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Reg. No. : .................................... Name : .........................................
Third Semester B.Tech. Degree Examination, November 2009 (2008 Scheme) Chemical Engineering Branch 08.306 : PARTICLE TECHNOLOGY (H) Time : 3 Hours Instructions :1) 2) 3) 4)
Max. Marks : 100 Answer all questions in Part A. Answer any one full question from each Module in Part B. Each question in Part A carries 4 marks. Graph sheets may be provided. PART – A
1. Define specific cake resistance and filter medium resistance. What are the units of these quantities in SI system ? 2. Compare open circuit and closed circuit grinding. 3. Explain the principle and working of an electrostatic precipitator. 4. List the various methods of sub-sieve analysis. Explain any one of them. 5. Define and explain angle of repose and friction. 6. What should be the diameter of a set of rolls to crush the feed size equivalent of 4 cm to 12.5 mm spheres, if the coefficient of friction is 0.29. P.T.O.
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7. Define and explain critical and optimum speed of a ball mill. 8. Estimate the overall effectiveness in a system in which the mass fractions of undersize cut in the feed, underflow and overflow are 0.56, 0.29 and 0.88 respectively. 9. Explain the principles in the design of a cyclone separator. 10. With reasons, recommend appropriate equipments for the following : i) to crush limestone from a feed size of 1 m to a product size of 5 cm ii) to grind ore for froth floatation iii) to reduce the size of particles to 10 microns.
(10×4=40 Marks)
PART – B MODULE – I 11. a) The size analysis of a powdered material on weight basis is represented by a straight line from zero percentage weight at 1 micron particle size to 100 weight percentage at 101 micron particle size. Calculate the surface mean diameter of the particles constituting the system. b) 3 kW has to be supplied to a machine crushing a material at a rate of 0.3 kg/s from 12.5 mm cubes to a product having the following sizes : 80% - 3.175 mm 10% - 2.5 mm 10% - 2.25 mm What would be the power which would have to be supplied to the machine to crush at the same rate and same material from 7.5 mm cube to 2 mm cube. (10+10=20) 12. a) Starting from basic differential equation, derive the laws of size reduction and give their size range of application. b) Derive an equation for the critical speed of a ball mill.
(10+10=20)
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MODULE – II 13. a) 1000 tons/day of a suspension is to be thickened from 186 g/litre to 1200 g/litre in a continuous thickener. Batch settling data on feed material gave the following data : Time (h)
0
0.1
0.25
0.5
0.75
1
2
4
Height of interface (cm)
90
60
42
27
19
14.4
7.5
3
Determine the minimum thickener area. b) Derive the equation for calculating the volume of filtrate collected at any time for constant pressure filtration. c) Explain the working of a rotary drum filter.
(10+5+5=20)
14. a) A plate and frame filter press employed for filtering a slurry gave a total of 8 m3 of filtrate in 1800 s and 11 m3 in 3600 s when filtration was stopped. Estimate the washing time in seconds if 3 m3 of wash water is used. b) Discuss the conditions under which the centrifuges are preferred as a solidliquid separating device. Give suitable examples. Also explain with a sketch the working of a tubular centrifuge. c) A concentrated suspension of spherical quartz particles in water settles under gravity. The particle diameter is 10 micron and the particle density is 2650 kg/m3. The initial voidage in the suspension is 0.8. i) Obtain the expression for the terminal settling velocity of a single particle assuming that Stoke’s law is valid. ii) Find the initial settling velocity of the particles in suspension using Maude and Whitmore formula taking n = 0.48.
(4+8+8=20)
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MODULE – III 15. a) A cyclone separator 0.3 m in diameter and 1.2 m long has a circular inlet of 75 mm diameter and outlet of same size. If the gas enters at 1.5 m/s, at what particle size will the theoretical cut occurs ? Viscosity of air is 0.018×10–3 kg/m.s. Density of air and particle are respectively 1.13 and 2700 kg/m3. b) Explain the principle and working of a bag filter for gas cleaning.
(10+10=20)
16. a) Describe the various methods of conveying bulk solids and compare their merits and demerits. b) Explain the technique used in heavy media separation for mineral beneficiation. (12+8=20) _____________________