Understanding Air Properties During Water Spray Contact

When unsaturated air comes into contact with water, especially through a spray of continuously recirculated water, a heat and mass transfer process occurs. Since the air is unsaturated, it has the capacity to absorb water vapor. As water evaporates from the spray into the air, the specific humidity of the air increases, meaning the amount of water vapor per unit mass of dry air goes up.

The process of evaporation requires energy, known as the latent heat of vaporization. This energy is primarily drawn from the sensible heat of the air itself. As the air loses sensible heat, its dry bulb temperature decreases.

Simultaneously, the water temperature in a continuously recirculated spray tends to approach the wet-bulb temperature of the incoming air. The air, as it becomes more saturated, also moves towards its wet-bulb temperature, which is lower than the initial dry bulb temperature for unsaturated air.

This process is essentially an evaporative cooling process, or adiabatic saturation, where:

• Specific humidity increases due to water evaporation.
• Latent heat required for evaporation is taken from the air's sensible heat.
• As sensible heat is removed, the dry bulb temperature decreases.
• The enthalpy of the air remains approximately constant (adiabatic process).

Therefore, if unsaturated air passes through a spray of continuously recirculated water, and the specific humidity increases, the dry bulb temperature will decrease.