In 70 deg. F or higher conditions, the droplets can evaporate in a distance of 5-10 feet. For cooler conditions, the droplets may float for 10-30 feet before fully evaporating. The operation of these devices is usually controlled by a humidistat that senses the relative humidity of the air and powers the mist-producing devices on and off as required to establish and maintain the desired relative humidity. Devices using the wetted pad technique have a fan to move air through the special porous pads.
Water is distributed at the top of the pad and trickles down the fibers or cells of the pad.
Small devices that use this principle are the room and furnace humidifiers. Larger units are the portable evaporative cooler units for greenhouses and general space cooling . These devices also can be controlled by a humidistat to maintain a desired relative humidity. A word of caution is expressed again about excessive humidity for lengthy tobacco conditioning can create too high moisture content in the tobacco and lead to storage and handling problems. Some have fan blade combinations to provide greater dispersion of the moist air.