Question

What physical assumptions necessary for a lumped capacity?

Answer 1

We know that a temperature gradient must exist in a material if heat energy is to be conducted into or out of the body. When Bi < 0.1, it is assumed that the internal thermal resistance of the body is very small in comparison with the external resistance and the transfer of heat energy is primarily controlled by the convective heat transfer at the surface. That is, the temperature within the body is approximately uniform. This idealised assumption is possible, if



(a) the physical size of the body is very small,



(b) the thermal conductivity of the material is very large, and



(c) the convective heat transfer coefficient at the surface is very small and there is a large