October 1998

5HB - Mechanical Operations - October 1998

Part A (20 x 2 = 40 Marks)

1. Define 'sphericity' for a non-spherical particle
2. What is 'blinding' of screens?
3. Cumulative analysis for determining surface is more precise than differential analysis. Why?
4. Differentiate between Grizzlies and Trommels
5. Define Rittinger's law of crushing
6. The operating speed of a ball mill should be less than the critical speed.
7. Define angle of nip for a roll crusher
8. What is distintegrator?
9. What is flotation? Give some of its applications
10. Define 'free settling'
11. Name the commonly used centrifuges for industrial applications
12. Differentiate between a thickener and a clarifier
13. What are filter aids? Name few commonly used filter aids
14. Give the classification of filters
15. Define compressibility coefficient of the cake
16. Explain the Kozeny's equation for determining the pressure drop across the cake for batch filtration
17. Differentiate between agitation and mixing
18. What are the main types of impellers?
19. Define flow number
20. Write the physical significance of Froude's number in agitation of fluids

Part B (5 x 12 = 60 Marks)

21. (a) Derive the expression for the effectiveness of a screen. How does this vary with capacity?

    Or

    (b) (i) What are the three types of industrial screens and how they are employed?

    (ii) Explain the principle of electrostatic precipitation in gas cleaning

22. (a) State and derive the expression for the three basic laws of size reduction. What is the size range of feed for their applicability?

Or

(b) (i) With the help of a neat sketch explain the working of a conical ball mill

(ii) What is critical speed of a grinding mill? Deduce a relation between the critical speed and diameter of a ball mill

23. (a) Discuss the basic principles involved in the benefication of ores by froth flotation. With suitable examples, explain the roll of collectors, frothing agents and modifiers in the operation

Or

(b) (i) Discuss Stoke's law and indicate its limitations and applications

(ii) Discuss how the area of a thickener can be calculated from batch sedimentation data

24. (a) Explain the working of a vacuum drum filter with a neat sketch and specify the fields of application

Or

(b) Write short notes on:

(i) Constant pressure and constant rate filtration

(ii) Classification and selection of filtration equipments

(iii) Ultra-filtration

25. (a) By dimensional analysis, derive the relationship between various dimensionless groups for estimation of power consumption for a turbine mixer

    Or

    (b) (i) Compare the performance, characteristics and applications of paddle, turbine and propeller type mixers

    (ii) Suggest with reasons, suitable mixing equipment for mixing of dry powder.