Hard-wall potential function for transport properties of alkali metal vapors

This study demonstrates that the transport properties of alkali metals are determined principally by the repulsive wall of the pair interaction potential function. The (hard-wall) Lennard-Jones (LJ) (15-6) effective pair potential function is used to calculate the transport collision integrals. Accordingly, reduced collision integrals of K, Rb, and Cs metal vapors are obtained from the Chapman-Enskog solution of the Boltzmann equation. The law of corresponding states based on the experimental transport reduced collision integral is used to verify the validity of a LJ(15-6) hybrid potential in describing the transport properties. LJ(8.5-4) potential function and a simple thermodynamic argument with the input PVT data of liquid metals provide the required molecular potential parameters. Values of the predicted viscosity of monatomic alkali metal vapor are in agreement with typical experimental data with average absolute deviations of 2.97% for K in the range of 700-1500 K, 1.69% for Rb, and 1.75% for Cs in the range of 700-2000 K. In the same way, the values of predicted thermal conductivity are in agreement with experiment within 2.78%, 3.25%, and 3.63% for K, Rb, and Cs, respectively. The LJ(15-6) hybrid potential with a hard-wall repulsion character conclusively predicts the best transport properties of the three alkali metal vapors.