The average residence time is defined as the ratio of the filled volume in one pair of screw elements to the volumetric flow rate:

$$\bar{t} = \frac{A_{Fr}L_{Be}\bar{f}}{\dot{V}} \tag{1}$$

For a constant density follows:

$$\bar{t} = \frac{m}{\dot{m}} \tag{2}$$

The overall average residence time is calculated by totalling the calculated minimum residence times in all sections of constant geometry.

$$\bar{t} = \sum_i \left(\frac{A_{Fr}L_{Be}\bar{f}}{\dot{V}}\right)_i \tag{3}$$