Regulation 2019
Academic Year 2022-2023
IFET COLLEGE OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
19UMEPC603 - HEAT AND MASS TRANSFER
UNIT: IV - RADIATION
PART-A (2 Marks)
Black Body Radiation
1. Define Radiation.
2. Classify the types of radiation.
3. Distinguish between emissive power and monochromatic emissive power.
4. Define black body.
5. How does the wavelength distribution of radiation emitted by a gas differ from that of a
surface at the same temperature?
6. What do you mean by absorptivity, reflectivity and transmissivity?
7. Assume the sun to be black body emitting radiation with maximum intensity at 0.52 m
, calculate the surface temperature of the sun.
8. Find the temperature of the sun assume the sun to be black body, if the intensity of
radiation is maximum at the wave length of 0.5 m .
9. State Wien’s displacement law and Planck’s distribution law.
10. State Stefan – Boltzmann law.
11. Define Emissivity.
12. Write the characteristics of Blackbody Radiation.
Grey body radiation:
13. Define grey body.
14. Write about Radiative Heat Transfer.
15. State Kirchoff’s law of radiation.
16. What is reradiating surface? What simplification does a reradiating surface offer in the
radiation analysis?
17. State Lambert’s cosine law for radiation.
18. What is meant by radiation surface? How they expressed? For what kind of surfaces is
the radiation surface resistance zero?
19. How does radiosity for a surface differ from the emitted energy? For what kind of
surfaces are these two quantities identical?
20. What are the assumptions made to calculate radiation exchange between the surfaces?
Shape Factor:
21. Distinguish between irradiation and radiosity.
22. Write the expression for Emissive Intensity.
23. Two parallel radiating planes 100  50 cm are separated by a distance of 50 cm. What is
the radiation shape factor between the planes?
24. What is the wave length band of thermal radiation?
Electrical Analogy:
25. Discuss the term electrical analogy.
26. Name the laws of variation used in heat transfer analysis.
27. What does the view factor represent? View factor from a surface to itself not zero.
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Regulation 2019
Justify?
Academic Year 2022-2023
28. Explain why surfaces usually have quite different absorptivity’s for solar radiation?
Justify
29. What is the crossed- strings method? For what kind of geometries is the crossed- strings
method applicable?
30. Give short note on opaque body.
31. What is a radiation shield? Why is it used?
32. Write about gas radiation
33. Define Beer’s Law.
34. How radiation from gases differs from solids?
43. Draw the Schematic diagram of a three-surface enclosure and its network diagram.
Radiation Shields:
35. Is the radiation shield used in nuclear reactor? Justify?
36. What are the reasons to present for a participating medium that complicates the
radiation analysis?
Radiation through gases
37. Explain the radiation characteristics of carbon dioxide and water vapour.
38. Does a blackbody actually exist? Why?
39. How is the thermal energy of a material affected by the absorption of incident
radiation?
40. Write down the expression for a thermometer used to measure the temperature of a
fluid.
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PART-B (16 MARKS)
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Black and Grey Body Radiation
Assume the sun to be block body emitting radiation with maximum intensity at
  0.5m , Calculate the surface temperature of the sun and the heat flux at its
surface.
(i) A 20 cm diameter spherical ball at 527oC is suspended in the air. The ball closely
approximates a black body. Determine the total black body emissive power, and
spectral black body emissive power at wavelength of 3  m
(ii) The filament of a 75W light bulb may be considered as a black body radiating into
a black enclosure at 70oC. The filament diameter is 0.10mm and length is 5cm.
Considering the radiation, determine the filament temperature.
(i) Derive Wien’s displacement law of radiation from Planck’s law
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(ii) Derive the expression for Radiation heat exchange between infinite parallel plates. (08)
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Calculate the following for an industrial furnace in the form of a black body and (16)
emitting radiation at 3000oC:
a) Monochromatic emitting power 1 m length
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b) Wavelength at which the emissive is maximum
c) Maximum emissive power
d) Total emissive power
Regulation 2019
Academic Year 2022-2023
5.
Consider a cylindrical furnace with outer radius = 1 m and height = 1m. The top (16) (A)
(surface 1) and the base (surface 2) of the furnace have emissivities 0.8 & 0.4 and are
maintained at uniform temperatures of 700 K and 500K respectively. The side surface
closely approximates a black body and is maintained at a temperature of 400 K. Find
the net rate of radiation heat transfer at each surface during steady state operation.
6.
Two large parallel planes are at 1000 K and 600 K. Determine the heat exchange per (16) (A)
unit area. (i) if surfaces are black (ii) if the hot one has an emissivity of 0.8 and the
cooler one 0.5 (iii) if a large plate is inserted between these two, the plate having an
emissivity of 0.2.
7.
