Spray Pressure Research Articles

Enhancing skimmed milk powder functionalities through multicriteria optimization of outlet drying air temperature and spraying air pressure

This study investigated the effects of spraying air pressure and outlet air temperature on the physicochemical and functional properties of skimmed milk powder. Experimental design methodology showed that higher outlet air temperatures improved dry matter content, gelation ability, and flowability, but strengthened colour, moisture sensitivity, and favoured protein denaturation. Spraying air pressure primarily influenced particle size, affecting powder rheological properties and colour. This study highlights the importance of controlling drying parameters to optimize powder properties. The use of a genetic evolutionary algorithm in the optimization process allowed the simultaneous improvement of several functionalities of skimmed milk powder. The findings of this study can contribute to the development of enhanced powders with tailored properties for specific industrial applications.

Relation between bubble behaviors in spray sheet and bubbly flow inside an air-induction fan nozzle: A visualization study

The present study aims to elucidate the relationship between bubble behaviors in the spray sheet and internal bubbly flow of the air-induction nozzle. An experimental work was performed using the visualization technique. Effects of the air inlet position and spray pressure were investigated. The results show that compared with the bubbles inside the air-induction nozzle, bubbles in the spray sheet have smaller volume but larger average diameter. Disturbance propagates in the horizontal air-inlet segment. When the air inlet position shifts toward the nozzle outlet, overall bubble volume inside the nozzle decreases by about 56%, while in the spray sheet, the bubble volume decreases by about 77%. Bubble breakup causes a decrease in overall bubble volume as bubbles travel from the inner flow passage of the nozzle to the environment. The coalescence and compression of bubbles induce the increase in average bubble diameter. When the spray pressure increases from 0.1 to 0.3 MPa, both the total bubble volume and average bubble diameter increase.

Multi-scale flow atomization characteristics of Jatropha biodiesel swirl liquid film breakup

The characteristics of the spray and droplets produced by liquid film breakup are crucial for understanding the atomization process in industrial furnace atomizers. This study employed high-speed camera technology to capture images of Jatropha biodiesel (JB) spray at various pressures and Ohnesorge numbers (Oh). Image processing methods were employed to analyze the evolution morphology and proper orthogonal decomposition (POD) of fuel swirl spray, revealing the instability, breakup length, spray cone angle, fractal characteristics of the liquid film breakup zone, and droplet distribution characteristics. The results indicated that the JB jet evolution progressed through stages: cylindrical jet, torsion liquid film, open swirl, complete swirl, and fully developed mode. The evolution and disintegration of the liquid film exhibited a complex structure with ligaments, perforations, and droplet separation. Flow disturbances induced the Klystron effect, characterizing microscopic droplet motion. As spray pressure increased, the growth rate of the disturbance wave increased, the breakup length decreased, the atomization cone angle enlarged, and the fractal dimension (FD) of the liquid film breakup zone increased. The droplet size distribution followed a log-normal distribution, with a substantial increase in the number of small droplets as injection pressure increased. This study provides valuable insights into the multi-scale flow atomization of biodiesel in industrial furnace, and is of great significance for the design, operation, and optimization of spraying systems in various industrial applications.

Optimizing Surface Characteristics of Stainless Steel (SUS) for Enhanced Adhesion in Heterojunction Bilayer SUS/Polyamide 66 Composites.

The increasing environmental concerns and stringent regulations targeting emissions and energy efficiency necessitate innovative material solutions that not only comply with these standards but also enhance performance and sustainability. This study investigates the potential of heterojunction bilayer composites comprising stainless steel (SUS) and polyamide 66 (PA66), aiming to improve fuel efficiency and reduce harmful emissions by achieving lightweight materials. Joining a polymer to SUS is challenging due to the differing physical and chemical properties of each material. To address this, various surface treatment techniques such as blasting, plasma, annealing, and etching were systematically studied to determine their effects on the microstructural, chemical, and mechanical properties of the SUS surface, thereby identifying mechanisms that improve adhesion. Chemical etching using HNO3/HCl and CuSO4/HCl increased surface roughness and mechanical properties, but these properties decreased after annealing. In contrast, K3Fe(CN)6/NaOH treatment increased the lap shear strength after annealing. Blasting increased surface roughness and toughness with increasing spray pressure and further enhanced these properties after annealing. Contact angle measurements indicated that the hydrophilicity of the SUS surface improved with surface treatment and further improved due to microstructure formation after annealing. This study demonstrates that customized surface treatments can significantly enhance the interfacial adhesion and mechanical properties of SUS/polymer heterojunction bilayer composites, and further research is recommended to explore the long-term stability and durability of these treatments under various environmental conditions.

