| The turbulent characteristics of liquid mixing and preparation of BaSO4 by co-precipitation in MOIT jet reactor were studied by the experiments, as well as the CFD numerical simulations. The effect of the configurations (e.g. the number of the orifices), the operational conditions (e.g. the velocity ratio), and the scale-up of the process on the liquid turbulent mixing characteristics has been investigated systematically. Then the jet reactors were applied to the intensification of the co-precipitation process for the preparation of BaSO4. The effect of the configurations of the MOIT jet reactors, the Reynolds number, and the initial concentrations of the reactants, on the size of the prepared particles and its particles size distribution (PSD) were studied.The turbulent mixing characteristics was predicted by large eddy simulation using the dynamic kinetic energy sub-grid stress model. The scale of the mesh grid has great effect on the accuracy of CFD simulation. The predicted results agree well with the experiments data when D/△x=55. Compared with the traditional T jet reactor, the turbulent vortices and the concentration distributions during the mixing process in the MOIT jet reactors are more uniform, thus leading better mixing efficiency. The velocity ratio plays a crucial role on the turbulent mixing in MOIT jet reactor. When the velocity ratio increases, the turbulent intensity and its sub-grid-scale dissipation rate increases, leading to high mixing efficiency. When the MOIT jet ractror are sized up, i.e. the diameters of the mixing pipe and orifices are sized up proportionally, whereas the number of the orifices and the operations conditions are kept constant, it is found that the mixing efficiency becomes lower. When the diameter of the mixing pipe and the total area of the injected orifices are constant, there is an optimal design for the number of the orifices, e.g. when the mixing pipe diameter is 40mm and the velocity ratio is 4:1, the highest mixing efficiency can be achieved when the orifice number, n= 12, and the diameter of the orifices, d= 5.78mm, respectively. Then the MOIT jet reactors were used to intensify the co-precipitation process of Na2SO4 and BaCl2 solution for the preparation of BaSO4 nano particles. The effect of theReynolds number on the particle size and its PSD was studied. The results show that the size of the particle decreases firstly (as well as the PSD becomes narrow), and then comes to a platform (as well as the PSD does not change) when Re increases, which implies that the effect of the mixing efficiency on the co-precipitation becomes less and less important. Moreover, the nano-particles prepared by the co-precipitation in the MOIT jet reactor have little aggregates and disperse in the water well.The co-precipitation process for the preparation of of BaSO4 was further studide by numercial simulation using k-ε turbulent model, coupled with a population balance model (PBM). The particle size and its PSD was predicted. It is found that the predicted results agree well with those from the experiments.When the Reynolds number increases, the micro mixing efficiency increase, thus leading to the reduction of the size of BaSO4 nano-particles firstly. When the micro-mixing catch up the reaction rates, i.e. the effcet of the micromixing is lower, the size of BaSO4 keeps a slight change. As the initial concentrations of the reactants increase, the supersaturation becomes larger, leading to the reduction of the size of BaSO4 nano-particles firstly, and then change slightly. When the operation conditions are fixed, the precipitation process can be intensified by increasing the number of the orifices when D= 4 mm. This intensification benefits from the more uniformed distribution of the supersaturation. When the MOIT jet reactor is sized up, i.e. the absolute mixing time scale becomes larger, the effect of the mixing on the co-precipitation reaction becomes significant, thus leading to an obvious increase of the size of BaSO4 nano-particles. |
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