Say for example, A Zeer Pot system undergoes cooling due to evaporation of water. Now what would be the minimum temperature at the center of the Pot considering the top and bottom are perfectly insulated.
It can be cooled to the surrounding temperature even by radiative equilibrium which may take long time. Any medium within the enclosed space me reduce this time by mixing
The minimum temperature attainable will be equal to wet bulb temperature .The air in the vicinity of the pot is more humid because of diffusion of moisture from pot to air.And this mass diffusion will continue until the air around pot has become completely saturated.At this point of time,the temperature of water in the pot will be almost equal to the "wet bulb temperature" of air..!!...
The process is an adiabatic cooling process where enthalpy remains constant and the best temperature you can get is very near to wet bulb temperature but it also depends on the ambient condition of the air throughout the day which varies day and night.