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Note: i) Attempt all questions.

ii) Assume data, if necessary.

Q.1 Attempt any three parts of this question. (3*4=12)

1. Define Fourier law of conduction and derive an expression for heat flow through a hollow sphere.

2. What do you mean by the natural and forced convection? Give examples.

3. What do you understand by unsteady state /transient heat transfer?

4. Write down the physical significance of following dimensionless number

I) Nusselt No. ii) Prandtl No. iii) Grashoff No. iv) Reynold’s No.

5. Derive the relation for radiation between two infinite parallel gray surfaces.

Q.2 Attempt any two parts of this question: (2*5 = 10)

1. Calculate the rate at which heat is being lost to the surrounding per unit length of an insulated steam pipe having following dimensions and specifications: I. D. = 30 mm ; thickness of pipe = 2 mm. thickness of insulation = 10mm; hi and ho = 11.63 W/m2. K; Temperature of steam = 373 K; surrounding temperature = 298 K ; thermal conductivities are 17.44 W/m.K for pipe and 0.58 W/m.K for insulation

2. Calculate the rate of heat loss from a thermoflask if the plosished silvered surfaces have emissivities of 0.05, the liquid in the flask is at 368 K and the casing is at 293 K. Calculate the loss if both surfaces were black.

3. A cylindrical hot gas duct , 0.5 m inside radius has an inner layer of fireclay bricks (k =1.3 W/m.k) of 0.27 m thickness. The outer layer 0.14 m thick, is made of special bricks (k= 0.92 W/m.k). The brick work is enclosed by an outer steel cover which has a temperature of 338 K . The inside temperature of the composite cylindrical wall of the duct is 673 K. Neglecting the thermal resistance of the steel cover, calculate the heat loss per meter length of the duct and also the interface temperatures of the different layers.

Q.3 Attempt any two parts from this question: (2*4 =8)

1. A thick walled tube of stainless steel [k= 19 W/m.k] with 2 cm ID and 4 cm OD is covered with a 3 cm layer of insulation [k=0.2 W/m.k] . If the inside wall temp. is 333 K , calculate the heat transfer per meter length.

2. What are the various heat transfer equipments? Explain any one of them.

3. Show that the critical radius for cylinder is k/h.

4. Write down the various equations involved in heat transfer with forced convection.

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