Pressure drop is an important indicator that affects the filtration performance of the pleated filter, and the deposition of dust particles within the pleats is crucial to the evolution of the ...pressure drop. In this study, the pressure drop during PM10 loading process was investigated for a series of V-shaped and U-shaped filters with a pleat height of 20 mm and different pleat ratios (the ratio of pleat height to pleat width: α = 0.71-3.57). In the numerical simulations, numerical models suitable for different pleated geometries were obtained through experimental verification on the local air velocity. Then, assuming that the dust cake thickness is proportional to the normal air velocity of the filters, the variation of the pressure drop with the dust deposition is derived by means of successive numerical simulations. This simulation method saved a significant amount of CPU time required for the growth of dust cake. It was found that the relative average deviations between experimental and simulated pressure drops were 3.12% and 1.19% for V-shaped and U-shaped filters, respectively. Furthermore, it was found that under the same pleat ratio and the mass of dust deposition per unit area, both the pressure drop and unevenness of normal air velocity of the U-shaped filter were lower than the V-shaped filter. Therefore, the U-shaped filter is recommended due to its better filtration performance.
In this study, a pressure drop model was developed through numerical simulation and experimentation for optimizing the design of the pleated structure of the filter media to extend the service life ...of the filter and reduce the ventilation energy consumption. The effect of the Stokes number on the dust deposition on the pleated filter media was revealed through numerical simulation. On this basis, a pressure drop model during dust loading was developed. The model suggests that under the same mass of dust deposition per unit area (W), the greater the pleat ratio (α), the greater the dust cake thickness and the effective filtration velocity in the effective filtration area. In addition, for V-shaped and U-shaped filters, the relative mean deviations between experimental and modeling total pressure drops are 3.68% and 4.82%, respectively. In other words, the proposed model accurately predicts pressure drop during dust loading. Furthermore, under the same α and Formula: see text, the total pressure drop of the U-shaped filter is lower than that of the V-shaped filter, demonstrating the superior filtration performance of the U-shaped filter.
In the hope of reducing the air supply flow of the powered air-purifying respirator (PAPR) and extending the service life of the filter, a breath-following powered air-purifying respirator (BF-PAPR) ...that can dynamically adjust the air supply flow according to the breathing flow is proposed. The BF-PAPR changes the air supply flow by adjusting the speed of the variable-frequency centrifugal fan according to the air velocity at the half mask outlet (v
) monitored by the modular wind speed transmitter. In the study, the air supply flow adjustment model of the BF-PAPR is developed. It is found that the filtration resistance barely influences v
. In addition, under the same mean inhalation flow, the minimum outlet air velocity increases first and then decreases with the increase of the duty cycle variation coefficient (λ), while the maximum outlet air velocity decreases first and then increases. Moreover, the minimum air supply flow of the BF-PAPR is achieved when the standard value of the air velocity is 13.4 m/s and the value of λ is 1. The BF-PAPR can reduce the air supply flow by 6.5%-8.6% and the energy consumption by approximately 20% compared with the PAPR, which is beneficial for reducing the usage cost and extending the continuous working time.
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Dust is one of the main disasters in underground tunneling. This study developed and verified a novel dust suppression device, which was systematically tested in laboratory and field ...conditions. Based on the basic principle of the Coanda effect, with a small amount of compressed air as power supply, and through a uniform layout of circular hole for high-speed jet to drive the center air movement together thus forming the entrainment effect, the main structure of the new dust removal device was designed. The external dusty air is then drawn in and the dust is removed by water spray. According to laboratory experiments, the optimal structural parameters for the inlet inclination angle θ1, the outlet inclination angle θ2, and the number of the compressed drainage gas nozzle n were determined. It was found that when the inlet angle is 15° and the outlet angle is 5°, the Coanda effect is the most significant, and the suction rate of the dust removal device is the highest. With the increase of the number of gas orifices n, the suction rate firstly increased and then decreased. In addition, through numerical simulation, the optimal position of the spray nozzle is determined. In field tests, compared to that of the original dust removal device, the new device improved respirable dust and total dust suppression efficiencies by 30.5% and 11.5% (A: the motorman position), 56.2% and 24.5% (B: Behind the drilling machine), 69.4% and 21.6% (C: 20 m behind the drilling machine), respectively, thus the new technology effectively improves the atmosphere in the mechanized underground coal mines, creating a safer and healthier working environment.
