A Numerical Study on the Design of a Diffuser Nozzle for Pulsed-Jet Cleaning of Cone Filter Cartridges

Abstract

For workplaces where the dust cakes have high viscosity, it is difficult to peel the dust cake from the surface of the dust filter cartridge. The problem of poor dust removal restricts the efficient and stable operation of the dust collector. This study proposes a diffuser nozzle to improve the pulsed-jet cleaning performance of cone filter cartridges. Through numerical modeling, the study investigates the improvement of pulsed-jet velocity and pressure by the diffuser nozzle, explores the influence of the diffuser angle (θ) and diffuser distance (D) on the jet field of the cone filter cartridge core, and compares the pulsed-jet intensity and uniformity of the dust removal filter cartridge. The findings show that the diffuser nozzle with appropriate parameters is conducive to enhancing the divergence and entrainment of the jet airflow, reducing the airflow velocity in the filter cartridge opening area and increasing the static pressure, while also increasing the airflow entrainment. The pulsed-jet intensity and uniformity, especially the pulsed-jet intensity in the upper part of the filter cartridge, vary significantly with θ or D, and the action mechanisms of θ or D are obtained. Under the recommended diffuser nozzle parameters (θ = 70° and D = 40 mm), the pulsed-jet intensity is 1086 Pa, which is 5.4% higher than that under the condition of the common round nozzle; the uniformity coefficient is 0.14, which is 60.0% better than that under the condition of the common round nozzle. For the upper part of the filter cartridge, the pulsed-jet intensity is 1.39 times that with the common nozzle. The result is significant as it offers a guide for improving the pulse-jet cleaning of dust removal filter cartridges.

1. Introduction

In recent decades, the industrial sector has witnessed rapid development, yet this progress has been accompanied by a significant increase in industrial dust emissions [1,2,3]. Industrial dust not only poses severe threats to human health, causing respiratory diseases and other ailments, but also exerts detrimental effects on machinery and equipment, leading to reduced efficiency and lifespan. To address these challenges, filter cartridge dust collectors have emerged as a promising solution, capable of effectively controlling dust emissions [4,5,6,7,8]. However, the critical process of pulsed-jet cleaning, which is essential for the continuous operation of these dust collectors, often suffers from inadequate cleaning performance. In particular, the cleaning of the upper part of the filter cartridge is poor [9,10,11,12]. In the upper part where the cleaning effect is minimal, dust cakes may still remain. Conversely, in areas where the pulse-jet effect is strong, over-cleaning may occur. The accumulation of residual dust cakes, which is commonly referred to as the formation of “cleaning dead zones”, can lead to filter material blockage, a sharp increase in resistance, and eventual failure of the dust removal system. Over-cleaning not only exacerbates the penetration of dust (especially fine particles) during subsequent filtration in that area but also accelerates the aging of the filter material. In severe cases, it may even cause the filter material to rupture directly, leading to system failure. This problem is particularly prominent in workplaces where the dust cakes have high viscosity, such as in rubber factories with carbon black dust, industrial dust containing MgO or Al₂O₃, asphalt fumes, coke oven emissions, and in environments with hygroscopic dust and high humidity. In these cases, the difficulty of dust cake removal is significantly greater, and the issue of inadequate cleaning becomes even more pronounced. This issue has become a bottleneck in the optimization of dust collection systems, necessitating further research and innovation to enhance the efficiency and reliability of this technology.

Hu et al. [13] applied a Laval nozzle to the pulse-jet cleaning of dust filter bags and demonstrated that the installation of the Laval nozzle increased the average pressure peak on the filter cartridge side wall by 53.2%. Xi et al. [14] studied the effect of adding a conical scatterer inside the nozzle on pulse-jet performance and proved that the scatterer, as an additional structure of the nozzle, can divert the blowing airflow and improve the cleaning effect of the filter cartridge. Su et al. [15] enhanced the pulse-jet effect of the filter cartridge by using a Venturi nozzle, increasing the pulse-jet intensity and uniformity by 1.72 times and 1.96 times, respectively. Qian et al. [16] found that the cleaning effect of the filter element first increased and then decreased with the increase in nozzle area ratio, with the best performance achieved at a nozzle area ratio of 38.72%. Additionally, the use of built-in rotators and perforations has also been shown to improve the cleaning performance of filter cartridges [17,18].

