Dead zone

A region in a flow system where fluid moves very slowly or remains nearly stagnant. Its weak exchange with surrounding flow can allow heat, contaminants, or particles to accumulate.

Flow separation: The detachment of a moving fluid from a surface, often creating a recirculating wake. Separated flow behind walls or obstacles can enclose slowly exchanging regions.
Fluid mechanics: The study of fluids at rest and in motion, including the forces and flows they exhibit. Dead zones are flow structures analyzed within this broader framework.
Pipe flow: The movement of liquid or gas through a closed conduit. Fittings and sudden changes in pipe geometry can create poorly flushed pockets.
Plug flow: An idealized flow pattern in which fluid moves through a conduit at a uniform velocity with little axial mixing. Unlike plug flow, a dead zone has very weak through-motion and limited exchange.
Recirculation zone: A flow region where fluid follows a looping path rather than moving steadily downstream. Circulating eddies can occupy a dead zone while exchanging little fluid with the main stream.
Boundary layer: A thin region near a surface where fluid velocity changes from the surface value to the outer flow. Slow near-wall motion can create or connect to poorly flushed regions.
Mixing vessel: A container designed to blend fluids or disperse materials using mechanical or fluid-driven motion. Dead zones leave portions of a vessel under-mixed despite continued agitation.
Laminar flow: Fluid motion in orderly layers with little mixing between them. Laminar flow can move steadily without being stagnant, unlike a dead zone.
Residence time: The time a fluid parcel or substance remains within a defined system or region. Long residence times quantify how slowly material leaves a dead zone.
Reynolds number: A dimensionless ratio comparing inertial forces with viscous forces in a fluid flow. It helps predict whether flow around a feature will remain orderly or become turbulent.

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