Both the Nusselt number and the Biot number have the same form. What are the differences between them in terms of the variables employed and their physical significance?

Both the Nusselt number and the Biot number have the same form. What are the differences between them in terms of the variables employed and their physical significance?


Both the Biot number and the Nusselt number are of the form (hL/k). However, for the Biot number, the thermal conductivity k used is that for the solid; for calculating Nusselt number the k value as that of the fluid. The Biot number is a measure of the ratio of the temperature drop in the solid material and the temperature drop between the solid and the fluid.

 The Nusselt number is a dimensionless version of the temperature gradient at the surface between the fluid and the solid, and it thus provides a measure of the convection occurring from the surface.


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