Number of Fourier

The Nombre of Fourier is a Nombre without dimension used usually in Heat transfer.

It is indicated by the Greek letter $\backslash \; tau$, or by Fo

Its expression is:

$Fo\; =\; \{At\; \backslash \; over\; L^2\}$

is the thermal Diffusivité has (in m ² /s)

T is the time to which one wants to calculate the number of Fourier (in seconds)

L is the length characteristic of the studied body

$L\; =\; \{V\; \backslash \; over\; S\}$

V is the volume of the studied body (in cubic meter)

S is its heat-transferring surface (in m ²)

The number of Fourier is used during problems where one wishes to study a body placed in a medium of different temperature. It characterizes the share of the Heat flow which is transmitted to the body at one moment given (at a time T) compared to the Chaleur stored by this body.

Physically, more the number of Fourier is large, more heat penetrates deeply inside the body in a given time.

See too

• thermal Conduction

• Convection
• Number without dimension

Category: Thermodynamics

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