HUMIDIFICATION AND DRYING

Question 1

Involves removal of moisture, usually water from a solid by allowing a composite material to come in contact with a drying medium that supplies the heat needed by moisture to evaporate.

Answer 1

Drying

Question 2

Moisture remove is the unbound/free moisture, capable of generating partial pressure equivalent to vapor pressure time of drying.

Answer 2

Drying Rate Period

Question 3

Moisture remove is bound moisture, water evaporates after capillary action/diffusion to the solids’ surface time of drying.

Answer 3

Falling Rate Period

Question 4

Drying medium conditions subjecting the solids are changing.

Answer 4

Variable Drying Conditions

Question 5

• tsolid and residual moisture = constant
• wet bulb temperature of air is constant

Answer 5

Adiabatic Dryers

Question 6

Rf is assumed linear and passing through origin, Rf independent of ΔH

Answer 6

Drying is not Adiabatic

Question 7

x > xc

Answer 7

Drying Rate Period

Question 8

x < xc

Answer 8

Falling Rate Period

Question 9

qL and qD = 0

Answer 9

Adiabatic Dryers

Question 10

Involves the transfer of material between a pure liquid phase and a fixed gas phase that is nearly insoluble in the liquid

Answer 10

Humidification

Question 11

• These operations are somewhat similar but simpler than absorption and stripping.

Answer 11

Humidification

Question 12

• The liquid contains only one component, there are no concentration
  gradients and no resistance to mass transfer in the liquid phase.

Answer 12

Humidification

Question 13

the gaseous form of the component that is also present
as liquid (liquid that can become gas)

Answer 13

• Vapor

Question 14

component present only in gaseous form (does not
condense)

Answer 14

Gas

Question 15

• Sometimes also called as Absolute Humidity
• This refers to the ratio of the mass of vapor per unit mass of vapor-free gas. This may be determined from the partial pressure exerted by the vapor (A) in the gas (B).

Answer 15

HUMIDITY

Question 16

• This refers to the maximum amount of vapor that a gas can contain which is in equilibrium with the liquid at a given temperature. The partial pressure of the vapor is in effect equal to the vapor pressure.

Answer 16

Saturation Humidity, HS.

Question 17

• This refers to the ratio of the partial pressure to the vapor pressure at a specified temperature of the gas-vapor mixture.

Answer 17

Relative Humidity, RH or HR

Question 18

• This refers to the ratio of the partial pressure to the vapor pressure at
  a specified temperature of the gas-vapor mixture.

Answer 18

Percentage Saturation or Percentage Humidity, HA

Question 19

This is the volume occupied by one pound of dry gas plus whatever vapor it contains at a given pressure and temperature.

Answer 19

Humid Volume, VH

Question 20

The specific volume if the gas is saturated with the vapor

Answer 20

Saturated volume, Vs

Question 21

This is the heat needed to raise the temperature of one pound of dry gas and the vapor it contains by 1 degree F

Answer 21

Humid Heat, Cs

Question 22

This refers to the total enthalpy content of 1 lb gas and its vapor at a given temperature

Answer 22

Enthalpy of Mixture, Hy

Question 23

• This refers to the steady state temperature attained by a gas-vapor mixture when saturated with vapor by spraying under adiabatic conditions.

Answer 23

Adiabatic Saturation Temperature, Ts

Question 24

This refers to the steady state temperature attained by a small mass of liquid immersed in a large body of gas.

Answer 24

Wet Bulb Temperature, Tw

Question 25

• This is the steady temperature attained when a vapor-gas mixture becomes saturated when cooled at constant humidity, that is pA= pA

Answer 25

Dew Point, Td

Question 26

Adiabatic Humidification

Answer 26

In order for humidification to be considered adiabatic, the following conditions must be met:
1. Tx1 =Tx2 =Tx =constant
2. TW1=TW2= Tx= constant
That is, the temperature of the water is constant and equal to the wet-bulb temperature of the gas which is also constant. This, of course, is a simplification which may not be achieved in reality.

Question 27

the air undergoes a non-adiabatic humidification process. Thus, the integrated design equations used are similar to that of dehumidification except that the limits are reversed.

Answer 27

Water Cooling

Question 28

Due to the approximate nature of the mass and heat transfer equations generated for water cooling and dehumidification, it is necessary to use a more accurate working design equation. If the system is limited to air-water, the design may be based on the enthalpy driving force as given by the ________

Answer 28

Merkel’s Equation.

Question 29

Presents Physical and thermal properties of moist air in a graphical form

Answer 29

Psychrometric Chart

Question 30

Actual temperature of air-vapor mixture

Answer 30

Dry Bulb Temperature

Question 31

lowest temperature at which air can be cooled by the evaporation of water into the air at a constant pressure

Answer 31

Wet Bulb Temperature

Question 32

Temperature at which H = Hs

Answer 32

Dew point