Optimizing the Efficiency of a Wet Scrubber with Airfoil-Shaped Louvered Vents: A CFD-Based Performance Analysis ^†

Abstract

Air pollution threatens human health and ecosystems, underscoring the need for effective pollutant control technologies. This study aims to optimize the performance of a wet scrubber for air pollution control in removing contaminants from exhaust gases. We analyzed the airflow dynamics within a wet scrubber equipped with louvered vents shaped with the NACA 0012 and NACA 4412 airfoil series at four different angles. By analyzing the impact of the geometric configurations on the pollutant removal efficiency, the most effective vent design for enhancing the scrubber’s performance was identified. The components were modeled in Onshape CAD software, and prototypes were fabricated using 3D printing. Computational fluid dynamics (CFD) simulations were conducted using COMSOL Multiphysics 5.6 to analyze and optimize the aerodynamic behavior and the pressure distribution across the various vent configurations. The results offer information on how to improve scrubbers’ efficiency by optimizing the vent angles and how to develop effective air pollution control solutions.

1. Introduction

The concentration of pollutants emitted from industrial production is generally toxic and hazardous and poses a serious health risk in terms of respiratory ailments (asthma, bronchitis, tuberculosis, etc.) in humans and photosynthesis in plants [1]. Therefore, air pollution control technologies have been significantly advanced. Wet scrubbers are used as one of the solutions for removing pollutants from industrial emissions. Scrubbers are the oldest industrial dust collectors, having been used for at least 120 years [2]. Scrubbers involve liquids, typically water, being used to capture and eliminate particulate matter and gases. Over time, wet scrubber technology has become efficient and adaptable for various applications. One of the advantages of wet scrubbers over other air pollution control devices is their ability to absorb gaseous pollutants while safely handling flammable and explosive dust particles [3]. A range of dust control techniques is commonly used in coal mines. Wet scrubbers are also used to remove dust from the air, rather than merely diluting or containing it [4]. Wet scrubbers are a promising and interesting alternative for nanoparticle collection [5].

A wet scrubber has been used to filter smoke generated in a painting workshop and capture the airborne dust particles and pollutants using liquid solvents before discharging the cleaned air into the environment. The wet scrubber prevents clogging of the pollutants and the release of harmful emissions into the atmosphere [6]. However, a considerable amount of water droplets are discharged from the wet scrubber, which reduces its effectiveness. Therefore, this wet scrubber must be improved. In this study, we introduced airfoil-shaped louver vents at the outlet to reduce the water droplet discharge and enhance the system’s efficiency. A new design for the wet scrubber was created using Onshape software through multiple iterations and corrections to optimize its structure. Additionally, the flow field analysis was conducted to evaluate the performance of the wet scrubber using COMSOL Multiphysics 5.6. The results provide the basis for understanding the wet scrubber’s behavior and effectiveness.

2. Methodology

2.1. The Operation Scheme

The wet scrubber was designed for effective air pollution control. As the wet scrubber effectively removes pollutants from exhaust gases [7], the integration of advanced features such as louvered vents ensures that the airflow is directed appropriately, thereby enhancing the system’s overall efficiency [8]. We improved the designs of the airfoil-shaped louvered vent and the water tank by analyzing a feasible airflow with an average and constant velocity through each outlet to soak the filter area. The experiment was performed using four different louver angles: −10, −22.5, −30, and −45°. The angles were selected based on results from the research on the optimal angle for louver vents, which are 10–45° [9,10]. At these angles, the airflow distribution and the velocity consistency across the filter area were evaluated. By adjusting the louver angles, we determined the optimal configuration that ensured efficient airflow and water flow through the system, maximizing the performance of the wet scrubber.

As shown in Figure 1, polluted air enters the wet scrubber from the inlet on the left side, where it undergoes a scrubbing process. In this process, water interacts with the incoming air stream, capturing contaminants such as particulate matter, dust, and harmful gases. At the outlet, an array of airfoil-shaped louver vents guides the airflow efficiently while reducing turbulence. The aerodynamic design of these airfoils allows the airflow stream to smoothly pass and residual pollutants to be separated efficiently. Airfoil louvers lower the pressure more than flat louvers can due to their streamlined geometry [11]. Clean air exits the outlet of the system through the airfoil-shaped louver vents on the right side, while the captured contaminants are retained within the scrubber for subsequent treatment or disposal. This integration of the wet scrubber with airfoil-shaped louvers enhances the system’s performance by improving the airflow dynamics and pollutant removal efficiency.

