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
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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).
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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
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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.
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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
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