Suhail (1989) describes air blenders and their use.
The air blender is a static device that can be used to blend outside air and return air within a predictable standard deviation. Aerodynamically designed for manageable pressure drops, the standard blender is fabricated of 0.08 in.-thick aluminum. Blenders have also been used as a diffusion device on the outlet of a centrifugal fan to provide uniform velocity across cooling coils downstream. One aspect about air blenders ...[to consider] is the length required to get mixing, which can add 5 to 8 feet to the unit. ...the length of ductwork that the blender requires for proper mixing ... is a minimum distance equal to the diameter of the blender face.