Modeling of gas oscillations in a methane pyrolysis reactor using a locally non-equilibrium Navier–Stokes equation

A locally non-equilibrium Navier–Stokes equation, which accounts for the mean free path and relaxation time of microparticles, has been derived based on a modified Newton's law for shear stress in laminar gas flow within a plane-parallel channel. A numerical study of its solution for the case of a harmonic pressure drop along the channel revealed that the velocity variation at every point also exhibits harmonic behavior. It was found that the velocity oscillation amplitude decreases with an increase in the mean free path and relaxation time of the microparticles. For fixed microparticle parameters, the oscillation amplitude decreases with increasing gas viscosity and decreasing channel width. In the limiting case where the channel width becomes comparable to the mean free path, the velocity oscillation amplitude reaches an almost zero value, despite the constant amplitude of the pressure drop oscillations. It is demonstrated that the generation of gas flow oscillations can be utilized to clean the internal surfaces of a methane pyrolysis reactor from carbon deposits, which reduce the efficiency of the process for producing hydrogen and carbon.