2.2. Device Specification

Several components of the wet scrubber were modified in this study. The box and fan were retained, but the water pump was removed. The airfoil-shaped louver vents were integrated to enhance control over the airflow [6]. Instead of using a water pump, the box and fan were modified by analyzing the airflow distribution and the performance of the airfoil-shaped louver vents at various angles.

2.3. Airfoils

The airfoils were designed by referring to the NACA 4-digit airfoil series, specifically NACA 0012 and NACA 4412. These airfoils are widely recognized for their aerodynamic characteristics and are used to optimize the airflow control within systems (Figure 2).

The NACA 0012 and NACA 4412 louver vent components were adopted in the wet scrubber system. The NACA 0012 airfoil has a symmetrical profile without a camber, with a maximum chord thickness of 12% and a chord length of 5 cm. This geometry enables a symmetrical pressure distribution between the upper and lower surfaces at 0° for aerodynamic stability. The NACA 4412 is an asymmetrical airfoil with a camber of 4% of the chord’s length. The airfoil is located at 40% of the chord’s length. This airfoil has the same maximum thickness, which is 12% of the chord, but because of its positive camber, the NACA 4412 is lifted at 0°. The airflow efficiency in the louver vent system is increased, especially in low-speed conditions [12]. In this wet scrubber design, the airflow velocity at the inlet is 3.5 m/s, and the airfoils manage the airflow distribution efficiently. The NACA 0012 and NACA 4412 airfoils enhance control over the airflow, reduce drag, and improve the overall efficiency of the wet scrubber’s filtration process.

2.4. The Design Process

Digital technology advancements, including advancements in software and hardware capabilities, are applied to design modeling, design analysis, design review, and design documentation [13,14,15]. Computer-aided design (CAD) drawings were used to design the vents and the water tank. Onshape, a cloud-based CAD software, was used, as it is known for its robust design and collaboration capabilities. Using Onshape, the airfoil-shaped louver vents and water tank components were modeled precisely (

Table 1. System dimensions.

Water Tank Measurement
Water tank length	500 mm
Water tank width	400 mm
Water tank height	430 mm
Distance between airfoils	25 mm
Airfoil chord length	50 mm
Distance between the airfoil leading edge and outlet	70 mm

). Onshape’s collaborative features enable the seamless coordination of design and engineering for prototyping and modification processes.

Figure 3 illustrates the dimensions of the water tank and the airfoil components used in the wet scrubber system. In part (a), the water tank has dimensions of 500 mm in width, 430 mm in height, and a water level of 385 mm, with a 25 mm clearance at the base. The airfoil-shaped louver vent is positioned with a spacing of 70 mm between the vent array and the side of the tank. Part (b) depicts the length of an individual airfoil in the vent, with a chord length of 50 mm.

2.5. Computational Fluid Dynamics (CFD) Analysis

A CFD model is an important means of simulating a product [16]. CFD is widely used to calculate parameters such as the lift, drag, pressure, and velocity in aerodynamics and hydrodynamics. In this study, CFD was employed to analyze and refine the design of the wet scrubber. COMSOL Multiphysics 5.6 was used for the simulation to analyze the airflow and air dynamics. The design of the airfoil-shaped louver vents was also simulated. For the computational analysis, a laminar flow was assumed in evaluating the airflow passing through the vent. An air velocity of 3.5 m/s was determined from prior tests using a specialized fan and was set as the inlet condition for the CFD simulation. The velocity was used to assess the performance and efficiency of the vent in managing the airflow distribution.

The velocity distribution of the water tank was analyzed by generating velocity streamlines. The movement of the airflow was simulated to assess its uniform flow pattern. Each design was imported into COMSOL Multiphysics 5.6 software, with air selected as the fluid medium.

