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In engineering, the Moody chart or Moody diagram (also Stanton diagram) is a graph in non-dimensional form that relates the Darcy–Weisbach friction factor f D, Reynolds number Re, and surface roughness for fully developed flow in a circular pipe. It can be used to predict pressure drop or flow rate down such a pipe.
The power number N p (also known as Newton number) is a commonly used dimensionless number relating the resistance force to the inertia force. The power-number has different specifications according to the field of application. E.g., for stirrers the power number is defined as: [1] = with
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
The Reynolds and Womersley Numbers are also used to calculate the thicknesses of the boundary layers that can form from the fluid flow’s viscous effects. The Reynolds number is used to calculate the convective inertial boundary layer thickness that can form, and the Womersley number is used to calculate the transient inertial boundary thickness that can form.
The Reynolds number is the ratio of inertial forces to viscous forces within a fluid that is subjected to relative internal movement due to different fluid velocities. A region where these forces change behavior is known as a boundary layer, such as the bounding surface in the interior of a pipe.
The Reynolds number and power number fall from the above analysis if , n, and D are chosen to be the basis variables. If, instead, μ {\textstyle \mu } , n , and D are selected, the Reynolds number is recovered while the second dimensionless quantity becomes N R e p = P μ D 3 n 2 {\textstyle N_{\mathrm {Rep} }={\frac {P}{\mu D^{3}n^{2}}}} .
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where is a function of the advance coefficient, is a function of the Reynolds' number, and is a function of the Froude number. Both f 2 {\displaystyle f_{2}} and f 3 {\displaystyle f_{3}} are likely to be small in comparison to f 1 {\displaystyle f_{1}} under normal operating conditions, so the expression can be reduced to: