Heat Transfer Multiple Choice Questions and Answers PDF


1. Which of the following property of air does not increase with rising in temperature
(a) thermal conductivity
(b) thermal diffusivity
(c) density
(d) dynamic viscosity
(e) kinematic viscosity.
Ans: c
2. The unit of Stefan Boltzmann constant is
(a) watt/cm2 °K
(b) watt/cm4 °K
(c) watt2/cm °K4
(d) watt/cm2 °K4
(e) watt/cm2 °K2.
Ans: d
3. In free convection heat transfer, the Nusselt number is a function of
(a) Grashoff no. and Reynold no.
(b) Grashoff no. and Prandtl no.
(c) Prandtl no. and Reynold no.
(d) Grashoff no., Prandtl no. and Reynold no.
(e) none of the above.
Ans: b
4. Stefan Boltzmann law is applicable for heat transfer by
(a) conduction
(b) convection
(c) radiation
(d) conduction and radiation combined
(e) convection and radiation combined.
Ans: c
5. The unit of overall coefficient of heat transfer is
(a) kcal/m2
(b) kcal/hr °C
(c) kcal/m2 hr °C
(4) kacl/m hr °C
(e) kcal/m3 hr °C.
Ans: c
6. Joule sec is the unit of
(a) universal gas constant
(b) kinematic viscosity
(c) thermal conductivity
(d) Planck’s constant
(e) none of the above.
Ans: d
7. The value of Prandtl number for air is about
(a) 0.1
(b) 0.3
(c) 0.7
(d) 1.7
(e) 10.5.
Ans: c
8. The value of the wavelength for maximum emissive power is given by —
(a) Wien’s law
(b) Planck’s law
(c) Stefan’s law
(d) Fourier’s law
(e) Kirchhoff’s law.
Ans: a
9. Log mean temperature difference in case of counterflow compared to parallel flow will be
(a) same
(b) more
(c) less
(d) depends on other factors
(e) none of the above.
Ans: b
10. The energy distribution of an ideal reflector at higher temperatures is largely in the range of
(a) shorter wavelength
(b) longer wavelength
(c) remains same at all wavelengths
(d) wavelength has nothing to do with it
(e) none of the above.
Ans: a
11. Total emissivity of polished silver compared to black body is
(a) same
(b) higher
(c) more or less same
(d) very much lower
(e) very much higher.
Ans: d
12. The thermal diffusivities for gases are generally
(a) more than those for liquids
(b) less than those for liquids
(c) more than those for solids
(d) dependent on the viscosity
(e) same as for the liquids.
Ans: a
13. The thermal diffusivities for solids are generally
(a) less than those for gases
(b) less than those for liquids
(c) more than those for liquids and gases
(d) more or less same as for liquids and gases
(e) Percy.
Ans: c
14. Thermal diffusivity of a substance is
(a) directly proportional to thermal con¬ductivity
(b) inversely proportional to the density of the substance
(c) inversely proportional to specific heat
(d) all of the above
(e) none of the above.
Ans: d
15. The ratio of the energy absorbed by the body to total energy falling on it is called
(a) absorptive power
(b) emissive power
(c) absorptivity
(d) emissivity
(e) none of the above.
Ans: a
16. 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
(a) 0.45
(b) 0.55
(c) 0.40
(d) 0.75
(e) 0.60.
Ans: a
17. The amount of radiation mainly depends on
(a) nature of a body
(b) the temperature of the body
(c) type of surface of the body
(d) all of the above
(e) none of the above.
Ans: d
18. A grey body is one whose absorptivity
(a) varies with temperature
(b) varies with the wavelength of the incident ray
(c) is equal to its emissivity
(d) does not vary with temperature and. the wavelength of the incident ray
(e) none of the above.
Ans: c
19. Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to the same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
(a) 1: 1
(b) 2: 1
(c) 1: 2
(d) 4: 1
(e) 1: 4.
Ans: c
20. A non-dimensional number generally associated with natural convection heat transfer is
(a) Grashoff number
(b) Nusselt number
(c) Weber number
(d) Prandtl number
(e) Reynold number.
Ans: a

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