Heat Transfer MCQs | Heat Transfer Objective Type Questions and Answers

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Questions
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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