Some researchers focused on optimizing cleaning performance through filter cartridge structural modifications. Li et al. [19] installed a conical body inside the filter cartridge and experimentally demonstrated that it increased the pressure on the side wall of the filter cartridge and improved the uniformity of cleaning. Zhang et al. [20] used numerical modeling to examine the differences in filtering and cleaning characteristics between conventional and conical-body filter cartridges. They found that the conical-body filter cartridge increased the filtration area, reduced airflow resistance, enhanced the vertical pressure distribution of the pulse-jet airflow inside the filter cartridge, and significantly improved the cleaning effect and extended the service life of the filter cartridge. Qiu et al. [21] established a numerical modeling of pleated conical filter cartridges and investigated the effect of varying internal cone heights on pulse-jet performance under a conventional nozzle. They found that a distinct negative pressure zone appeared at the top of the filter cartridge when the cone height was less than 660 mm, while the negative pressure zone disappeared when the cone height reached 760–860 mm. This demonstrated that increasing the cone height improved the uniformity of static pressure distribution within the pleated conical filter cartridge. Chen et al. [22] explored the combination of a diffuser nozzle and a conical filter cartridge using two-dimensional CFD modeling and found that this combination increased the blowing intensity by 1.66 times. Park et al. [23] experimentally investigated the effect of the ratio of pleat height to pleat spacing on filter cartridge cleaning and found that a ratio of 1.48 was most favorable for cleaning. Li et al. [24] added a conical filter surface inside a pleated filter cartridge and analyzed the internal flow field of the double-layer filter cartridge through numerical modeling. They concluded that a filter cartridge with an inner diameter of 140 mm achieved the best performance, with a blowing intensity of 1175 Pa, while an inner diameter exceeding 160 mm had a negative effect. Chen et al. [25] simulated filter cores with different pleat shapes and compared parameters such as pressure and flow field. The results indicated that convergent-pleat filter cores exhibited better cleaning performance.

To further enrich the techniques for improving the cleaning performance of dust filter cartridges and to explore enhanced pulsed-jet effects, this study focuses on the cleaning improvement of the new cone filter cartridge. To achieve a more uniform effect of jet airflow on the filter material, especially enhancing the effect on the upper part of the filter cartridge, a divergent director nozzle is put forward to optimize the cleaning performance. Through numerical modeling, we investigate the impact of the divergent director nozzle on the velocity and pressure of the pulse-jet flow. The effects of the cone angle (θ) and the cone distance (D) in the divergent director nozzle on the pulsed-jet flow field within the cone filter cartridge are examined. The improvements in pulsed-jet intensity and uniformity of the dust filter cartridge are compared and analyzed. The diffuser nozzle is found to enhance the performance of the pulse-jet cleaning for the cone filter cartridge.

2. Methods and Materials

2.1. Physical Dust Collector System

The laboratory’s physical dust collector was taken as the basic numerical modeling model. The main chamber of the dust collector has dimensions of 1225 mm × 750 mm × 1550 mm. Dust collection filter cartridges are installed in the filtration chamber, with nozzles mounted directly above the filter cartridges. The experimental system mainly includes a pressure air reservoir with a volume of 20 L, an electromagnetic pulse valve (DMF-Z-25 type, 1-inch, Shenchi Pneumatic Co., Ltd., Leqing, China), a pulse controller (QYM-ZC-10D, Lingchuan Auto Technology Co., Ltd., Changzhou, China), and a high-frequency pressure acquisition subsystem (piezoelectric pressure transducers of MYD-1530A type with a range of 0–100 kPa, a sensitivity of 6–13 pC/kPa, and a size of ϕ7 × 17 mm; data acquisition rate is 250 Hz; Mianyang Minyu Electronics Co., Ltd., Mianyang, China).

The basic operating process of the dust collector experimental system is as follows: Under the action of the fan, the dust laden air is drawn into the dust collector through the inlet. In the dust loading chamber, the dust is captured on the outer surface of the filter cartridge, while the clean airflow passes through the filter cartridge to reach the clean air chamber and is then exhausted by the fan. When the filter cartridge needs to be cleaned, the electromagnetic pulse valve is triggered. High-pressure air from the air tank is ejected through the nozzle into the filter cartridge. The dust on the outer surface of the filter cartridge is dislodged and falls into the ash hopper due to the action of the reverse pulse-jet airflow.

