Stanton number for heat transfer, St, is a dimensionless parameter relating heat transfer coefficient to heat capacity of the fluid stream per unit cross-sectional area per unit time, i.e.,
where α is heat transfer coefficient; , mass flux; cp, specific heat capacity of the fluid; μ is velocity, and ρ, fluid density.
The analagous Stanton number for mass transfer is
where β is mass transfer coefficient.
The total rate of heat transfer, , to a fluid flowing inside a tube of diameter D and length L is given by
where and are appropriately averaged values of heat transfer coefficient and driving temperature difference, respectively, and ΔT is the temperature rise of the fluid over the length L. Hence
Therefore Stanton number, for a given geometry, is proportional to the temperature change in the fluid divided by the driving temperature difference.
A similar relationship can be derived for StM with concentration differences replacing temperature differences.
Hewitt, G. F., Shires, G. L., and Bott, T. R. (1994) Process Heat Transfer, CRC Press.