Solve any four:

1 (a)
What is meant by film condensation and dropwise condensation?

5 M

1 (b)
What is Fin? What are the various types of fins?

5 M

1 (c)
Explain the number of transfer units (NTU).

5 M

1 (d)
Define Thermal Diffusivity and state its significance.

5 M

1 (e)
Define: Radiosity and Irradiation.

5 M

2 (a)
Derive the relation for heat transfer through fin with insulated tip. State the assumptions clearly.

10 M

2 (b)
Explain the term 'Time Constant' of thermocouple.

3 M

2 (c)
A copper wire of radius 0.5mm is insulated uniformly with plastic (k=0.5 W/m K) sheathing 1mm thick. The wire is exposed to atmosphere at 30°C and the outside surface coefficient is 8 W/m

^{2}K. Find the maximum safe current carried by the wire so that no part of the insulated plastic is above 75°C. Also calculate critical thickness of insulation. For copper, thermal conductivity = 400 W/m K, specific electrical resistance=2 X10^{-8}ohm-m.
7 M

3 (a)
Using dimensional analysis, derive an expression for forced convection:- Nu=Constant X(Re)

^{m}X (Pr)^{n}.
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3 (b)
Air at atmospheric pressure and 207deg;C flows with 6 m/s velocity through main trunk duct of air condisioning system. The duct is rectangular in cross-section and measures 40cm × 80cm. Determine heat loss per meter length of duct corresponding to unit temperature difference.

The relevant thermo-physical properties of air are: v=15×10

Use Nu=0.023 (Re)

The relevant thermo-physical properties of air are: v=15×10

^{-6}, α=7.7×10^{-2}m^{2}/hr, k=0.026 W/m-deg-k.Use Nu=0.023 (Re)

^{0.8}× (Pr)^{0.4}.
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3 (c)
What is meant by Fouling in Heat Exchangers.

4 M

4 (a)
Distinguish between specular and diffuse radiation.

4 M

4 (b)
Prove that the total emissive power of black surface is π time the intensity of radiation.

6 M

4 (c)
16.5 kg/s of the product at 650°C (c

_{p}=3.55 kJ/kg K), in a chemical plant, are to be used to heat 20.5 kg/s of the incoming fluid from 100°C (c_{p}=4.2 kJ/kg K). If the overall heat transfer coefficient is 0.95 kW/m^{2}K and the installed heat transfer surface is 44 m^{2}, calculate the fluid outlet temperature for the counter flow and parallel flow arrangements.
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5 (a)
Derive the relationship between the effectiveness and the number of transfer units for a parallel flow heat exchanger.

10 M

5 (b)
A thermocouple indicates a temperature of 800°C when placed in a pipeline where a hot gas is flowing at 870°C. If the convective heat transfer cofficient between the thermocouple and gas is 60 W/m

^{2}K, find the duct wall temperature, ε (thermocouple)=0.5.
5 M

5 (c)
A thin copper sphere with its internal surface highly oxydises, has a diameter of 20 cm. How small a hole must be made in the sphere to make an operating that will have an absorptivity of 0.9?

5 M

Write a short note (Any Two):

6 (a) (i)
Heisler chart.

4 M

6 (a) (ii)
Importance of numerical methods.

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6 (a) (iii
Heat Pipe.

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6 (b)
Draw the boiling curve and identify the different boiling regimes.

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6 (c)
A 15 mm diameter mild steel sphere (k=42 W/m °C) is exposed to coding airflow at 20°C resulting in the convective coefficient h=120 W/m

Determine the following:

i) Time required to cool the sphere from 550°C to 90°C

ii) Instantaneous heat transfer rate 2 minutes after the start of cooling.

For mild steel take: ρ=7850 kg/m

^{2}°C.Determine the following:

i) Time required to cool the sphere from 550°C to 90°C

ii) Instantaneous heat transfer rate 2 minutes after the start of cooling.

For mild steel take: ρ=7850 kg/m

^{3}, c=475 J/kg °C, α=0.045 m^{2}/h.
7 M

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