## MCQs

Total Questions : 70 | Page 6 of 7 pages
Question 51. The temperature distribution in a large thin plate with uniform surface temperature will be
1.    Logarithmic
2.    Hyperbolic
3.    Parabolic
4.    Linear
Question 52. The rate of heat transfer for a plane wall of homogenous material with constant thermal conductivity is given by
1.    Q = kA (t₁-t₂)/δ
2.    Q = 2kAx/ δ
3.    Q = 2kAδx
4.    Q = 2k/δ x
Answer: Option A. -> Q = kA (t₁-t₂)/δ
Question 53. The interior of an oven is maintained at a temperature of 850 degree Celsius by means of a suitable control apparatus. The oven walls are 500 mm thick and are fabricated from a material of thermal conductivity 0.3 W/m degree. For an outside wall temperature of 250 degree Celsius, workout the resistance to heat flow
1.    0.667 degree/W
2.    1.667 degree/W
3.    2.667 degree/W
4.    3.667 degree/W
Answer: Option B. -> 1.667 degree/W
Question 54. A plane slab of thickness 60 cm is made of a material of thermal conductivity k = 17.45 W/m K. Let us assume that one side of the slab absorbs a net amount of radiant energy at the rate q = 530.5 watt/m². If the other face of the slab is at a constant temperature t₂ = 38 degree Celsius. Comment on the temperature with respect to the slab?
1.    87.5 degree Celsius
2.    32 degree Celsius
3.    47.08 degree Celsius
4.    32.87 degree Celsius
Answer: Option C. -> 47.08 degree Celsius
Question 55. Let us assume two walls of same thickness and cross-sectional area having thermal conductivities in the ratio 1/2. Let us say there is same temperature difference across the wall faces, the ratio of heat flow will be
1.    1
2.    1/2
3.    2
4.    4
Question 56. Three metal walls of same thickness and cross sectional area have thermal conductivities k, 2k and 3k respectively. The temperature drop across the walls (for same heat transfer) will be in the ratio
1.    3:2:1
2.    1:1:1
3.    1:2:3
4.    Given data is insufficient
Question 57. Heat is transferred from a hot fluid to a cold one through a plane wall of thickness (δ), surface area (A) and thermal conductivity (k). The thermal resistance is
1.    1/A (1/h₁ + δ/k + 1/h₂)
2.    A (1/h₁ + δ/k + 1/h₂)
3.    1/A (h₁ + δ/k + h₂)
4.    A (1/h₁ + δ/k + 1/h₂)
Answer: Option A. -> 1/A (1/h₁ + δ/k + 1/h₂)
Answer: (a).1/A (1/h₁ + δ/k + 1/h₂)
Question 58. A composite wall is made of two layers of thickness δ₁ and δ₂ having thermal conductivities k and 2k and equal surface area normal to the direction of heat flow. The outer surface of composite wall are at 100 degree Celsius and 200 degree Celsius. The minimum surface temperature at the junction is 150 degree Celsius. What will be the ratio of wall thickness?
1.    1:1
2.    2:1
3.    1:2
4.    2:3
Question 59. Let us say thermal conductivity of a wall is governed by the relation k = k0 (1 + α t). In that case the temperature at the mid-plane of the heat conducting wall would be
1.    Av. of the temperature at the wall faces
2.    More than average of the temperature at the wall faces
3.    Less than average of the temperature at the wall faces
4.    Depends upon the temperature difference between the wall faces
Answer: Option B. -> More than average of the temperature at the wall faces
Answer: (b).More than average of the temperature at the wall faces
Question 60. A pipe carrying steam at 215.75 degree Celsius enters a room and some heat is gained by surrounding at 27.95 degree Celsius. The major effect of heat loss to surroundings will be due to
1.    Conduction
2.    Convection