Sedimentation Flashcards
This is where the particles are separated from the liquid by gravitational forces.
Sedimentation
It includes the _________ from liquid sewage wastes, settling of crystals from the mother liquor, and separation of the liquid-liquid mixture from a solvent extraction.
Removal of solids
When the particles are crowded, they settle at a lower rate. A particle is sufficiently far from the walls of the container and other particles so that it stays and is not affected by them.
The first statement is true. The second statement is false.
In some sedimentation processes, the purpose is to remove the particles from the fluid stream so that the fluid is free of particle contaminants. Fluid can exist in the form of a liquid or gas, and it can be either stationary or in motion.
Both statements are true
It is the proportionality constant and dimensionless
Drag coefficient
Whenever a particle moves through a fluid, one force will act on the particle.
The statement is false
The resultant force must be equal to the force due to?
Acceleration
Gravity acting_____, buoyant force acting______, and drag force acting ______
Downward, upward, downward
The buoyant force on the particle will counterbalance the external force and the particle will move relative to the fluid.
The statement is false
The external force of gravity is needed to impart motion to the particle. Density is not needed between the particle and the fluid.
The first statement is true. The second statement is false.
What is the process called when a dilute slurry separates by gravity into a clear fluid and a slurry of higher solids concentration?
Sedimentation
What is the primary mechanism of sedimentation?
Gravity
What is the purpose of a batch settling test?
To measure the settling velocity of a slurry
What is the purpose of a batch settling test in determining settling velocities and mechanisms of settling?
To determine the settling velocity of particles
What happens to the particles in zone B during the batch settling test?
They settle at a uniform rate
What happens to the height z during the batch settling test?
It decreases
What is the clear liquid zone in the batch settling test?
Zone A
What happens during compression in the batch settling test?
Liquid is expelled upward from zone D
What is the critical point in the batch settling test?
The point where compression first appears
What is the method proposed by Talmage and Fitch for determining thickener area?
Talmage and Fitch procedure
For many cases in settling, a small number of particles are present. The velocity gradients surrounding each particle are affected by the close presence of other particles.
The first statement is true. The second statement is false.
In settling, the surrounding particles interfere with the motion of ______ particles.
Individual
The particles in settling in the liquid displace the solid. An appreciable downward velocity of the liquid is generated.
Both statements are false
The velocity of the liquid is appreciably ____ with respect to the particle than with respect to the apparatus itself.
Greater
The true drag force is greater in the suspension because?
‘Because of the interference of other particles.
The higher viscosity of the mixture is equal to what?
The actual viscosity of the liquid
The empirical correction factor depends upon what?
The volume fraction of the slurry mixture occupied by the liquid
When the Reynolds number is less than 1, the settling is in the?
Stokes` Law regime
When will the wall effect be exerted on the particle?
When the diameter of the particle becomes appreciable with respect to the diameter of the container.
What happens to the terminal velocity when the wall effect is exerted on the particle?
It reduces
The Spitzkasten classifier separates particles based on what principle?
Size and density
In which industry is the Spitzkasten classifier commonly used?
Mining industry
What is the advantage of using a Spitzkasten classifier?
It can handle large volumes of material and is relatively inexpensive.
What is the limitation of a Spitzkasten classifier?
It may not be suitable for very fine particles.
What is the other name for the sedimentation process called?
Thickening
What is the main purpose of a sedimentation thickener in wastewater treatment?
To separate solids from the liquid using gravity
What is the shape of a typical sedimentation thickener?
Cylindrical
What is the advantage of using a sedimentation thickener?
It is a simple and cost-effective method for thickening sludge.
What is the limitation of a sedimentation thickener?
Overfeeding the thickener can lead to reduced efficiency.
In a laboratory set-up, what happens to the solids in the suspension after the sedimentation process?
They settle at the bottom of the tank.
Brownian motion is present if the particles are?
quite small
How does Brownian motion affect the settling of particles?
It may occur slowly or not at all
At what particle size (approximately) does Brownian motion become appreciable?
a few micrometers
Which of the following methods can help reduce the effect of Brownian motion for very small particles?
applying centrifugal force
What is the term used for a particle falling under the action of gravity that will accelerate until the drag force balances gravitational force?
Terminal velocity
What factors can cause fluctuations in the settling of particles?
Vortex shedding and particle shape
Where did the drag crisis occur?
At lower Reynolds number when the free stream is turbulent.
What is the random motion imparted to the particle by collisions between the molecules of the fluid surrounding the particle and particle?
Brownian Motion
Internal circulation inside the particle and particle deformation can occur when the particles are?
Non-rigid
In the turbulent Newton’s law region above a Reynolds number of about , the drag coefficient is?
0.44
Helps in separating coal samples according to the difference in their respective specific gravities in a heavy liquid medium.
Sink and Float Method
Devices for the separation of solid particles into several fractions based upon their rates of flow or settling through fluids are known as _____
Classifiers
Sink and float method is dependent on the sizes of the particles and depends only upon the relative densities of the two materials. This means liquid used must have densities greater than water, since most solid has high densities
The first statement is false. The second statement is true
Utilizes the difference in terminal velocities that can exist between substances of different densities
Differential Settling method
What is the disadvantage of the Differential Settling method
the larger, light particles settle at the same rate as the smaller heavy ones and mixed fraction is obtained
In the Sink and Float method, what happens to the heavy and light material?
the heavy material sinks through the medium while the lighter material floats
Use of Differential Settling method
to bring in the concept of equal-settling particles
This method is also called heavy-fluid separation
Sink and Float method
In the sink and float method, both light and heavy materials settle through the same medium. This method also brings in the concept of the equal-settling method
Both statements are false
What is the advantage of the Sink and Float method?
the separation depends only on the difference in the densities of the two substances and is independent of the particle size
The time given by dividing the vertical height of the chamber by the settling velocity must be ______ the residence time of air
less than
Which of the following factors most significantly affects the settling velocity of particles in a batch sedimentation tank?
particle size and density difference between the particles and the liquid
Which of the following statements about the advantages of batch sedimentation is NOT true?
it is a continuous process, allowing for constant operation
The main purpose of a primary settling tank in wastewater treatment is to:
remove a significant portion of settleable organic matter and grit through gravity separation
Which of the following applications is NOT well-suited for batch sedimentation?
continuous production of a chemical product
When designing a batch sedimentation tank, it’s important to consider the strength and stability of the structure. What factor plays a crucial role in determining the required wall thickness?
the depth of the tank and the volume of liquid it will hold.
Compared to some other wastewater treatment technologies, batch sedimentation offers the advantage of:
being a relatively simple and low-tech process with minimal moving parts
The overall efficiency of a batch sedimentation process can be limited by:
incomplete removal of settled solids during the unloading stage, leading to solids carryover in the effluent
Materials used for the construction of a batch sedimentation tank should be:
chemically resistant to the wastewater being treated
How does properly operating and maintaining a primary settling tank impact a wastewater treatment plant?
improved effluent quality and reduced downstream treatment burden
