# Effect of Venturi Structures on the Cleaning Performance of a Pulse Jet Baghouse
## 3 Results and Discussion  
Effect of Pulsing Air Pressure and Pulsing Air Injection Time on the Cleaning Performance of the Filter Bag  
Figure 5 shows the peak pressure distribution of the airflow in the filter bag under different pulsing air pressure values (0.3, 0.4, and 0.5 MPa) at a pulsing air injection time of 100 ms. According to the data, the peak pressure (\(P_{\text{P}k}\)) on the side wall of the filter bag increased with increasing pulsing air pressure values (\(P_{\text{P}u}\)) and the peak pressure decreased from the top (1000 mm) to the bottom (8000 mm) in the bag. In addition, the attenuation range of the peak pressure in the upper half of the filter bag was significantly greater than that observed in the lower half. This occured because when the compressed airflow was ejected from the nozzle, it would move downward rapidly and induce a large amount of secondary airflow to enter the filter bag. The compressed airflow (the primary airflow) and the secondary airflow mixed to form the total cleaning airflow. The cleaning airflow expanded as it moved downward, thus increasing the air pressure in the space it passed through. Moreover, due to the air permeability of the filter bag, the cleaning airflow was continuously diffused to the outside of the filter bag. Furthermore, the cleaning airflow would rub against the filter bag in the downward movement process, which inevitably consumed a certain amount of energy. Therefore, the peak pressure on the filter bag decreased with the increase of the distance between the measuring points and the bag mouth. On the other hand, the greater the pulsing air pressure, the greater the kinetic energy of the cleaning airflow, the more the amount of the cleaning airflow diffused outside the filter bag, and the more intense the friction with the filter bag, so the peak pressure differed greatly on the upper part of the filter bag under different pulsing air pressure values. When the cleaning airflow moved to the lower half of the filter bag, the friction between the cleaning airflow and the filter bag was weakened due to the energy attenuation of the cleaning airflow so that the gap of the peak pressure on the lower part of the filter bag became smaller under the different pulsing air pressure values. Further analysis showed that, at a pulsing air pressure (\(P_{\text{P}u}\)) of 0.5 MPa, the peak pressure of the filter bag at the three measuring points was 53.57% (top), 51.04% (middle), and 113.33% (bottom) higher than that obtained with a pulsing air pressure of 0.3 MPa, respectively. A similar analysis comparing a pulsing air pressure of 0.4 MPa and 0.3 MPa indicated that the values were of 28.57% (top), 30.21% (middle), and 83.33% (bottom), correspondingly. However, when the pulsing air pressure was 0.4 MPa, the peak pressure at the three measuring points was only 16.28% (top), 13.79% (middle), and 14.06% (bottom) lower than that obtained at a pulsing air pressure of 0.5 MPa. This indicated that as the pulsing air pressure increased, the rate of increase in the peak pressure of the filter bag decreased. Figure 6 shows that the peak pressure arrival time (\(t_{R}\)) decreased with an increase in the pulsing air pressure (\(P_{Pu}\)) at the three measuring points. In addition, at the \"top\" point, the peak pressure arrival time values obtained under the three different pulsing air pressures were almost the same. Moreover, with an increasing distance between the measuring points and the bag mouth, the difference between the peak pressure arrival time under the three pulsing air pressures increased. The peak pressure arrival time at the \"bottom\" point was 262 ms (0.3 MPa), 204 ms (0.4 MPa), and 202 ms (0.5 MPa); thus, when the pulsing air pressure was 0.3 MPa, the peak pressure arrival time at the lower part of the filter bag was significantly higher than that obtained at a pulsing air pressure of 0.4 and 0.5 MPa.