| One of the most important factors affecting the atmospheric pollution is the total suspended particulate (TSP) pollution, especially the pollution of PM2.5, which greatly improves the probability of the haze phenomenon and respiratory diseases. It is showed that the 60% discharge of PM2.5 is caused by the industrial pollution on particle product. The common disadvantages of electrostatic precipitator&bag filter are the high costs and secondary pollution. The advantage of traditional cyclone is a low cost, however, the shortcoming is poor collection efficiency of PM2.5. In order to improve the fine particle separation efficiency of cyclone, Professor Liu Genfan invented a new radial jet cyclone (RJC), which is based on the centrifugal separation principle. The separation efficiency of RJC exceeds 94% when the diameter of particle is close to 1 micron. The main content of this paper is about theoretical and numerical simulation study on the separation performance of RJC.On the theoretical study of separation efficiency, the velocity distributions in the flow channel were calculated based on the continuity equation. The calculated cut-off size was given based on the force balance equation and residence time model (RTM). The calculated grade efficiency was deduced from the cut-off size and the experimental results. The relationship between the grade efficiency and geometric dimensions was discussed. The influence of volume flow on the grade efficiency was also studied.In the chapter of theoretical pressure loss (also called pressure drop), the pressure loss was dividied into fricitional loss and local loss by the causing of loss, according to the characteristics of geometry and distribution of flow field in RJC. The flow space consists of three independent parts, the total pressure drop was summed by the pressure drop of each part respectively. The experimental results of D=170mm model were used to fit the local pressure loss coefficient. The relationship between the overall pressure drop and geometric dimensions was discussed by the analysis of the theoretical formula.For the experimental study, three different diameter of the cylinder (D=114mm, 140mm,170mm) prototype RJC were used to built the test platforms of collection efficiency and pressure drop. The difference of pressure drop under five different volume flows was discussed. The pressure drop of inlet decreased by 30% after the optimum of structure. Talcum powder particles were used to test the collection efficiency. Based on the distribution of particle size, the cut-off size and grade efficiency were obtained from the results of experiment. However, the experiment result was showed that there was a critical value of volume flow for separation efficiency and pressure drop when the geometric dimension was changed.For discussing the mechanism of the effect of volume flow, the soft ware Fluent was used to simulate the distribution of inner flow field. The simulation results of tangential velocity was showed that the increasing tangential velocity near the wall in the upper zone of cylinder would greatly improve the centrifugal force of fine particles. The time of paritlce moved to the wall was shorten by the increasing of centrifugal force. At the same time, the particle was moved downword by the axial velocity, which leaded to the collection probility of the fine particle greatly improvement. This is an absurtlute advantage for RJC. The different tangential velocity and axial velocity distributions of different geometric dimensions caused by the volume flow was studies. The reason is the different axial velocity caused by the length of cylinder body induced the different tangential velocity and collection efficiency. The result of simulation showed that the critical value of voluine flow is 42 m2/h when the diametel of cyclone was 140mm, which was greatly agreement with the experimental result. |
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