Mechanical Operations (CHE-205) (Makeup) [EngineeringDuniya.com]

Reg. No.

MANIPAL UNIVERSITY

THIRD SEMESTER B.E., (CHEMICAL ENGINEERING) END - SEMESTER EXAMINATION-NOVEMBER 2008

Time: 3 Hrs

SUBJECT: MECHANICAL OPERATIONS (CHE 205) MAKE UP EXAM Max. Marks: 100

Instructions to Candidates: * All questions carry equal marks.( 5 X 20 = 100 ) * Missing data, if any, may be suitably assumed

1.a.

What is meant by Aperture? Explain the working principle of different types of screens used [10] in Industry.

1.b.

It is desired to separate a mixture of crystals into three fractions, a coarse fraction retained on an 8 mesh screen, a middle fraction passing on 8 mesh but retained on a 14 mesh screen and a fine fraction passing a 14 mesh screen. Two screens in series are used an 8 mesh and 14 mesh, conforming to the Tyler standard. Screen analyses of feed, coarse, medium and fine fractions are given in the following Table. Assuming the analyses are accurate .What do they show about the ratio by weight of each of the fraction actually obtained? What is the overall effectiveness of the screen?. Screen 3/4 4/6 6/8 8/10 10/14 14/20 20/28 28/35 35/48 Total

Feed 3.5 15.0 27.5 23.5 16.0 9.1 3.4 1.3 0.7 100.0

Coarse fraction 14.0 50.0 24.0 8.0 4.0 ------------100.0

Middle fraction ---4.2 35.8 30.8 18.3 10.2 0.7 ------100.0

Fine fraction ---------20.0 26.7 20.2 19.6 8.9 4.6 100.0

[10]

2.a

2.b

Define Terminal settling velocity. Obtain an expression for the terminal settling velocity of spherical particle settling freely in a medium under the influence of gravity in Viscous region and Newton’s region. Indicate all the assumption.

[12]

State the difference between Classifier and Clarifier. A spherical particle in water is flowing upwards at a velocity of 12 cm/sec. The particle 3 diameter is 0.975 mm and the density is 218.5 lb/ft . The viscosity of water is 0.98 cp. Determine in which region the particles settles and with what velocity whether in upward or downward direction ?.

[02]

3.a.

Draw a neat sketch and explain briefly the construction and working principle of Electrostatic Precipitator (ESP).Mention its advantages and disadvantages.

[10]

3.b..

Write a short notes on Filter aids. A small test filtration of Crystals in an acetone suspension uses a filter medium of negligible resistance. It gives the following data Time(sec)

10

20

30

Volume of filtrate (Lit)

0.5

0.707

0.866

[06]

[02]

[08]

In finding this data we have used a filter(Buchner funnel) having a diameter of 10.7 cm and a pressure drop of 8.53 ft of water. We now plan to filter a much larger crop of crystals containing 7300 Lit of 4 2 solution by using a filter area of 1.3 X 10  cm  . How ever this larger crystals has a 3 Concentration of 0.175 lb/ft solution, less than that in our test filtration data ,which is 0.21 3 lb/ft of solution. How long will it take to filter this new larger crystal have a pressure 2 drop of 0.26 kgf/cm . 4.a.

4.b.

Give a brief account of 1). Flow patterns in Agitated Vessel. 2). Draft tubes

Write the purpose of Agitation. A Curved blade turbine with six blades is installed centrally in a vertical tank. The tank is 9 ft in diameter; the turbine is positioned 2 ft from the bottom of the tank. The turbine blades are 6 inches wide; The tank is filled with to depth of 9 ft with a solution of 50 % caustic 3 soda at 150 F , which has a viscosity of 12 cp and a density of 93.5 lb/ft .The turbine is operated at 90 rpm. The tank is baffled. What power will be required in terms of HP to operate the mixer? and Calculate the power required by the motor?

[07] [03]

[02]

◦

[08]

5.a.

Classify the different size reduction equipments with examples.

[08]

5.b

With neat sketches explain any two size reduction equipments.

[12]

6.

Briefly explain any FOUR of the following

[20]

1). 2). 3). 4). 5).

Storage of solids. Double cone Classifier. Magnetic separator. Ribbon blender Laws of size reduction. ***