Multi-Scale Simulation And Study On Turbulent Reacting Flows In Ejector On High Schmidt Number

Ejector is a conversion unit with high-intensity mixing performance. As a type of reactor, it can strengthen mixing process, reduce concentration gradient and temperature gradient, accelerate reaction progress, restrain side reaction and improve selectivity. Due to these merits, it is employed in most fields of industry such as petrochemical, chemical, environmental protection and medical. For the complexity of multi-scale turbulent reacting flows in ejector, researches on the theory of it and scale-up laws are rare at present. A good understanding of the main factors affecting the mixing performance and turbulent reacting flows characteristics can help to master the scale-up laws of ejectors. And, it can provide references for the optimization and scale-up of ejectors.Firstly, three kinds of k ?εturbulent models used in numerical simulation are verified by planar laser induced fluorescence (PLIF) technique. The results reveal that both Standard k ?εturbulent model and Realizable k ?εturbulent model can give the real information on macro-mixing process in ejector.Secondly, jet reactor is simulated with Realizable k ?εturbulent model in this paper with the help of computational fluid dynamics (CFD) software Fluent6.2 to study its mixing characteristics. Macro-mixture fraction variance and micro-mixture fraction variance are used to measure the macro-mixing performance and micro-mixing performance in jet reactor .At the same time, the criterion judging the mixing performance is built to analyze the dependence of mixing performance on operating conditions.The results show: 1) For a fixed entrained flow velocity, the larger the nozzle velocity is , the better the micro-mixing performance and the macro-mixing performance is ; 2) For a fixed nozzle velocity, the larger the entrained flow velocity is, the worse the micro-mixing performance and the macro-mixing performance is; 3) For a fixed ratio of nozzle velocity and entrained flow velocity, the larger the velocities are, the better the micro-mixing performance and the macro-mixing performance is; 4) For the cases in this paper, micro-mixing is the control step of the whole mixing process.Finally based on studies on mixing characteristics of jet reactor, a parallel-competitive reaction is employed to measure the turbulent reacting flows in jet reactor. DQMOM-IEM model is used to describe the turbulent reacting flows in jet reactor and the model is solved by Fluent6.2. The information on turbulent reacting flows in jet reactor is obtained. Conversion (X) of slow reaction is used as a criterion to analyze the dependence of turbulent mixing-reacting characteristics on operating conditions. The results show: 1) The DQMOM-IEM model can provide exact information on turbulent reacting process in jet reactor; 2) For a fixed entrained flow velocity, the larger the nozzle velocity is , the higher selectivity is and the better mixing performance is; 3) For a fixed nozzle velocity, the larger the entrained flow velocity is, the lower selectivity is and the worse mixing performance is ; 4) The larger the ratio of nozzle and entrained flow velocity is, the higher selectivity is and the better mixing performance is; for a fixed ratio of nozzle velocity and entrained flow velocity ,the larger the nozzle and entrained flow velocities are, the higher selectivity is and the better mixing performance is; 5) For a fixed nozzle velocity ,there has a linear relation between X and Damkoler number and the slope is determined by the nozzle velocity; 6) Turbulent reacting flow in jet reactor is controlled by both mixing process and reacting process. The energy consumption and the selectivity should be simultaneously considered to determine the operating conditions in practical production.