Consequently, a value of the air-side heat transfer coefficient
exists that maximizes the mass transfer rate because of the offset
relationship between the increasing mass transfer coefficient and
decreasing absolute humidity difference with increasing air velocity.
This value of the air-side heat transfer coefficient is referred to
as the critical air-side heat transfer coefficient. The critical air-side
heat transfer coefficient (i.e., the air-side heat transfer coefficient
that maximizes the mass transfer rate) can be defined by: