# 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

## 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)

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

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

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

## 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
(D) None of these

## Q8. Free convection flow depends on

(A) Density
(B) Coefficient of viscosity
(C) Gravitational force
(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

## 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
(D) Conduction and convection

## 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
(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

## 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

## 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

## 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.

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