Heat Transfer multiple choice questions

 Heat Transfer

1. Units for thermal conductivity
a) J/kg.K
b) J/mol.K
c) J.ohm/sec.K2
d) W/m.K
Answer: W/m.K
2. The ratio of energy transferred by convection to that by conduction is called
a) Stanton number
b) Nusselt number
c) Biot number
d) Preclet number
Answer: Biot number
3. Air at 20° C blows over a plate of 50 cm x 75 cm maintained at 250° C. If the convection heat transfer coefficient is 25 W/m2 °C, the heat transfer rate is
a) 215.6 kW
b) 2156 kW
c) 2.156 kW
d) 21.56 Kw
Answer: 2.156 kW
4. If the body is at thermal equilibrium, then the
a) Emissivity = absorptivity
b) Emissivity > absorptivity
c) Emissivity < absorptivity
d) None of the above
Answer: Emissivity = absorptivity
5. The body which absorbs all radiations incident upon it, is called as
a) Black body
b) White body
c) Opaque body
d) Transparent body
Answer: Black body
6. In radiative heat transfer, a gray surface is one
a) which appears gray to the eye
b) whose emissivity is independent of wavelength
c) which has reflectivity equal to zero
d) which appears equally bright from all directions
Answer: whose emissivity is independent of wavelength
7. The Stefan Boltzman law states that
a) E α T
b) E α T2
c) E α T3
d) E α T4
Answer: E α T4
8. Heat is mainly transferred by conduction, convection and radiation in
a) insulated pipes carrying hot water
b) refrigerator freezer coil
c) boiler furnaces
d) condensation of steam in a condenser
Answer: boiler furnaces
9. Fourier law of heat conduction is based on the assumption that
a) Heat flow through a solid is one dimensional
b) Heat flow is in steady state
c) both (a) and (b)
d) None of the options
Answer: both (a) and (b)
10. What happens when the thickness of insulation on a pipe exceeds the critical value?
a) Heat transfer rate increases
b) Heat transfer rate decreases
c) Heat transfer rate remain constant
d) none of these
Answer: Heat transfer rate decreases
11. In heat exchangers, the value of logarithmic mean temperature difference should be
a) maximum possible
b) minimum possible
c) Zero
d) constant
Answer: maximum possible
12. The heat is absorbed by
a) Condenser
b) Evaporator
c) Compressor
d) Thermostat
Answer: Evaporator
13. The process of heat transfer from one particle of the body to another without actual motion of the particle is called
a) Radiation
b) Conduction
c) Convection
d) None of these
Answer: Radiation
14. The value of Biot number is very small (less than 0.01) when
a) The convective resistance of the fluid is negligible
b) The conductive resistance of the solid is negligible
c) The conductive resistance of the fluid is negligible
d) None of these
Answer: The conductive resistance of the solid is negligible
15. Heat transfer takes place according to
a) First Law of Thermodynamics
b) Second Law of Thermodynamics
c) Third Law of Thermodynamics
d) Zeroth Law of Thermodynamics
Answer: Second Law of Thermodynamics