisture content?
The portion of water that is more difficult to remove, also known as bound water
What are the factors that need to be considered when selecting the drying method?
Heat sensitivity of materials used
Materials physical characteristics
Solvent/liquid to be removed e.g. boiling point
Efficient mass transfer of evaporated liquid
Efficient vapour removal from drying air
Amount of material to be processed e.g. scale up considerations
What are the advantages of a fluidised bed dryer?
Efficient heat transfer (minimise effects on thermo-sensitive materials)
Homogenous process - movement of particles guarantees drying of all individual ones
Free movement of particles reduces the migration process and separation/aggregation phenomena
What are the disadvantages of a fluidised bed dryer?
Turbulence might damage granules
Small particles might need specific attention to be removed from the fluidising air
Particle movement in turbulence and warm environment might cause charges of static electricity
Vacuum ovens are generally used for large scale processes. True or false?
False - small scale
Which type of dryer is used with heat-sensitive materials?
A spray dryer generates a large surface area to promote what?
Heat exchange and heat transfer
The higher the flow rate of a spray dryer, the smaller the droplets. True or false?