# Mechanical Operations Questions and Answers – Average Particle Size

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This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Average Particle Size”.

1. The volume surface mean diameter, can be defined as ___
a) 6/ΦsAwPp
b) 6/ΦsAwVp
c) 6/ΦsAwDp
d) 6/ΦsAwSp

Explanation: The average particle size of a mixture is defined by the volume surface mean diameter Ds which is related to Aw as 6/ΦsAwPp.

2. Volume of any particle, can be given as ______
a) a*Dp3
b) a*Dp2
c) a*Dp
d) a*Sp

Explanation: The volume of any particle is proportional to the cube of the diameter of the given shape
i.e. Vp = a*Dp3, where a is shape factor.

3. Crushing efficiency is the ratio of ____
a) Energy wasted to Energy wasted
b) Energy wasted to Energy created
c) Energy created Energy wasted
d) Energy Destroyed to Energy wasted

Explanation: The ratio of surface energy created by crushing to the energy absorbed y the solid is defined as the crushing efficiency nc.
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4. Crushing Efficiency ranges between ____
a) 0.06 and 1%
b) 0.05 and 2%
c) 0.5 to 5%
d) 60 to 90%

Explanation: The surface energy create is comparatively low with the total mechanical energy stored in the material, crushing efficiency is therefore low.

5. The ratio of energy absorbed to the energy input is defined as the ___
a) Crushing Efficiency
b) Mechanical Efficiency
c) Work Done
d) Final Power

Explanation: The mechanical efficiency id denoted by nm and is defined as the ratio of energy absorbed to the energy input (w).

6. On which of the equation below, Energy absorbed can be calculated?
a) es(A1-A2)/Dp
b) es(A1-A2)/nc
c) es(A1-A2)/wc
d) es(A1-A2)/sc

Explanation: The energy absorbed can be given as es(A1-A2)/wc, where es is the surface energy per unit area and A1 and A2 are the area of mass of feed and product.

7. The power required, can be given by ____
a) w*Dp
b) w*As
c) w*nc
d) w*m

Explanation: The power required by the machine can be calculate by P = w*m, where m is the feed rate and the w is the energy absorbed.

8. The surface are of the particle, is given as _____
a) πd2s
b) Φd2s
c) πV2s
d) πP2s

Explanation: If Sp is taken as to be the surface area of the particle, then it is given by πd2s, where ds is the diameter of the sphere particle.

9. The Bubble or Drop size diameter, is referred to _____
a) Frisch diameter
b) Bubble diameter
c) Sauter diameter
d) Sphere diameter

Explanation: When surface area and the bubble are controlling parameters then, in such cases these diameters are called as Sauter diameter.

10. What is arithmetic mean diameter?
a) Sidi/Si
b) Vidi/Vi
c) Nidi/Ni
d) Widi/Wi

Explanation: Arithmetic mean diameter DN is given as the ratio of number of particles of size‘d’ to the total number of particles.

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