INTERDIFFUSIVITIES AND MASS-TRANSFER COEFFICIENTS OF NAF GAS

To clarify the vaporization phenomena of sodium fluoride (NaF), the in terdiffusivities of NaF in N-2, Ar, and He were measured by thermograv imetric analysis from 1300 to 1770 K. At 1540 K, the interdiffusivity of NaF in N-2 (2.46 cm(2)/s) was slightly larger than that in Ar (2.40 cm(2)/s), while the interdiffusivity of NaF in He (6.00 cm(2)/s) was significantly larger than those in the N-2 and Ar systems. The Chapman -Enskog equation was used to calculate the interdiffusivities of NaF i n N,, Ar, and He. Calculated results were in good agreement with obser vations for nitrogen and argon; however, calculated results for the Na F-He system were significantly higher than those observed. Overall exp erimental mass transfer coefficients were described by a Ranz-Marshall type correlation based upon the Nusselt number (Nu), the Reynolds num ber (Re), and the Schmidt number (Sc): Nu = 7.0 + 0.28 (Re)(4)(Sc)(2) in which the viscosities in the NaF-N-2, Ar, or He system were calcula ted from the Lennard-Jones parameters developed in this study.