CHEMICAL ENGINEERIGN – 2004, PAPER-I, SECTION – A

                      Time Allowed: Three Hours           maximum Marks: 200

Candidates should attempt Questions 1 and 5 which are compulsory and any THREE of the remaining questions, selecting at least ONE question form each section. If any data is considered insufficient, assume suitable values.

SECTION – A

1.       Answer any four of the following:

(a)    (i) What is the time dependent flow? With the help of this phenomenon, explain the meaning of Thyrotrophic liquid and Rheopeptic substances.

(ii)  Write the power law equation for dilatants and pseudo plastic fluids, and explain the terms ‘flow consistency index’ and ‘flow behavior index’.

(b)   Derive an equation for steady conduction in the radial direction of a hollow cylinder. From the equation, explain the term log-mean radius. Under what condition, can the log-mean radius be replaced by arithmetic mean radius?

(c)    In a double pipe heat exchanger, an hour fluid is cooled from 150 to 100˚C by using cold water, which is heated form 30 to 50˚C. Derive a suitable expression to prove that there is a distinct advantage of using it in parallel flow.

(d)   Explain how thermal condition of feed influences the column. What common factor can be used for characterizing five different feed conditions? From the value of this common factor, explain the meaning of horizontal & vertical feed lines.

(e)   Explain the phenomenon of primary nucleation in the process of crystallization, and illustrate the difference between homogeneous and heterogeneous nucleation.

2.       (a) For an incompressible fluid, write the Bernoulli equation for frictionless flow. What correction would you apply for incorporating fluid friction? Explain the difference between skin friction and form friction.

(b) What is terminal velocity? Write the equation for terminal velocity for the flow of a single particle through a fluid under the action of (i) gravity and (ii) centrifugal force.

How is the equation for terminal velocity under free setting condition modified for hindered setting conditions?

(c) What is a ball mill? Derive an equation for the critical speed of a ball mill.

(d) What is a venturimeter? Describe the principle of working of a venturimeter and write an expression for the venture coefficient.

3.       (a)  An air water system has a dry bulb temperature of 65.5˚C and a wet bulb temperature of 54.5˚C.

(i)                  If the air cooled to 37.8˚C, what per cent of the moisture will condense?

(ii)                If the air is again heated to 65.5˚C, how much heat will be required per kg of dry air? Specific heat of air= 0.23 kcal/ (kg˚C)

(b) A spherical particle of ethanol of 10mm diameter is evaporating in an air stream at 26˚ C. The thickness of the stagnant air surrounding the particle is 1.5 mm. Vapour pressure of ethanol at 26 ˚C is 60 mm Hg and the mole fraction of ethanol in the main stream of the air is 0.005.  The diffusion coefficient of ethanol in air is 1.04 x 10ˉ⁵ m² /sec and the value of R is 82.06 x 10ˉ³ m³ atm/kg moles. Determine

(i) The mole fraction of ethanol at different positions across the stagnant layer.

(ii) Rate of evaporation of the particle per second.

(c)  What are different types of pickings that are used in an absorption tower? Explain a simple procedure for calculating the height of a packed tower for absorption of a single component form a gas mixture.

(d) What is critical moisture content? Describe the method for drying of a wet solid before it reaches the critical moisture content.   

4.       (a) Develop a relation between heat transfer and fluid friction by using the Reynold’s Analogy.

(b) (i) What is a radiation shield? How does it help in reducing radiant heat loss?

(ii)  A double walled spherical container is used for storing liquid oxygen. The diameter of the inner and outer walls of the container is 30 cm 36 cm, respectively. The surfaces of both the spheres are plated, so that their emissivity is 0.05. Determine the rate at which oxygen will evaporate at -183˚ C, when the outer wall of the sphere is maintained at 20˚C. Latent heat of evaporation of oxygen is 57.2 kcal/ kg

(C) What are drop wise and film wise condensation? Mention the conditions that favour drop wise condensation. Describe how the heat transfer coefficient in a vertical condenser is influenced by the height of the condenser.

(d) What is effectiveness of a heat exchanger? Derive a relation between the effectiveness and number of transfer units for a counter- current heat exchanger.