Regarding air wet-bulb temperature and dry-bulb temperature

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I came across the chapter in Chemical Engineering Principles on the simultaneous transfer of heat and mass: 1. The gas phase remains in its original state, while the liquid phase changes. The limit temperature for the liquid phase is the wet-bulb temperature tw (occurs when there is a large amount of air in contact with a small amount of water over an extended period). 2. The liquid phase stays unchanged, while the gas phase changes. The limit temperature for the liquid phase is the adiabatic saturation temperature tas (occurs when there is a small amount of air in contact with a large amount of water over an extended period). I’m not quite understanding these two scenarios: regarding the wet-bulb temperature, what does it mean that the gas phase remains unchanged? How can it remain unchanged? What kind of device is it that allows large amounts of air and small amounts of water to be in direct long-term contact? Is it a cooling tower? Regarding the adiabatic saturation temperature, under what conditions does the liquid phase state remain unchanged, and how does it remain unchanged? What kind of device or situation does long-term contact with a small amount of air and a large amount of water entail? I hope everyone can help answer this