Formation of dynamic and thermal boundary layers in a methane pyrolysis with variable viscosity and thermal diffusivity

Abstract

Abstract

The integral method of heat balance was applied for analytical solutions of a problem about forming dynamic and thermal boundary layers in a pyrolysis reactor (thermal decomposition of methane) with the conditions of variable viscosity and thermal diffusivity values (variable within the layers span). It was demonstrated that a layer of quiescent gas at the wall temperature on the inner surface of reactor wall is heated up to a temperature of 1000 °C (this occurs due to a high viscosity and a high thermal diffusivity within these layers). The isotaches and isotherms in this layer are oriented normal to the wall surface. In this case, boundary layers are formed at a certain distance from the wall. Within this layer, the velocity is almost zero, and the layer temperature equals the wall temperature (exceeding the gas temperature beyond the layers). At high temperatures, the nearwall layer of gas at rest is a place for intense production of carbon (the pyrolytic graphite) which deposits on the reactor walls up to a total carbon-based plugging of the reactor cross-section and the halt in pyrolysis process.