### Heat Transfer

11. 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

1. 15 min
2. 22 min
3. 44 min
4. 51 min
51 min

12. 1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is

1. 520
2. 200
3. 400
4. 500
400

13. 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid).

1. 0.5
2. 0.05
3. 0.1
4. 0.15
0.1

14. A _________ evaporator employs an annular downtake.

2. Horizontal
3. Long tube vertical
4. None of these

15. A _________ surface has the maximum thermal emissivity out of the following.

1. Black & smooth
2. Black & rough
3. White & smooth
4. White & rough
Black & rough

16. A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be

1. Greater than that for un-insulated steam pipe
2. Less than that of the un-insulated steam pipe
3. Equal to that of the un-insulated steam pipe
4. Less than the steam pipe with 5 cms insulation
Less than that of the un-insulated steam pipe

17. A 2-4 heat exchanger involves

1. Only counter-flow of fluids
2. Only parallel-flow of fluids
3. Both counter and parallel-flow of the fluids
4. Smaller pressure drop compared to 1-2 exchanger
Both counter and parallel-flow of the fluids

18. A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides

1. Higher economy
2. Lower capacity
3. Both (A) & (B)
4. Lower economy
Higher economy

19. A black body does not _________ radiation.

1. Absorb or emit
2. Refract
3. Reflect
4. Both (B) & (C)