Heat Transfer
Thermal conductivity of a gas at low density, __________ with increase in temperature.

May increase or decrease; depends on the gas
Increases
Remains unchanged
Decreases

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Heat Transfer
A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because

Boiling point elevation in a single effect system is much higher than that in any effect in a multieffect system
Total heat transfer area of all the effects is -less than that in a single effect evaporator system
Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
Heat transfer co-efficient in a single effect is much lower than that in any effect in a multieffect system

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Heat Transfer
1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m² and the overall heat transfer co-efficient to the liquid is 1500 W/m².°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be

44 min
15 min
51 min
22 min

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