# Mass flow

Physical size
Surname Mass flow
Formula symbol ${\ displaystyle q_ {m}}$ Size and
unit system
unit dimension
SI kg · s -1 M · T −1

A mass flow , also known as mass throughput , is the mass of a medium that moves through a cross-section over a period of time .

The mass flow is given in kilograms per second, also per minute or hour with slow flow.

The mass flow

${\ displaystyle q_ {m} = {\ dot {m}} = {\ frac {\ mathrm {d} m} {\ mathrm {d} t}}}$ is calculable in fluid mechanics through

${\ displaystyle {\ dot {m}} = \ varrho \ cdot {\ dot {V}} = \ varrho \ cdot c \ cdot A = {\ frac {\ gamma} {g}} \ cdot {\ dot {V }}}$ With

${\ displaystyle \ varrho}$ : Density of the medium in kg / m³,
${\ displaystyle c}$ : mean flow velocity in m / s,
${\ displaystyle A}$ : Cross-sectional area in m²,
${\ displaystyle {\ dot {V}}}$ : Volume flow in m³ / s,
${\ displaystyle \ gamma}$ : specific weight in N / m³ = kg / (m²s²) and
${\ displaystyle g}$ : Acceleration of gravity in m / s².

With regard to density, it should be noted that in the case of gases ( i.e. compressible media) the calculation must be expanded to include the possible changes in volume. The mean flow velocity is determined via integration , see also volume flow . To measure the flow there are different measurement methods.

Examples of mass flows: wind , exhaust gas mass flow , river , ocean current , landslide , landslide , grain flow , debris flow , pyroclastic density flow

## literature

• Alfred Böge (Hrsg.): The technician's manual, basics and applications of mechanical engineering . 15th edition. Vieweg, Braunschweig and Wiesbaden 1999, ISBN 3-528-34053-3 .

## Individual evidence

1. ^ A b Alfred Böge Das Techniker Handbuch , p. 320.
2. ^ Alfred Böge Das Techniker Handbuch , p. 337.
3. ^ Alfred Böge Das Techniker Handbuch , p. 330.
4. Holger Foysi: Measurement of volume and mass flow. (PDF; 1.8 MB) University of Siegen , April 2, 2015, accessed on November 25, 2018 .