Drew number

Drew number

[′drü ‚nəm·bər] (physical chemistry) A dimensionless group used in the study of diffusion of a solid material A into a stream of vapor initially composed of substance B, equal to where MA and MB are the molecular weights of components A and B, MV and MW are the molecular weights of the mixture in the vapor and at the wall, and YAW and ZA are the mole fractions of A at the wall and in the diffusing stream, respectively. Symbolized ND.