Heat and Mass Transfer – Set 01

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Q1. Unit of thermal conductivity in M.K.S. units is

(A) K cal/kg m² °C
(B) K cal m/hr m² °C
(C) K cal/hr m² °C
(D) K calm/hr °C

Answer:(B) K cal m/hr m² °C


Q2. Heat transfer in liquid and gases takes place by

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

Answer:(B) Convection


Q3. Temperature of steam at around 540°C can be measured by

(A) Thermometer
(B) Thermistor
(C) Thermocouple
(D) None of these

Answer: (C) Thermocouple


Q4. Thermal conductivity of glass wool varies from sample to sample because of variation in

(A) Composition
(B) Density
(C) Porosity
(D) All of the above

Answer:(D) All of the above


Q5. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

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

Answer: (C) Conduction


Q6. In counter flow heat exchangers

(A) Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
(B) Both the fluids at inlet are in their hottest state
(C) Both the fluids at exit are in their hottest state
(D) One fluid is in hottest state and other in coldest state at inlet

Answer: (B) Both the fluids at inlet are in their hottest state


Q7. 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

Answer: (A) Wien’s law


Q8. 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

Answer: (C) More than those for liquids and gases


Q9. 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

Answer: (B) Directly proportional to


Q10. 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

Answer: (A) Added insulation will increase heat loss


Q11. 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

Answer: (A) 25 mm


Q12. Thermal diffusivity is a

(A) Function of temperature
(B) Physical property of a substance
(C) Dimensionless parameter
(D) All of these

Answer: (B) Physical property of a substance


Q13. The heat transfer takes place according to

(A) Zeroth law of thermodynamics
(B) First law of thermodynamics
(C) Second law of thermodynamics
(D) Kirchhoff’s law

Answer: (C) Second law of thermodynamics


Q14. Thermal diffusivity of a substance is

(A) Directly proportional to the thermal conductivity
(B) Inversely proportional to density of substance
(C) Inversely proportional to specific heat
(D) All of the above

Answer: (D) All of the above


Q15. According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

(A) Absolute temperature
(B) Square of the absolute temperature
(C) Cube of the absolute temperature
(D) Fourth power of the absolute temperature

Answer: (D) Fourth power of the absolute temperature


Q16. The heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity)

(A) Q = [2πlk (T₁ – T₂)]/2.3 log (r₂/r₁)
(B) Q = 2.3 log (r₂/r₁)/[2πlk (T₁ – T₂)]
(C) Q = [2π (T₁ – T₂)]/2.3 lk log (r₂/r₁)
(D) Q = = 2πlk/2.3 (T₁ – T₂) log (r₂/r₁)

Answer: (A) Q = [2πlk (T₁ – T₂)]/2.3 log (r₂/r₁)


Q17. The ratio of surface convection resistance to the internal conduction resistance is known as

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

Answer: (B) Biot number


Q18. The heat of sun reaches to us according to

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

Answer: (C) Radiation


Q19. 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

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


Q20. 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

Answer: (B) Decrease


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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