Questions and answers for exam Preparation

MCQs

Total Questions : 75 | Page 3 of 8 pages

Question 21. For parabolic fin, the curve follows which law?

y = C/x^2
y = C x^4
y = C x^2
y = C x^(1/2)

Discuss Question

Answer: Option C. -> y = C x^2
Answer: (c).y = C x^2

Question 22. The correction length for cylindrical fin is
(Where, d is the diameter)

L C = L + d/4
L C = 2 L + d/4
L C = 3 L + d/4
L C = 4 L + d/4

Discuss Question

Answer: Option A. -> L C = L + d/4
Answer: (a).L C = L + d/4

Question 23. Provision of fins on a given heat transfer surface will be more effective if there is

Fewer but thick fins
Large number of thick fins
Fewer but thin fins
Large number of thin fins

Discuss Question

Answer: Option D. -> Large number of thin fins
Answer: (d).Large number of thin fins

Question 24. The heat dissipation at any section of parabolic fin is given by

(t2 – t1) (b) (δ)
k (t2 – t1) (b) (δ)
k (t2 – t1) (δ)
k (t2 – t1) (b)

Discuss Question

Answer: Option B. -> k (t2 – t1) (b) (δ)
Answer: (b).k (t2 – t1) (b) (δ)

Question 25. Which one is true regarding rectangular fin?

A C = b δ and P = 2(b + δ)
A C = 2 b δ and P = 2(b + δ)
A C = 3 b δ and P = 2(b + δ)
A C = 4 b δ and P = 2(b + δ)

Discuss Question

Answer: Option A. -> A C = b δ and P = 2(b + δ)
Answer: (a).A C = b δ and P = 2(b + δ)

Question 26. Analysis of heat flow from the finned surface is made with the following assumptions
(i) Uniform heat transfer coefficient, h over the entire fin surface
(ii) No heat generation within the fin generation
(iii) Homogenous material
Identify the correct option

i only
i and ii only
i, ii and iii
ii only

Discuss Question

Answer: Option C. -> i, ii and iii
Answer: (c).i, ii and iii

Question 27. If heat conducted into the element at plane x is Q X = – k A C (d t/d x) X. Then heat conducted out of the element at plane (x + d x) is

– 2k A C d/d x (t + d t/d x (d x))
– k A C d/d x (t + d t/d x (d x))
– 3k A C d/d x (t + d t/d x (d x))
– 4k A C d/d x (t + d t/d x (d x))

Discuss Question

Answer: Option B. -> – k A C d/d x (t + d t/d x (d x))
Answer: (b).– k A C d/d x (t + d t/d x (d x))

Question 28. A heating unit is made in the form of a vertical tube of 50 mm outside diameter and 1.2 m height. The tube is fitted with 20 steel fins of rectangular section with height 40 mm and thickness 2.5 mm. The temperature at the base of fin is 75 degree Celsius, the surrounding air temperature is 20 degree Celsius and the heat transfer coefficient between the fin as well as the tube surface and the surrounding air is 9.5 W/m² K. If thermal conductivity of the fin material is 55 W/m K, find the amount of heat transferred from the tube without fin