Drying

DRYING 1.

The vapor pressure exerted by the moisture contained in a wet solid depends upon the a) nature of the moisture  b) temperature c) nature of the solid d) all a, b, and c

2. To remove all the moisture from a wet solid requires exposure to a) perfectly dry air  b) highly humid air c) air at high temperature d) none of these 3.

Milk is dried usually in a a) freeze dryer b) spray dryer c) tray dryer d) rotary dryer

4.

Equilibrium-moisture curves of different solids a) are different  b) are same c) depend on the humidity of the gas d) none of these

5.

Detergent solution is dried to a powder in a a) spray dryer  b) spouted bed dryer c) tunnel dryer d)  pan open to atmosphere.

6.

If moisture content of a solid on dry basis is X then the same on wet basis is  X a)   

X+1  X  b)   

c)

1 - X  1 + X   

d)

 X  1 –  1 –  X  X   

 X

7.

In paper industry, paper is dried in a) tunnel dryer b) heated cylinder dryer c) conveyor dryer d) festoon dryer

8.

Moisture content of a substance when at equilibrium with a given partial pressure of the vapor is called a) free moisture

 b) unbound moisture c) equilibrium moisture d)  bound moisture 9.

Calcium ammonium nitrate (a fertilizer) is dried in a a) rotary dryer  b) vacuum dryer c) tunnel dryer d) none of these

10. Moisture in a substance exerting an equilibrium vapor pressure less than that of pure liquid at at the same temperature is a) bound moisture  b) unbound moisture c) critical moisture d) none of these 11. Rotary dryer cannot handle a) free flowing materials  b) dry materials c) sticky materials d) granular materials 12. Moisture in a solid exerting an equilibrium vapor pressure equal to that of the pure liquid at the same temperature is a) unbound moisture  b) critical moisture c) free moisture d)  bound moisture 13. Refractory bricks are usually dried in a a) tray dryer b) tunnel dryer c) conveyor dryer d) festoon dryer 14. Heat sensitive materials like certain pharmaceuticals and food stuff can be dried a) in indirect tray dryer  b) in spray dryer c) by freeze drying d) none of these 15. Moisture contained by a substance in excess of the equilibrium moisture is called a) unbound moisture b) free moisture c) critical moisture d)  bound moisture

16. Flights in a rotary dryer are provided to a) lift and shower the solids thus exposing it thoroughly to the drying action of the gas

 b) c) d)

reduce the residence time of solid increase the residence time of the solid none of these

17. In the constant rate period of the rate of drying curve for batch drying a) cracks develop on the surface of the solid  b) rate of drying decreases abruptly c) surface evaporation of unbound moisture occurs d) none of these 18. The falling rate period in the drying of a solid is characterized by a) increase in rate of drying b) increasing temperatures both on the surface and within the solid c) decreasing temperatures d) none of these 19. Dryer widely used in a textile industry is a) cylinder dryer  b) conveyor dryer c) tunnel dryer d) festoon dryer 20. Sticky material can be dried in a a) tray dryer  b) rotary dryer c) fluidized bed dryer d) none of these 21. Drying of a solid involves a) only heat transfer  b) only mass transfer c) both heat and mass transfer d) none of these 22. A solid material shows case hardening properties while drying. Which of the following should be controlled to control the drying process? a) flow rate of inlet air  b) relative humidity of outlet air c) humidity of inlet air d) temperature of the solid 23. Capacity of a rotary dryer depends on a) its r.p.m  b) its inclination with ground surface c) both a and b d) neither a nor b 24. Air at a particular humidity is heated in a furnace. The new dew point a) decreases b) increases c) depends on the extent of heating d) remains unchanged 25. The critical moisture content in case of drying indicates a) beginning of falling rate period  b)  beginning of constant rate period

c) d)

end of falling rate period none of these

26. A slurry is to be dried to produce flaky solid. Which dryer would you recommend? a) spray dryer  b) drum dryer c) rotary dryer d) dielectric dryer 27. For continuous drying of granular or crystalline material, the dryer used is a) tunnel  b) tray c) rotary d) none of these 28. All moisture in a non-hygroscopic material is……moisture a) free  b) equilibrium c) unbound d)  bound 29. During constant rate period, the rate of drying decreases with a) decrease in air temperature  b) increased air humidity c) both a and b d) neither a nor b 30. Which is the controlling factor for a drum dryer? a) diffusion b) heat transfer c)  both a and b d) neither a nor b 31. Paper industry employs……..dryers a) cylinder  b) rotary c) spray d) fluidized bed 32. Sand is dried in foundaries in a ……..dryer  a) rotary b) fluidized bed c) vacuum d) spray 33. Free flowing granular materials can be best dried in a a) rotary dryer  b) cylinder dryer c) drum dryer d) freeze dryer

HUMIDIFICATION 1.

Humidification involves mass transfer between a pure liquid phase and a fixed gas which is: a) insoluble in the liquid  b) soluble in the liquid c) non-ideal in nature d) at a fixed temperature

2.

At a fixed total pressure, humidity depends only on the a) partial pressure of vapor in the mixture  b) heat capacity of the vapor c) density of the vapor d) none of these

3.

In saturated gas, the a) vapor is in equilibrium with the liquid at the gas temperature  b) vapor is in equilibrium with the liquid at the room temperature c)  partial pressure of vapor equals the vapor pressure of the liquid at room temperature d) none of these

4.

Relative humidity is the ratio of the a)  partial pressure of the vapor to the vapor pressure of the liquid at room temperature b) partial pressure of the vapor to the vapor pressure of the liquid at gas temperature c) actual humidity to saturation humidity d) none of these

5.

The percentage humidity is less than the relative humidity only at a) zero percentage humidity  b) hundred percent humidity c) both zero or hundred percent humidity d) none of these

6.

Heat is BTU necessary to increase the temperature of 1 lb. of gas and its accompanying vapor by 1 o F is called the a) latent heat  b) humid heat c) specific heat d) sensible heat

7.

Humid volume is the total volume in cubic feet of 1 lb. of a) vapor laden gas at 1 atm. And room temperature  b) gas plus its accompanying vapor at 1 atm. and room temperature c) gas plus its accompanying vapor at 1 atm. and gas temperature d) vapor laden gas at 1 atm. and gas temperature

8.

The temperature to which a vapor gas mixture must be cooled (at varying humidity) to become saturated is a) dew point  b) wet bulb temperature c) dry bulb temperature d) none of these

9.

The dew point of a saturated gas phase equals the a) gas temperature  b) room temperature c) wet bulb temperature d) none of these

10. Steady state temperature reached by a small amount of liquid evaporating into a large amount of unsaturated vapor-gas mixture is a) dry-bulb temperature b) wet bulb temperature c) dew point d) adiabatic saturation temperature 11. Dry bulb temperature of the gas is a) less than the wet-bulb temperature b) greater than the wet-bulb temperature c) equal to the wet-bulb temperature d) none of these 12. The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is a) positive  b) negative c) zero d) none of these 13. When the temperature and humidity of air is low we usually use a) natural draft cooling tower  b) forced draft cooling tower c) induced draft cooling tower d) none of these 14. The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is a) natural draft cooling tower  b) induced draft cooling tower c) spray chamber d) none of these

15. The most efficient cooling tower out of the following is a) induced draft  b) forced draft c) natural draft d) atmospheric 16. Critical humidity of a solid salt means the humidity a) above which it will always become damp  b)  below which it will always stay dry c) both a and b d) above which it will always become dry and below which it will always stay damp. 19. Percentage saturation is…………..the relative saturation. a) always smaller than  b) always greater than

c) d)

not related to none of these

20. Wet bulb and dry bulb temperatures become identical at a) 100% saturation curve  b) 50% saturation curve c) 78% saturation curve d) none of these 21. Which of the following processes is followed by unsaturated air (with dry bulb temperature 12oC and relative humidity 47%) passing through water spray washer (temperature of water being constant at 40oC)? a) humidification only  b) heating only c) both heating and humidification d) evaporative cooling 22. Which of the following remains constant during sensible cooling process? a) specific humidity  b)  partial pressure of vapor c) both a and b d) neither a nor b 23. During sensible cooling process a) relative humidity decreases  b) relative humidity increases c) wet bulb temperature increases d) both b and c 24. A mixture of 10% C6H6 vapor in air at 25 oC and 750 mm Hg has a dew point of 20 oC. Its dew point at 30oC and 700 mm Hg will be around a) 21.7oC  b) 20oC c) 27.3oC d) 18.7oC 25. Which of the following remains constant during evaporative cooling process with recirculated water supply? a) relative humidity  b)  partial pressure of vapor c) wet bulb temperature d) none of these 26. Dew point of a gas-vapor mixture a) increases with temperature rise  b) decreases with temperature rise c) decreases with increases in pressure d) increases with increases in pressure 27. Which of the following decreases during evaporative cooling process with recirculated water supply? a) wet bulb temperature  b) relative humidity c)  partial pressure of vapor d) none of these

28. Which of the following increases during evaporative cooling process with recirculated water supply? a) wet bulb temperature  b) relative humidity c)  partial pressure of vapor d) both b and c 29. The relative saturation of a partially saturated mixture of vapor and gas can be increased by a) reducing the total pressure of the mixture  b) increasing the total pressure of the mixture c) reducing the temperature of the mixture d) both b and c 30. Condensation of a vapor-gas mixture just begin when a)  p = P  b)  p   P  c)  p    P  d)  p>= P  where:  p = partial pressure of the vapor  P  = vapor pressure of the liquid 31. Unsaturated air (with dry and wet bulb temperatures being 35 oC and 25 oC respectively) is  passed through water spray chamber maintained at 35 oC. The air will be a) cooled  b) humidified c) both a and b d) dehumidified 32. In case of unsaturated air a) dew point  wet bulb temperature  b) wet bulb temperature  dry bulb temperature c) both a and b d) neither a nor b 33. Unsaturated air (with dry bulb temperature and dew point being 35 oC and 18oC respectively) is passed through a water spray chamber maintained at 15 oC. The air will be a) cooled and humidified  b) cooled and dehumidified with increase in wet bulb temperature c) cooled at the same relative humidity d) cooled and dehumidified with decrease in wet bulb temperature 34. Which of the following parameters remains almost constant during adiabatic saturation of unsaturated air? a) dry bulb temperature  b) dew point c) wet bulb temperature d) none of these 35. Unsaturated air (with dry bulb and wet bulb temperatures being 45 oC and 25oC respectively) is passed through a water spray chamber maintained at 23 oC. The air will be a) cooled and humidified with wet bulb temperature decreasing  b) cooled and humidified at constant wet bulb temperature c) cooled and dehumidified d) none of these