Examples of Heat Transfer in Engineering MCQ Test - Set 11 - ObjectiveBooks
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# Practice Test: Question Set - 11

1. The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are
(A) Re.Gz
(B) Nu, Pr
(C) Nu, Pr, Re
(D) Nu, Gz

2. Which of the following has maximum thermal conductivity?
(A) Iron
(B) Coal
(C) Nitrogen
(D) Tar

3. In case of heat transfer by conduction in a hollow cylinder, __________ mean area is used to calculate the heat transfer rate.
(A) Geometric
(B) Arithmetic
(C) Logarithmic
(D) Either (a), (b) or (c)

4. The absorptivity of a grey body at a given temperature __________ with increasing wavelength of radiation.
(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase or decrease; depends on the material

5. Thermal diffusivity of a material
(A) Has the unit m2 /sec
(B) Is defined as K/ρ . Cp
(C) Is the ratio of thermal conductivity to thermal capacity
(D) All (a), (b) and (c)

6. Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator?
(A) Long vertical evaporator
(B) Horizontal tube evaporator
(C) Agitated film evaporator
(D) Calandria vertical tube evaporator

7. Nusselt number is the ratio of the temperature gradient at the wall to
(A) Temperature difference
(B) Heat flux
(C) That across the entire pipe
(D) None of these

8. Which of the following has the lowest overall heat transfer co-efficient?
(A) Dowtherm
(B) Molten sodium
(C) Water
(D) Air

9. What is the unit of thermal conductivity?
(A) Kcal/hr. m2 °C
(B) Kcal/hr.m.°C
(C) Kcal/hr.m
(D) Kcal/hr. °C

10. Indirect contact heat exchangers are preferred over direct contact heat exchangers, because
(A) Heat transfer co-efficient are high
(B) There is no risk of contamination
(C) There is no mist formation
(D) Cost of equipment is lower

11. Tubes are held between top and bottom tube sheets in Calandria type evaporator by keeping
(A) Both the tube sheets fixed
(B) Both the tube sheets floating
(C) The top tube sheet floating and bottom tube sheet fixed
(D) The top tube sheet fixed and the bottom tube-sheet floating

12. Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is
(A) 0.2
(B) 0.4
(C) 0.6
(D) 0.8

13. What is the emissivity of a black body?
(A) 0
(B) 1
(C) 0.5
(D) 0.90

14. The actual temperature drop across the heating surface of an evaporator depends on the
(A) Liquid depth over the heating surface
(B) Solution being evaporated
(C) Pressure difference between the steam chest and the vapor space above the boiling liquid
(D) All (a), (b) and (c)

15. In SI units, thermal conductivity is expressed in
(A) Watt/m.°K
(B) Watt/m2. °K
(C) Watt/m2. °K
(D) Watt/m4. °K

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