Optimization of glass spray tempering parameters based on response surface methodology and economic analysis

Glass curtain walls have gained significant popularity as building enclosure structures, owing to their exceptional performance. Consequently, it becomes imperative to reduce energy consumption during the glass tempering process to ensure sustainable development within the construction industry. In this study, an experimental design was conducted using the response surface methodology (RSM). The particle count and cooling energy consumption were selected as the response value, while the influencing factors included four process parameters, namely, the spray distance (H), mist load fraction (f), spray pressure (p), and final cooling temperature (Tz). The second order model fitting of the RSM was used to obtain the polynomial regression equation between each response and each factor. Under the optimized conditions of H = 200 mm, f = 1.03, p = 0.5 MPa, and Tz = 150 °C, the number of fractured glass particles was found to be 234, and the cooling energy consumption was 0.00048 kW·h. Further analysis indicated that under these spray conditions, the net present value was 523.90 k$, and the dynamic payback period was 1.1 years. Compared to traditional air-cooled tempering, spray tempering demonstrated superior economic performance.

Fine-grained method for determining size and velocity distribution patterns of flat-fan nozzle-atomised droplets based on phase doppler interferometer

Pesticides are commonly applied by using agricultural nozzles to generate droplets during delivery process. Initial spray atomization characteristics including droplet size and velocity are important factors that affect the pesticide utilization rate. Exploring efficient methods for atomization measurement is helpful to deeply understanding nozzle sprays. In this study, droplet size and velocity of a flat-fan nozzle were measured with phase doppler interferometry (PDI), and sub-area statistics method was adopted to establish a fitting model for atomization characteristics analyse. The results demonstrated that the distribution patterns and value contrasts of droplet size and velocity in different sub-areas visually reflect the nozzle atomization characteristics under varying spray pressures. The quantized model of droplet size and velocity within spatial sub-areas of spray atomization revealed significant differences in droplet size and velocity at various positions within the atomization area. Near the edge of the initial atomization zone, droplet size increases while velocity exhibits a decreasing trend. Additionally, the coefficient of determination for the x-axis position within the atomization zone, in relation to droplet size and velocity, was above 90%. The PDI with the sub-area statistical method employed in this study offers a fine-grained approach for investigating nozzle atomization characteristics.

An algae-based polymer material as a pesticide adjuvant for mitigating off-target drift

Off-target pesticide drift from cropland is a major source of pesticide exposure to pollinating insects inhabiting crop and wildlands in the lower Mississippi Delta (LMD) in the USA. This study is aimed to develop a drift-reducing pesticide adjuvant that is less/nontoxic to honeybees. Ongoing toxicology experiments with two widely-used insecticides and sodium alginate (SA) pointed out reductions in honeybee mortality compared to an industry standard reference polyacrylamide (PAM). When used as an adjuvant to spray the same insecticides described above, SA did not interfere in killing the target pests. Therefore, SA has been tested as a drift-reducing pesticide adjuvant to protect honeybees. Spray experiments in the lab were carried out in four sets: (i) water only, (ii) water and adjuvant, (iii) water and pesticide, and (iv) water, pesticide and adjuvant. Each set contained 18 treatment combinations to cover the ranges in spray pressure (three), adjuvant dose (three), and spray nozzles (two). The droplet spectrum was analyzed using a P15 image analyzer. Diameters of 10 %, 50 % and 90 % volumes (DV10, DV50, and DV90), droplet velocity, standard deviation and relative span were measured. The drift reduction potential (DRP) of SA was analyzed by (i) dose, (ii) spray pressure, and (iii) nozzle type. The DRP of SA is compared to that of PAM. Additionally, three field experiments were carried out to analyze the efficiency of SA in reducing pesticide drift. The results from our experiments collectively indicate that SA has significant potential in mitigating drift as well as minimizing pesticide toxicity to honeybees.

