Heat and Mass Transfer – Set 04

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Q1. The critical thickness of insulation for a sphere is

(A) k/h₀
(B) 2k/h₀
(C) h₀/k
(D) h₀/2k

Answer: (B) 2k/h₀


Q2. The most commonly used method for the design of duct size is the

(A) Velocity reduction method
(B) Equal friction method
(C) Static regains method
(D) Dual or double method

Answer: C) Static regains method


Q3. Radiation is the process of heat transfer in which heat flows from a __, in a straight line, without affecting the intervening medium.

(A) Cold body to hot body
(B) Hot body to cold body
(C) Smaller body to larger body
(D) Larger body to smaller body

Answer: (B) Hot body to cold body


Q4. Conduction is a process of heat transfer

(A) From one particle of the body to another without the actual motion of the particles
(B) From one particle of the body to another by the actual motion of the heated particles
(C) From a hot body to a cold body, in a straight line, without affecting the intervening medium
(D) None of the above

Answer: (A) From one particle of the body to another without the actual motion of the particles


Q5. The unit of overall coefficient of heat transfer is

(A) W/m²K
(B) W/m²
(C) W/mK
(D) W/m

Answer: (A) W/m²K


Q6. The total emissivity power is .defined as the total amount of radiation emitted by a black body per unit

(A) Temperature
(B) Thickness
(C) Area
(D) Time

Answer: (D) Time


Q7. Thermal conductivity of non-metallic amorphous solids with decrease in temperature

(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase or decrease depending on temperature

Answer: (B) Decreases


Q8. Pick up the wrong case. Heat flowing from one side to other depends directly on

(A) Face area
(B) Time
(C) Thickness
(D) Temperature difference

Answer: (C) Thickness


Q9. Thermal conductivity of air with rise in temperature

(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase or decrease depending on temperature

Answer: (A) Increases


Q10. Moisture would find its way into insulation by vapour pressure unless it is prevented by

(A) High thickness of insulation
(B) High vapour pressure
(C) Less thermal conductivity insulator
(D) A vapour seal

Answer: (D) A vapour seal


Q11. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as

(A) Emissivity
(B) Transmissivity
(C) Reflectivity
(D) Intensity of radiation

Answer: (D) Intensity of radiation


Q12. According of Kirchhoff’s law

(A) Radiant heat is proportional to fourth power of absolute temperature
(B) Emissive power depends on temperature
(C) Emissive power and absorptivity are constant for all bodies
(D) Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body

Answer: (D) Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body


Q13. Total emissivity of polished silver compared to black body is

(A) Same
(B) Higher
(C) More or less same
(D) Very much lower

Answer: (D) Very much lower


Q14. According to Stefan’s law, the total radiation from a black body per second per unit area is proportional to

(A) Absolute temperature
(B) T²
(C) T⁵
(D) T

Answer: (D) T


Q15. Thermal conductivity of water in general with rise in temperature

(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase or decrease depending on temperature

Answer: (D) May increase or decrease depending on temperature


Q16. LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is

(A) Higher
(B) Lower
(C) Same
(D) Depends on the area of heat exchanger

Answer: (A) Higher


Q17. The ratio of the energy absorbed by the body to total energy falling on it is called

(A) Absorptive power
(B) Emissive power
(C) Absorptivity
(D) Emissivity

Answer: (A) Absorptive power


Q18. According to Dalton’s law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

(A) Pb = pa – pv
(B) Pb = pa + pv
(C) Pb = pa × pv
(D) Pb = pa/pv

Answer: (B) Pb = pa + pv


Q19. The critical radius is the insulation radius at which the resistance to heat flow is

(A) Maximum
(B) Minimum
(C) Zero
(D) None of these

Answer: (B) Minimum


Q20. A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as

(A) A.Cmin/U
(B) U/A.Cmin
(C) A.U.Cmin
(D) A.U/Cmin

Answer: (D) A.U/Cmin


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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