Flow Decay

Flow decay describes the progressive decrease in permeate or filtrate flow through a medium over time at constant pressure. It quantifies the combined effects of pore blocking, cake buildup, and concentration polarization. Mathematically, the decline is expressed as the ratio J/J₀ between instantaneous and initial flux. A steep early drop indicates rapid pore constriction, while a gradual slope reflects stable cake growth. Engineers analyse flow-decay curves to identify fouling mechanisms—complete blocking, standard blocking, or cake filtration—and to select optimal cleaning intervals. Regular backflushing, flow reversal, or chemical cleaning slows decay and extends media life. Recording flow decay under defined operating conditions provides a reproducible fingerprint of filter stability and cleaning efficiency.