Fourier Number

Fourier Number

In physics and engineering, the Fourier number (Fo) or Fourier modulus, named after Joseph Fourier, is a dimensionless number that characterizes heat conduction. Conceptually, it is the ratio of the heat conduction rate to the rate of thermal energy storage. Together with the Biot number, it characterizes transient conduction problems. It is defined as:

where:

• α is the thermal diffusivity
• t is the characteristic time
• R is the length through which conduction occurs

For transient mass transfer by diffusion, there is an analogous mass Fourier Number (also denoted Fo) defined as:

where:

• "D" is the Diffusivity
• "t" is the characteristic timescale
• "L" is the length scale of interest