Heat and Mass Transfer Objective Questions with Answers – Set 09

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All questions answers in the last paragraph


Q1. The critical thickness of insulation for a sphere is

(A) k/h₀
(B) 2k/h₀
(C) h₀/k
(D) h₀/2k


Q2. The transfer of heat by molecular collision is known as

(A) Conduction
(B) Convection
(C) Radiation
(D) None of these


Q3. The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called

(A) Conduction
(B) Convection
(C) Radiation
(D) None of these


Q4. Thermal conductivity of water in general with rise in temperature

(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase or decrease depending on temperature


Q5. LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is

(A) Higher
(B) Lower
(C) Same
(D) Depends on the area of heat exchanger


Q6. The amount of radiation mainly depends on

(A) Nature of body
(B) Temperature of body
(C) Type of surface of body
(D) All of the above


Q7. 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


Q8. 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


Q9. Depending on the radiating properties, a body will be white when
(Where a = absorptivity, p = reflectivity, x = transmissivity)

(A) P = 0, x = 0 and a = 1
(B) P=1, T = 0 and a = 0
(C) P = 0, x = 1 and a = 0
(D) X = 0, a + p = 1


Q10. The emissivity for a black body is

(A) 0
(B) 0.5
(C) 0.75
(D) 1


Q11. The transfer of heat by molecular collision is smallest in

(A) Solids
(B) Liquids
(C) Gases
(D) None of these


Q12. 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


Q13. 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


Q14. The expression Q = ρ AT4 is called

(A) Fourier equation
(B) Stefan-Boltzmann equation
(C) Newton Reichmann equation
(D) Joseph-Stefan equation


Q15. A steam pipe is to be lined with two layers of insulating materials of different thermal conductivities. For the minimum heat transfer,

(A) The better insulation must be put inside
(B) The better insulation must be put outside
(C) One could place either insulation on either side
(D) One should take into account the steam temperature before deciding as to which insulation is put where


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All questions answers

QUESTION NO : ANSWERS :
1(B)
2(B)
3(B)
4(D)
5(A)
6(D)
7(A)
8(C)
9(B)
10(D)
11(C)
12(A)
13(C)
14(B)
15(A)

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