scope:

MASS transfer by either molecular diffusion or convection is the transport of one component of a mixture relative to the motion of the mixture and is the result of a concentration gradient. In air conditioning, water vapor is added or removed from the air by simultaneous transfer of heat and mass (water vapor) between the airstream and a wetted surface. The wetted surface can be water droplets in an air washer, wetted slats of a cooling tower, condensate on the surface of a dehumidifying coil, a spray of liquid absorbent, or wetted surfaces of an evaporative condenser. Equipment performance with these phenomena must be calculated carefully because of the simultaneous heat and mass transfer.