Heat and Mass Transfer (handouts)

Question 1

1. Heat sensitive materials can be concentrated in an evaporator employing.

Question 2

2. kg of liquid evaporated per hour in an evaporator is defined as its.

Question 3

3. The number of kg vaporized per kg of steam fed to the evaporator is defined as.

Question 4

4. What is the steam economy in case of a single effect evaporator system?

Question 5

5. Evaporation of 1kg of water from a solution in a single effect evaporator requires about ______ kg of steam.

Question 6

6. The rate of heat transfer is a product of overall heat transfer coefficient, the difference in temperature and the.

Question 7

7. Increasing the liquor level in the evaporator results in the.

Question 8

8. It is not preferable to use superheated steam in evaporators, because of its very.

Question 9

9. Small scale evaporation is done in a.

Question 10

10. Viscous and heat sensitive liquids are concentrated in ______ evaporators.

Question 11

11. Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator?

Question 12

12. A ______ evaporator employs an annular down take.

Question 13

13. Which is the most suitable for the concentration of foamy and frothy liquors?

Question 14

14. Boiling point elevation for a strong and concentrated solution is found by Duhring’s rule, which states that at the same pressure, the boiling point of a solution is a linear function of the ______ of pure water.

Question 15

15. Boiling point of a solution according to Duhring’s rule is a linear function of the ______ of water.

Question 16

16. In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer coefficient.

Question 17

17. In case of evaporators, liquid entrainment results primarily due to.

Question 18

18. Multiple effect evaporation is generally recommended, when the.

Question 19

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

Question 20

20. In a backward feed multiple effect evaporator.

Question 21

21. For evaporation of viscous solution in a multiple effect evaporator, the preferred feeding scheme is.

Question 22

22. In a forward feed multiple effect, the pressure build up will be.

Question 23

23. For the same heat transfer area and the terminal conditions, the ratio of the capacities of a single effect evaporator to a triple effect evaporator is.

Question 24

24. Black liquor generated during paper manufacture is concentrated in.

Question 25

25. Which of the following accessories is provided in the vapor line of an evaporator for removing the entrained liquid?

Question 26

26. The driving potential for the crystal growth during crystallization is the ______ of the solution.

Question 27

27. A solution of Na₂SO₄ in water is saturated at 50 °C. When a saturated solution of Na₂SO₄ is cooled, crystals of Na₂SO₄ x 10H₂O separate from the solution. If 1000 kg of this solution is cooled to 10 °C, the percentage yield obtained is.

Question 28

28. A tank holds 10000 kg of a saturated solution of Na₂CO₃ at 30ºC. You want to crystallize from this solution 3000 kg Na₂CO₃ x 10 H₂O without any accompanying water. To what temperature must the solution be cooled?

Question 29

29. Crystallization of solids from a homogeneous solution is a/an ______ process.

Question 30

30. In most of the vacuum crystallizer, vacuum is generally produced by means of a.

Question 31

31. What is the yield of sodium acetate crystals (CH₂COONa x 3H₂O) obtainable from a vacuum crystallizer operating at 1.33 kN/m² when it is supplied with 0.56 kg/s of a 40 percent aqueous solution of the salt at 353 K?

Question 32

32. At a fixed pressure, the humidity depends upon the partial pressure of vapor in the mixture. Humidity of a vapor free gas is ______ percent.

Question 33

33. ______ is the temperature at which a gas-vapor mixture becomes saturated, when cooled at constant total pressure out of contact with a liquid.

Question 34

34. Weight of 1 m³ of humid air as compared to 1 m³ of dry air, under the same conditions, is.

Question 35

35. Condensation of a vapor-gas mixture just begins, when (where, p = partial pressure of the vapor P = vapor pressure of the liquid).

Question 36

36. When an unsaturated air-water mixture is heated at constant pressure, then.

Question 37

37. Steady state temperature reached by a small amount of liquid evaporating into a large amount of unsaturated vapor-gas mixture is.

Question 38

38. Which of the following remains constant during evaporative cooling process with recirculated water supply?

Question 39

39. When the temperature and humidity of air is low, we usually use ______ draft cooling tower.

Question 40

40. Moisture contained by a substance in excess of the equilibrium moisture is called.

Question 41

41. Moisture in a substance exerting an equilibrium vapor pressure less than that of pure liquid at the same temperature is called the ______ moisture.

Question 42

42. Drying operation under vacuum is carried out to.

Question 43

43. A wet solid is dried in a batch after under constant drying conditions from 25% db to 10% db in 4.17 hours. The critical moisture content is 15% db and its equilibrium moisture content is 5% db. How long will it take to dry the solid from 30% db to 8% db under the same drying conditions?

Question 44

44. A solid material shows case hardening properties while drying. Which of the following should be controlled to control the drying process?

Question 45

45. Wet solid is dried in a batch dryer under constant drying conditions from 35% to 10% in 7 hours. The critical moisture content is 20% and the equilibrium moisture is 4%. All moisture contents are on dry basis. How long should it take to dry the same solid from 10% to 5% moisture under the same drying conditions?

Question 46

46. Wet solid is to be dried from 40 to 10% in 5 hours under constant drying conditions. The critical moisture is 20% and the equilibrium moisture content is 7%. All moisture contents are on a dry basis. The time needed to dry from 15% to 5% free moisture under the same drying conditions is.

Question 47

47. A porous material dies in the open air at a rate approximately proportional to its moisture content. If a sheet hangs in the wind losses half its free moisture in the first hour, when will it have lost 99%, weather conditions remaining the same?

Question 48

48. The initial moisture content of a food product is 77% (wet basis), and the critical moisture content is 30% (wet basis). If the constant drying rate is 0.1 kg H₂O / m²-s, compute the time required for the product to begin the falling rate drying period.

Question 49

49. Milk is dried usually in a ______ dryer.

Question 50

50. Heat sensitive materials like certain pharmaceuticals and food stuff can be dried.

Question 51

51. Large scale drying of sugar is done in a ______ dryer.

Question 52

52. Free flowing granular materials can be best dried in a ______ drier.

Question 53

53. Pick out the wrong statement pertaining to the rotary dryer.

Question 54

54. Flights in a rotary dryer are provided to.

Question 55

55. Which of the following is not a continuous drier?