Adiabatic cooling / adiabatic humidification



Point A Point B Increase
Humidity (%)
Temperature (ºC)
Water per
volume (g/m3)
g of water per kg
of dry air (g/kg)
Enthalpy (kJ/kg)

For a more detailed calculation go to the online psychrometric diagram.

What is adiabatic humidification or cooling?

In an adiabatic thermodynamic process there is no exchange of heat between the system and its surroundings. In our case the temperature change is produced by the evaporation of water, not from an external source of heat. Evaporation of water needs energy, and it comes from the air that will reduce its temperature. So, at the same time, humidification and cooling is produced.
As there is no exchange of heat, the enthalpy will not change, so the point moves from A to B along the constant enthalpy line on the psychrometric chart. Note that the constant enthalpy and the constant wet bulb line on a psychrometric diagram are almost parallel. This means that wet bulb will remain almost constant as well.
There are several technologies to produce adiabatic humidification by introducing water into air, some of them works dispersing water droplets and others let water evaporate from a wetted media. In either case, the temperature will decrease and the relative humidity will increase. Examples of adiabatic cooling or humidifying are: high pressure fogging systems, ultrasonic humidifiers and wetted evaporative media.

Advantages of adiabatic cooling

Adiabatic humidification and adiabatic cooling can reduce energy costs. When we boil water to increase the ambient relative humidity we need a source of energy. However, adiabatic humidifiers or adiabatic coolers use the heat already present in air to produce the vapor. Their power consumption is very small in comparison with a steam humidifier (isothermal).