Fourier Number

From Chemepedia

The Fourier number (Fo) is a dimensionless number that is used to describe transient heat conduction. It is the ratio of the conductive/diffusive transport rate to the heat/matter storage rate.

Definition

In general, the Fo is defined as


            (1)


For heat transfer the Fourier number is defined as


            (2)

where

  • is the thermal diffusivity
  • is time, and is the length through which conduction occurs


For diffusive transient mass transfer the Fourier number is defined as


            (3)

where

  • is the diffusivity
  • is the time
  • is the length of interest

Usage

The Fo can be used with the Biot number (Bi) to determine the unsteady state heating or cooling of an object. If Bi is less than 0.1, then the lumped capacitance model can be used, which can be seen on the Biot number page.

References

[1]

  1. Incropera, Frank P.; DeWitt, David P. Fundamentals of Heat and Mass Transfer (5th ed.). Wiley.