2.2. Simplification and Construction of the Dust Collector Model

Considering that the filter cartridge is the core area of numerical modeling and has a centrally symmetric structural characteristic, the dust collector model can be simplified. First, the model is sectioned along the axis of the filter cartridge, and then half of the section is taken to obtain a two-dimensional model, as shown in Figure 1. This two-dimensional model can be rotated around the axis to obtain a cylindrical dust collector equivalent to the physical dust collector in space. In the calculation domain of the model, the height of the dust collector box is 1400 mm, the radius is 750 mm, the height of the filter cartridge is 660 mm, the outer diameter is 320 mm, the thickness of the filter material is 0.6 mm, the height of the inner cone part of the filter cartridge is 760 mm, and the bottom diameter is 200 mm.

The outlet diameter of the common round tube nozzle is 25 mm. In the model of this study, a diffuser cone part is set below the round tube nozzle to form the new diffuser nozzle. The diffuser angle θ, which is the maximum angle between the isolines of the diffuser cone, and the diffuser distance D, which is the distance from the cone tip to the outlet of the common round nozzle, are the two key dimensions to be studied.

The calculation domain was meshed with unstructured grids, using three grid densities with maximum sizes of 5 mm, 3 mm, and 1 mm, corresponding to low, medium, and high grid qualities, with the corresponding number of grids being 24,895, 65,646, and 524,073, respectively.

2.3. Modeling Parameter Settings

In the numerical modeling solver, the bottom outlet of the round tube nozzle is set as the jet pressure inlet in the calculation domain, the top and bottom of the model are set as pressure outlets, the axis is set as a symmetry boundary, the cell plate and the side box body are set as walls, and the inner cone part and the outer cylinder part of the filter cartridge are both set as porous zones.

During the pulsed cleaning process, the pressure of the airflow jetted from the nozzle experiences a process of first increasing and then decreasing. To realize the numerical modeling research in this paper, a high-frequency pressure sensor was installed 10 mm below the nozzle, with the air tank pressure set at 0.5 MPa, pulse duration at 0.15 s, and jet distance at 250 mm. The pressure changes in front of the nozzle were measured and recorded in real time during the pulsed-jet cleaning process using the high-frequency pressure sensor. The pressure change function with time was fitted through the processing and analysis of the measured data, as shown in Equation (1).

$$P_c=\left\{\begin{array}{l}0, \\ 5589.4·t-47.976, \\ -172.77·t+98.55, \\ -4304.4·t+765.77, \\ 0, \end{array}\begin{array}{l}t<0.0086\\ 0.0086\le t<0.0254\\ 0.0254\le t<0.1615\\ 0.1615\le t<0.0178\\ 0.0178\le t\end{array}\right.$$

(1)

In the solver, these pressure change functions are imported in the form of UDF (user defined function) to ensure that the modeling process can reflect the actual airflow pressure changes. The time step is set to 0.0005 s in the calculation.

For the porous zone of the filter cartridge, the viscosity loss coefficient, 1/α, is 2.0 × 10¹¹ m⁻², and the inertial resistance coefficient is 675.53 m⁻¹.

2.4. Model Validation

To evaluate the accuracy of the modeling results, grid independence verification and experimental verification are required.

Comparing the pressure inside the filter cartridge simulated under three grid densities (Figure 2), it can be found that the differences are not significant. Specifically, the pressure values of the observation points in Case I grid are slightly higher, while the pressure values of the observation points in Case II and Case III grids are very close. Therefore, it is considered that the grid under Case II meets the requirement of grid independence.

Comparing the modeling values with the experimental results, the experimental values fluctuate more significantly, but the trend is consistent with the modeling values. The pressure value fluctuations in the experiment are more obvious most probably due to the vibration of the filter cartridge wall surface under the influence of the pulsed airflow, which causes the sensor to vibrate. Overall, the modeling values are close to the experimental values and the trends are consistent, so it can be considered that the modeling results meet the requirements.

