Humidification Flashcards
This topic involves the contact of a pure liquid with a gas for the purpose of changing the vapor content of the gas and/or adding or removing heat from the contacting phase for purposes of heating or cooling.
humidification
humidification operation may also be classified as
dehumidification, air conditioning and water cooling
The operation involves two components and two phases.
phase equilibria
Based on the Gibb’s phase rule, the number of degrees of freedom to define equilibrium conditions is
two
This refers to the ratio of the mass of vapor per mass of vapor-free gas.
Absolute Humidity
through this, the partial pressure exerted by the vapor A in the gas B can be determined
Absolute humidity
This refers to the maximum amount of vapor that a gas can contain which is in equilibrium with the liquid at a given temperature.
Relative Humidity
The partial pressure of the vapor is in effect equal to the vapor pressure.
Relative Humidity
pressure exerted by a vapor that is in equilibrium with its condensed state
Vapor pressure
Ratio of absolute humidity and Saturation humidity is equal to the
percentage saturation or percentage humidity
This is the volume occupied by one pound of dry gas plus whatever vapor it contains at a given pressure and temperature.
humid volume
The specific volume if the gas is saturated with the vapor.
Saturated Volume
This is the heat needed to raise the temperature of one pound of dry gas and the vapor it contains by 1°F.
Humid Heat
Total enthalpy content of 1 lb of dry gas and its vapor at a given temperature.
Enthalpy of Mixture
This refers to the steady state temperature attained by a gas-vapor mixture when saturated with vapor by spraying under adiabatic conditions.
Adiabatic Saturation Temperature
This refers to the steady state temperature attained by a small mass of liquid immersed in a large body of gas.
Wet bulb temperature
for air-water system the wet bulb temperature becomes identical with the
adiabatic saturation temperature
steady temperature attained when a vapor-gas mixture becomes saturated when cooled at constant humidity
Dew Point
Many of the humidification properties for air-water system can be obtained from the ________________ at 1 atm pressure.
humidity chart
In this operation, the temperature of water is constant and equal to the wet bulb temperature of the gas
adiabatic humidification
the air undergoes a non-adiabatic humidification
water cooling
in humidification, if the system is limited to air-water, the design may be based on the enthalpy driving force as given by
Merkel’s Equation
for water cooling, the Hg is
height of a transfer unit (HTU)
for water cooling, the Ng is
number of transfer units (NTU)
consists of the enthalpy of air at saturation based on the temperature of water
equilibrium curve
equal to the internal energy of the system plus the product of pressure and volume.
enthalpy
in humidification, ploting of the operating line is generated using the
enthalpy balance
in humidification, the slope of operating line is
L/w
obtained by dividing enthalpy transfer equation by the liquid phase heat transfer equation
slope of the tie line
if the operating line and equilibrium curve are linear, Ng (Number transfer of unit) can be evaluated by
logarithmic mean driving force
if the resistance to heat transfer in the liq phase can be neglected
the slope of tie line becomes infinite
for dehumidification and air conditioning
in ref to the humidification:
- similar equation
- reversed limit
- operating line is above the equilibrium curve
Mickley’s graphical method can be used to determine the
temperature profile
plotting of the differential equation obtained from the enthalpy transfer equation and the gas phase heat transfer
mickley’s equation
limiting flow rates of liquid and gas based on the equilibrium conditions may be obtained from
slope of operating line when it intersects equilibrium curve at the enthalpy temperature diagram
