E-PolyLearning

41. Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone.
a. laminar
b. transition
c. both 'a' & 'b'
d. highly turbulent
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Answer: (d).highly turbulent

42. The actual temperature drop across the heating surface in an evaporator depends on the
a. feed.
b. depth of liquid over heating surface.
c. pressure difference between steam chest and vapour space.
d. all (a), (b) and (c).
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Answer: (d).all (a), (b) and (c).

43. Which of the following is not used as a medium for high temperature heating ?
a. Dowtherm
b. mercury
c. liquid metal (e.g. molten sodium)
d. fused salts (e.g., an eutectic mixture of 53% KNO₃, 40% NaNO₂and 7% NaNO₃)
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Answer: (b).mercury

44. Presence of a non-condensing gas in a condensing vapour
a. increases the rate of condensation.
b. decreases thermal resistance.
c. is desirable to increase the film co-efficient.
d. none of these.
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Answer: (d).none of these.

45. The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film )
a. (ΔT)²
b. √ΔT
c. (ΔT)^1/4
d. (ΔT)^3/2
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Answer: (c).(ΔT)^1/4