Heat Transfer Questions and Answers – Shape Factor

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This set of Heat Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Shape Factor”.

1. Which of the following is a wrong statement according to the shape factor is equal to one?
a) For any surface completely enclosed by another surface
b) For infinite parallel planes radiating only to each other
c) For a flat or convex surface with respect to itself
d) Inside cylinder to outer cylinder of a long co-axial cylinder
View Answer

Answer: d
Explanation: For a flat or convex surface, the shape factor with respect to itself is zero. This aspect stems from the fact that for any part of flat or convex surface, one cannot see any other part of the same surface.

2. Establish a relation for the shape factor of cylindrical cavity with respect to itself of depth h and diameter d. The cavity is closed on its outer surface with a flat plate
Find relation for shape factor of cylindrical cavity with respect to itself of depth h
a) 4 h/4 h + d
b) 4 h + d/h
c) 4 h + d/4 h
d) h/4 h + d
View Answer

Answer: a
Explanation: F 11 + F 12 = 1 and F 21 + F 22 = 1. But F 22 = 0, so F 11 = 1 – A 2 / A 1.

3. The reciprocity theorem states that
a) F 12 = F 21
b) A 1 F 12 = A 2 F 21
c) A 1 F 21 = A 2 F 12
d) A 2 F 21 = A 1 F 12
View Answer

Answer: b
Explanation: It indicates the net radiation exchange can be calculated by computing one way configuration factor from either surface to the other.
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4. Two radiating surface A 1 = 6 m2 and A 2 = 4 m2 have shape factor F 12 = 0.1. Then the shape factor F 21 will be
a) 0.12
b) 0.18
c) 0.15
d) 0.10
View Answer

Answer: c
Explanation: A 1 F 12 = A 2 F 21.

5. What is the value of shape factor for two infinite parallel surfaces separated by a distance x?
a) 0
b) 1
c) x
d) Infinity
View Answer

Answer: b
Explanation: All the radiation emitted by one falls on the other so shape factor is unity.

6. What is the shape factor of a sphere of diameter d inside a cubical box of length l = d?
Find the shape factor of a sphere of diameter d inside a cubical box of length l = d
a) π/6
b) 2 π/6
c) π/3
d) π/4
View Answer

Answer: a
Explanation: F 11 + F 12 = 1 or F 12 = 1. So, F 21 = π/6.

7. What is the shape factor of hemispherical surface closed by a plane surface of diameter d?
a) 0
b) 1.5
c) 1
d) 0.5
View Answer

Answer: d
Explanation: F 11 + F 12 = 1 and F 21 = 1. Therefore, F 11 = 0.5.
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8. Establish a relation for shape factor for a conical cavity with respect to itself of depth h and diameter d. The cavity is closed on its outer surface with a flat plate
Relation for shape factor for cavity of depth & diameter is 1 – d/ (4 h 2 + d 2) 1/2
a) 1 – d/ (4 h 2 + d) 1/2
b) 1 – d/ (4 h 2 + d 2) 1/2
c) 1 – d/ (4 h + d 2) 1/2
d) 1 – d/ (h 2 + d 2) 1/2
View Answer

Answer: b
Explanation: F 11 = 1 – A 2 / A 1 = 1 – 2 sin α = 1 – d/ (4 h 2 + d 2) ½.

9. What is the shape factor for a hemispherical bowl with respect to itself of diameter d? The cavity is closed on its outer surface with a flat plate
a) 1.5
b) 1
c) 0.5
d) 2.5
View Answer

Answer: c
Explanation: F 11 = 1 – A 2 / A 1 = 0.5.
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10. Consider a system of concentric spheres of radius r 1 and r 2 (r 2 is greater than r 1). If r 1 = 5 cm, determine the radius r 2 if it is desired to have the value of shape factor F 21 equal to 0.6
Find the radius r 2 if it is desired to have the value of shape factor F 21 equal to 0.6
a) 6.45 cm
b) 7.45 cm
c) 8.45 cm
d) 9.45 cm
View Answer

Answer: a
Explanation: From reciprocity theorem, A 1 F 12 = A 2 F 21.

Sanfoundry Global Education & Learning Series – Heat Transfer.

To practice all areas of Heat Transfer, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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