2.5. Modeling Scheme Design

(1) The temporal and spatial distribution of the jet airflow velocity and pressure under the conditions of common round nozzle and diffuser nozzle were compared and examined, and the main influence laws of the diffuser nozzle on the flow field qualitatively analyzed.

(2) The influence of the diffuser angle (30°, 40°, 50°, 60°, 70°, 80°) of the diffuser nozzle on the jet flow field was investigated, and the pulsed-jet performance calculated and compared.

To monitor the changes in the pressure on the filter cartridge inner wall surface, five observation points were set at equal distances from top to bottom on the inner surfaces of the inner and outer filtering surfaces of the filter cartridge, respectively, marked as i1–i5 and o1–o5 (see Figure 1).

According to previous studies [15,21], the positive peak pressure on the inner surface of the filter cartridge can represent the cleaning effect of the pulse jet. Therefore, the average value of the positive peak pressures at three observation points P1, P2, and P3 is taken as the pulsed-jet intensity, and the coefficient of variation (C.V.) is used as the pulsed-jet uniformity.

(3) The influence of the diffuser distance (10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm) on the jet performance was investigated.

3. Results and Discussion

3.1. Temporal and Spatial Distribution of Jet Airflow Velocity

Under the conditions of a jet distance of 250 mm, an initial pressure value of the gas bag set at 0.5 MPa, and a pulse duration of 0.15 s, the temporal and spatial distributions of the airflow velocity under the conditions of using the common round tube nozzle and diffuser nozzles are compared, as shown in Figure 3.

It is found that the airflow velocity exceeds 10 m/s after the airflow is jetted from the nozzle. When using different nozzles, the airflow characteristics show obvious differences. The common round nozzle makes the airflow more concentrated, and this concentrated airflow feature makes the airflow loss speed faster, resulting in a significant difference in the velocity between the upper and lower parts of the filter cartridge. Before the airflow collides with the cone top of the filter cartridge, the airflow maintains its concentrated characteristics. After the collision, the airflow flows along the surface of the inner cone, and this flow process extends to the bottom of the filter cartridge at about t = 0.020 s. Due to the energy loss in the airflow during collision and flow, the airflow velocity observed at the bottom of the filter cartridge is significantly reduced, below 2 m/s, and significantly lower than the airflow velocity in the upper part of the filter cartridge. The airflow velocity begins to attenuate after 0.160 s. This is directly related to the end of the pulsed airflow jet.

After using the diffuser nozzle, the airflow is dispersed through the diffuser, thus avoiding direct collision with the cone top of the filter cartridge. This significantly reduces the energy loss of the airflow, making the overall deceleration of the airflow velocity more gentle, and the duration of airflow diffusion is also extended, with the airflow outlet velocity controlled within a lower range of 8–10 m/s. When entering the filter cartridge, the airflow can be uniformly distributed due to the diffusion effect, and the airflow can fill the inside of the filter cartridge in an extremely short time (t = 0.0125 s). As the airflow continues to diffuse, the airflow velocity at the bottom of the filter cartridge stabilizes at about 6 m/s.

By comparing the effects of using the two nozzles, it is found that although the initial airflow velocity of the diffuser nozzle is smaller, its coverage area inside the filter cartridge is wider, and the duration of the airflow is longer. This significantly improves the airflow velocity at the bottom of the filter cartridge, and the overall uniformity of the airflow velocity inside the filter cartridge is also better.

3.2. Temporal and Spatial Distribution of Jet Pressure

The pressure inside the filter cartridge can be mainly divided into dynamic pressure and static pressure. Dynamic pressure is generated by the movement of the airflow, and static pressure is generated by the collision of the airflow with the filter cartridge wall surface. The static pressure on the side wall of the filter cartridge is an important indicator to measure the cleaning performance [10,26]. Therefore, the temporal and spatial distribution of the static pressure under the conditions of using common nozzles and diffuser nozzles is compared, as shown in Figure 4.