Experimental parametric study on two-phase spray cooling of HEF 7100 using flat spray nozzles

Spray cooling is an effective method and thus finds many applications, including thermal management and energy production. In this regard, spray cooling with flat sprays is particularly crucial in applications with space constraints, as it efficiently dissipates heat while conforming to limited spatial requirements. Flat sprays ensure a wide yet uniform distribution of coolant, making it ideal for cooling systems in compact and densely packed environments. Motivated by these advantages, in this study, we performed an experimental study on the effect of major flat spray parameters, which are the spray flow rate (160 mL/min), spray upstream pressure (2.5 and 5.0 bars), spray angle (0, 30, and 90°), spray distance (3 and 10 cm), spray temperature (23 and 61 °C) and wall heat flux (10–100 W/cm2), on the two-phase heat transfer performance. According to the results, unlike full cone nozzles, the spray distance enhances heat transfer. While the cooling rate increased with the upstream pressure, the inlet temperature had a deteriorating effect on the heat transfer performance of the system. The results also indicated that the heat transfer rate decreased with the spray angle. The spray angle-induced effect on the system performance diminished with the spray pressure and temperature. The obtained results were used to develop two correlations for single phase and nucleate boiling heat transfer in flat sprays. The findings of this study suggest that flat sprays, with their significantly lower flow rates compared to full spray cone nozzles, effectively meet the requirements for direct thermal management by offering precise control, reduced fluid consumption, and enhanced efficiency.

Enhanced mechanical and tribological properties of ultrasonically assisted stir-cast AA7075 metal matrix composites in challenging corrosive environments

Aluminum-based metal matrix composites (AMMCs) find extensive applications in aerospace, defence, automotive, and various sectors on account of remarkable mechanical properties, lightweight nature, and excellent dimensional stability. In this research, AA7075 matrix material was reinforced with tungsten carbide ceramic particles with various 0, 5, 10, 15 and 20 weight percentages (wt%) with the use of Ultrasonic assisted stir casing setup. The stir casted AA7075 MMCs were subjected to XRD, SEM, and density test to investigate the presence of elements, microstructure and density. The tensile, micro hardness, and wear test were performed on AL7075 based MMCs after conducting NaCl based spray test at the condition of spray pressure of 1.2 kg cm−2, spray duration of 120 h and PH value of 8.2 to determine the wear resistance, micro hardness and Ultimate Tensile Strength. The XRD test confirmed the presence of secondary phases such as Al2Cu, W2C, and MgZn2 with Al and WC phases. The SEM test confirmed the uniform dispersion and no more cluster formation upto 15 wt% WC addition and agglomeration of WC was occurred in the addition of 20 wt% of WC. The enhancing of wt% of WC improved the corrosion resistance, Micro hardness, UTS, wear and up to 15 wt% addition and decreases by the 20 wt% WC addition. The higher tensile strength 312 MPa was obtained from AA7075/15 wt%WC composite. The lower wear rate 0.11 mg m−1 was obtained from AA7075/15 wt%WC at 1000 m sliding distance with 1.2 m s−1 sliding velocity. The improved mechanical and tribological properties were mainly depended on strengthening mechanisms such as load transfer mechanism and dislocation strengthening mechanism.

Computational analysis of spray cooling heat transfer and Influential factors during glass tempering

The spray cooling and tempering technology has a series of advantages, such as improving the tempering quality and reducing energy consumption. In order to optimize the tempering technological parameters, it is necessary to accurately control the thermal history and temperature distribution of a hot glass surface during spray cooling. However, measuring the inner temperature of tempered glass proved challenging. The Euler-Lagrangian approach was utilized for simulating the process of spray cooling the glass surface. To validate the accuracy of model predictions, experimental studies were conducted on the tempering of glass by a single nozzle. The numerical outcomes exhibit strong correspondence with the experimental findings. Building upon the foundation, the study analyzed the heat transfer mechanisms in different states including film boiling, nucleate boiling, and forced convection. Subsequently, the effects of spray distance, spray loading fraction, spray pressure, and final cooling temperature on the heat transfer rate and temperature homogeneity were discussed. The results revealed that reducing the spray distance, increasing the spray loading fraction and spray pressure can improve the cooling rate and reduce energy consumption, but it aggravated the uneven distribution of temperature over the glass surface. Moderately increasing the final cooling temperature had little effect on the tempering quality of glass, but it significantly reduced the energy consumption for spray cooling. Within the experimental range, the optimal final cooling temperature was 573.15 K.

