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

Abstract

AbstractMixtures of hydrogen (H2) and methane (CH4) 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 D11 in gaseous binary mixtures of H2 and CH4 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 CH4 mole fractions $$x_{{{\text{CH}}_{{4}} }}$$ 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, D11, or a mixed diffusivity Dmix representing both a and D11 is performed by considering D11 calculated by the Chapman–Enskog kinetic theory, experimental D11 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 $$x_{{{\text{CH}}_{{4}} }}$$ x CH 4 , D11 at low $$x_{{{\text{CH}}_{{4}} }}$$ x CH 4 , and Dmix at $$x_{{{\text{CH}}_{{4}} }}$$ x CH 4 ≈ 0.3. All data are summarized in the form of correlations providing a and D11 as a function of T, p, and $$x_{{{\text{CH}}_{{4}} }}$$ x CH 4 .