# Heat and Mass Transfer MCQ – Set 06

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## Q1. 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

## Q2. The value of the wavelength for maximum emissive power is given by

(A) Wien’s law
(B) Planck’s law
(C) Stefan’s law
(D) Fourier’s law

## Q3. The thermal diffusivities for solids are generally

(A) Less than those for gases
(B) Less than those for liquids
(C) More than those for liquids and gases
(D) More or less same as for liquids and gases

## Q4. The total radiation from a black body per second per unit area is __ fourth power of the absolute temperature. This statement is known as Stefan Boltzmann law.

(A) Equal to
(B) Directly proportional to
(C) Inversely proportional to
(D) None of these

## Q5. Upto the critical radius of insulation,

(A) Added insulation will increase heat loss
(B) Added insulation will decrease heat loss
(C) Convective heat loss will be less than conductive heat loss
(D) Heat flux will decrease

## Q6. A perfect black body is one which

(A) Is black in colour
(B) Reflects all heat
(D) Absorbs heat radiations of all wave lengths falling on it

## Q7. 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

## Q8. The heat of sun reaches to us according to

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

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

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

## Q10. The insulation ability of an insulator with the presence of moisture would

(A) Increase
(B) Decrease
(C) Remain unaffected
(D) May increase/decrease depending on temperature and thickness of insulation

## Q11. Unit of thermal diffusivity is

(A) m²/hr
(B) m²/hr °C
(C) kcal/m² hr
(D) kcal/m. hr °C

## Q12. In regenerator type heat exchanger, heat transfer takes place by

(A) Direct mixing of hot and cold fluids
(B) A complete separation between hot and cold fluids
(C) Flow of hot and cold fluids alternately over a surface
(D) Generation of heat again and again

## Q13. The concept of overall coefficient of heat transfer is used in case of heat transfer by

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

## Q14. Log mean temperature difference in case of counter flow compared to parallel flow will be

(A) Same
(B) More
(C) Less
(D) Depends on other factors

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