Thermal Diffusivity and Fick Diffusion Coefficient in Mixtures of Hydrogen and Methane by Dynamic Light Scattering

Mixtures of hydrogen (H 2 ) and methane (CH 4 ) are given in many technical applications where accurate thermophysical property data are required for the design and optimization of corresponding processes. This work evaluates the accessibility of the thermal diffusivity a and the Fick diffusion coefficient D 11 in gaseous binary mixtures of H 2 and CH 4 by dynamic light scattering (DLS). The investigations are performed at temperatures T and pressures p of (293, 333, 363, and 393) K and (5, 10, and 15) MPa with varying CH 4 mole fractions x_CH_4 of (0.05, 0.3, 0.6, and 0.8). For all thermodynamic states investigated, only one hydrodynamic mode was observable by DLS. The assignment of the single related diffusivity to either a , D 11 , or a mixed diffusivity D mix representing both a and D 11 is performed by considering D 11 calculated by the Chapman–Enskog kinetic theory, experimental D 11 literature data, a predicted by using two different approaches, and calculations of the so-called Rayleigh ratio. The findings indicate that DLS gives access to a at high x_CH_4 , D 11 at low x_CH_4 , and D mix at x_CH_4 ≈ 0.3. All data are summarized in the form of correlations providing a and D 11 as a function of T , p , and x_CH_4 .