Heat transfer Objective Questions & Answers - ObjectiveBooks

Heat transfer Objective Questions & Answers

Practice Test: Question Set - 35


1. Pick out the wrong statement.
    (A) The condensing film co-efficient is about 3 times lower for vertical condenser as compared to the equivalent horizontal condenser for identical situation
    (B) Film co-efficient for vaporization decreases as a result of vapor binding
    (C) In industrial practice, sub-cooling of condensate is required, when the condensate is a volatile liquid and is to be transferred for storage
    (D) Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film co-efficient, which is higher

2. Viscous & heat sensitive liquids are concentrated in __________ evaporators.
    (A) Open pan
    (B) Long tube
    (C) Agitated film
    (D) None of these

3. When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids?
    (A) At high fluid velocity
    (B) At low velocity
    (C) When fluid flows past a smooth surface
    (D) None of these

4. During crystallization, formation of crystal can occur in __________ solution only.
    (A) Saturated
    (B) Supersaturated
    (C) Under-saturated
    (D) All (a), (b) and (c)

5. Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m2.°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the
    (A) Higher condensing film co-efficient is desired
    (B) Condensate is corrosive in nature
    (C) Lower pressure drop through the exchanger is desired
    (D) Temperature of the incoming vapor is very high

6. Viscosity of gases __________ with increase in temperature.
    (A) Increase very rapidly
    (B) Increase slowly
    (C) Decrease slowly
    (D) Remain unaffected

7. In case of surface condensers, a straight line is obtained on plotting 1/U vs. __________ on an ordinary graph paper.
    (A) 1/V̅ -0.8
    (B) -0.8
    (C) -2
    (D) 1/ -2

8. A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest?
    (A) Cube
    (B) Plate
    (C) Sphere
    (D) All will cool at the same rate

9. A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the center of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the center) under identical conditions? Assume that the conductive heat transfer co-efficient is infinitely large.
    (A) 5 minutes
    (B) 10 minutes
    (C) 20 minutes
    (D) 40 minutes

10. At what value of Prandtl number, the hydrodynamic and thermal boundary layers are identical?
    (A) 0.5
    (B) 1
    (C) 1.5
    (D) 80

11. The equation, (h.D/K) is called the __________ number.
    (A) Nusselt
    (B) Peclet
    (C) Rayleigh
    (D) Grashoff

12. Nusselt number for full developed, laminar, constant property flow in a pipe at uniform heat flux is
    (A) 0.72
    (B) 4.364
    (C) 18
    (D) 83

13. Water always boils when its
    (A) Temperature reaches 100° C
    (B) Vapor pressure equals 76 cm of Hg
    (C) Saturated vapor pressure equals the external pressure on its surface
    (D) Saturated vapor pressure is less than the atmospheric pressure

14. Pick out the wrong statement.
    (A) By increasing the number of shell passes, the temperature cross in a shell and tube heat exchanger can be prevented
    (B) An under-designed steam trap will back up the condensate instead of discharging it out
    (C) Steam condensate is corrosive because of the presence of dissolved oxygen in it
    (D) Film boiling is desirable in commercial equipments due to high heat transfer rate at low temperature drop

15. (NRe . NPr) (D/L) is called the __________ number
    (A) Peclet
    (B) Stanton
    (C) Graetz
    (D) None of these

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