# Practice Test: Question Set - 06

**1. In counter flow heat exchangers**

- (A) Both the fluids at inlet (of heat exchanger
where hot fluid enters) are in their coldest state

- (B) Both the fluids at
inlet are in their hottest 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

**2. The ratio of surface convection resistance to the internal conduction resistance is known as**

- (A) Grashoff
number

- (B) Biot
number

- (C) Stanton
number

- (D) Prandtl
number

**3. A steam pipe is to be insulated by two insulating materials put over each other. For best results**

- (A) Better insulation should be put over pipe
and better one over it

- (B) Inferior insulation should be put over pipe
and better one over it

- (C) Both may be put in
any order

- (D) Whether to put inferior OIL over pipe or
the better one would depend on steam temperature

**4. Kirchhoff's law states that**

- (A) The total
radiation from a black body per second per unit area is directly proportional
to the fourth power of the absolute temperature

- (B) The
wave length corresponding to the maximum energy is proportional to the absolute
temperature

- (C) 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

- (D) None
of the above

**5. 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) Regular surfaces
having non-uniform temperature gradients

**6. The critical thickness of insulation for a sphere is**

- (A)

*k*/

*h₀*

- (B) 2

*k*/

*h₀*

- (C)

*h₀*/

*k*

- (D)

*h₀*/2

*k*

**7. According of Kirchhoff's law**

- (A) Radiant heat is proportional to fourth
power of absolute temperature

- (B) Emissive power
depends on temperature

- (C) Emissive power and
absorptivity are constant for all bodies

- (D) Ratio of emissive power to absorptive power
for all bodies is same and is equal to the emissive power of a perfectly black
body

**8. Film coefficient is defined as the ratio of**

- (A) Thermal
conductivity to the equivalent thickness of the film of fluid

- (B) Temperature
drop through the films of fluids to the thickness of film of fluids

- (C) Thickness of
film of fluid to the thermal conductivity

- (D) Thickness
of film of fluid to the temperature drop through the films of fluids

**9. All radiations in a black body are**

- (A) Reflected

- (B) Refracted

- (C) Transmitted

- (D) Absorbed

**10. The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as**

- (A) Conduction

- (B) Free
convection

- (C) Forced
convection

- (D) Radiation

**11. According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a**

- (A) Grey body

- (B) Brilliant white
polished body

- (C) Red hot body

- (D) Black body

**12. When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,**

- (A)

*α = 1, ρ = 0 and τ = 0*

- (B)

*α = 0, ρ = 1 and τ = 0*

- (C)

*α = 0, ρ = 0 and τ = 1*

- (D)

*α + ρ = 1 and τ = 0*

**13. The concept of overall coefficient of heat transfer is used in case of heat transfer by**

- (A) Conduction

- (B) Convection

- (C) Radiation

- (D) Conduction and
convection

**14. 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) Wien's law

- (B) Stefan's law

- (C) Kirchhoff's
law

- (D) Planck's
law

**15. The unit of overall coefficient of heat transfer is**

- (A) kcal/m²

- (B) kcal/hr °C

- (C) kcal/m² hr °C

- (D) kcal/m hr °C

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