Assessing the potential spray drift of a six-rotor unmanned aerial vehicle sprayer using a test bench and airborne drift collectors under low wind velocities: impact of atomization characteristics and application parameters.

The unmanned aerial spraying systems (UASS) have gained widespread use for plant protection in recent years. However, spray drift from UASS is a major concern when controlling weeds over large areas and warrants a thorough investigation. This study examined the atomization characteristics of the herbicide florpyrauxifen-benzyl under downwash airflow using a UASS spray test platform. Potential spray drift was assessed using a test bench (TB) and airborne drift collectors (ADCs) in the field under low wind speeds (<1 m s-1). Atomization characteristics were significantly affected by the spray liquid, adjuvant, nozzle type and spray pressure. The addition of an adjuvant reduced the liquid sheet length, improved physicochemical properties and increased droplet size under the downwash airflow field. Drift evaluation in the field using the TB revealed that sediment spray drift predominantly occurred from the middle to the entire length of the device when fine-to-medium droplets were produced after the sprayer passed. ADC assessment found that higher flight altitudes and finer droplets resulted in higher drift values, whereas the addition of an adjuvant and the use of an air-induction nozzle reduced drift <3 m aboveground. The combination of using TB in the target area and ADCs in the off-target area as an alternative method to determine residual droplets in the current airflow provided valuable insights into airborne drift assessment for UASS. © 2024 Society of Chemical Industry.

Spray of water-in-oil emulsified heavy oil with high water content

The spray of water-in-oil emulsified heavy oils with water content up to 30 % was studied at temperatures of 125 to 200 °C and pressures of 4 to 10 MPa. The spray based on four series of model emulsified heavy oil shows that the effects of spray temperature and pressure on the Sauter mean diameter (SMD) of oil droplets and spray cone angle (θs) follow the traditional breakup model. The emulsification increases the viscosity and surface tension of heavy oils, hindering disintegration of liquid jet into fine droplets during spray. The combination of appropriate water content and superheated degree allows flash boiling of water to overcome the above adverse effects, resulting in a decrease in SMD and an increase in θs. In the spray of the upgraded emulsified heavy oil obtained by visbreaking in high-pressure steam environments, the SMD of oil droplets could be lowered to 39 μm, which is only half of the corresponding value of the raw heavy oil.

Study of spray atomization law and dust suppression effect of a wet dust catcher on a hydraulic support

To control effectively large dust concentrations and their diffusion during coal cutting and shifting of shearers at fully mechanized mining faces, a wet dust catcher on a hydraulic support was developed. The spray nozzle suitable for wet dust collection devices was optimized through spray experiments, and the effects of the spray pressure Pw and nozzle tilt angle θ on the droplet size and fog field concentration were analyzed with Fluent. The numerical simulation results show that the wide-angle solid cone nozzle (with an X-type swirl core) with a diameter of 2.4 mm, water pressure Pw of 6 MPa, and nozzle tilt angle θ of 10° toward the windward side can form a better water curtain. Finally, the wet dust catcher was applied at a 22104 fully mechanized mining face of the Shangwan Coal Mine. The dust removal rate of the shearer driver reached 86.20 %, and that at other positions reached 85 % on average. Evidently, the hydraulic support wet dust catcher can effectively control the diffusion of coal dust at fully mechanized mining faces.

Spray field characteristics and the effect of spray-local exhaust ventilation on the control of high-temperature buoyant jets

Process equipment limitations resulted in constraints on the location of the exhaust hood, which in turn caused escape of high-temperature buoyant jets. In response to this situation, spray system is installed as an auxiliary measure to improve the control effect by spray cooling and weakening the momentum. However, the correlation between spray parameters and its atomization characteristics in high temperature ambient is not clear, reasonable spray parameters directly affect the performance of spray-local exhaust ventilation (SLEV). In this study, we discuss the spray field characteristics under the action of high-temperature buoyant jets, the effects of exhaust and spray parameters on the capture efficiency of SLEV, combined with orthogonal test to get the optimization order. Influences discussed include: exhaust velocity, spray pressure, and nozzle hole diameter. The results showed that SLEV provides superior control of high-temperature buoyant jets, up to two times that of the local exhaust ventilation (LEV). Compared to nozzle hole diameter, the spray pressure significantly effects spray field characteristics. Under high-temperature buoyant jets conditions, the statistical mean diameter obeys a power function relationship with spray pressure, and the capture efficiency was 75% as the spray pressure of 2.0 MPa and nozzle hole diameter of 1.8 mm. The factors affecting the performance of SLEV were found to be exhaust velocity > spray pressure > nozzle hole diameter by range analysis. The research results are expected to contribute to the optimization and enhancement of the SLEV.

