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Questions and Answers
What happens to the manometric pressure gradient when a fluid passes upward through a packed bed and U increases?
What happens to the manometric pressure gradient when a fluid passes upward through a packed bed and U increases?
At which point do the particles become free to move around in the fluid?
At which point do the particles become free to move around in the fluid?
What is the equation that relates the pressure difference across the bed to the properties of the particles?
What is the equation that relates the pressure difference across the bed to the properties of the particles?
What is the term used to describe the state of the particles when they are supported by the fluid and not by neighboring particles?
What is the term used to describe the state of the particles when they are supported by the fluid and not by neighboring particles?
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What is the purpose of the graph shown in Figure 5.4?
What is the purpose of the graph shown in Figure 5.4?
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What is the term used to describe the velocity at which the particles become fluidized?
What is the term used to describe the velocity at which the particles become fluidized?
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What is the purpose of Table 5.1?
What is the purpose of Table 5.1?
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What is the name of the researcher who classified fluidized bed applications according to predominating mechanisms?
What is the name of the researcher who classified fluidized bed applications according to predominating mechanisms?
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What is the term used to describe the movement of particles in a fluidized bed?
What is the term used to describe the movement of particles in a fluidized bed?
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What is the term used to describe the transfer of heat and/or mass between the gas and particles in a fluidized bed?
What is the term used to describe the transfer of heat and/or mass between the gas and particles in a fluidized bed?
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Study Notes
Fluidization
- When a fluid passes upward through a packed bed, the manometric pressure gradient increases as the fluid velocity (U) increases.
- At a certain point, the pressure drop is just sufficient to support the immersed weight of the particles, and the particles become "fluidized" and free to move around in the fluid.
- At this point, the manometric pressure gradient (Dp) is related to the bed height (H) and the minimum fluidization porosity (εmf) by the equation: Dp=H ¼ ð1 εmfÞ rp r g (5.2)
Characteristics of Fluidized Beds
- Bubbles form in a fluidized bed, with gas and solid velocities shown in Figure 5.3.
Classification of Fluidized Bed Applications
- Table 5.1 provides a classification of fluidized bed applications according to predominating mechanisms, including:
- Physical processes
- Chemical processes
- Heat and/or mass transfer between gas/particles
- Heat and mass transfer between particle/particle or particle/surface
- Heat transfer between bed/surface
- Gas/gas reactions in which solid acts as catalyst or heat sink
- Gas/solid reactions in which solids are transformed
- Examples of industrial processes that use fluidized beds include:
- Solids drying
- Absorption of solvents
- Cooling of fertilizer prills
- Food freezing
- Plastic coating of surfaces
- Coating of pharmaceutical tablets
- Granulation
- Mixing of solids
- Dust filtration
- Heat treatment of textile fibers, wire, rubber, glass, metal components
- Constant temperature baths
- Oil cracking, reforming
- Manufacture of various chemicals and materials
- Coal combustion
- Coal gasification
- Roasting of nickel and zinc sulphides
- Incineration of liquid and solid waste
- Production of various chemicals and materials
- Catalyst regeneration
- Decomposition of limestone
- Production of UF6, AlF3
- Production of UO2, UO3
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Description
This quiz covers the concept of fluidization in a packed bed, where the fluid's pressure gradient increases with velocity, and the particles become suspended and free to move.
