The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of ‘a’ in SI system will be________________?

A. W/m.k
B. W/m
C. W/m.k2
D. None, ‘a’ is just a number

The statement that “maximum wavelength of radiation is inversely proportional to the temperature” is ______________ law?

A. Stefan-Boltzmann’s
B. Planck’s
C. Wien’s displacement
D. None of these

A body is called grey if the monochromatic emissivity of the body is___________________?

A. Zero
B. Unity
C. Same for all wavelengths
D. Different for all wavelengths

At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical ?

A. 1
B. 1
D. None of these

When vaporisation takes place directly at the heating surface, it is called________________?

A. Film boiling
B. Nucleate boiling
C. Vapour binding
D. None of these

The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as______________?

A. (ΔT)1/4
B. (ΔT)1/2
C. (ΔT)5/4
D. (ΔT)3/4

The equation, Nst = f/2, is the _____________ analogy?

A. Colburn
B. Reynolds
C. Prandtl
D. None of these

What is the emissivity of a black body ?

A. 0
B. 1
C. 0.5
D. 0.90

An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is___________________?

A. 4000
B. 9000
C. 4600
D. 3000

A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions? Assume that the conductive heat transfer co-efficient is infinitely large ?

A. 5 minutes
B. 10 minutes
C. 20 minutes
D. 40 minutes