July 31, 2020 at 2:17 pm

Karthik R

Administrator

Hello @kkanade , you can use Biot number to quickly check if the lumped-capacitance assumption is valid or not for a particular problem. Biot Number is the ratio of conduction resistance to convective resistance. It is mathematically defined as:

Bi = h*L / k

where,

h = heat transfer coefficient [W/(m^2-K)]

L = conduction length scale [m],

k = thermal conductivity [W/(m-K)]

For Smaller values of Biot number the heat conduction inside the body is faster than the heat convection at its outer surfaces, and therefore the temperature gradients inside the body can be neglected. Bi in the range of <0.1 typically leads to an error of <5% if lumped-capacitance model is used.