High humidity and high dust concentration in deep coal mines may severely challenge the performance of respirators worn by coal miners. This paper aims at quantitatively evaluating the respirators ...used in deep coal mines and providing scientific guidance for the respiratory protection of miners. Based on the self-designed in-situ PM2.5 collector, controllable PM2.5 generator, human breathing simulator, and respirator simulation testing system, under the simulated deep mine working condition, this study investigated the effects of dust loading, wearing time, and dust concentration on the filtration efficiency, breathing resistance, and quality factor of N95 elastomeric respirators. With the increase of dust loading, the respirator filtration efficiency firstly decreased, then increased (minimum value 97.5%). The breathing resistance increased exponentially from 120 to 180 to 1020–1530 Pa, and the quality factor decreased logarithmically from 0.051 to 0.076 to 0.0058–0.0085 Pa−1. As the PM2.5 coal dust concentration increased from 5 to 50 mg/m3, the wearing time for the respirator breathing resistance to exceed 300 Pa reduced from 7 h to less than 1 h. One N95 elastomeric respirator is not able to perform an 8-h work shift. To avoid the excessive breathing resistance caused by dust loading, more filter cartridges are needed for coal miners.
Wet dedusting is the main coal dust suppression technique in coal mines, and coal wettability is the main factor affecting dust suppression efficiency. To investigate the main factors affecting the ...coal wettability and improve it, the coal–water contact angle was used as an index to characterize the coal wettability, and the wettability of six coal samples with different metamorphic degree was studied by analyzing the relationship between the physicochemical properties and the contact angle. To improve the coal wettability, the nonionic surfactant alkyl polyglycoside (APG), anionic surfactant sodium dodecyl benzene sulfonate (SDBS), and polymer surfactant polyacrylamide (PAM) were applied to the coal samples. The results show that SDBS is the most effective surfactant to improve the coal wettability, followed by APG, while the application of PAM would lead to more hydrophobic coal. It is also found that the coal wettability shows a high–low–high trend with the increase in the metamorphic degree. The wettability of long flame coal is the strongest and that of gas coal is the weakest. Moisture is the main hydrophilic factor of coal, while 1,4-dimethylbenzene is the main hydrophobic factor. The main factors affecting the treatment effect of APG, SDBS, and PAM on wettability are the aromatic methylbenzene, hydroxyl, and hydroxyl content of coal, respectively. Therefore, according to the content of hydroxyl in different coals, an SDBS solution can be prepared to improve the coal wettability. For coal with a low hydroxyl content, a higher concentration SDBS solution could be needed.
Cluster analysis of 3D head shapes plays a crucial role in the mass customization design of products related to the head. Head shapes exhibit variations across different races, and designing helmets ...exclusively for Chinese individuals cannot solely rely on or reference foreign head models. Currently, research on cluster analysis of Chinese head shapes is limited, especially concerning shape variances. To address this, we developed an improved k-medoids algorithm and integrated Cluster Validity Index as an assessment metric. This enabled us to cluster 339 Chinese young males aged 18 to 30 into 7 groups based on their head shapes. By comparing our improved algorithm to the traditional k-medoids method, we affirmed its superiority in achieving higher sample participation rates and reducing inter-cluster sample disparities. To simplify the helmet design and editing process, and to improve the efficiency of mass customization, we have developed a parametric modeling program for bicycle helmets based on the head shape clustering results. Results from the Helmet Fit Index and stress simulation analysis demonstrate that our approach significantly enhances helmet fit and wearer comfort.
During hot environment work tasks with whole-body enclosed anti-bioaerosol suit, the combined effect of heavy sweating and exhaled hot humid air may cause the N95 medical respirator to saturate with ...water/sweat (i.e., water-blocking).
