This study compared mixing efficiencies of the symmetric and asymmetric airfoil blades in a continuous stirred tank reactor (CSTR) at various mixing velocities and angles of attack. The symmetric airfoil blades (NACA0009 and NACA0015) and asymmetric airfoil blades (NACA2414 and NACA4412) were set at different angles of attack and mixing velocities. The tank reactor was equipped with two sets of three airfoil blades at the upper and the lower parts of the stirring shafts at the angles of attack 0 deg, 10 deg, 16 deg, and 20 deg, and the mixing velocities of 80, 110, 140, and 190 rpm. The mixing efficiencies were evaluated from the homogenous appearance of plastic particles (5 mm in diameter) dispersed in water by an image processing technique. The results indicated that the mixing efficiencies of both the symmetric and asymmetric airfoil blades increased with increasing mixing velocities and at the angles of attack 0 deg and 10 deg, and slightly decreased with increasing mixing velocities at the angles of attack 16 deg and 20 deg due to the blade stall and mixing saturation as well as short-circuiting flow from the high flowrate. There was no significant mixing velocity effect on mixing efficiencies at the angles of attack 10 deg, 16 deg, and 20 deg except 0 deg of the symmetric and asymmetric airfoil blade systems. The two asymmetric airfoil blade types gave higher mixing efficiencies than the two symmetric airfoil blade types. The results from this study can be applied for a novel blade design for an efficient mixing flow, which will be beneficial for industrial biogas production.

This research aimed to evaluate spray humidifiers as evaporation processes. The tube in evaporation processes in this research was designed in the form of a ven This research aimed to evaluate spray humidifiers as evaporation processes. The tube in evaporation processes in this research was designed in the form of a ven

Submicron particulate matter in the 0.1–1.0 µm range is difficult to remove using conventional air pollution control devices because of its low capture efficiency. Condensation-induced particle enlargement has therefore been proposed as a preconditioning method to increase particle size before collection. This study aims to numerically investigate the condensation-induced growth of submicron particles in a cylindrical tube under different pressure-recovery conditions and to clarify how pressure-controlled supersaturation affects droplet-growth kinetics. A three-dimensional computational fluid dynamics (CFD) model was developed in ANSYS Fluent by coupling the Discrete Phase Model (DPM) with a custom User-Defined Function (UDF) growth law to predict droplet growth, condensation time, and associated heat and mass transfer characteristics. Initial particle diameters of 0.1–1.0 µm were examined for growth to a target diameter of 5 µm under initial pressure conditions of 0.5–0.9 bar followed by recovery to 1 atm, corresponding to calculated nominal supersaturated RH values of 202.65–112.58%, respectively. The results show that pressure-induced supersaturation is the dominant factor controlling condensation kinetics. Lower initial pressures resulted in shorter condensation times and higher mass and heat transfer rates. For an initial diameter of 0.5 µm, the condensation time decreased from approximately 0.1434 s at 0.9 bar to 0.0167 s at 0.5 bar, corresponding to an 88.35% reduction. These findings indicate that pressure-controlled supersaturation can significantly accelerate submicron particle enlargement and provide design guidance for condensation-assisted fine-particle removal technologies.

Biogas produces from the degradation of organic compounds of garbage and water wastes from various sources such as ranch and agricultural industries, usually by the fermentation process with anaerobic microorganisms. Layers of sediment are often occurred that can block the flow and longer mixing time is required for a more homogenous mixing. The objective of this study is to solve the non-uniform and non-homogenous as well as to save the mixing time in the fermentation process of biogas production using a model-mixing reactor. Flow analysis using an image processing technique of the symmetric airfoil NACA0015 blade at different angles of attack and mixing velocities in a Continuous Stirred Tank Reactor (CSTR) was examined. The CSTR was equipped with two and three airfoil blades at the angles of attack 0, 10, 16(stall angle) and 20° operated at the mixing velocities at 80, 110, 140 and 190 rpm. The mixing efficiency was evaluated from the homogenous appearance of plastic particles (5 mm diameter) dispersed in water by an image processing technique. The results showed that the mixing efficiencies of CSTR with three blades were higher than that of the CSTR with two blades of about 1.3 folds. The mixing efficiency increased with increasing mixing velocities and angles of attack, and was almost constant when the blade angles of attack increased from 16° to 20° and the mixing velocity increased from 140 to 190 rpm. This may be due to the airfoil blade stall and the saturation of the mixing. A new blade design for the CSTR system from this study can give a more efficient stir and mixing flow which will not only be beneficial for biogas production in the laboratory scale, but also a model design for the industrial biogas production as well.

Upper Northern Thailand continues to face a protracted structural crisis from fine-particulate matter (PM_2.5), primarily driven by biomass burning and wildfires. Conventional mechanical capture systems, such as cyclones, often suffer a drastic efficiency drop when treating sub-micron particles. This study introduces an innovative Evaporative Condensation Growth Scrubber (ECGS) designed to bridge this technological gap by promoting the growth of fine particles through heterogeneous nucleation. Experimental testing across 10 different nozzle configurations was conducted to optimize the system’s performance. The results revealed that the ECGS system significantly outperformed the dry cyclone (Baseline) across all nine testing configurations. While the Baseline showed inherent limitations in capturing sub-micron particles, the ECGS demonstrated relative efficiency improvements ranging from 39.53% to 83.23% for PM_2.5, and 26.10% to 61.50% for PM₁₀ compared to the baseline. Optimal performance was achieved using a 90-degree injection angle and a 10 cm distance, which created a complete spray curtain and maximized collision probability. Under these conditions, the outlet PM_2.5 concentration stabilized at 11.81 µg/m³ within 180 s of water injection. Crucially, despite sensor interference caused by high relative humidity, the system’s effectiveness was confirmed by a significant difference in performance in PM₁₀ and PM_2.5 removal. The PM₁₀ collection efficiency outperformed that of PM_2.5 by 28.82%, providing empirical evidence that PM_2.5 particles successfully acted as nuclei for condensation and grew into the larger PM₁₀ size range. This particle growth enabled more effective centrifugal separation, demonstrating that the ECGS system offers a viable and efficient solution for fine particle removal in highly polluted environments.

Fine particulate matter PM_2.5 continues to pose a critical public health risk in Northern Thailand, particularly in Chiang Mai, where traditional filtration methods often face limitations in cost and efficiency for large-scale applications. This study introduces a novel “Evaporator Condensation Growth Particle Scrubber (ECGP)” designed to enhance the collection efficiency of sub-micron particles by enlarging their physical size through a pressure-driven growth mechanism. The ECGP system utilizes synergistic effects between solid nuclei, high relative humidity, and mechanical pressure modulation. The ECGP system integrates solid nuclei, ~95% relative humidity and mechanical pressure modulation within a single chamber. Using incense smoke as a PM surrogate, the process utilizes controlled adiabatic cycles to induce stable heterogeneous condensation. The results indicate that the integrated process effectively shifts particle size distribution, reducing the PM_2.5/PM₁₀ mass ratio from 1.00 to 0.83. This indicates that approximately 17.5% (with a standard deviation < 1% across 10 trials, p < 0.05) of the fine mass successfully transitioned into the larger, more filterable PM₁₀ fraction and exhibited high physical stability and resistance to re-evaporation, effectively overcoming the low-efficiency threshold (typically <10%) of standard mechanical scrubbers and cyclones for sub-micron dust. This study concludes that ECGP technology offers a promising, cost-effective alternative for improving indoor air quality in large public infrastructures by leveraging particle inertia for enhanced removal, providing a scalable solution to the persistent smog crisis.