Engineering Heat Transfer Questions Answers - Set 07 - ObjectiveBooks

Engineering Heat Transfer Questions Answers - Set 07

Practice Test: Question Set - 07

1. The Graetz number is concerned with the
    (A) Mass transfer between a gas and a liquid
    (B) Absorption with chemical reaction
    (C) Heat transfer in turbulent flow
    (D) Heat transfer in laminar flow

2. At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe?
    (A) 0.5
    (B) < 0.5
    (C) > 0.6
    (D) < 0.1

3. The unit of conductance in SI unit is
    (A) W/m
    (B) W/m2
    (C) W/°K
    (D) W/m°K

4. Pick out the wrong statement.
    (A) Bubble size increases with the dynamic viscosity of the liquid in case of nucleate pool boiling
    (B) Thermal conductivity of a dry material is more than that of the damp material
    (C) Ratio of its capacity to economy equals the steam consumption in kg/hr in an evaporator
    (D) Vaporization of organic substances in evaporator mostly causes foam formation

5. Pick out the correct statement.
    (A) Higher is the temperature of the radiating body, higher is the wavelength of radiation
    (B) Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder
    (C) The wavelength corresponding to maximum mono-chromatic emissive power increases with rise in temperature
    (D) Solid angle subtended by the finite surface at the radiating element is called the angle of incidence

6. Nucleate boiling is promoted
    (A) On polished surfaces
    (B) On rough surfaces
    (C) In the absence of agitation
    (D) None of these

7. Which of the following has the lowest Prandtl number?
    (A) Molten sodium (a coolant used in fast breeder reactor)
    (B) Water
    (C) Transformer oil
    (D) Dilute H2SO4

8. The thermal boundary layer at NPr > 1
    (A) Is thicker than hydrodynamic boundary layer
    (B) Is thinner than hydrodynamic boundary layer
    (C) And the hydrodynamic boundary layers are identical
    (D) Disappears

9. In case of a multipass shell and tube heat exchanger, the temperature drop in the fluid
    (A) Is inversely proportional to the resistance across which the drop occurs
    (B) And the wall are proportional to individual resistances
    (C) And the wall is not related
    (D) None of these

10. Which of the following is directly concerned with the heat transfer?
    (A) Strouhal number
    (B) Sherwood number
    (C) Euler number
    (D) Grashoff number

11. The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the
    (A) Solution has an elevation of boiling point
    (B) Evaporators operate under vacuum
    (C) Evaporators operate at atmospheric pressure
    (D) None of these

12. The equation, Nst = f/2, is the __________ analogy.
    (A) Colburn
    (B) Reynolds
    (C) Prandtl
    (D) None of these

13. Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer.
    (A) Grashoff
    (B) Biot
    (C) Stanton
    (D) Reynolds

14. Forced circulation evaporators are normally used for concentrating liquids having
    (A) Scaling characteristics
    (B) High viscosity
    (C) Both (a) & (b)
    (D) Neither (a) nor (b)

15. Radiation energy is emitted by all the substances, which are above
    (A) 0°K
    (B) 0°C
    (C) 100°C
    (D) Room temperature

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