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In physics and engineering, in particular fluid dynamics, the volumetric flow rate (also known as volume flow rate, or volume velocity) is the volume of fluid which passes per unit time; usually it is represented by the symbol Q (sometimes ˙). It contrasts with mass flow rate, which is the other main type of fluid flow rate.
In many engineering applications the local flow velocity vector field is not known in every point and the only accessible velocity is the bulk velocity or average flow velocity ¯ (with the usual dimension of length per time), defined as the quotient between the volume flow rate ˙ (with dimension of cubed length per time) and the cross sectional area (with dimension of square length):
For a compressible fluid in a tube the volumetric flow rate Q(x) and the axial velocity are not constant along the tube; but the mass flow rate is constant along the tube length. The volumetric flow rate is usually expressed at the outlet pressure. As fluid is compressed or expanded, work is done and the fluid is heated or cooled.
Mass flow rate can be calculated by multiplying the volume flow rate by the mass density of the fluid, ρ. The volume flow rate is calculated by multiplying the flow velocity of the mass elements, v , by the cross-sectional vector area, A .
In a compressible fluid, it is convenient to define the total conditions (also called stagnation conditions) for all thermodynamic state properties (such as total temperature, total enthalpy, total speed of sound). These total flow conditions are a function of the fluid velocity and have different values in frames of reference with different ...
Flow may be measured by measuring the velocity of fluid over a known area. For very large flows, tracer methods may be used to deduce the flow rate from the change in concentration of a dye or radioisotope.
Q is the volumetric flow rate (m 3 /s), A is the pipe's cross-sectional area (A = πD 2 / 4 ) (m 2), u is the mean velocity of the fluid (m/s), μ (mu) is the dynamic viscosity of the fluid (Pa·s = N·s/m 2 = kg/(m·s)), ν (nu) is the kinematic viscosity (ν = μ / ρ ) (m 2 /s), ρ (rho) is the density of the fluid (kg/m 3), W ...
The velocity at all points at a given distance from the source is the same. Fig 2 - Streamlines and potential lines for source flow. The velocity of fluid flow can be given as - ¯ = ^. We can derive the relation between flow rate and velocity of the flow. Consider a cylinder of unit height, coaxial with the source.