The Biot number (Bi) is a dimensionless number used in unsteady-state and heat transfer calculations. It relates the heat transfer resistance inside and at the surface of a body.
It is defined as follows:
Where:
Values of the Biot number larger than 1 imply that the heat conduction inside the body is slower than at its surface, and temperature gradients
are non-negligible inside it.
It is named after the French physicist Jean-Baptiste Biot (1774-1862)