In the laminar flow model, a stationary solver was used to analyze the velocity and pressure distribution within the water tank. In the simulation, the inlet and outlet boundaries were defined, and the inlet velocity was set to 3.5 m/s. The outlet boundary condition was set to zero pressure to accurately study the airflow dynamics through the system (Figure 4).

3. Results and Discussion

All of the designed components were 3D-printed. The performance of the wet scrubber was evaluated in CFD simulations. The configuration with the highest efficiency was determined. The airflow patterns, pressure distributions, and overall system performance were optimized to enhance the pollutant removal and energy efficiency.

3.1. Velocity Distribution

The CFD simulation process was carried out using COMSOL 5. A velocity distribution simulation was performed to optimize the design and analyze the airflow patterns and performance. The velocity distribution data were used to determine the most efficient configuration of the airfoil-shaped louver vents and improve the airflow control and overall effectiveness of the system.

3.1.1. The NACA 0012

The results of the CFD analysis for the NACA 0012 is as follows. The velocity distribution in the wet scrubber with airfoil-shaped louvered vents using the NACA 0012 airfoil at varying angles showed significant variations in the airflow patterns (Figure 5). For louver angles of −10, −22.5, −30, and −45°, the maximum velocities were 4.68979, 5.86955, 6.62578, and 10.1286 m/s, respectively. At −10°, the best performance was observed in terms of the velocity distribution and a smooth airflow through the scrubber, with minimal flow separation and resistance. At −22.5°, obstruction of the flow was observed, and the efficiency was reduced. At −30° and −45°, significant reductions in the velocity and airflow efficiency were observed, making them less appropriate for practical applications due to the high resistance created at these angles.

Figure 6 shows that the maximum velocity increases with the angle of the airfoil. A linear relationship between the maximum velocity and the angle was also found. This is critical for optimizing the design and performance of the wet scrubber, as adjusting the angle of the louver vents significantly enhanced the airflow velocity. An increased airflow velocity improves the system’s ability to effectively transport air through the filter media, thus enhancing the pollutant removal and the overall operational efficiency.

3.1.2. The NACA 4412

The velocity distribution of the wet scrubber equipped with the NACA 4412 airfoil-shaped louvered vents at angles of −10, −22.5, −30, and −45° and an inlet velocity of 3.5 m/s revealed significant variations in the airflow patterns. The maximum velocities achieved at these respective angles were 5.32124, 6.25755, 6.63451, and 10.3343 m/s. At −10°, the NACA 4412 airfoil had the best velocity distribution, maintaining an efficient airflow through the scrubber with minimal flow separation and resistance. At −22.5°, a reasonable performance was ensured, but obstruction of the flow and a larger low-velocity region were created. At −30° and −45°, the airflow became significantly obstructed, resulting in substantial reductions in the velocity and overall efficiency, making these angles less appropriate for practical applications (Figure 7).

The positive linear relationship between the maximum velocity and the angle in Figure 8 indicates that as the angle of the airfoil-shaped louver vent increased, the maximum velocity within the wet scrubber increased. This correlation is critical for optimizing the scrubber’s design and operational performance. By adjusting the louver angle, the airflow velocity increased, thereby improving the scrubber’s efficiency in capturing and removing pollutants. The NACA 4412 airfoil-shaped louvers in the wet scrubber system enhanced the airflow as the angle of attack (AoA) increased, thereby improving the system’s ability to accelerate the flow through the vent. The positive correlation between the AoA and airflow velocity is crucial for optimizing the design and operational efficiency of the wet scrubber for more effective pollutant removal.

3.2. Pressure Distribution

A pressure distribution analysis is essential for evaluating the performance of the wet scrubber system, as it provides information on the factors that influence its operational efficiency. A pressure drop is an indicator of airflow resistance, a higher pressure drop reduces flow efficiency and may compromise filtration performance. By analyzing the pressure variations, regions of flow separation and turbulence are determined, which disrupt the uniformity of the airflow and diminish the scrubber’s effectiveness in pollutant removal.

