A gravity settling chamber removes particles by
Answer: A
Reducing the velocity gives the particles time to fall the height of the chamber before the gas leaves it. Only particles above about fifty micrometres settle fast enough to be caught, which confines the device to a pre-cleaning duty ahead of something more capable.
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Stokes law gives the terminal settling velocity of a small particle as proportional to
Answer: B
Because the dependence is quadratic, halving the diameter quarters the settling velocity and quadruples the chamber length needed to catch it. That steep falling-off is exactly why gravity settling is useless for the fine fraction that matters most to health.
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A cyclone separates particles by
Answer: C
The gas enters tangentially and spirals downward, and particles too massive to follow the turning streamlines strike the wall and fall into the hopper. Nothing moves and nothing is consumed, which makes the cyclone the most robust device in the family.
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The cut diameter of a cyclone is the particle size at which
Answer: D
It is the single figure by which cyclones are compared, and efficiency rises steeply above it and falls away below. A high efficiency cyclone achieves a smaller cut diameter by using a narrower body, and pays for it in pressure drop.
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A high efficiency cyclone achieves a smaller cut diameter chiefly by
Answer: A
A smaller radius means a greater centrifugal acceleration for the same tangential velocity, so smaller particles reach the wall. The penalty is a pressure drop several times that of a conventional cyclone, and the fan power that goes with it.
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A fabric filter collects particulate principally
Answer: B
The fabric provides the support and the initial collection, but within minutes the cake it carries does most of the work and captures far finer particles than the weave could. Over-cleaning that removes the cake entirely is a common cause of poor performance.
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The air to cloth ratio of a fabric filter is
Answer: C
It expresses the average velocity through the medium and is the primary sizing parameter for a baghouse. Too high a value drives dust into the fabric, raises the pressure drop and shortens bag life, so it is chosen conservatively.
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Reverse air, shaker and pulse jet describe
Answer: D
Each dislodges the accumulated cake in a different way, and each permits a different air to cloth ratio. Pulse jet cleaning is the most aggressive and allows the highest ratio, which is why it dominates new installations.
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An electrostatic precipitator collects particles by
Answer: A
A high voltage discharge electrode creates a corona that charges passing particles, and the electric field then drives them to the collecting plate. Because the gas itself is not obstructed, the pressure drop is remarkably low for the efficiency achieved.
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The Deutsch-Anderson equation relates precipitator efficiency to
Answer: B
Efficiency appears as one minus an exponential in the product of area and migration velocity divided by flow. Because the relationship is exponential, each further increment of efficiency costs disproportionately more plate area.
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