STUPIDSID
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/m2 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)mX (Pr)n.
8 M
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=15×10-6, α=7.7×10-2 m2/hr, k=0.026 W/m-deg-k.
Use Nu=0.023 (Re)0.8 × (Pr)0.4.
The relevant thermo-physical properties of air are: v=15×10-6, α=7.7×10-2 m2/hr, k=0.026 W/m-deg-k.
Use Nu=0.023 (Re)0.8 × (Pr)0.4.
8 M
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 (cp=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 (cp=4.2 kJ/kg K). If the overall heat transfer coefficient is 0.95 kW/m2 K and the installed heat transfer surface is 44 m2, calculate the fluid outlet temperature for the counter flow and parallel flow arrangements.
10 M
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/m2 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.
4 M
6 (a) (iii
Heat Pipe.
4 M
6 (b)
Draw the boiling curve and identify the different boiling regimes.
5 M
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/m2 °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/m3, c=475 J/kg °C, α=0.045 m2/h.
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/m3, c=475 J/kg °C, α=0.045 m2/h.
7 M
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