A dimensionless number used in the study of mass transfer, equal to the mass-transfer coefficient times the thickness of a layer through which mass transfer is taking place divided by the moleculor diffusivity. Symbolized Nu_m; N_Num. Also known as Sherwood number (N_Sh ).

A dimensionless number used in the study of forced convection which gives a measure of the ratio of the total heat transfer to conductive heat transfer, and is equal to the heat- transfer coefficient times a characteristic length divided by the thermal conductivity. Symbolized N_Nu .