# Biot Number Calculation

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**Formula:** `Bi = hL / k`

The Biot number (Bi) is a dimensionless quantity used in heat transfer calculations. It is defined as the ratio of the heat conduction resistance within an object to the convective heat transfer resistance across the object's surface. In the formula, ** Bi** represents the Biot number,

**is the heat transfer coefficient (expressed in W/m²K),**

*h***is the characteristic length which is typically considered as the volume of the object divided by the surface area through which the heat is being transferred (expressed in meters), and**

*L***is the thermal conductivity of the object's material (expressed in W/mK).**

*k*This number is of critical importance in the field of thermodynamics and heat transfer, as it indicates whether the temperature gradients within an object are more significant than the temperature difference between the object's surface and the surrounding fluid. A small Biot number (Bi < 0.1) implies that the conductive heat transfer resistance within the object is small, and the object can be assumed to have a uniform temperature. A large Biot number (Bi > 0.1) indicates that the conductive resistance is significant, and temperature gradients within the object cannot be ignored.

Tags: Thermodynamics, Heat Transfer, Biot Number