Mechanical Operations

31. A centrifugal filtration unit operating at a rotational speed of w has inner surface of the liquid (density ρL) located at a radial distance R from the axis of rotation. The thickness of the liquid film is δ and no cake is formed. The initial pressure drop during filtration is

1. ½w² . R² . ρL
2. ½w² . δ² . ρL
3. ½w² . δρL (2R + δ)
4. ½w² . R . ρL(R + 2δ)

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32. A compressible cake has the

1. Maximum porosity at the upstream side
2. Maximum porosity at the filter medium
3. Same porosity throughout the cake thickness
4. None of these

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33. A cottrell precipitator makes use of the _________ for dusty air cleaning.

1. Electric spark
2. Corona discharge
3. Alternating current
4. None of these

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34. A filter press is

1. A batch filter
2. Not suitable, if the liquid is the main product
3. Having prohibitively high maintenance cost
4. Not suitable for wide range of materials under varying operating conditions of cake thickness and pressure

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35. A fluid energy mill is used for

1. Cutting
2. Grinding
3. Ultra grinding
4. Crushing

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36. A pebble mill

1. Is a ball mill
2. Employs flints or ceramic pebbles as the grinding medium
3. Is a tube mill lined with ceramic or other non-metallic liner
4. Both (B) and (C)

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37. A propeller agitator

1. Produces mainly axial flow
2. Is used for mixing high viscosity pastes
3. Runs at very slow speed (2 rpm)
4. All (A), (B) and (C)

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38. A sand mixture was screened through a standard 10-mesh screen. The mass fraction of the oversize material in feed, overflow and underflow were found to be 0.38, 0.79 and 0.22 respectively. The screen effectiveness based on the oversize is

1. 0.5
2. 0.58
3. 0.68
4. 0.62

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39. A screen is said to be blinded, when the

1. Over-sizes are present in undersize fraction
2. Under-sizes are retained in oversize fraction
3. Screen is plugged with solid particles
4. Screen capacity is abruptly increased

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40. A straight line is obtained on plotting reciprocal of filtration rate vs. the volume of filtrate for _________ flow of filtrate.

1. Compressible cakes and laminar
2. Incompressible cake and laminar
3. Compressible cake and turbulent
4. Incompressible cake and turbulent

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