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Heat Transfer MCQs | Heat Transfer Objective Type Questions and Answers

(21) A non-dimensional number generally associated with natural convection heat transfer is
[A] Grashoff number
[B] Nusselt number
[C] Weber number
[D] Prandtl number
Answer: Grashoff number
(22) In counter flow heat exchangers
[A] both the fluids at inlet (of heat ex¬changer where hot fluid enters) are in their coldest state
[B] both the fluids at inlet are in their hot¬test state
[C] both the fluids .at exit are in their hottest state
[D] one fluid is in hottest state and other in coldest state at inlet
Answer: both the fluids at inlet are in their hot¬test state

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(23) Fourier’s law of heat conduction is valid for
[A] one dimensional cases only
[B] two dimensional cases only
[C] three dimensional cases only
[D] irregular surfaces
Answer: one dimensional cases only
(24) All radiations in a black body are
[A] Reflected
[B] Refracted
[C] Transmitted
[D] Absorbed
Answer: Absorbed
(25) The unit of overall coefficient of heat transfer is
[A] kcal/m2
[B] kcal/hr °C
[C] kcal/m2 hr °C
[D] kacl/m hr °C
Answer: kcal/m2 hr °C
(26) Joule sec is the unit of
[A] universal gas constant
[B] kinematic viscosity
[C] thermal conductivity
[D] Planck’s constant
Answer: Planck’s constant
(27) 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
Answer: Wien’s law
(28) 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
Answer: Shorter Wavelength
(29) According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
[A] absolute temperature
[B] square of temperature
[C] fourth power of absolute temperature
[D] fourth power of temperature
Answer: fourth power of absolute temperature
(30) Which of the following property of air does not increase with rise in temperature
[A] Thermal Conductivity
[B] Thermal Diffusivity
[C] Density
[D] Dynamic Viscosity
Answer: Density
31 The unit of Stefan Boltzmann constant is
[A] watt/cm2 °K
[B] watt/cm4 °K
[C] watt2/cm °K4
[D] watt/cm2 °K4
Answer: watt/cm2 °K4
32 In free con-vection heat transfer, Nusselt number is 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.
Answer: Grashoff no. and Prandtl no.
33 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
Answer: more than those for liquids
34 Thermal diffusivity of a substance is
[A] directly proportional to thermal con¬ductivity
[B] inversely proportional to density of substance
[C] inversely proportional to specific heat
[D] all of the above
Answer: all of the above
35 The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
[A] Krichoff’s law
[B] Stefan’s law
[C] Wien’ law
[D] Planck’s law
Answer: Krichoff’s law
36 According to Wien’s law, the wavelength corresponding to maximum energy is proportion to
[A] absolute temperature (T)
[B] I2
[C] f
[D] All Of The Above
Answer: absolute temperature (T)
37 Depending on the radiating properties, a body will be white when
[A] p = 0, x = 0 and a = 1
[B] p=l,T = 0anda = 0
[C] p = 0, x = 1 and a = 0
[D] x = 0, a + p = 1
Answer: p=l,T = 0anda = 0
38 Depending on the radiating properties, a body will be black when
[A] p = 0, x = 0 and a = 1
[B] p= l,T = 0anda = 0
[C] p = 0, x = 1 and a = 0
[D] none of the above
Answer: p = 0, x = 0 and a = 1
39 Depending on the radiating properties, a body will be opaque when
[A] p = 0, x = 0 and a = 1
[B] p=l,x = 0anda = 0
[C] p = 0, x = 1 and a = 0
[D] x – 0, a + p = 1
Answer: x – 0, a + p = 1
40 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
Answer: 0.45

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