Mass Flux

In the previous chapter, we discussed the principle of mass balance and saw how it can be used in terms of mass or mass rates, to analyse, design and operate biosystems over a wide length scale, i.e. from a cell to a bioprocess. In this chapter, let us look at a concept that is central to many engineering disciplines, and especially to biological engineering, namely, flux. A flux of a quantity is defined as the amount of that quantity that is transported per unit time across a unit area that is perpendicular to the direction of transport. Thus, mass flux is defined as the amount of mass transported per unit time across a unit area that is perpendicular to the direction of mass transport.