#### Anna University, B.TECH. DEGREE EXAMINATION, FIFTH SEMESTER

#### CHEMICAL ENGINEERING

#### Mechanical Operations

**Part A (10 x 2 = 20 marks)**

**Part A (10 x 2 = 20 marks)**

Answer all the Questions

1. Define the shape factor spherecity of a particle.

2. How is mesh number of a screen related to the size of the opening?

3. State the function of Silo/Bin

4. What is work index?

5. What is critical speed of a ball mill?

6. What is the separation principle in flotation?

7. Explain thorough washing in filtration operation

8. What is the function of filter aids?

9. List the mixing equipment used to mix solids and pastes.

10. What is significance of power number?

**PART B (5 x 16 = 80 marks)**

11.i) Derive an expression for rate of filtration at constant pressure.

ii) A slurry of lime powder giving 50kg of cake solid per cubic meter of filtrate is to be filtered at a constant pressure drop of 5 atm and a temperature of 30°C. Experiments on this sludge and the filter cloth to be used gave a value of Rm = 8.5 x 10^{10} m^{-1 }and cake resistance of 6.38 x 10^{10} m/kg. A pressure filter of tank type is to be used. How many square meters of filter surface is needed to give 6 cubic meter of filtrate in a I-h filtration? The viscosity of water at 30°C is 0.8 cP.

12.A i) Define average size, volume-surface mean diameter and specific surface area.

ii) Calculate the mean size and specific surface area of the cement sample from the size distribution data given below. The particle density of cement sample may be taken as 3260 kg/m^{3}.

Particle Size, ?m |
75-53 | 53-37 | 37-25 | 25-20 | 20-15 | 15-10 | 10-5 | 5-0 |

Weight fraction | 0.05 | 0.12 | 0.18 | 0.23 | 0.14 | 0.12 | 0.1 | 0.06 |

# OR

12.Bi) Derive an expression for effectiveness of a screen.

ii) Explain the principle and function of vibrating screens

13.A i) Explain the principles of grinding and classical laws for prediction of energy consumption in size reduction operations.

ii) Explain the closed circuit grinding and effect of method of feeding on performance of mill.

OR

13.B i) Explain the process of batch sedimentation.

ii) The data given below were obtained from a single batch sedimentation tests on an ore-slurry. The true density of the solids in the slurry was 2500 kg/m^{3} and the density of liquid was 1000 kg/m^{3}. Determine the minimum area required for thickener to handle 100 tons of solids per day from a feed concentration of 64.5kg/m^{3} to an underflow concentration of 485.0 kg/m^{3.}

Concentration C, kg/m^{3} |
64.5 | 70.9 | 94.3 | 111.7 | 139.9 | 173.9 | 222 | 331 |

Setting velocity, v, cm/h | 139.9 | 103.6 | 71.9 | 49.4 | 27.1 | 16.8 | 10.0 | 6.4 |

14.A i) Explain with neat sketch the working principle of disk centrifuge.

ii) What is the capacity in m^{3}/h of clarifying centrifuge operating under following conditions?

Diameter of bowl, mm | 600 | Specific Gravity of liquid | 1.2 |

Thickness of liquid layer, mm | 75 | Specific gravity of solid | 1.6 |

Depth of bowl, mm | 400 | Viscosity of liquid, cP | 2 |

Speed, rpm | 1200 | Cut size of particle, ?m | 30 |

OR

14.B i) Explain the different types and function of impellers used in agitating the liquids.

ii) Explain the methods of preventing swirling in agitated vessels.

15.A i) Discuss the equipment used for mixing solids and pastes. With neat sketches, explain their working principles.

ii) Define the mixing index for solids and pastes.

OR

15.B i) What are different types of bins used to store bulk solid material?

ii) Explain the flow problems in silo.