# Humidifying Air by Adding Steam or Water

## Air can be humidified by adding water or steam

Air can be humidified by

### Humidifying Air by adding Water

If water is added to the air without any heat supply the state of the air changes adiabatic along a constant enthalpy line - h - in the Mollier or psychrometric chart. The dry temperature of the air decreases as indicated in the process from A to C in the Mollier diagram above.

The amount of water required to change the specific humidity can be calculated as

mw = v ρ (xC - xA)                                      (1)

where

mw = mass of added water (kg/s)

v = volume air flow (m3/s)

ρ = density of air - varies with temperature - 1.293 kg/m3 at 20oC (kg/m3)

x = humidity ratio (kgh2o/kgdry_air)

If water is added at the same temperature as the air the enthalpy change is zero.

#### Example - Humidifying Air by adding Water

An airflow of 3000 m3/h at 25oC and 10% relative humidity (A) is humidified to 60% relative humidity (C) by adding water through spray nozzles.

Using the Mollier diagram following the constant enthalpy line 30 kJ/kg from A to 60% relative humidity, the state at C can be found at 14.7oC.

The humidity ratio at (A) is 0.002 kg/kg and at (C) 0.0062 kg/kg.

The amount of water:

mw = ((3000 m3/h) / (3600 s/h)) (1.184 kg/m3) ( (0.0062 kg/kg) - (0.002 kg/kg) )

= 0.0041 kg/s

= 14.9 kg/h

### Humidifying Air by adding Steam

If steam is added to the air the state will change along a constant dh/dx - line for steam as indicated in process A to B in the Mollier diagram above.

When adding saturated steam at atmospheric pressure the constant line dh/dx = 2502 kJ/kg (the evaporation heat of water at atmospheric pressure). When adding saturated steam at atmospheric pressure the temperature rise is very small - in general less than 1oC. For practical purposes the process of adding saturated steam at atmospheric pressure approximates the horizontal temperature line.

The water vapor added can be calculated using (1).

The enthalpy added can be estimated by using the Mollier diagram or a psyhrometric chart.

### Example - Humidifying Air by adding Steam

An airflow of 3000 m3/h at 25oC and 10% relative humidity (A) is humidified to 60% relative humidity (B) by adding saturated steam at atmospheric pressure.

Using the Mollier diagram the process from (A) to (B) can be approximated by following the constant temperature line 25oC to 60% relative humidity and approximately 25.5oC (a temperature increase less than 1oC).

Note! - by adding enough steam the state of air (B) is moved to the saturation line where the air is fully saturated. By adding even more steam the process starts following the saturation line - moisture content and dry bulb temperature will increase - and droplets or fog may be introduced in the moist air.

The humidity ratio at (A) is 0.002 kg/kg and at (B) 0.012 kg/kg.

The amount of water added can be calculated as:

mw = ((3000 m3/h) / (3600 s/h)) (1.184 kg/m3) ( (0.012 kg/kg) - (0.002 kg/kg) )

= 0.01 kg/s

= 35.5 kg/h

The enthalpy change can be estimated from the Mollier diagram. The enthaply at (A) is 30 kJ/kg and at (B) 55 kJ/kg. The enthalpy difference is

dh = (55 kJ/kg) - (30 kJ/kg)

= 25 kJ/kg

The total heat added by the steam can be calculated as:

q = ((3000 m3/h) / (3600 s/h)) (1.184 kg/m3) (55 kJ/kg - 30 kJ/kg)

= 24.7 (kJ/s, kW)

### Example - Humidifying Air with Steam in the Psychrometric Chart

The chart below indicates a similar process of humidifying air with steam in the psychrometric chart.

## Related Topics

• Air Psychrometrics - The study of moist and humid air - psychrometric charts, Mollier diagrams, air-condition temperatures and absolute and relative humidity and moisture content

## Tag Search

• en: humid air steam water
• es: agua vapor aire hÃºmedo
• de: feuchte Luft Wasserdampf

## Search the Engineering ToolBox

- "Search is the most efficient way to navigate the Engineering ToolBox!"

## Engineering ToolBox - SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your SketchUp model with the Engineering ToolBox - SketchUp Extension/Plugin - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Translate the Engineering ToolBox!