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The cumulative weight percentage up to 0.5 μ particle size class is 30.7%.
True
26.76% of the total sample is less than 1.5 μ.
False
The total cumulative weight is 40 grams.
False
All particles with a size class of 4.0 μ have a cumulative weight percentage of 1.3%.
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The cumulative weight percentage up to 2.0 μ particle size class is 85.2%.
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73.24% of the total sample is less than 1.5 μ.
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The particle size class of 1.0 μ has a cumulative weight percentage of 30.7%.
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The cumulative weight percentage up to 3.0 μ particle size class is 94.1%.
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The main objective of size separation is to increase the production cost.
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The size separation range for sieving is 0.5-100μm.
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The wire mesh of the sieves should be of rectangular cross-section.
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Data on particle size distributions are normally collected by centrifugation.
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The separation method used affects the size-separation efficiency.
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Particle size measurement is only dependent on the nature of the material to be sized.
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Sieving is a method used for particle size measurement in the range of 0.1-10μm.
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Particle size distributions are always presented in graphical form.
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The particle size class of 0.5 μ has a cumulative weight of 98.62%
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The graph on the right shows the relative amount of particles in each size class.
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The cumulative frequency curve is a step function.
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The particle size class of 1.5 μ has a weight of 1.5 grams.
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The cumulative weight of particles in the size class of 0.1 μ is 1.38 grams.
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The graph on the left shows the cumulative weight of particles in each size class.
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The particle size class of 5 μ has a cumulative weight of 100%
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The cumulative frequency curve can be used to determine the percentage weight of particles in each size class.
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The cumulative weight percentage is plotted against the particle size class on the x-axis.
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Microscopy is a method to determine particle size distribution that can measure particles up to 1000m.
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Sedimentation methods are based on the principle of size separation by sedimentation, which utilizes the differences in settling velocities of particles with different diameters.
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Stokes' Law predicts the settling velocity of small spheres in fluid, either air or water, and is given by the equation w = g.
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Centrifugal sedimentation is used for particle size ranges up to 1000m.
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Gravitational sedimentation is used for particle size ranges from 4-1000m.
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Sedimentation is the process by which particulates settle to the top of a liquid and form sediment.
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A simple technique of sedimentation classification uses a chamber containing a suspension of solid particles in a liquid, which is usually water.
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In a sedimentation method, the feed enters the outer wall of the bowl and the suspension passes through each chamber in turn.
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The coarse particles deposit in the outer chamber and the increasingly fine particles deposit on the subsequent chambers.
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Elutriation is a technique in which the fluid flows in the same direction as the sedimentation movement.
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In elutriation, particles are divided into different size fractions depending on the density of the fluid.
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The highest velocity is found in the tube walls and the lowest velocity at the tube center.
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The size of particles that will be separated depends on their position in the tube, the smallest particles in the center, the largest towards the outside.
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The suspension is introduced tangentially at fairly low velocity in cyclone methods.
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In cyclone methods, the rotary movement takes place within the vessel at low velocity.
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Study Notes
Particle Size Separation
- Particle size separation is a process by which powder particles are removed from gases or liquids.
- The objective of size separation is to:
- Recover valuable products or byproducts
- Prevent environmental pollution
- The efficiency of size separation depends on:
- Particle and fluid properties
- The separation method used
- Separation efficiency is determined as a function of the effectiveness of a given process in separating particles into oversize and undersize fractions.
Size Separation Methods
- Sieving:
- Size separation ranges: 5-10000μm
- Most widely used method of analysis
- Different grades of sieves are used for sifting the powders
- The wire mesh of the sieves should be of uniform circular cross-section and possess adequate strength to avoid distortion and be resistant to chemical action.
- Method selection considerations:
- Nature of the material to be sized
- Estimated particle size and particle size range
- Solubility
- Ease of handling
- Toxicity
- Flowability
- Intended use
- Cost
- Specification requirements
- Time restrictions
Particle Size Measurement
- Data presentation:
- Table form
- Graph form
- Statistical summarizing:
- Particle size distributions are normally collected by sieving
- Cumulative weight percentage can be calculated
Sedimentation Methods
- Separation ranges:
- Centrifugal sedimentation up to 4μm
- Gravitational sedimentation, 4-1000μm
- Principle:
- Size separation by sedimentation utilizes the differences in settling velocities of particles with different diameters
- Stokes' Law predicts the settling velocity of small spheres in fluid
- Sedimentation techniques:
- A. Simple technique: uses a chamber containing a suspension of solid particles in a liquid
- B. Alternative: uses a series of chambers with increasing distances from the axis
Elutriation Methods
- Principle:
- Elutriation is a technique in which the fluid flows in an opposite direction to the sedimentation movement
- Particles move vertically downwards while the fluid travels vertically upwards
- Types of elutriation:
- Based on counter flow of fluid (air/water) and settling particles through vertical columns
- Uses a distribution of velocities across the tube in which a fluid is flowing
Cyclone Methods
- Principle:
- The suspension is introduced tangentially at fairly high velocity, so that a rotary movement takes place within the vessel.
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Description
Learn about particle size separation, its objectives, and the factors affecting its efficiency. Understand the importance of size separation in recovering valuable products and preventing environmental pollution.
