# Effect of Venturi Structures on the Cleaning Performance of a Pulse Jet Baghouse
## 3 Results and Discussion
### Effect of Venturi Length and Throat Diameter on the Cleaning Performance of the Filter Bag  
Figure 9a illustrates the variation of the peak pressure on the filter bag under different venturi throat diameters (40, 50, and 60 mm) at a pulsing air pressure of 0.4 Mpa, pulsing air injection time of 100 ms, and venturi length of 200 mm. The peak pressure in the point P0 was negative, later increasing until reaching a maximum value at the point P1. Subsequently, the peak pressure decreased with an increasing distance from the measuring point to the bag mouth. Finally, the peak pressure rose again at point P8. As shown in Figure 9b, when the typical venturi-type tube was installed in the bag cage, the area near the bag mouth was in the \"blind action zone\" of the cleaning airflow (primary airflow and secondary airflow). In addition, when the cleaning airflow was ejected from the venturi tube, the airflow outside the filter bag near P0 would be induced to the inside, creating a negative pressure zone in the area near the bag mouth. It can be seen that the area near P0 is the one with the worst cleaning performance. This inference is consistent with the literature [3,20]. Since, in this point, the dust layer cannot be effectively cleaned, the filter material in this area loses its filtration ability. Thus, it should be considered that installing the typical venturi-type tube implies that the area near the filter bag mouth will exhibit low filtration performance. The maximum value of the peak pressure occurred at P1, which was consistent with the results of literature [21,22]. In the process of moving downward from the bag mouth, the cleaning airflow expanded and diffused outside the filter bag. Since the cleaning airflow could not be infinitely expanded, and the consumption and energy loss of the cleaning airflow accompanied the whole process, it was inevitable that there would be a maximum pressure on the side wall of the filter bag. After the maximum pressure occurred, the expansion effect of the cleaning airflow decreased and the energy attenuation increased. Later, the peak pressure on the filter bag decreased. The peak pressure at P8 was larger than that obtained at P7, which was likely caused by the refluxing of the cleaning airflow. According to Figures 9a and 10, with an increase in the venturi throat diameter, the peak pressure on the filter bag increased and the peak pressure arrival time decreased. This indicates that a better cleaning effect can be obtained by increasing the throat diameter of the venturi. This may be explained by the fact that the smaller the venturi throat diameter, the greater the resistance of the clearing airflow (the primary airflow + the secondary airflow) passing through the venturi, which led to the greater energy loss of the cleaning airflow, thus making the peak pressure smaller and the peak pressure arrival time greater. Figure 8: Effect of the pulsing air injection time on the peak pressure arrival time of filter bag. Figures 11 and 12 show the influence of different venturi lengths (160, 180, and 200 mm) on the peak pressure and the peak pressure arrival time, respectively. Experiments were run at a pulsing air pressure of 0.4 MPa, pulsing air injection time of 100 ms, and a venturi throat diameter of 60 mm. According to the results, as venturi tube length decreases, the peak pressure increases; however, the peak pressure arrival time decreases. This suggests that it is possible to improve the cleaning effect by reducing the length of the venturi tube. In addition, when reducing the venturi length, a larger effect was observed on the peak pressure in the upper half of the filter bag, compared to that in the second half. On the contrary, a more significant effect was observed in the lower half of the bag for the peak pressure arrival time under the same reduced-venturi length condition. This occurred because, for the cleaning airflow, the venturi tube is a resistance component.