The CFD Numerical Simulation Of Rapid Gas-gas Mixing

Mixing two or more gases is a very common unit in chemical industry. In this work, we designed a cross jet mixer that could make two fluids mixed rapidly and uniformly by CFD numerical simulation. Then we optimized the configuration parameters of the mixer and operating conditions according to the good or bad of the mixing performance. The reliability and accuracy of numerical simulation were verified by the cold model experiments. At last, we got the rapid mixing in a small space and in a short time in the cross jet mixer we designed. Some conclusions are listed as follows.1) The mixing will be more uniform when the side-hole diameter is small, and its number is large. The top-hole diameter hardly affects the mixing behavior in a small scale while the hole pitch should be bigger than 2 times diameter.2) The side-to-top momentum ratio has significant importance on the mixing quality. The momentum ratio, not smaller than 10, is a prerequisite for the uniform mixing. In addition, cheap, pollution-free, easy recovery of inert gas could be added together with side feeds as a thinner to replace the additional reactant gas when increasing the momentum ratio.3) The homogeneous mixing could be achieved within the distance one times the length of the mixer diameter in the cross jet mixer.4) The jet Reynolds number, based on the jet velocity and hole diameter, should be above the critical Reynolds number 300. The flow field distribution would be not changed a lot under different velocities when the side-to-top velocity ratio is fixed.5) The expanded, straight and constricted flow channels in the mixers generate different flow fields. Among them, the concentration distribution in the constricted mixer is most uniform while that in the expanded mixer is worst, that in the straight mixer between the former and the latter.6) From the comparison of simulation results with experiment results, it could be concluded that the numerical simulation is quite reasonable and credible providing an effective method to research the complex mixing process that has difficulty in performing physical experiments.7) From the comparison of simulation results of the cross jet mixer with two industrial mixers, it is conducted that the cross jet mixer is much better than the other two. More uniform mixing could be obtained in the cross jet mixer.