multiphase flow

Phase distinctness

Record phase identities separately from chemical species and identify the observations or thermodynamic reasoning supporting each distinction.

1. Which gas, liquid, or solid phases are present, and which chemical components belong to each? definition
2. What observation or phase-state calculation establishes each phase under the actual pressure and temperature? provenance

Transport and solid role

Specify the motion that makes this a flow and distinguish participating solids from fixed boundaries or a porous skeleton.

1. Across what control volume and time interval is phase motion being assessed? boundary
2. Are solids transported particles, a dynamically interacting bed, deposits, or a fixed matrix, and how does that choice affect phase counting? definition

Resolved or dispersed structure

Record whether interfaces are individually represented or described through averaged phase occupancy and dispersed populations; this distinction is used in [COMSOL's multiphase modeling guidance](https://www.comsol.com/blogs/modeling-and-simulation-of-multiphase-flow-in-comsol-part-1).

1. Which phases form connected regions and which occur as bubbles, droplets, or particles at the observation scale? measurement
2. What interface area, film thickness, or dispersed-size distribution is known, and by which averaging convention? measurement

Regime evidence and transition

Treat regime labels as geometry-dependent classifications, preserving mixed patterns, transition uncertainty, and any history dependence.

1. Which regime classification or flow map is being used, and does its geometry, orientation, and phase pair match this case? provenance
2. What time-resolved evidence distinguishes a persistent regime from intermittent or transitional behavior? measurement
3. Which changes in phase rates or boundary conditions could cross the supported regime boundary? action

Fraction and velocity basis

Record fraction denominators, velocity definitions, reference conditions, and averaging scales before relating phase occupancy to throughput.

1. Does each reported fraction represent in-situ volume, mass, volumetric throughput, or pore-volume saturation? definition
2. Are velocities intrinsic or superficial, and what phase-pair slip follows from compatible measurements? measurement

Inventory balance

Reconcile each phase inventory with measured fluxes and transfer terms, while keeping interphase conversion distinct from external addition or removal.

1. Do inlet rates, outlet rates, accumulation, and phase conversion close each phase mass balance within measurement uncertainty? measurement
2. Where phase inventories change, what evidence separates conversion from entrainment, deposition, leakage, or unmeasured storage? provenance

Force and closure selection

Record the relevance and evidential basis of drag, lift, added-mass effects, turbulent dispersion, and particle contacts rather than assuming every mechanism applies.

1. Which momentum exchanges materially affect phase slip or distribution in this configuration? measurement
2. What evidence supports the selected force closures for the observed size, concentration, shape, and flow regime? provenance

Exchange and population evolution

Track heat and species transfer, phase appearance or disappearance, breakup, and coalescence as distinct mechanisms with different balance effects.

1. Are phases at a common temperature and local equilibrium, or must finite heat and mass transfer be represented? boundary
2. Which observations distinguish evaporation, condensation, dissolution, or solidification from breakup and coalescence? measurement
3. When a phase appears or disappears, which assumptions and measurements must be reconsidered? action

Confinement, wetting, and pathways

Record geometry, orientation, wall interaction, and porous-medium effects where they materially control the flow.

1. Which dimensions, inclinations, restrictions, and gravity directions control phase segregation or interface shape? measurement
2. Do wetting, capillary entry, relative permeability, or trapping need representation, and what establishes their relevance? boundary

Intervention envelope

Evaluate changes against case-specific evidence for pressure loss, intermittent loading, phase carryover, solids accumulation, or thermal limits.

1. Which phase feed rates, pressures, heat inputs, or outlet conditions can be changed, and what response is sought? action
2. Which observed or validated thresholds constrain the proposed change for this geometry and phase system? provenance
3. Which measurements would show that the intervention caused an unwanted regime transition or loss of transport? measurement

Sensor-to-phase inference

Separate directly observed quantities from inferred phase fractions, velocities, sizes, and regimes.

1. Which phase quantities are directly resolved, and which depend on calibration, reconstruction, or assumed phase properties? provenance
2. Can the spatial resolution and sampling rate capture the relevant bubbles, films, particles, and intermittency? measurement

Model applicability

Record which interfaces or particles are resolved and which are averaged, then assess closures separately from numerical convergence; constitutive-model evaluation is an explicit purpose of [NETL's MFiX work](https://www.netl.doe.gov/carbon-management/simulation-based-engineering/multiphase-flow-science).

1. Why is an interface-resolving, Eulerian multifluid, mixture, particle-tracking, or porous-medium representation adequate for the decision? boundary
2. Which independent measurements validate the required outputs, and over what phase fractions, rates, sizes, and geometries? provenance
3. What additional evidence is required before using the prediction outside its validated range? action

Check these first

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these check these first hold for the sense of multiphase flow this model covers, and on what evidence? provenance

Kinds and varieties

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these kinds and varieties hold for the sense of multiphase flow this model covers, and on what evidence? provenance

Real-world use

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these real-world use hold for the sense of multiphase flow this model covers, and on what evidence? provenance

Typical measurements

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these typical measurements hold for the sense of multiphase flow this model covers, and on what evidence? provenance

Failure modes and hazards

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these failure modes and hazards hold for the sense of multiphase flow this model covers, and on what evidence? provenance

Neighbouring kinds and how to tell them apart

Recalled without web access and unsourced; every item is a lead to verify.

1. Which of these neighbouring kinds and how to tell them apart hold for the sense of multiphase flow this model covers, and on what evidence? provenance