32 young male subjects with different body mass indexes (BMI) in whole-body protection (N95 medical respirator + one-piece protective suit + head covering + protective face screen + gloves + shoe covers) were asked to simulate waste collecting from each isolated room in a seven-story building at 27∼28°C, and the weight, inhalation resistance (Rf), and aerosol penetration of the respirator before worn and after water-blocking were analyzed.
All subjects reported water-blocking asphyxia of the N95 respirators within 36∼67 min of the task. When water-blocking occurred, the Rf and 10∼200 nm total aerosol penetration (Pt) of the respirators reached up to 1270∼1810 Pa and 17.3∼23.3%, respectively, which were 10 and 8 times that before worn. The most penetration particle size of the respirators increased from 49∼65 nm before worn to 115∼154 nm under water-blocking condition, and the corresponding maximum size-dependent aerosol penetration increased from 2.5∼3.5% to 20∼27%. With the increase of BMI, the water-blocking occurrence time firstly increased then reduced, while the Rf, Pt and absorbed water all increased significantly.
This study reveals the respirator water-blocking and its serious negative impacts on respiratory protection. When performing moderate-to-high-load tasks with whole-body protection in a hot environment, it is recommended that respirator be replaced with a new one at least every hour to avoid water-blocking asphyxia.
Nano-to-micron-sized coal dust can cause coal workers’ pneumoconiosis (CWP), and cutting and drilling are the main coal dust-generating processes. Based on a self-developed simulated coal cutting and ...drilling dust generation system, the effects of cutting parameters (tooth tip cone angle, impact angle, roller rotary speed, cutting speed) and drilling parameters (drill bit diameter, drilling speed) on the mass concentration distribution, number concentration distribution and fractal dimension of 10 nm – 10 μm coal dust were investigated. Results show that the mass concentration of 10 nm – 10 μm coal dust generated by cutting/drilling peak at 5.7 – 7.2 μm, while the number concentrations during cutting and drilling respectively peak at 60 – 90 nm and 20 – 30 nm. During both cutting and drilling processes, the generated coal dust particles in 10 – 300 nm account for > 90% of the total 10 nm – 10 μm coal particles, while PM2.5 in PM10 is generally below 18%. It is also found that smaller tooth tip cone angle, larger impact angle, lower roller rotary speed, smaller drill bit diameter, or lower drilling speed can reduce the generation of 10 nm – 10 μm coal dust with a fractal dimension of 0.94 – 1.92. This study reveals the distribution characteristics of nano- to micron-sized coal dust particles under different cutting and drilling parameters, and the research results can serve as reference for adjusting cutting and drilling parameters to lower down the 10 nm – 10 μm coal dust generation and thus prevent the CWP.
Simultaneous extraction of the coal and gas is an effective method of eliminating coal mine gas disasters while safely exploiting the coal and achieving efficient gas drainage in China, which is ...widely accepted by the main coal-producing countries around the world. However, the concrete definition of simultaneous extraction is vague and there is little accurate theoretical support for the simultaneous extraction of coal and gas, which makes it difficult to determine an efficient gas drainage method appropriate to the features of coal seams. Based on theoretical analysis, laboratory tests and field observations, a specific definition of simultaneous extraction of coal and gas is proposed after analyzing the characteristics of coal seam occurrences in China, and we developed the mechanism of mining-enhanced permeability and established the corresponding theoretical model. This comprises a process of fracture network formation, in which the original fractures are opened and new fractures are produced by unloading damage. According to the theoretical model, the engineering approaches and their quantitative parameters of ＇unloading by borehole drilling＇ for single coal seams and ＇unloading by protective seam mining＇ for groups of coal seams are proposed, and the construction principles for coal exploitation and gas-drainage systems for different conditions are given. These methods were applied successfully in the Tunlan Coal Mine in Shanxi Province and the Panyi Coal Mine in Anhui Province and could assure safe and efficient simultaneous extraction of coal and gas in these outburst coal mines.
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