Under the condition of using the common nozzle, after the pulsed airflow is triggered from the nozzle, the high-speed airflow strongly entrains the surrounding air, causing the airflow to expand rapidly. Subsequently, this expanding airflow collides with the top of the built-in cone and enters the inside of the filter cartridge. Inside the filter cartridge, the airflow collides with the filter cartridge wall surface, generating a static pressure accumulation. It is observed that at t = 0.040 s, the pressure inside the filter cartridge reaches a peak and lasts until t = 0.160 s. Thereafter, as the pulsed airflow jet stops, the pressure inside the filter cartridge begins to gradually decrease.

Further analysis of the pressure distribution inside the filter cartridge shows that the pressure distribution in the horizontal direction is basically consistent, but in the upper part of the filter cartridge, the pressure on the inner cone side is significantly higher than that on the outer side wall. This is because after the airflow collides with the built-in cone, part of the airflow is directed to the inner cone side, resulting in an increase in pressure in that area. In the vertical direction, the pressure shows a characteristic of being large at the bottom and small at the top. Specifically, the pressure at the bottom of the filter cartridge exceeds 1000 Pa, while the pressure at the top of the filter cartridge is below 300 Pa, and there is even a negative pressure area. This is mainly because the airflow accumulates static pressure from the bottom to the top inside the filter cartridge. The pulsed airflow collides significantly with the filter cartridge at the bottom, and the kinetic energy is converted into static pressure energy. In the upper part, it mainly relies on the rebound airflow to accumulate static pressure from the bottom to the top. However, the rebound airflow is often insufficient, resulting in low static pressure in the upper part of the filter cartridge and poor cleaning effect [27]. In the long-term operation, this uneven pressure distribution may lead to the gradual loss of cleaning efficiency in the upper part of the filter cartridge, while the bottom is prone to damage due to excessive jet pressure.

After switching to the diffuser nozzle, it can be seen from Figure 4b that the diffusion area of the airflow is significantly increased, thereby increasing the contact range with the surrounding air, and thus increasing the entrainment of the airflow. At t = 0.040 s, the pressure inside the filter cartridge reaches a maximum value and lasts until t = 0.160 s, which is consistent with the pressure accumulation process when using the common nozzle. However, it is worth noting that after using the diffuser nozzle, the pressure inside the filter cartridge is greater than 300 Pa, which significantly increases the cleaning pressure in the upper part of the filter cartridge and effectively reduces the originally existing insufficient cleaning area.

3.3. Influence of Diffuser Angle on Jet Performance

The diffuser nozzle mainly improves the airflow diffusion angle through the diffuser to reduce the collision of the airflow with the cone of the filter cartridge, and to increase the jet pressure on the upper part of the filter cartridge and the uniformity of the pressure on the side wall of the filter cartridge. To improve the pulsed-jet performance on the filter cartridge, the structure of the diffuser is optimized by changing the diffuser angle, θ, of the diffuser cone. As shown in Figure 5, the airflow distribution is compared when the airflow inside the filter cartridge reaches a stable state under the influence of different diffuser angles.

When θ is small, the jet airflow enters the filter cartridge at a high speed and forms a large negative pressure near the top of the inner cone of the filter cartridge. As θ increases, the degree of airflow diffusion also gradually increases, which increases the amount of entrained air. When the airflow enters the filter cartridge, the airflow velocity near the top of the inner cone decreases. When θ reaches above 60°, the upper part of the inner cone of the filter cartridge has basically achieved positive pressure, which can realize effective cleaning.

To further quantify the pressure distribution on the filter cartridge wall surface, the evolution of pressures at the observation points on the inner wall of the filter cartridge is compared, as shown in Figure 6.

It can be seen that the pressure on the wall surfaces of inner cone and outer cylinder parts show different characteristics. On the inner cone part, the jet pressure rises rapidly to the highest value after the jet begins, and then gradually decreases after maintaining the peak pressure for a period of time. This indicates that when the inner cone part is impacted by the pulsed airflow, the pressure accumulates rapidly and reaches a peak, and then gradually decreases as the airflow gradually weakens.

The jet pressure at the outer cylinder part shows a fluctuating trend. After the jet begins, the pressure of the outer layer filtering surface also rises rapidly, but then there is a brief drop stage. This may be caused by part of the diffused airflow colliding with the filter cartridge side wall, and the main airflow collides with the filter cartridge bottom and then rebounds to the side wall, resulting in a brief drop in pressure. As the airflow continues to act, the pressure at the outer cylinder part rises again to the peak, and then gradually decreases to the initial pressure after staying unchanged for a period of time.

