Mechanical Operations

181. In case of grinding in a ball mill

1. Wet grinding achieves a finer product size than dry grinding
2. Its capacity decreases with increasing fineness of the products
3. Grinding cost and power requirement increases with increasing fineness of the products
4. All (A), (B) and (C)

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182. In classification, particles are said to be equal settling, if they have the same terminal velocities in the

1. Different fluids
2. Same fluid
3. Same field of force
4. Both (B) and (C)

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183. In closed circuit grinding as compared to open circuit grinding, the

1. Specific surface of product is more
2. Product has lesser size uniformity
3. Production rate at a given limiting size is lower
4. Operation is economical

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184. In coal washeries, three products namely the valuable product (i.e. clean/washed coal), discarded product (i.e. mineral matter) and an aD⁵itional concentrated product called _________ is produced.

1. Concentrate
2. Tailing
3. MiD⁵ling
4. None of these

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185. In constant pressure filtration,

1. Resistance decreases with time
2. Rate of filtration is constant
3. Rate of filtration increases with time
4. Rate of filtration decreases with time

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186. In continuous filtration (at a constant pressure drop), filtrate flow rate varies inversely as the

1. Square root of the velocity
2. Square of the viscosity
3. Filtration time only
4. Washing time only

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187. In filtration, the use of 'filter aid' helps in

1. Reducing the filtration pressure
2. Accelerating the rate of filtration
3. Deplugging the filter medium
4. Enhancing the cake porosity in case of a dense impermeable cake

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188. In froth floatation, chemical agent aD⁵ed to cause air adherence is called

1. Collector
2. Frother
3. Modifier
4. Activator

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189. In screen analysis, the notation +5 mm/-10 mm means particles passing through

1. 10 mm screen and retained on 5 mm screen
2. 5 mm screen and retained on 10 mm screen
3. Both 5 mm and 10 mm screens
4. Neither 5 mm nor 10 mm screen

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190. In the cyclone separator used for separation of dust from dust laden gas, the gas

1. Enters the cyclone from the top
2. Is admitted tangentially at high velocity
3. Develops a helical motion inside the chamber
4. Both (B) and (C)

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