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Biot number (mass transfer)

The Biot number (Bi) is a dimensionless quantity used in heat transfer calculations. Gives a simple index of the ratio of the heat transfer resistances ... more

Diffusion coefficient (Mass diffusivity) for gases

Diffusivity or diffusion coefficient is a proportionality constant between the molar flux due to molecular diffusion and the gradient in the concentration ... more

Diffusion Coefficient for two different gases (related to Fick's laws)

Diffusion is the net movement of a substance (e.g., an atom, ion or molecule) from a region of high concentration to a region of low concentration. For two ... more

Diffusion Coefficient - related to Fick's laws of diffusion

Diffusion is the net movement of a substance (e.g., an atom, ion or molecule) from a region of high concentration to a region of low concentration. This is ... more

Rayleigh number (for geophysical applications - related to bottom heating of the mantle from the core)

In fluid mechanics, the Rayleigh number (Ra) for a fluid is a dimensionless number associated with buoyancy-driven flow, also known as free convection or ... more

Knudsen diffusivity for diffusing species

Knudsen diffusion is a means of diffusion that occurs when the scale length of a system is comparable to or smaller than the mean free path of the ... more

Fourier number ( thermal )

The Fourier number (Fo) or Fourier modulus, is a dimensionless number that characterizes heat conduction. it is the ratio of diffusive/conductive transport ... more

Reynolds number (for a magnetic field)

The magnetic Reynolds number is the magnetic analogue of the Reynolds number, a fundamental dimensionless group that occurs in magnetohydrodynamics. It ... more

Worksheet 300

Calculate the Reynolds number N′R for a ball with a 7.40-cm diameter thrown at 40.0 m/s.


We can use the Reynolds number equation calculate N’R , since all values in it are either given or can be found in tables of density and viscosity.


We first find the kinematic viscosity values:

Kinematic Viscosity

Substituting values into the equation for N’R yields:

Reynolds number


This value is sufficiently high to imply a turbulent wake. Most large objects, such as airplanes and sailboats, create significant turbulence as they move. As noted before, the Bernoulli principle gives only qualitatively-correct results in such situations.

Reference : OpenStax College,College Physics. OpenStax College. 21 June 2012.
Creative Commons License : http://creativecommons.org/licenses/by/3.0/

Roshko number

In fluid mechanics, the Roshko number is a dimensionless number describing oscillating flow mechanisms.It is related to the Strouhal number and the ... more

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