Under the condition of using the common nozzle, the positive pressure duration inside the filter cartridge is about 0.160 s (from t = 0.010 s to t = 0.170 s). After switching to the diffuser nozzle, the positive pressure time is extended to 0.215 s (from t = 0.010 s to t = 0.225 s), which is increased by 0.055 s compared with the former.

For different pressure observation points, the pressure on the inner cone part is in the order i2 > i3 > i5 > i4 > i1, and this pressure distribution can be attributed to the collision effect of the airflow entering the filter cartridge with the top of the inner cone. When the airflow collides with the top of the inner cone, part of the jet airflow directly passes through the filtering medium, and the other part of the airflow passes along the inner cone to the bottom. After the airflow collides with the filter cartridge bottom plate, static pressure is generated, and then, the airflow rebounds. The interaction between this rebound airflow and the continuing incoming airflow leads to a pressure difference at different positions of the inner cone filtering surface. The jet pressure on the outer cylinder part is in the order o5 > o4 > o3 > o2 > o1, and in the case of using the common nozzle, the pressure values at o5, o4, and o3 are relatively similar, while the pressure value at o1 is relatively small. After switching to the diffuser nozzle, the pressure values at o5 and o4 are relatively close. This pressure distribution on the outer cylinder part’s surface is mainly due to the fact that after the airflow collides and rebounds inside the filter cartridge, the pressure is gradually accumulated from the bottom to the top, which is consistent with the results of Liu, Chen and others [22,28].

To further investigate the evolution of the pressure on the filter cartridge wall surface, the peak pressure changes at each observation point are compared, as shown in Figure 7.

When using the diffuser nozzle, the peak pressure on the inner cone part surface of the filter cartridge gradually increases with the increase in θ, while the pressure at other observation points shows a gradually decreasing trend. On the upper part of the outer cylinder part, the pressure changes at o1 and o2 observation points show a trend of first increasing and then decreasing. When θ increases to 70°, the pressure at these two observation points reaches the maximum value. Among them, the maximum pressure at o1 observation point is 826 Pa, which is 1.39 times higher than that under the condition of using the common nozzle; the maximum pressure at o2 observation point is 1068 Pa, which is 1.07 times higher. However, as θ continues to increase, the pressure values at other observation points on the outer layer filtering surface gradually decrease. In addition, the peak pressure on the inner cone part surface is generally higher than that on the outer cylinder part. This is because the inner cone part directly faces the nozzle, and the jet airflow can be directly collided, thus generating higher pressure. When using the diffuser nozzle with θ = 30–50°, the highest pressure value on the inner cone part is significantly increased, from 3525 Pa under the condition of using the common nozzle to 4670 Pa, an increase of 32.48%.

The performance of the pulsed jet is generally represented by pulsed-jet intensity and pulsed-jet uniformity, and the average value of the positive pressure peaks at each observation point is often used as an indicator of pulsed-jet intensity, while the coefficient of variation of the peaks is often used as an indicator of pulsed-jet uniformity [9,29,30]. Therefore, the pulsed-jet intensity and uniformity on the side wall of the filter cartridge are further obtained, as shown in Figure 8.

It can be seen that the pulsed-jet intensity shows a gradually decreasing trend with the increase in θ. In the range of θ = 30–70°, the pulsed-jet intensity corresponding to the diffuser nozzle is higher than that under the condition of the ordinary nozzle. When θ = 30°, the pulsed-jet intensity is 1234 Pa, which is 19.8% higher than that of the common nozzle. When θ = 80°, the pulsed-jet intensity reaches the minimum value, but even so, the pulsed-jet pressure still reaches 992 Pa, only 38 Pa lower than that of the common nozzle. This shows that even at the minimum pulsed-jet intensity, the performance of the diffuser nozzle is still close to that of the common nozzle, showing its good performance.

