10.Humidification

DAY 2: CHEMICAL ENGINEERING – Humidification

HUMIDIFICATION Review Questions 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) b) c) d)

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

3. In a) b) c) d)

saturated gas, the vapor is in equilibrium with the liquid at the gas temperature vapor is in equilibrium with the liquid at the room temperature partial pressure of vapor equals the vapor pressure of the liquid at room temperature 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 1o 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

DAY 2: CHEMICAL ENGINEERING – Humidification

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. 17. 18.

DAY 2: CHEMICAL ENGINEERING – Humidification

19. Percentage saturation is…………..the relative saturation. a) always smaller than b) always greater than c) not related to d) 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 25oC and 750 mm Hg has a dew point of 20oC. 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

DAY 2: CHEMICAL ENGINEERING – Humidification

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 25oC respectively) is passed through water spray chamber maintained at 35oC. The air will be a) cooled b) humidified c) both a and b d) dehumidified 32. In a) b) c) d)

case of unsaturated air dew point  wet bulb temperature wet bulb temperature  dry bulb temperature both a and b 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

DAY 2: CHEMICAL ENGINEERING – Humidification

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