Simulating the hydrocarbon waste pyrolysis in reactors of various designs

The study presents a simulation of pyrolysis reactors of various designs performed in the COMSOL Multiphysics software package. The non-isothermal flow (k–ε turbulent flow) module is used. The advantages this technique has over other commonly used ones are shown. The results indicate that under the same conditions, heating in sectional reactors is more intense. To achieve optimal results, the coolant flow rate in new reactors maybe by an order of magnitude less compared to the conventional design. The use of sectional reactors for multi-flow processing of hydrocarbon waste is advisable. Keywords: sectional reactor; pyrolysis; hydrocarbon waste; heat transfer; turbulent flow.

Grain crops extrusion process mathematical model at a non-isothermal flow of their melt up to the temperature of the Maillard reaction start

The equations of motion, the equation of continuity, the equation of energy (heat balance), the rheological equation were chosen to describe the non-isothermal flow of the cereals melt in the extruder as the initial equations. The following assumptions were made to solve the model: the flow of a moving viscous medium is assumed to be laminar and steady; the forces of inertia and gravity are so small compared to the forces of friction and pressure that they can be neglected; a viscous medium (melt) is an incompressible liquid characterized by constant thermal conductivity and thermal diffusivity; the change in thermal conductivity in the longitudinal direction was neglected due to the fact that convective heat transfer in the flow direction is higher than the heat transfer by thermal conductivity; heat transfer in the direction perpendicular to the flow of the melt occurs only due to thermal conductivity. The numerical finite difference method was used to solve a system of equations taking into account convective heat transfer. Its essence of use lies in the fact that the considered area (extruder channel) is divided into calculated cells using a grid. The grid consisted of rectangular cells with a constant step between nodes, which exactly lie on the boundaries of the integration region. In this case, the differential equations were transformed into difference equations by replacing the derivatives at a point with finite differences along the cell boundaries. The mathematical model of non-isothermal melt flow in the extruder channel was obtained as a result of the solution. To solve a mathematical model of the process of grain crops extrusion with a non-isothermal flow of their melts, a program in the algorithmic language C ++ was compiled. A non-isothermal mathematical model of the process of extrusion of grain crops at temperatures of the beginning of the Maillard reaction, i.e., up to 120–125 ?, was obtained. It allows us to identify the nature of the temperature change along the length of the extruder. Comparative analysis of the results of the numerical solution and experimental data showed good convergence: the standard deviation did not exceed 12.7%.

Shear viscosity calculation for particle-based flow

A particle-based method called multi-particle collision (MPC) dynamics is considered, and the shear viscosity is calculated theoretically. As part of the particle-based mechanism, velocities of particles change due to collisions and due to an applied external force used to create flow. The system's temperature increases due to the external force, and a thermostat is used to remove this excess temperature so as to maintain constant temperature (isothermal) flow conditions. A theoretical expression for the shear viscosity is derived and compared to existing viscosity expressions. Additionally, results for MPC flow through a local constriction are assessed. The novelty of the numerical results in this Thesis come from using a local thermostat rather than a global thermostat that had been used in the past.