A cylindrical shaped furnace is 1 m dia and 1 m high. The top surface having an (16) (A)
emissivity of 0.7 emit a uniform heat flux of 7 kW/m2. The bottom surface with an
emissivity of 0.4 is maintained at 350 K. The sides are insulated and function as
reradiating surfaces. Determine the heat transfer to bottom surface and also the
temperatures of the top and sides.
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Shape Factor
(i) Two parallel rectangular surfaces 1m  2m are opposite are opposite to each other
at a distance of 4m. The surfaces are black and at 100oC and 200oC respectively.
Calculate the heat exchange by radiation between the two surfaces.
(ii) Two rectangular surfaces are perpendicular to each other with a common edge of
2m. The horizontal plane is 2m long and vertical plane is 3m long. Vertical plane is at
1200K and has an emissivity of 0.4. The horizontal plane is 18oC and has an
emissivity of 0.3. Determine the net heat exchange between the planes.
(i) In a cylindrical surface of 50cm in diameter and 100cm high, the upper and lower
surfaces are maintained at 727oC and 427oC. Their emissivities are 0.8 and 0.7. The
cylindrical surface is made of refractory material. Find the net heat transfer between
the upper and lower surfaces.
(ii) Two black discs of diameter 50cm are placed directly opposite at a distance of
1m. The discs are maintained at 1000K and 500K. Calculate the heat flow between
the discs.
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Radiation Shields
Emissivities of two large parallel plates maintained at 800oC and 300oC are 0.3 and (16)
0.5 respectively. Find the net radiant heat exchange per square metre for these plates.
Find the percentage reduction in heat transfer when a polished aluminum radiation
shield (   0.05 ) is placed between them. Also find the temperature of shield.
Consider double wall as two infinite parallel planes. The emissivity of the walls is 0.3 (16)
and 0.8 respectively. The space between the walls is evacuated. Find the heat
transfer/unit area when inner and outer surface temperatures are 300oC and 260oC. To
reduce the heat flow, a shield of polished aluminum with (   0.05 ) is inserted
between the walls. Find the reduction in heat transfer.
(i) A thin aluminum sheet with an emissivity of 0.1 on both sides is placed between (8)
two very large parallel plates that are maintained at uniform temperatures T1 = 800 K
and T2 = 500 K and have emissivities  1  0.2 and 1  0.7 , respectively
respectively. Determine the net rate of radiation heat transfer between the two plates
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Regulation 2019
Academic Year 2022-2023
per unit surface area of the plates and compare the result to that without the shield.
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(ii) Determine the radient heat exchange between two large parallel steel plates of (8)
emissivities 0.8 and 0.5 held at temperature of 1000K and 500K. A thin copper plate
of emissivity 0.1 is introduced as a radiation shied between the two plates. Use
𝜎 =5.67× 10−8 𝑊/𝑚2 𝐾 4.
Two large parallel planes at temperature 1000 K and 800 K having emissivity of 0.5 (16)
and 0.8 respectively. A radiation shield having an emissivity 0.5 on one side (facing
hot place) and an emissivity of 0.04 on the other is placed in between the planes.
Determine the heat transfer rates by radiation with and without radiation shield.
Two very large parallel planes exchange heat by radiation. The emissivities of the (16)
planes are respectively 0.3 and 0.8. To minimize the radiation exchange between the
planes; a polished aluminum radiation shield is placed between them. If the emissivity
of the shield is 0.04 on both sides, find the percentage reduction in heat transfer rate.
Heat exchanger between non-black bodies- infinite parallel planes
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Two parallel plates of size 1.0m  1.0 spaced 0.5 m apart are located in very large (16)
room, the walls are maintained at a temperature of 27oC. One plate is maintained at a
temperature of 900oC and the other at 400oC. Their emissivities are 0.2 and 0.5
respectively. If the plate’s exchanges heat between themselves and surroundings, find
the heat transfer to each plate and to them. Consider only the plate surfaces facing
each other.
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Effects of radiation from gases and vapour
Two large parallel planes are at T1 =800 K,  1 =0.3, T2 =400 K,
 2 =0.7 and are (16)
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separated by a gray gas having  g =0.2, τg=0.8. Calculate the heat-transfer rate
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between the two planes and the temperature of the gas using a radiation network.
Compare with the heat transfer without presence of the gas.
A gas turbine combustion chamber is 0.35 m in diameter and the walls are maintained (16)
at 500oC. The products of combustion are at 1000oC and a pressure of 1 atm and
contain 12% CO2 and 10% H2O vapour by volume. Determine the net radiant heat
transfer per unit surface area.
A cylindrical furnace whose height and diameter are 5 m contains combustion gases (16)
at 1200 K and a total pressure of 2 atm. The composition of the combustion gases is
determined by volumetric analysis to be 80 % N2, 8% H2O, 7%O2 and 5 % CO2.
Determine the effective emissivity of the combustion gases
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