3.2.1. The NACA 0012

The wet scrubber equipped with a NACA 0012 airfoil-shaped louver vent showed notable variations in its performance (Figure 9). At a −10° AOA, the pressure gradient became smooth, with minimal flow separation and lower pressure differences across the vent, indicating less obstruction to the airflow, resulting in a smaller pressure drop and a higher flow efficiency. At −22.5°, the pressure difference became pronounced, suggesting the onset of flow separation and increased turbulence, though there was a balance between airflow control and the pressure loss. This angle is an alternative angle for efficiency. At −30°, the pressure gradient increased significantly, with greater flow separation and higher pressure at the leading edge of the louver, causing a substantial decrease in pressure due to the increased resistance and turbulence, which reduced the scrubber’s overall performance. At −45°, the pressure difference reached its peak, with substantial flow separation and turbulence, leading to the largest decrease in pressure and maximum obstruction to the airflow.

At a −10° AOA, the louver vent showed the best performance by minimizing the pressure loss and maintaining a smooth airflow. An angle of −22.5° can be adopted for balancing the airflow control with a pressure drop, but angles steeper than −30° introduce excessive pressure loss and reduce the efficiency of the wet scrubber.

3.2.2. The NACA 4412

The pressure distribution in a wet scrubber using a NACA 4412 asymmetrical airfoil-shaped louver vent is presented in Figure 10. At a −10° AOA, the pressure distribution showed a noticeable pressure difference, with lower pressure on the upper surface of the airfoil due to the higher airflow velocity typical of asymmetrical designs. At 10°, effective airflow control with a relatively low pressure drop was ensured for efficient operation with minimal energy loss. At −22.5°, the pressure gradient increased, with a more pronounced pressure differential across the airfoil. While there was flow separation, the louver managed the airflow efficiently, balancing between a pressure drop and flow control. This angle is appropriate for applications that require aggressive flow management while keeping the pressure losses within acceptable limits.

At −30°, the pressure difference became significantly larger, with more evident flow separation and turbulence. The increased resistance at the leading edge of the louver decreased the pressure considerably, reducing the scrubber’s overall efficiency by obstructing the airflow and increasing its energy consumption. At −45°, the pressure difference was the highest, with substantial flow separation and turbulence, leading to the highest decrease in pressure at all angles. This resulted in considerable airflow resistance and significant inefficiency in the scrubber’s operation due to the associated energy losses.

At a −10° AOA, the NACA 4412 airfoil showed the best performance by minimizing the pressure loss and maintaining efficient airflow control. An angle of −22.5° could be an alternative for balancing the pressure drop and improved flow control. However, at −30° and −45°, substantial pressure losses and decreases in the scrubber’s efficiency were observed, which indicated that these angles are not appropriate for practical applications.

4. Conclusions

The pressure and velocity distributions of NACA 0012 and NACA 4412 airfoil-shaped louver vents were analyzed at various AOAs. The NACA 4412 airfoil at −10° showed the best performance for the wet scrubber. A uniform and efficient airflow was ensured with a smooth velocity distribution and minimal flow separation. The pressure distribution of the NACA 4412 at −10° was well suited to wet scrubber systems, as its smoother and more uniform pressure gradient minimized the energy losses, reduced the turbulence, and maintained a steady airflow through the louvers, ultimately improving the system’s efficiency. The NACA 0012 airfoil also demonstrated an efficient airflow, especially at −10°, but a negative pressure outlet was preferred for the better efficiency of the system, a consistent airflow, lower energy consumption, and better contaminant removal. The positive pressure at the outlet of the NACA 0012 inhibited the process, making negative pressure a more effective option in the outlet area. Using the NACA 4412 airfoil at −10° is the best choice for optimizing the wet scrubber’s performance, as it delivers superior airflow management with minimal energy losses, ensuring the system’s operational efficiency.

For future studies, it is recommended to optimize the wet scrubber system by integrating a water curtain and analyzing its interaction with the airflow and droplet dynamics. The water curtain, acting as a continuous sheet of water, could enhance the system’s ability to trap fine particulate matter and gaseous pollutants. CFD simulations need to be used to model the droplet size, distribution, and velocity, as they affect the pollutant removal efficiency. The optimal thickness and flow rate of the water curtain must be optimized to balance effective scrubbing with minimal airflow resistance. This could lead to a more efficient and versatile wet scrubber design for capturing pollutants effectively while minimizing the energy and water consumption.