A ________ evaporator is placed in the airstream to cool and remove humidity.

A direct expansion evaporator operates by directly circulating refrigerant through the evaporator coils that are exposed to the airstream. As warm air passes over these coils, the refrigerant absorbs heat and evaporates, leading to a cooling effect in the air. This process not only lowers the air temperature but also reduces its humidity because the cooling effect causes moisture in the air to condense on the evaporator coils. This condensation is then drained away, effectively removing humidity from the air stream.

The other types of evaporators serve different functions or use different methods. A chilled water coil requires a secondary fluid (water) to transfer heat, rather than directly cooling the air. Dry expansion evaporators might use a similar principle, but they are commonly associated with systems that utilize a fixed expansion device, limiting their application in standalone configurations. A flooded evaporator operates by continuously flooding the heat exchanger with refrigerant, which is not typically placed directly in the airstream for cooling purposes. Thus, a direct expansion evaporator is the most effective choice for cooling and dehumidifying air directly, making it the correct answer.