Heat and Mass Transfer – Set 06

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Q1. The automobile radiator is a heat exchanger of

(A) Parallel flow type
(B) Counter flow type
(C) Cross flow type
(D) Regenerator type

Answer: (C) Cross flow type


Q2. Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)

(A) h = k/ ρS
(B) h = ρS/k
(C) h = S/ρk
(D) h = kρ/S

Answer: (A) h = k/ ρS


Q3. According to Newton’s law of cooling, the heat transfer from a hot body to a cold body is

(A) Directly proportional to the surface area
(B) Directly proportional to the difference of temperatures between the two bodies
(C) Either (A) or (B)
(D) Both (A) and (B)

Answer: (D) Both (A) and (B)


Q4. When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a

(A) Black body
(B) Grey body
(C) Opaque body
(D) White body

Answer: (A) Black body


Q5. 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

Answer: (C) Forced convection


Q6. The transfer of heat by molecular collision is known as

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

Answer: (B) Convection


Q7. 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

Answer: (B) Convection


Q8. Free convection flow depends on

(A) Density
(B) Coefficient of viscosity
(C) Gravitational force
(D) All of these

Answer: (D) All of these


Q9. In a shell and tube heat exchanger, baffles are provided on the shell side to

(A) Improve heat transfer
(B) Provide support for tubes
(C) Prevent stagnation of shell side fluid
(D) All of these

Answer: (D) All of these


Q10. Depending on the radiating properties, a body will be opaque when

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

Answer: (D) X = 0, a + p = 1


Q11. When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by

(A) Conduction
(B) Convection
(C) Radiation
(D) Conduction and convection

Answer: (A) Conduction


Q12. Which of the following is a case of steady state heat transfer?

(A) I.C. engine
(B) Air preheaters
(C) Heating of building in winter
(D) None of the above

Answer: (D) None of the above


Q13. The concept of overall coefficient of heat transfer is used in heat transfer problems of

(A) Conduction
(B) Convection
(C) Radiation
(D) Conduction and convection

Answer: (D) Conduction and convection


Q14. According to Prevost theory of heat exchange

(A) It is impossible to transfer heat from low temperature source to t high temperature source
(B) Heat transfer by radiation requires no medium
(C) All bodies above absolute zero emit radiation
(D) Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

Answer: (C) All bodies above absolute zero emit radiation


Q15. A grey body is one whose absorptivity

(A) Varies with temperature
(B) Varies with wavelength of the incident ray
(C) Is equal to its emissivity
(D) Does not vary with temperature and. wavelength of the incident ray

Answer: (C) Is equal to its emissivity


Q16. 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

Answer: (D) Black body


Q17. 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: (C) Density


Q18. 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

Answer: (B) P=1, T = 0 and a = 0


Q19. Which of the following statement is correct?

(A) A grey body is one which absorbs all radiations incident on it.
(B) At thermal equilibrium, the emissivity and absorptivity are same.
(C) The energy absorbed by a body to the total energy falling on it, is called emissivity.
(D) A perfect body is one which is black in colour.

Answer: (B) At thermal equilibrium, the emissivity and absorptivity are same.


Q20. An ordinary passenger aircraft requires a cooling system of capacity.

(A) 2 TR
(B) 4 TR
(C) 8 TR
(D) 10 TR

Answer: (C) 8 TR


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Heat and Mass Transfer – Set 01
Heat and Mass Transfer – Set 02
Heat and Mass Transfer – Set 03
Heat and Mass Transfer – Set 04
Heat and Mass Transfer – Set 05
Heat and Mass Transfer – Set 06
Heat and Mass Transfer – Set 07
Heat and Mass Transfer – Set 08