In fluid dynamics, a fluid parcel, also known as a fluid element or material element, is an infinitesimal volume of fluid, identifiable throughout its dynamic history while moving with the fluid flow.[1] As it moves, the mass of a fluid parcel remains constant, while—in a compressible flow—its volume may change,[2][3] and its shape changes due to distortion by the flow.[1] In an incompressible flow, the volume of the fluid parcel is also a constant (isochoric flow).
Material surfaces and material lines are the corresponding notions for surfaces and lines, respectively.[1][4]
The mathematical concept of a fluid parcel is closely related to the description of fluid motion—its kinematics and dynamics—in a Lagrangian frame of reference. In this reference frame, fluid parcels are labelled and followed through space and time. But also in the Eulerian frame of reference the notion of fluid parcels can be advantageous, for instance in defining the material derivative, streamlines, streaklines, and pathlines; or for determining the Stokes drift.[1]
The fluid parcels, as used in continuum mechanics, are to be distinguished from microscopic particles (molecules and atoms) in physics. Fluid parcels describe the average velocity and other properties of fluid particles, averaged over a length scale which is large compared to the mean free path, but small compared to the typical length scales of the specific flow under consideration. This requires the Knudsen number to be small, as is also a pre-requisite for the continuum hypothesis to be a valid one.[2][4][5] Further note, that unlike the mathematical concept of a fluid parcel which can be uniquely identified—as well as exclusively distinguished from its direct neighbouring parcels—in a real fluid such a parcel would not always consist of the same particles. Molecular diffusion will slowly evolve the parcel properties.[2][4]
In fluid dynamics, a fluidparcel, also known as a fluid element or material element, is an infinitesimal volume of fluid, identifiable throughout its...
for shipment Parcel (film), 2019 Bengali film Parcel (package), sent through the mail or package delivery Fluidparcel, a concept in fluid dynamics Land...
physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several...
a fluidparcel will conserve its properties for a characteristic length, ξ ′ {\displaystyle \ \xi '} , before mixing with the surrounding fluid. Prandtl...
fluid motion where the observer follows an individual fluidparcel as it moves through space and time. Plotting the position of an individual parcel through...
material derivative then describes the temperature change of a certain fluidparcel with time, as it flows along its pathline (trajectory). There are many...
The residence time of a fluidparcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body)...
motion in fluid dynamics, the Stokes drift velocity is the average velocity when following a specific fluidparcel as it travels with the fluid flow. For...
(isochoric flow) refers to a flow in which the material density of each fluidparcel — an infinitesimal volume that moves with the flow velocity — is time-invariant...
The potential density of a fluidparcel at pressure P {\displaystyle P} is the density that the parcel would acquire if adiabatically brought to a reference...
mixing) the fluid. This causes fluidparcels from various initial positions, and thus various associated concentrations, to penetrate into fluid regions with...
the fluidparcel is now in a location with a lower density than itself and the parcel will just sink down to its original position; the fluidparcel is...
is the downward movement of a fluidparcel and its properties (e.g., salinity, temperature, pH) within a larger fluid. It is closely related to upwelling...
with the cross product of the position (vector) r of a particle (or fluidparcel) and its absolute linear momentum p, equal to mv, the product of mass...
drift – phenomenon in fluid dynamics where a fluidparcel is permanently displaced after the passage of a body through a fluidPages displaying wikidata...
fluidparcel acquires momentum during the passage of the solitary wave, and comes to rest again after the passage of the wave. But the fluidparcel has...
approximated by a continuum in which, at each point, there is a particle or fluidparcel that is assigned the average of the properties of atoms in a small region...
specific strength and vertical distribution that the trajectories of the fluidparcels are closed circles. This is in contrast with the usual experimental...
the epicyclic frequency is the frequency at which a radially displaced fluidparcel will oscillate. It can be referred to as a "Rayleigh discriminant". When...
parcels above their level of neutral buoyancy. Buoyancy restoring forces therefore act to excite a vertical oscillation of the perturbed air parcels at...
surfaces in a fluid (such as the ocean) where the equation of state nonlinearly depends on multiple components (e.g. salinity and heat). Fluidparcels remain...
equation (which expresses the conservation of energy of an incompressible fluidparcel as it moves between two points on the same streamline) can be rewritten...
mass of air (called an air parcel) if it rose vertically through the entire atmosphere. Positive CAPE will cause the air parcel to rise, while negative CAPE...
by the weight of fluid it displaces. This holds for a fluidparcel of density ρ {\displaystyle \rho } surrounded by an ambient fluid of density ρ 0 {\displaystyle...
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