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.

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.