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What happens to cream when whole milk is allowed to stand?
What happens to cream when whole milk is allowed to stand?
What is the primary advantage of using a centrifuge over natural sedimentation?
What is the primary advantage of using a centrifuge over natural sedimentation?
Which equation correctly describes the centrifugal force acting on a particle in circular motion?
Which equation correctly describes the centrifugal force acting on a particle in circular motion?
At what point can the effects of gravity usually be neglected in the analysis of separation in industrial centrifuges?
At what point can the effects of gravity usually be neglected in the analysis of separation in industrial centrifuges?
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What does the variable 'N' represent in the equation for centrifugal force?
What does the variable 'N' represent in the equation for centrifugal force?
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How can the centrifugal acceleration be expressed for comparative purposes?
How can the centrifugal acceleration be expressed for comparative purposes?
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Using a centrifuge, what is the resultant centrifugal acceleration derived from a rotational speed of 2000 rev/min and a radius of 10cm?
Using a centrifuge, what is the resultant centrifugal acceleration derived from a rotational speed of 2000 rev/min and a radius of 10cm?
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What will likely happen if the rotational speed of a centrifuge is increased significantly?
What will likely happen if the rotational speed of a centrifuge is increased significantly?
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What factor significantly influences the settling velocity of a particle according to Stokes' Law?
What factor significantly influences the settling velocity of a particle according to Stokes' Law?
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What does the constant 's' represent in the empirical relationship for compressibility?
What does the constant 's' represent in the empirical relationship for compressibility?
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What is the condition for Stokes' Law to be applicable?
What is the condition for Stokes' Law to be applicable?
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What is the primary function of the mechanical support in filtration equipment?
What is the primary function of the mechanical support in filtration equipment?
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What is the value of the viscosity of air used in the calculations?
What is the value of the viscosity of air used in the calculations?
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In a plate and frame filter press, where does the filter cake build up during filtration?
In a plate and frame filter press, where does the filter cake build up during filtration?
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Which diameter of dust particle would settle faster in air, assuming other factors remain constant?
Which diameter of dust particle would settle faster in air, assuming other factors remain constant?
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What is the Reynolds number for the 60μm particles calculated to be?
What is the Reynolds number for the 60μm particles calculated to be?
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What happens when the space between the frames of a plate and frame filter press becomes filled with cake?
What happens when the space between the frames of a plate and frame filter press becomes filled with cake?
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Which of the following best describes the operation of a plate and frame filter press during the filtration cycle?
Which of the following best describes the operation of a plate and frame filter press during the filtration cycle?
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What does the term 'free settling' imply in the context of sedimentation?
What does the term 'free settling' imply in the context of sedimentation?
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What is a significant disadvantage of plate and frame filter presses?
What is a significant disadvantage of plate and frame filter presses?
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In what scenario is it necessary to seek more detailed references instead of using Stokes' Law?
In what scenario is it necessary to seek more detailed references instead of using Stokes' Law?
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What must be done occasionally to maintain the efficiency of a plate and frame filter press?
What must be done occasionally to maintain the efficiency of a plate and frame filter press?
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What is the proportional relationship of settling velocity (vm) for different diameters of particles?
What is the proportional relationship of settling velocity (vm) for different diameters of particles?
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In which situation might it be necessary to wash the filter cake?
In which situation might it be necessary to wash the filter cake?
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What is terminal velocity?
What is terminal velocity?
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Which factors influence terminal velocity?
Which factors influence terminal velocity?
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What does the drag force on a particle depend on?
What does the drag force on a particle depend on?
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What does the equation $Fs = Va (\rho_p - \rho_f)$ represent in particle motion?
What does the equation $Fs = Va (\rho_p - \rho_f)$ represent in particle motion?
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What is the significance of the coefficient known as the drag coefficient (C)?
What is the significance of the coefficient known as the drag coefficient (C)?
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Which of the following equations represents terminal velocity for spherical particles?
Which of the following equations represents terminal velocity for spherical particles?
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What role does sedimentation play in fluid dynamics?
What role does sedimentation play in fluid dynamics?
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How is the projected area (A) of a spherical particle defined?
How is the projected area (A) of a spherical particle defined?
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What must be considered when performing sieve analysis on particles that differ greatly from spherical shape?
What must be considered when performing sieve analysis on particles that differ greatly from spherical shape?
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What type of sieves are typically used in the flour-milling industry for particle separation?
What type of sieves are typically used in the flour-milling industry for particle separation?
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What is critical for achieving effective separation with vibrating screens?
What is critical for achieving effective separation with vibrating screens?
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Which industrial sieve type utilizes a horizontal cylinder for particle separation?
Which industrial sieve type utilizes a horizontal cylinder for particle separation?
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What does Stokes' Law help to determine in the context of particle separation?