Compared with using the common round nozzle, the pulsed-jet uniformity is significantly improved after using the diffuser nozzle. This is mainly because under the condition of the common nozzle, the cleaning pressure in the upper part of the filter cartridge is obviously insufficient, especially the pressure at o1 observation point is only 593 Pa, while the jet pressure at the bottom of the filter cartridge is abnormally high, and that at the o5 observation point reaches 1621 Pa. This uneven pressure distribution between the upper and lower parts leads to a high coefficient of variation, affecting the uniformity of the cleaning effect. In the range of θ = 30–70° for the diffuser nozzle, the coefficient of variation shows a decreasing trend, indicating that the diffuser nozzle in this angle range can better achieve uniform airflow distribution. When θ = 70°, the coefficient of variation reaches the lowest value, which is only 0.12.

3.4. Influence of Diffuser Distance on Jet Performance

To further optimize the pulsed-jet performance of the diffuser nozzle on the filter cartridge, the structure of the diffuser is further optimized by changing the diffuser distance (D). As shown in Figure 9, the airflow distributions when the airflow inside the filter cartridge reaches a stable state under the influence of different diffuser distances (D = 10–70 mm, with an interval of 10 mm) are compared.

It can be concluded that when D is small, the diffused airflow will quickly converge. As D increases, the concentrated jet airflow gradually moves down, and the diffuser at an appropriate distance can effectively guide the jet airflow to collide with the top of the cone filter cartridge to convert the maximum static pressure energy. As the D value continues to increase, the degree of airflow diffusion also increases accordingly, and the position where the airflow collides with the inner cone of the filter cartridge gradually shifts downward. When D = 70 mm, the airflow diffusion is obvious and does not collide with the top of the inner cone of the filter cartridge, reducing the airflow loss. The pressure distribution inside the filter cartridge also shows that the pressure difference in the horizontal direction of the filter cartridge is very small; and the pressure at the bottom of the filter cartridge is large, and the pressure at the top is small in the vertical direction.

To further investigate the evolution of the pressure on the filter cartridge wall surface, the peak pressure changes at each observation point are compared, as shown in Figure 10.

It can be seen that the total peak jet pressure fluctuates slightly with D, showing a relatively stable trend. The peak pressure on the side wall of the filter cartridge shows a trend of first increasing and then decreasing with the increase in D. The upper observation points (o1, o2) obtained the maximum value under the condition of D = 40 mm: the peak pressure at o1 observation point is 826 Pa, which is 1.39 times higher than that under the condition of using the common nozzle; the peak pressure at o2 observation point is 1067 Pa, which is 1.07 times that of the common nozzle. This result indicates that under the condition of D = 40 mm, the diffuser nozzle can more effectively guide the airflow to the upper part of the filter cartridge, thereby improving the jet effect in the upper area.

For different pressure observation points, the pressure on the surface of the inner cone part shows the order i2 > i3 > i5 > i4 > i1, and that on the outer cylinder surface shows o5 > o4 > o3 > o2 > o1, which is consistent with the overall distribution law under different θ conditions, indicating that the influence of D on the filter cartridge pressure is small.

The pulsed-jet intensity and uniformity on the side wall of the filter cartridge are further obtained, as shown in Figure 11.

Using the diffuser nozzle, the pulsed-jet intensity shows a trend of first decreasing, then increasing, and then decreasing again with the increase in D. This phenomenon can be attributed to the accumulation and diffusion characteristics of the airflow under different D values. Specifically, when the D value is small, the airflow collides with the diffuser before entraining surrounding air sufficiently, and a small D causes large flow resistance. As the D value gradually increases, the airflow has more space for entrainment and then dispersion by the diffuser, and the pulsed-jet intensity is therefore improved. However, when the D value is too large, the airflow diffuses too close to the filter cartridge, causing too much airflow to disperse, failing to effectively enter the inside of the filter cartridge, thereby causing the pulsed-jet intensity to decrease.

Under the condition of D = 40–60 mm, the airflow diffusion is moderate and can fully enter the inside of the filter cartridge, so the pulsed-jet intensity is higher than that under the condition of using the common nozzle. Under other D values, due to reasons of airflow dissipation or overflow, the pulsed-jet intensity is lower than that of the common nozzle. At D = 40 mm, the pulsed-jet intensity reaches the maximum value of 1086 Pa, which is 5.4% higher than that under the condition of using the common nozzle (1030 Pa). It is particularly worth noting that the pulsed-jet intensity in the upper part (which is prone to cleaning “blind spots”) of the filter cartridge reaches the maximum value of 826 Pa, which is 1.39 times that of the common nozzle.

