As the name implies, during this process, the air temperature drops and its humidity increases. This process is shown in Figure 8.12. As shown in the figure, this can be achieved by spraying cool water in the air stream. The temperature of water should be lower than the DBT of air but higher than its DPT to avoid condensation (TDPT < T2 < T1).
Figure 8.12 Cooling and Humidification Process
During this process there is sensible heat transfer from air to water and latent heat transfer from water to air. Hence, the total heat transfer depends upon the water temperature. If the temperature of the water sprayed is equal to the WBT of air, then the net heat transfer rate will be zero as the sensible heat transfer from air to water will be equal to latent heat transfer from water to air. If the water temperature is greater than WBT, then there will be a net heat transfer from water to air. If the water temperature is less than WBT, then the net heat transfer will be from air to water. Under a special case when the spray water is entirely recirculated and is neither heated nor cooled, the system is perfectly insulated and the make-up water is supplied at WBT, then at steady state, the air undergoes an adiabatic saturation process, during which its WBT remains constant. This is the process of adiabatic saturation. The process of cooling and humidification is encountered in a wide variety of devices such as evaporative coolers, cooling towers, etc.
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