# Mechanical Operations Questions and Answers – Pressure Filters

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This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Pressure Filters”.

1. When more than two components are to be mixed, they should always be mixed in _____ order of weight.
a) Ascending
b) Descending
c) Maximum
d) Minimum

Explanation: When more than two components are to be mixed, they should always be mixed in ascending order of their weights so as to ensure uniform mixing of the ingredients.

2. Due to overfilling, efficiency is _____
a) Constant
b) Infinity
c) Maximum
d) Minimum

Explanation: The mixer must allow sufficient space for dilation of the bed. Overfilling reduces the efficiency and may prevent mixing entirely.

3. Degree of mixing approaches, its limiting equilibrium value ____
a) Elliptically
b) Asymptotically
c) Exponentially
d) Bilaterally

Explanation: Since the degree of mixing will approach its limiting equilibrium value asymptotically. Hence, there is an optimum time for mixing for any particular situation.
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4. Which of the following has lowest efficiency?
a) Agitator mixer
b) Propeller mixer
c) Impellor mixer
d) Tumbling mixer

Explanation: Agitator mixers for powders can take a similar form to paddle mixers for liquids, but their efficiency is low.

5. A double cone mixer consists of a vessel with two cones _____
a) Base to base
b) Base to top
c) Top to top
d) Top to base

Explanation: A double cone mixer consists of a vessel with two cones base to base, with or without a cylindrical section in between, it is so mounted that it can be rotated at right angles.

6. The cone mixer has a rotating angle of ____
a) 20 – 500
b) 10 – 900
c) 0 – 3600
d) 00

Explanation: The mixing barrel can be tilted freely at the angle of 0°~360° degrees for discharging and cleaning purpose.

7. If the solid is not too coarse, the solid can be suspended in _____
a) Liquid
b) Gas
c) Mixer
d) Steam

Explanation: If the solid is not too coarse, the liquid is not too viscous and the percentage of solids is not too great, solids can be suspended in liquids by the use of a propellers.

8. At what speeds shear mixers can works?
a) 3000 to 15,000 rpm
b) 1000 to 1500 rpm
c) 5000 to 10,000 rpm
d) 500 to 1000 rpm

Explanation: The rotor works at a speed of the order of 3000 to 15000 r.p.m. and the clearance can be adjusted between 50 and 500 micrometers.

9. The main function of the colloid mill is to ____
a) Ensure mixing
b) Ensure agglomeration
c) Ensure drying
d) Ensure separation

Explanation: The main function of the colloid mill is to ensure a breakdown of agglomerates or in the case of emulsions to produce droplets of fine size around 1 micron.

10. What are the speeds of colloid mixer?
a) 3000 to 20,000 rpm
b) 1000 to 1500 rpm
c) 5000 to 10,000 rpm
d) 500 to 1000 rpm

Explanation: Rotational speed of the rotor varies from 3,000-20,000 r.p.m. with the spacing between the rotor and stator capable of very fine adjustment varying from 0.001 to 0.005 inch.

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