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) V̅ -0.8
- (C) V̅ -2
- (D) 1/ V̅ -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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