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Biot number

Biot number

Biot number is a dimensionless number that represents the ratio of thermal convection from solid surface and thermal conduction from solid interior.

It can be expressed in the following equation.

 


where;
: Heat transfer coefficient [W/(m2・K)]
: Characteristic length [m]
: Thermal conductivity[W/(m・K)]

Biot number indicates how fast heat can be transferred by thermal conduction.

When Biot number is small, thermal conduction of solid interior is faster than thermal convection, which underlines that thermal distribution of object interior is more or less uniform. When Biot number is greater than 1, thermal conduction of solid interior is slower than thermal convection which means that temperature gradient of solid interior need to be taken into account.

Biot number is named after the French physicist Jean-Baptiste Biot.