Heat Transfer MCQ with Answer.

Q.no 51. What will be the heat flux across a flat board of thickness 40 mm and area 2 m2 if the temperature difference across its surfaces is 30°C. Assume that the thermal conductivity of the material is 0.095 W/mK

A : 356.3 W/m2
B : 35.63 W/m2
C : 3.563 W/m2
D : 3563 W/m2

Q.no 52. A mild steel ball of diameter 1.2 cm is initially at a temperature of 873 K and is exposed to air at 300 K. Find the time needed to cool the steel ball to 368 K. Assume that the convection heat transfer coefficient is 0.114 kW/m2 K. Also find the heat transfer rate after 120s.

A : 2.1 min, 3.9 W
B : 2.1 min, 8.9 W
C : 2.1 min, 4.9 W
D : 2.1 min, 5.9 W

Q.no 53. Find the heat gain per hour by a 2-m long copper tube that is 1 cm in diameter carrying F12 at −30°C when exposed to still air at 40°C

A : 53 W
B : 54W
C : 58 W
D : 59 W

Q.no 54. The radiant flux emitted by a body from its surface is its

A : Emissive power
B : Emissivity
C : Absorptivity
D : Reflectivity

Q.no 55. What should be the temperature difference across a slab of thickness 1 m, having a thermal conductivity 0.1 W/m K, in order to obtain a heat flux of 3 W/m2

A : 0.38°C
B : 308°C
C : 380°C
D : 0.038°C

Q.no 56. Steam at 373K is condensed over a cylindrical surface of diameter 25 mm maintained at 357 K, heat transfer coefficient is 10864 W/m2K, the rate of heat transfer per unit length of cylinder is

A : 16.35kW/m
B : 13.65kW/m
C : 12.56kW/m
D : 15.36kW/m

Q.no 57. The ratio of the total emissive power of the surface to the total emissive power of the black surface at the same temperature is

A : Emissive power
B : Emissivity
C : Absorptivity
D : None of these

Q.no 58. A surface having the same value of the monochromatic hemispherical emissivity at all wavelength is a

A : Black body
B : Gray body
C : White Body
D : None of these

Q.no 59. Which of the following is expected to have highest thermal conductivity

A : Steam
B : sol ice
C : melting ice
D : water

Q.no 60. The Grashoff number is defined as the ratio of the

A : buoyancy to inertial forces.
B : buoyancy to viscous forces
C : inertial to viscous forces.
D : buoyancy to surface tension forces

Answer for Question No 51. is b
Answer for Question No 52. is a
Answer for Question No 53. is a
Answer for Question No 54. is a
Answer for Question No 55. is b
Answer for Question No 56. is b
Answer for Question No 57. is b
Answer for Question No 58. is b
Answer for Question No 59. is b
Answer for Question No 60. is b