Experiment Study And Multi-Scale Simulation Of Turbulent Reaction In Jet Reactors On High Schmidt Number

Reactions in chemical industry normally proceed in condition of turbulent flow. Mixing of reactive materials has an important effect on yield and selectivity of the reactions. As a new type of high-intensity-mixing reactor, jet reactors have been widely used in the field of petroleum, chemical, environment and pharmacy industries. However, turbulent reaction in jet reactors is a complex multi-scale process and studies on it are not enough. Up to now, design and scale-up of jet reactors are depend on experiments. The work in this thesis aims to study the complex process of turbulent reaction in jet reactors on high Schmidt. The effects of macro-, meso-, micro- mixing and reactions on reactors were studied by means of scale theory analysis, PLIF experiments and CFD simulations.1. The turbulent reaction in jet reactors on high Schmidt number was analyzed with scale theory. The characteristic time of micr-, meso-, macro-mixing process and reaction on normal conditions were calculated and the control step was obtained. These data could provide useful information for the incipient design and detail computation of jet reactor.2. The macro-mixing in jet reactor was studied through PLIF experiments and the mixing performance was analyzed by means of intensity of segregation (IOS). Results showed that the nozzle velocity and entrained flow velocity have opposite effects on the mixing performance. The larger of the ratio of nozzle and entrained flow velocities is, the better the mixing performance is; In the case of the constant ratio , the larger the velocities are, the better the mixing performance is. Three turbulent model were tested by the PLIF experiments, and the results showed that the RNG k-εmodel gave worst data compared with that of experiments, but both the standard and realizable k-εmodel gave satisfied results.3. EBU model was used to compute the conversion of the acid-base neutralization, and the conversion was used to measure the macro-mixing performance. This method avoids the shortcoming of the EBU model and at the same time, the effect of reaction to mixing process is allowed. Based on the method, the macro-mixing in jet reactors was studied on different operation condition and different configuration parameters, and the rule of scale-up was also considered:(1) The smaller the angle of diffuser section is, the better the macro-mixing and the higher conversion rate can be achieved, but at the same time more kinetic energy is consumed; An optimum value for the ratio of diameter between nozzle and mixing section existed. If the value is larger than the optimum value, the conversion rate in the jet reactor would decrease, while if the value is smaller than the optimum value, more kinetic energy would be consumed but could not improve conversion rate any more; The farther the distance between nozzle outlet and mixing section are, the faster the reaction completes. The best case was obtained when the nozzle outlet shares the same plane with the center of suction inlet.(2) The scaled up rules of the velocity similarity principle the Reynolds number similarity principle are not proper to jet reactor, however, improving velocity and changing geometry size simultaneously gave satisfied results. The CFD simulation results showed that the optimum value of velocity ratio was increased with the increasing of velocity and diameter in initial conditions. Two formulas of the velocity ratio and initial configuration of jet reactors with the velocity were regressed based the simulation results4. The variances of macro- and micro- mixture fraction were used to represent the performance of macro- and micro-mixing. Multi-scale simulation and study were made of jet reactor and the characteristic times of macro- and micro-mixing were obtained on different operation conditions. The results showed that in the case of constant entrained flow velocity, the mixing time to reach complete mixing was decreased when the nozzle velocity was increased; In the case of constant nozzle velocity, the mixing time to reach complete mixing was increased when the entrained flow velocity was increased; In the case of constant velocity ratio of nozzle and entrained flow, the mixing time to reach complete mixing was decreased when both the velocity were increased; All the cases studied in this thesis, the control step of the turbulent mixing in jet reactor was micro-mixing process.5. The turbulent reactions of typical parallel-competitive reactions were simulated and studied using DQMOM model. The results showed:(1) The DQMOM model can be used to simulate turbulent reactions in jet reactor appropriately and can give detailed information inside the reactor. This information can be used for optimized design of jet reactor.(2) In the case of constant entrained flow velocity, with the nozzle velocity increased, the mixing performance of jet reactor became better, the time needed to reach complete mixing was decreased, the selectivity and of parallel-competitive reactions was increased and the conversion of the side reaction was decreased. In the case of constant nozzle velocity, with the entrained flow velocity increased, the mixing performance of jet reactor became bad, the time needed to reach complete mixing was increased, the selectivity and of parallel-competitive reactions was decreased and the conversion of the side reaction was increased. In the case of constant velocity ratio of nozzle and entrained flow, with the nozzle and entrained flow velocity increased, the mixing performance of jet reactor became better, the time needed to reach complete mixing was decreased, the selectivity and of parallel-competitive reactions was increased and the conversion of the side reaction was decreased.(3) In the case of constant nozzle velocity, the conversion of the second reaction has a linear relationship with Damkoler number, and the slope of the line was connected with nozzle velocity.