Optimization of Spray Characteristics of Full Cone Nozzles Used in Pesticide Application Using the Taguchi Method

The present study aims to reduce the amount of pesticide that can be released into environment, soil, air, and water by minimizing the type of nozzle and the use of excess pesticides by making use of the Taguchi method. For this purpose, studies were carried out to determine the spray characteristics of the pesticide. The sodium fluorescein was used in the experiments. In this study, the effects of the nozzle-to-surface distance (spray height), spray pressure, nozzle orifice diameter, and nozzle position angle on the droplet diameter and flow characteristics were investigated using the Taguchi method. The mean diameter values were determined first. Then, the volumetric median diameter (VMD) was considered as performance parameter and L9(34) orthogonal sequence was chosen as the experimental plan for four parameters that were determined. Calculating the VMD considered as the performance characteristics, optimum results were obtained using 6 bar spray pressure, 100 mm spray height, 30o nozzle position angle, and 1.10 mm nozzle orifice diameter. The VMD values were calculated using the image processing method and the effects of the parameters on the droplet diameter were interpreted using charts.

Design of inductive electrostatic boom spray system based on embedded closed electrode structure and droplet distribution test in soybean field.

The large water demand, insufficient deposition on the back of the leaf and the uneven distribution of droplets are the problems of traditional agricultural ground plant protection machinery, which leads to low agricultural control efficiency. Combined with the advantages of electrostatic spray technology and the characteristics of high working efficiency and low probability of droplets drift of ground sprayer, an inductive electrostatic boom spray system based on embedded electrode structure is designed and mounted on a large self-propelled boom sprayer for field testing. Based on the working characteristics of the fan nozzle and the analysis of the theory of charge, the inductive electrostatic spray device is designed. The performance of the device is tested and the rationality of the system design is verified by COMSOL numerical simulations, charge-to-mass ratio, and particle size distribution measurements. The spray deposition scanning software and the Box-Behnken experimental design method are used to analyze the spray droplet deposition rate and coverage density of the sprayer on the front and back of the target leaves. The results show that the embedded closed electrode structure designed in this paper can avoid the problem of electrode wetting, and the electric field generated by it is mainly concentrated in the spray liquid film area, and the intensity reaches 6~7 V/m. At the conventional application height (500 mm), the maximum charge-to-mass ratio is 2.91 mC/kg, and the average particle size is 168.22 μm, which is 12.87% lower than that of ordinary spray, when the spray pressure is 0.3 MPa and the electrostatic voltage is 12 kV. The results of field experiments show that the optimum combination of the working parameters with the spray speed is 8.40 m/s, the spray pressure is 0.35 MPa, the charging voltage is 11.50 kV, the amount of droplet deposition in the lower dorsal area of the blade is 1.44 µL·cm-2. This study can provide a certain basis for the application of electrostatic spray technology in ground sprayers.

Numerical Simulation and Experimental Study of Gas–Solid Two-Phase Spraying of Dry Powder Fire-Extinguishing System Based on Fire-Extinguishing Inspection Robot

In order to solve the problem where the traditional intelligent inspection robot only has a single inspection function, we studied the use of a dry powder (including an ultra-fine dry powder) as a fire-extinguishing medium for the first time. In fire-extinguishing robots, the spray pressure is difficult to control, and there are several other issues. For integrated inspection, an intelligent, nitrogen-driven fire-extinguishing robot using a dry powder in a pressure-controlled spray was developed. On this basis, in order to investigate nitrogen-driven dry powder particle spraying as a gas–solid two-phase mechanism, as well as the flow characteristics and the influence of relevant parameters on the spraying effect, a nitrogen-driven dry powder particle spraying system was established as part of a gas–solid two-phase computational fluid dynamics model. The flow field of the spraying system and the particle motion characteristics were analyzed to explore the micro-mechanisms of the influence of different driving pressures, pipe diameters, and nozzle configurations on the spraying of the dry powder. In order to investigate the macroscopic effect of dry powder spraying where the gas–solid two-phase micro-mechanisms could not be revealed, an experimental platform was set up, and the experiments verified the accuracy of the numerical simulation results. We also investigated the dry powder spraying effect under different driving pressures, pipe diameters, nozzle configurations, and loading ratios. Finally, an orthogonal test was designed based on the results of the single-factor experiments to find the best combination of parameters required to achieve the optimal spraying effect. The research results can provide a theoretical and technical reference for the design and development of nitrogen-driven dry powder spraying systems.

