Steady State Conduction(Heat Transfer ) Questions and answers for exam Preparation

Question 1. The annealing furnace for continuous bar stock is open at the ends and has interior dimensions of 0.6 m * 0.6 m * 1.5 m long with a wall 0.3 m thick all around. Calculate the shape factor for the furnace?

15.24 m
16.34 m
14.54 m
13.76 m

Explanation:-

Answer: Option A. -> 15.24 m
Answer: (a).15.24 m

Question 2. The shape factor for complete rectangular furnace is
Where a, b and c are the inside dimensions and d x is the wall thickness

2/ d x (a b + b c + c a) + 4 (0.64) (a + b +c) + 8 (0.45) d x
2/ d x (a b + b c + c a) + 4 (0.44) (a + b +c) + 8 (0.35) d x
2/ d x (a b + b c + c a) + 4 (0.34) (a + b +c) + 8 (0.25) d x
2/ d x (a b + b c + c a) + 4 (0.54) (a + b +c) + 8 (0.15) d x

Explanation:-

Answer: Option D. -> 2/ d x (a b + b c + c a) + 4 (0.54) (a + b +c) + 8 (0.15) d x
Answer: (d).2/ d x (a b + b c + c a) + 4 (0.54) (a + b +c) + 8 (0.15) d x

Question 3. Which is true regarding a complete rectangular furnace?

6 walls, 12 edges and 6 corners
0 walls, 2 edges and 4 corners
6 walls, 12 edges and 8 corners
2 walls, 6 edges and 8 corners

Explanation:-

Answer: Option C. -> 6 walls, 12 edges and 8 corners
Answer: (c).6 walls, 12 edges and 8 corners

Question 4. Shape factor for sphere is

4 π r₁ r₂
4 π r₁ r₂/r₂ – r₁
4 π /r₂ – r₁
r₁ r₂/r₂ – r₁

Explanation:-

Answer: Option B. -> 4 π r₁ r₂/r₂ – r₁
Answer: (b).4 π r₁ r₂/r₂ – r₁

Question 5. For the same material and same temperature difference, the heat flow in terms of shape factor is given by

S k d t
k d t/S
2S k/d t
2S/3

Explanation:-

Answer: Option A. -> S k d t
Answer: (a).S k d t

Question 6. A cable of 10 mm outside is to be laid in an atmosphere of 25 degree Celsius (h = 12.5 W/m² degree) and its surface temperature is likely to be 75 degree Celsius due to heat generated within it. How would the heat flow from the cable be affected if it is insulated with rubber having thermal conductivity k = 0.15 W/m degree?

43.80 W per meter length
53.80 W per meter length
63.80 W per meter length
73.80 W per meter length

Explanation:-

Answer: Option B. -> 53.80 W per meter length
Answer: (b).53.80 W per meter length

Question 7. Maximum value of critical radius is

0.01 m
0.04 m
0.06 m
0.0001 m

Explanation:-

Answer: Option A. -> 0.01 m
Answer: (a).0.01 m

Question 8. Chose the correct one with respect to critical radius of insulation

There is more heat loss i.e. conductive
There occurs a decrease in heat flux
Heat loss increases with addition of insulation
Heat loss decreases with addition of insulation

Explanation:-

Answer: Option C. -> Heat loss increases with addition of insulation
Answer: (c).Heat loss increases with addition of insulation

Question 9. A heat exchanger shell of outside radius 15 cm is to be insulated with glass wool of thermal conductivity 0.0825 W/m degree. The temperature at the surface is 280 degree Celsius and it can be assumed to remain constant after the layer of insulation has been applied to the shell. The convective film coefficient between the outside surface of glass wool and the surrounding air is estimated to be 8 W/m² degree. What is the value of critical radius?

9.31 mm
10.31 mm
11.31 mm
12.31 mm

Explanation:-

Answer: Option B. -> 10.31 mm
Answer: (b).10.31 mm

Question 10. For an object i.e. spherical the value of critical radius would be

2k/3h
3k/h
2k/h
k/h

Explanation:-

Answer: Option C. -> 2k/h
Answer: (c).2k/h