### Mechanical Operations - Semester Exam Question

5HB - Mechanical Operations - October 1997

Part A (20 x 2 = 40 Marks)

1. What are the different ways adopted for size reduction in process industries?
2. Explain the Bond’s crushing law and work index
3. Explain differential screen analysis
4. What is the ratio of actual mesh dimension in one screen to that of the next smaller screen as per Tyler’s standard scale?
5. Explain the terms ‘Capacity’ and ‘Effectiveness’ of screens
6. What is mixing index? Explain its significance
7. What are the different methods adopted for prevention of swirling in an agitated tank?
8. What is the difference between a clarifier and classifier?
9. Define the terms ‘Critical speed’ and ‘Centrifuging’ in a ball mill
10. What are the different types of impellers commonly used for agitation of liquids?
11. Write the relationships between drag coefficient and Reynolds number in various regimes of settling
12. Explain the different types of filtration
13. Explain the principle of centrifugal sedimentation
14. What are open circuit and closed circuit operations?
15. Classify the particle size measuring techniques on the basis of size range
16. Explain briefly the various flotation methods
17. Explain the principle of electrical precipitation
18. Explain the term "Terminal Settling Velocity"
19. What are the requirements for selecting a suitable filter media?
20. What are sorting classifiers?
21. Part B ( 5 x 12 = 60 Marks)

22. (a) Classify screening equipment with the help of neat sketches. Compare between ideal and actual screens
23. Or

(b) What are the various equipment used for storage of solids? Discuss them with neat sketches

24. (a) State the basic laws of crushing and derive them from the following equation:
25. dE/dL = -CLP where the terms have their standard nomenclature. Indicate the limitations of these laws

(b) Prove that the critical speed of a ball mill follows the following relationship:

where R and r represent the radius of the mill and ball respectively, g = acceleration due to gravity

Or

(c) Classify communiting equipment. Explain the working principle of operation of any one of the crushers with the help of a neat sketch.

(d) A pair of rolls take a feed equivalent to 20 mm in diameter and crush them to spheres of 10 mm diameter. What should be the diameter of crushing rolls if the coefficient of friction is 0.25?

26. (a) Explain the process of sedimentation and derive an expression for calculating the minimum thickener are required by a batch sedimentation test
27. Or

(b) What are the various types of flotation equipment commercially employed in industry? With the help of a neat sketch, discuss any one of them in detail

28. (a) Classify the types of filtration equipment and explain the operation of a plate and frame filter press with the help of a neat sketch
29. Or

(b) What are filter aids and filter media?

(c) Distinguish between constant rate and constant pressure filtration

(d) Calculate the specific filter cake resistance during the filtration of an incompressible sludge (density = 5 gm/cc) if specific cake surface was found to be 6.5 x 104 cm2/ cm3 of solids. Porosity of the cake is 0.6

30. (a) Prove that power required for agitation of Newtonian liquids can be represented by the following relationships:
31. NP = f (NRe, NFr) where NP, NRe and NFr represent dimensionless groups.

Or

(b) Classify and draw neat sketches for the equipment used to cause mixing of solids and pastes

(c) Write the purposes of agitation of liquids. Draw neat sketches of various impellers and explain their specific features.

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