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F192005 Pages:3

PART ‏تا‎
‎Answer any three full questions, each carries 10 marks.

Explain Lumped system analysis
The temperature of a gas stream is measured with a thermocouple. The junction
may be approximated as a sphere of diameter 1 mm, thermal conductivity
25W/mK, density 8400kg/m*, specific heat 400J/kgK. The heat transfer
coefficient between the junction and the gas stream is 560 W/m’K. How long
will it take for the thermocouple to record 99% of the applied temperature
difference?
Aluminium fins of triangular profile are connected to a plane wall whose
temperature is 250°C. The fin base thickness is 2 mm and length is 6 mm. The
system is in ambient air at a temperature of 20°C and surface convection
coefficient is 40W/m?K. What are the fin efficiency and effectiveness? What is
the heat dissipated per unit width by a single fin? Properties may be evaluated at
base temperature.
Explain the effectiveness of a heat exchanger
A shell and tube steam condenser is to be constructed of 2.5 cm outer diameter
and 2.2 cm inner diameter single pass horizontal tubes with steam condensing at
54°C outside the tubes. The cooling water enters each tube at 18°C with a flow
rate of 0.7 kg/s and leaves at 36°C. The heat transfer coefficient for the
condensation of steam is 8000W/m°K. Calculate the tube length neglecting wall
thermal resistance.
Illustrate with sketches, the temperature profiles for hot and cold fluids as a
function of distance along the flow path for a counter flow heat exchanger with
கேடே Ch=Ce, ஜேடே Cn and ಛೈ represent the heat capacities of hot and cold
fluid respectively.
Derive an equation for the effectiveness (൭ of a concentric tube counter flow
heat exchanger in terms of NTU and Capacity Ratio (C)

PART (^

Answer any four full questions, each carries 10 marks.

Explain the terms-Radiation intensity, Emissive power, Radiosity
What is Wein’s Displacement Law? Explain with the help of Planks distribution
With proper figures, derive an equation for view factor of two arbitrarily oriented
surfaces and arrive at the reciprocity relation

What is a diffuse emitter? For such an emitter, how is the intensity related to the

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