## 4 Results and Discussions
### Simulation and Prediction of Magnetic Field Effect under Different Flue Gas Velocities  
The working voltage is set as 60 kV, in the environment with and without magnetic field; Figure 12 shows the variation curves of PM2.5 grade efficiency under different flue gas velocities and temperatures, and it is not difficult to observe the following:  
1. With or without a magnetic field, as well as considering the changes in flue gas flow rate and temperature, the efficiency of PM2.5 grade efficiency and dust-removal increases with the increase in particle size, and the gradient of the increase gradually decreases. 2. Regardless of the influence of magnetic field, the grade efficiency of particles declines as the flue gas velocity ascends, gradually reduces with the increase in temperature, and the decreased gradient drops. 3. Whether there is a change in flue gas velocity and temperature or not, the grade efficiency in the magnetic field environment is higher compared with that in the absence of a magnetic field, which indicates that the magnetic field can effectively promote the capture of particles. 4. Regardless of the magnetic field, the difference in grade efficiency at different temperatures becomes smaller as the flue gas velocity increases, which shows that the temperature has less influence on the grade efficiency at high flue gas velocity. 5. In the presence or absence of a magnetic field, the higher the temperature, the lower the weakened gradient of the flue gas velocity on the grade efficiency, which suggests that the increase in temperature reduces the influence of the flue gas velocity on the grade efficiency. Figure 11: Comparison and relative error between predicted values and simulated data of grade efficiency. Figure 10: Comparison of relative error and 45\({}^{\circ}\) line between two models. To gain a clearer understanding of the relationship between magnetic field and flue gas velocity, the grade efficiency with and without a magnetic field at 873 K and at different flue gas velocities can be obtained based on Figure 10, as shown in Figure 13:  
1. At the same temperature, the difference in grade efficiency among different flue gas velocities gradually decreases and flattens with the increases in particle size, indicating that the magnetic field has a more pronounced effect on enhancing the grade efficiency of smaller particle sizes. 2. The larger the flue gas velocity, the greater the increased magnitude of magnetic field on the grade efficiency, showing that the magnetic field effect becomes more significant at a higher flue gas velocity. 3. The grade efficiency achieved when the flue gas velocity increases by 2.0 m/s is roughly equivalent to that obtained when a 0.5 Tesla magnetic field is applied. This indicates that, although the increase in the flue gas velocity reduces the dust-removal efficiency, the introduction of a magnetic field makes up for the weakening resulting from flue gas velocity. The simulated data of Figure 12--representing the grade efficiency under different flue gas velocities (1.0 m/s, 3.0 m/s) and temperatures (473 K, 673 K, and 873 K) with magnetic field strengths of 0.0 T and 0.5 T--are selected as the training data, and the PSO-SVM and the BPNN models are then used to predict the grade efficiency. Comparing the predicted values of the two models with the simulated data, as depicted in Figure 14, the following can be found:  
Figure 12: Grade efficiency at different temperatures and flue gas velocities with and without magnetic field. Figure 13: Grade efficiency at 873 K with and without magnetic field. 1. No matter what the flue gas velocity is, the variation law of the curves predicted by the BPNN and the PSO-SVM models is basically consistent with that of simulated ones, indicating that the two models possesses a certain level of reliability in predicting the magnetic field effect under different flue gas velocities. 2.