COMSOL 6.4 - Glossary of Terms

Glossary of Terms

acoustophoretic radiation force

acoustophoresis

The migration of particles in spatially nonuniform acoustic pressure and acoustic velocity fields.

A physics feature that evaluates expressions on particles, adding the value to dependent variables defined in the domain mesh elements the particles pass through or the boundary elements they hit.

Brownian motion

The random drifting of particles suspended in a fluid due to the collisions of molecules with the particle surface.

The force between charged particles which is inversely proportional to the square of the distance between the particles.

dielectrophoretic force

dielectrophoresis

The phenomenon in which a spatially nonuniform electric field exerts a force on a particle. Unlike the electric force, the dielectrophoretic force can be nonzero even if the particle is electrically neutral.

A fluid–particle system where particle–fluid and particle–particle interactions need to be accounted for in the model.

The force exerted on a body by the surrounding fluid, in the direction parallel to the relative velocity of the fluid. Contrast with .

The force exerted on a charged particle by an electric field.

A convenient way of describing how a system of particles interact with surrounding fields. The Hamiltonian is usually defined as the sum of the kinetic and potential energy.

A grid of points consisting of uniformly spaced circular rings, each containing six more points the previous ring.

Kelvin–Helmholtz instability

Unstable growth of waves on the surface of a fluid, such as a liquid droplet, or at the interface between two fluids arising from velocity shear. One of the mechanisms of droplet breakup.

The ratio of the mean free path of molecules in a gas to a representative length scale such as particle diameter; often used to classify the extent to which the surrounding gas can be modeled as a continuum flow.

A convenient way of describing how a system of particles interact with surrounding fields. The Lagrangian is usually defined as the kinetic energy minus the potential energy.

The force exerted on a body by the surrounding fluid, in the direction perpendicular to the relative velocity of the fluid. Contrast with .

The force exerted on a moving charged particle by a magnetic field.

magnetophoretic force

magnetophoresis

The phenomenon in which a spatially nonuniform magnetic field exerts a force on a particle. Unlike the electric force, the dielectrophoretic force can be nonzero even if the particle is electrically neutral.

Maxwell evaporation model

One of the simplest models for evaporation of a spherical drop; a purely diffusive model in which the vapor pressure at the droplet surface is always saturated.

Maxwellian velocity distribution

Describes the probability that a velocity is near a given value as a function of the temperature of the system.

The combined electric and magnetic force on a charged particle.

primary particle

A model particle whose release is not contingent upon the existence of any other particle.

random number seed

An argument to a pseudorandom number generator.

Rayleigh–Taylor instability

Instability at a fluid–fluid interface caused by normal acceleration of the less dense fluid in the direction of the denser fluid. One of the mechanisms of droplet breakup.

Relative Reynolds number

The Reynolds number, when the particle diameter is used instead of the characteristic length scale of the model geometry. Used to determine which drag laws are applicable.

Release feature

Any of a number of physics features, such as or , that control the number of particles in a model as well as their initial position and velocity.

Reynolds number

A dimensionless quantity that characterizes a fluid flow. It indicates the ratio of inertial forces and viscous forces in the flow. It is a function of fluid velocity, kinematic viscosity, and a geometry length scale.

Reynolds-averaged Navier–Stokes

Modification of the Navier–Stokes equations for fluid flow, in which a time-averaging operation has been performed on the equations of motion. The Reynolds’ stresses (correlations between fluctuating velocity components) obtained from this averaging operation have to be obtained from an additional set of equations, a closure. Turbulence models like the k-ε and Spalart–Allmaras models constitute closures to the RANS equations.

The average amount of time that a particle spends in a particular system. The residence time can be computed by adding Auxiliary dependent variables.

secondary particle

A particle that is released due to an existing, currently active particle satisfying a given criterion, such as being subjected to a sufficiently high force or coming in contact with a surface.

space charge effects

When the number density of charged particles is sufficiently high, they can affect the field in which they are placed. This is often referred to as a “space charge effect.”

A particle laden flow is described as a sparse flow when the particles have no appreciable effect on the motion of the fluid.

The convective transport of mass away from the surface of an evaporating liquid.

Stefan–Fuchs evaporation model

A droplet evaporation model that extends upon the simpler model by including an additional term to account for Stefan flow away from the droplet surface.

The simplest model of drag on a sphere in a fluid. Applicable when the relative Reynolds number is much less than unity.

thermophoretic force

The phenomenon in which particles migrate in a spatially nonuniform temperature field.

transmission probability

The probability that a particle transmits from a given selected boundary or domain to another.

turbulent dispersion

The random diffusion of particles in a turbulent flow due to the random creation and annihilation of eddies in the flow.

The effect of contact with a boundary on a particle’s motion. Absorption and specular reflection are examples of wall conditions.