Heat Transfer MCQ with Answer.

Q.no 41. What is Nusselt number?

A : Cp µ /k
B : hD/k
C : K /Cp µ
D : None of these

Q.no 42. Heat transfer occurs by natural convection because change in temperature causes difference in

A : viscosity
B : density
C : thermal conductivity
D : heat capacity

Q.no 43. The Grashof 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

Q.no 44. Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the

A : existence of thermal boundary layer
B : temperature gradient produced due to density difference
C : buoyancy of the bubbles produced at active nucleation site
D : none of these

Q.no 45. Thermal conductivity of a gas at low density, __ with increase in temperature

A : Decreases
B : Increases
C : remains unchanged
D : may increase or decrease; depends on the gas

Q.no 46. slab made up of carbon steel is initially at a temperature of 500°C (Ti) and it is exposed to air at 30°C (Ta). The thickness of the slab is 1 cm (L). What will be the temperature of the slab after one minute (t)? Assume that the convective heat transfer coefficient (h) on the surface of the slab is 40 W/m2K.

A : 0.832
B : 0.899
C : 0.841
D : 0.862

Q.no 47. A body which absorb all the radiation falling on it regardless of its wavelength ordirection is a

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

Q.no 48. The temperatures of two plates connected by a copper rod are maintained at (T1) 500 K and (T2) 350 K. Find the rate of heat transfer through the rod if the diameter (d) of the rod is 15 cm and length (L) is 1.5 m. Assume that the thermal conductivity is 0.4 kW/nK and there is no heat transfer on the surface of the rod.

A : 707 kW
B : 0.707 kW
C : 70.7 kW
D : 0.0707 kW

Q.no 49. Prandtl and Reynolds analogy are same, when Prandtl number is

A : 0.5
B : 1
C : >2
D : 1.5

Q.no 50. The frequency at which the electromagnetic radiation given off by a black body radiator is most intense , is completely determine by the black body’s

A : Frequency
B : Size
C : Shape
D : Temperature

Answer for Question No 41. is b
Answer for Question No 42. is b
Answer for Question No 43. is b
Answer for Question No 44. is d
Answer for Question No 45. is b
Answer for Question No 46. is a
Answer for Question No 47. is a
Answer for Question No 48. is b
Answer for Question No 49. is b
Answer for Question No 50. is d