Full-scale study on the coupling settling behavior of droplets and PM10 particles based on the CLSVOF method and wetting experiments

Coal mines produce large quantities of dust during production and transportation of coal, especially respirable particulate matter of diameter < 10 µm (PM10). This not only jeopardizes the health of workers but also pollutes the environment. Currently, spraying is the most commonly used dust reduction technology. Traditional spraying techniques use pure water; however, the wetting and condensing of dust by pure water droplets is poor, resulting in low dust reduction efficiency. To address this issue, we used orthogonal tests to determine the optimal ratio of composite dust-reducing agents. Using the coupled level set and volume of fluid (CLSVOF) method, we investigated the dynamic wetting process of PM10 when using solutions of dust-reducing agents. We found that a particle size ratio of ≥ 2 and an initial velocity of droplets of 20–40 m/s resulted in optimal wetting and encapsulation of dust particles by droplets. We then conducted macroscopic experiments and found that the settling efficiency of PM10 reached 88.98 % when using a 1.5-mm caliber fine atomizing nozzle and a spray pressure of 6 MPa. Our findings reveal the dynamic wetting law of droplets and dust during the process of spray dust reduction, which could lead to improved efficiency of dust-reducing agents and better management of respirable dust. These findings will help to improve clean production in coal mines and the occupational health of coal miners.

The Influence of Spray Cooling Parameters on Workpiece Residual Stress of Turning GH4169.

To effectively reduce residual stresses in GH4169 workpieces, thus enhancing fatigue strength and operational lifespan, this study investigates the influence of spray cooling parameters on surface residual stresses during GH4169 turning in spray cooling conditions, utilizing both simulation and experimental approaches. A simulation model of residual stresses was established using finite element analysis when GH4169 was cut in spray cooling. The effects of spray pressure and flow rate on residual tensile stresses were analyzed. The analysis reveals that with increasing spray pressure, residual tensile stresses show a decreasing trend, gradually stabilizing. Conversely, with an increasing spray flow rate, residual tensile stresses initially decrease and then increase. The turning experiments of GH4169 were conducted under different spray parameters. After the experiment, the workpiece was sectioned and analyzed for residual stresses using X-ray diffraction instrumentation. The value residual stress measured closely matched those of simulation, with a relative error within 6%, validating the accuracy of the simulation model and confirming the appropriateness of parameter settings. These results contribute to the further promotion of spray cooling technology and facilitate the rational selection of spray parameters.

Optimization of wind-and-water coordinated dust reduction device for coal mine return airway based on CFD technology

High-concentration respirable dust is generated in fully mechanized mining faces, causing health hazards to operators in return airways. To effectively solve this problem, we developed a wind-and-water coordinated dust reduction device. Firstly, the effectiveness of the numerical simulation was validated through spray experiments. Next, the orthogonal experiment method was employed using software such as Fluent and CFD-Post to conduct numerical simulations. This enabled the analysis of the influence of the fan airflow rate (Q), spray pressure (Pw), and nozzle diameter (D) on the coverage capability of the return air roadway and the distribution pattern of the mist field. The results of the numerical simulations indicated that the optimal combination of parameters was Q = 500 m3/min, D = 1.6 mm, and Pw = 5 MPa. Through field application and actual measurement in the return air tunnel of 117 fully mechanized mining face of Jinjitan Coal Mine, the average dust reduction efficiency reaches 91.05%. After dust reduction, the respiratory dust concentrations in the return airway at 20 m, 50 m and 80 m from the air inlet of the return airway are 0.214 mg/m3, 0.172 mg/m3 and 0.153 mg/m3 respectively, which effectively solves the problem of dust pollution in the return airway and reduces dust harm.