Question

How to find biot-number?

Answer 1

To solve this problem first we will discuss about what is biot-number, it’s uses , how the temperature gradient of the body will be affected due to its small or large value and how to calculates its value for lumped heat analysis, and in further sections heat transfer dependency on biot number will be discussed.
Formula used:
${{B}_{I}}=\dfrac{hL}{{{K}_{S}}}$

Complete answer:
Biot-number helps to calculate the rate of heat transfer in a body from its surface to its interior or we can say how much temperature inside the body will vary by heating the surface part of the body.
Biot-number is calculated by the below given formula,
$=>{{B}_{I}}=\dfrac{hL}{{{K}_{S}}}$
Here, h (Heat transfer coefficient of the material), L (length of the body exchanging heat through convection) and ${{K}_{S}}$(thermal conductivity of the material).

Additional information:
If the Biot-number is much smaller than one then the temperature on the surface and inside the body will approximately similar or we can say material is good conductor of heat so it is uniformly distributed throughout the body and if the Biot-number is larger than one then there will be large temperature gradient (difference in temperature at two different point) inside the body which causes variation of temperature inside the body.

Note:
During the heating process two things are important to remember. First, the surface of the material starts to warm up in the initial stage and the process depends on heat transfer coefficient of material and second, how quickly this heat will transfer from surface to interior in the body will depend on thermal conductivity of the material.