residence time (hydraulic retention time), \(t_{\text{r}}\)

in biotechnology
The average time a particle or volume element of the culture resides in a bioreactor (or other device) through which a liquid medium continously flows. residence time of the liquid is the reciprocal of dilution rate.
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 164 (