What is Mass Flux?
Mass flux is the rate of flow of mass through a unit area perpendicular to the flow.
For diffusion processes, the mass flux is the rate of transport of mass caused by either molecular diffusion, or by larger scale eddies in turbulent flows (turbulent diffusion). The mass flux must be included in the equations of conservation of mass across a control volume in a computational fluid dynamics model (Navier-Stokes equations).
In chemical engineering the mass flux is important where there is a flow through a porous medium such as a filtration system. In biological processes the mass flux may involve the transport of mass across a semi-permeable membrane.