What does Stokes' Law help to determine in the context of particle separation?
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In sieve analysis, what typically occurs to the finer particles as they progress along a continuous vibrating sieve?
In sieve analysis, what typically occurs to the finer particles as they progress along a continuous vibrating sieve?
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What is the primary purpose of using air classification below the sieves in certain industrial applications?
What is the primary purpose of using air classification below the sieves in certain industrial applications?
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What size range of particles can typically be screened industrially?
What size range of particles can typically be screened industrially?
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What is the primary function of the conical plates in liquid/liquid separation centrifuges?
What is the primary function of the conical plates in liquid/liquid separation centrifuges?
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What challenge do solids present in liquid/solid separation within a centrifuge?
What challenge do solids present in liquid/solid separation within a centrifuge?
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How do nozzles function in the context of handling solids in a centrifuge?
How do nozzles function in the context of handling solids in a centrifuge?
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What is the role of telescoping action in a centrifugal bowl?
What is the role of telescoping action in a centrifugal bowl?
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In a horizontal bowl centrifuge with scroll discharge, what happens to the liquid during operation?
In a horizontal bowl centrifuge with scroll discharge, what happens to the liquid during operation?
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What is the recommended scroll speed relative to the bowl speed in a horizontal bowl centrifuge operating at 2000 rev/min?
What is the recommended scroll speed relative to the bowl speed in a horizontal bowl centrifuge operating at 2000 rev/min?
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Why is it important to maintain differential speeds between the scroll and the bowl in centrifuges?
Why is it important to maintain differential speeds between the scroll and the bowl in centrifuges?
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What potential issue arises from using stationary ploughs in a liquid/solid separation centrifuge?
What potential issue arises from using stationary ploughs in a liquid/solid separation centrifuge?
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Study Notes
Mechanical Separations
- Mechanical separations are categorized into four groups: sedimentation, centrifugal separation, filtration, and sieving.
- Sedimentation separates immiscible liquids or a liquid and a solid based on density differences using gravity. Centrifugal forces can often speed up the process.
- Filtration separates a solid from a liquid by passing the mixture through a material with fine pores small enough to stop the solid particles, but allowing the liquid to pass.
- Sieving is used to classify solid particles by using a barrier that allows only smaller particles to pass through.
- Mechanical separation of particles from a fluid is influenced by forces such as gravity, centrifugal force, pressure forces, and restraining forces (sieving/filtration). Particle characteristics (size, shape, density) and fluid properties (viscosity, density) are crucial in the separating process.
Velocity of Particles Moving in a Fluid
- Under constant force (e.g., gravity), particles in a fluid initially accelerate then reach a uniform velocity called terminal velocity.
- Terminal velocity depends on particle size, density, shape, and fluid properties.
- Two key forces act on particles moving in a fluid: the external force causing motion and a drag force due to fluid friction.
- The net external force on a moving particle is the difference between the applied force and the resisting drag force.
Sedimentation
- Sedimentation uses gravitational force to separate particles from fluids, often in food industries.
- Particles settle at different rates based on density, size, and shape.
- Stokes' Law is a fundamental equation used to calculate settling velocity of particles.
Flotation
- Flotation is a technique used to separate fine particles, which might not settle effectively by gravity.
- Flotation involves using air bubbles to lift the particles to the surface, changing their buoyancy.
- Surface active agents can enhance flotation.
Centrifugal Separations
- Centrifugal separators use rapid rotation to increase the separation rate of particles.
- Centrifugal force is calculated using the formula Fc = (mv²)/r.
- Heavier particles are forced outward in centrifuges due to centrifugal force, lighter particles move inward.
- Centrifugal force greatly increases separation rate compared to relying just on gravity. This is used in dairy products for separating milk from cream.
Filtration
- Filtration is a method for removing solids from a liquid based on the pore size.
- Filter resistance is determined by the filter medium and filter cake.
- Factors like pressure difference, filter cloth properties, and velocity of the filtrate affect filtration rate.
- Constant rate filtration occurs based on the filter medium resistance and when a constant pressure difference drives the filtration.
Sieving
- Sieving separates particles based on size using screens or meshes.
- Particle size, shape, and shaking intensity affect the sieving rate.
- Sieving is used for sorting materials and determining particle size distribution.
Equations in this Section
- Many equations are given describing the forces and velocities associated with these separation methods. Note the importance of consistent units when using these equations. Various equations are used for different situations (e.g., Stokes' Law, centrifugal force equation, filtration rate equation). Understanding and being able to apply these equations are key to solving problems.
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Description
Test your understanding of mechanical separation methods such as sedimentation, filtration, and sieving. This quiz covers the principles and characteristics that influence the separation of particles from fluids. Get ready to explore the physics behind these essential procedures!