Cross-flow filtration

Cross-flow filtration separates a flowing fluid with a membrane: permeate passes through the membrane while retained material travels along its surface.

Transmembrane pressure: The pressure difference across a membrane that drives fluid through it. It drives permeate through the membrane against resistance from the membrane and deposited material.
Membrane: A selective barrier that permits some substances to pass while retaining others. Its selectivity and permeability set the separation achievable in cross-flow filtration.
Tangential-flow filtration: Membrane filtration in which feed flows tangentially across the membrane surface. This closely related term is widely used for laboratory and bioprocess systems.
Dead-end filtration: Filtration in which feed flows toward a filter surface and retained material accumulates on it. Unlike cross-flow, the full feed stream is directed into the filter rather than swept along its surface.
Permeate flux: The volume of fluid crossing a membrane per unit area and time. It measures filtration output and changes as pressure, flow, and fouling change.
Feed (fluid): The fluid introduced into a separation or processing operation. Its composition and suspended material determine what the membrane must retain.
Microfiltration: Membrane filtration that primarily removes suspended particles and microorganisms at micrometer-scale pore sizes. Cross-flow microfiltration clarifies liquids while carrying retained particles along the membrane.
Cake filtration: Filtration in which retained solids form a porous layer that itself becomes a major filtering medium. Cross-flow seeks to limit persistent cake growth by transporting solids along the membrane.
Concentration polarization: The accumulation of rejected solutes near a membrane, creating a concentration gradient at its surface. Retained material builds up near the membrane even before a durable fouling layer forms.
Retentate: The portion of a feed stream that remains on the feed side of a membrane. It carries rejected particles along the membrane and exits more concentrated.

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Membrane filtrationCompared with: Tangential flow limits surface buildup compared with dead-end operation.