After comparison among cases with different Ds, it is found that the coefficient of variation fluctuates slightly overall, and the pulsed-jet uniformity is better than that of the common nozzle, reaching the lowest value of 0.14 at D = 40 mm, which is 60.0% higher than that under the condition of using the common nozzle.

Considering the pulsed-jet intensity and uniformity comprehensively, the diffuser nozzle with D = 40 mm can obtain the best pulsed-jet intensity and the best uniformity.

3.5. Mechanism Analysis

Figure 12 summarizes the mechanism of improving the pulse-jet performance of the cone filter cartridge by the diffuser nozzle.

When using the common nozzle, the jet airflow forms a significant vortex of airflow in the upper part of the filter cartridge, forming a large negative pressure area and a cleaning “blind spot”.

When using the diffuser nozzle with appropriate parameters, the dispersion effect of the diffuser increases the contact range of the jet airflow with the surrounding air, thereby increasing the entrainment of the airflow. At the same time, after moderate dispersion, the airflow velocity in the opening area of the filter cartridge is reduced and the static pressure is enhanced, thus improving the jet performance in the upper area of the filter cartridge. A small diffuser angle, θ, will lead to a poor entrainment effect, while a large one will cause the pulse airflow to escape. A large diffuser distance, D, will cause the airflow to diffuse excessively, while a small one will cause large flow resistance and the diffused airflow to converge quickly.

4. Conclusions

This paper takes the cone filter cartridge as the research object and proposes and designs a diffuser nozzle to improve the pulse-jet cleaning performance. The numerical modeling is used to investigate the variation laws of the jet airflow velocity and pressure inside the cone filter cartridge; the structure of the diffuser nozzle is optimized with respect to the diffuser angle (θ) and diffuser distance (D), and the improvement of the jet performance is investigated. The following conclusions are drawn:

(1) Compared with the common round tube nozzle, a diffuser nozzle with appropriate parameters is conducive to enhancing the divergence and entrainment of the jet airflow, reducing the airflow velocity in the opening area of the filter cartridge and increasing the static pressure, while also increasing the airflow entrainment. At the recommended nozzle parameters of θ = 70° and D = 40 mm, the pulsed-jet intensity is 1086 Pa, which is 5.4% higher than that under the condition of the common nozzle; the uniformity is 0.14, which is 60.0% higher than that under the condition of the common nozzle. The pulsed-jet intensity in the upper part is 1.39 times that with the common nozzle.

(2) As the most prone to cleaning “blind spots”, the pulsed-jet intensity on the upper part of the outer layer filtering surface of the filter cartridge first increases and then decreases with the increase in the diffuser angle θ, reaching the maximum value at θ = 70°. An excessive θ will cause the airflow to diffuse too much and reduce the jet energy. Due to the dispersion and blocking effect of the inner cone of the diffuser nozzle on the airflow, the overall pulsed-jet intensity inside the filter cartridge decreases with the increase in the diffuser angle θ, but the pulsed-jet uniformity increases.

(3) Compared with the diffuser angle θ, the cone distance D has a smaller impact on the jet performance. The pulsed-jet intensity shows a trend of first increasing and then decreasing with the increase in the cone distance D. A small distance will cause the diffused airflow to converge quickly, while a large distance will cause the airflow to diffuse too much. At D = 40 mm, the cone effectively guides the jet airflow to collide with the cone top of the filter cartridge, achieving the maximum pulsed-jet intensity.

This paper improves the internal jet airflow of the cone filter cartridge by optimizing the diffuser nozzle, enhancing the uniformity of the jet and particularly increasing the jet intensity in the upper open area of the filter cartridge. The research conclusions are conducive to promoting the efficient and stable operation of the cone filter cartridge dust collector. Further investigations will be conducted on the actual dust cake removal effect of the diffuser nozzle under the condition of dust cake load on the filter cartridge surface, as well as on the dust removal efficiency, operating resistance of the dust collector, and energy consumption of the pulse jet.