# Heat and Mass Transfer Objective Questions with Answers Set – 11

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## Q1. 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.

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

## Q3. The process of heat transfer from one particle of the body to another is called conduction, when the particles of the body

(A) Move actually
(B) Do not move actually
(C) Affect the intervening medium
(D) Does not affect the intervening medium

(A) Glass
(B) Water
(C) Plastic
(D) Air

## Q5. Joule sec is the unit of

(A) Universal gas constant
(B) Kinematic viscosity
(C) Thermal conductivity
(D) Planck’s constant

## Q6. 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

(A) One
(B) Two
(C) Three
(D) Four

## Q8. Fourier’s law of heat conduction gives the heat flow for

(A) Irregular surfaces
(B) Nonuniform temperature surfaces
(C) One dimensional cases only
(D) Two dimensional cases only

## Q9. A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is

(A) h₁ + h₂ + h₃
(B) (h₁.h₂.h₃)1/3
(C) 1/h₁ + 1/h₂ + 1/h₃
(D) None of these

(A) Steam
(B) Solid ice
(C) Melting ice
(D) Water

(A) 0.1
(B) 0.3
(C) 0.7
(D) 1.7

(A) Conduction
(B) Convection

## Q13. The ratio of Nusselt number and the product of Reynold’s number and Prandtl number is equal to

(A) Stanton number
(B) Biot number
(C) Peclet number
(D) Grashoff number

## Q14. The product of Reynolds number and Prandtl number is known as

(A) Stanton number
(B) Biot number
(C) Peclet number
(D) Grashoff number

## Q15. An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be

(A) 25 mm
(B) 40 mm
(C) 160 mm
(D) 800 mm

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