In droplet separation by granular bed filters, the transient loading regime plays an important role because, for gases with low droplet concentrations, steady state will be reached only after a long time. A mathematical model describing this transient loading regime as well as steady state was developed. It is based on differential balances for the dispersed droplets and for the separated liquid. The time-dependent and spatially resolved liquid loading is calculated and compared with data obtained by magnetic resonance imaging (MRI), a noninvasive measuring technique. The good agreement between simulated and measured loading curves proves the general applicability of the model.