# Two-phase flow Two-phase flow is what happens when gas and liquid travel in the same pipe — or liquid and solid, as in a slurry. It is far harder than single-phase [[Fluid_dynamics]] because the interface between the phases moves, deforms, and rearranges, so the flow adopts one of several distinct regimes and can switch between them without warning. Nearly every [[WT!Energy_Center_of_Excellence|power]] plant, refinery, and [[WT!Space_Mining_In_Minnesota|slurry line]] runs two-phase somewhere. ## Regimes, not equations In a horizontal pipe the flow may be stratified with the liquid lying beneath the gas, or wavy, or slug flow in which liquid plugs surge through, or annular with a film on the wall and a gas core, or dispersed bubbles. Which one appears depends on the two flow rates, the [[Density]] ratio, and the pipe angle, and the standard tool is a map rather than a formula. Slug flow is the one operators fear: the plugs hit bends with real [[Force]] and cause [[Vibration]] and [[Fatigue_(material)|fatigue]], and the transition into it is a [[Kelvin–Helmholtz_instability]]. ## Boiling, cavitation, and the crisis Add a [[Phase_transition]] and the flow makes its own second phase. A boiler tube generates vapour along its length and passes through several regimes on the way; exceed a critical heat flux and the wall dries out, heat transfer collapses, and the tube fails — a central constraint in [[Energy_engineering]]. Falling below the local vapour pressure instead of raising temperature gives [[Cavitation]]. Solids in liquid follow their own rules, where the concern is keeping particles suspended above a deposition [[Velocity]]. **Microsim brief (next pass):** Horizontal pipe cross-section; two sliders for gas and liquid rate. The regime map is drawn alongside with a moving dot, and the pipe redraws as stratified / wavy / slug / annular / bubbly. **On the spine:** [[Cavitation]] · [[Kelvin–Helmholtz_instability]] · [[Surface_tension]] · [[Fluid_dynamics]] · [[Two-phase_flow]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Two-phase_flow) : [Wikitube](https://en.wikitube.io/wiki/Two-phase_flow) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Physics]], [[PORTAL_Energy]]. --- *Fluid seed wave · 2026-09-10 · seed register · microsim layer pending.*