Search Results (7)

Humic substances (HSs) pose a significant challenge to safe drinking-water production due to their ubiquity, limited removal by conventional methods, and their role in forming toxic disinfection by-products, reinforcing the need for more efficient, energy-favorable, and scalable treatment technologies. This study developed and evaluated a compact hydrodynamic cavitation (HC) system that simultaneously induces coagulation and generates microbubbles for flotation-based HS removal. For the first time, HC is explored as a multifunctional unit capable of integrating rapid mixing, coagulant destabilization, and flotation within a single device. Optimal coagulation conditions were established at pH 5.0 and 9.5 mg L⁻¹ of ferric chloride. Process optimization using a Rotated Central Composite Design demonstrated that inlet pressure, flotation time, and initial HS concentration were the dominant operational factors, enabling the HC system to achieve a maximum removal efficiency of 81.9%. Five Venturi geometries with divergent angles of 4°, 8°, 11°, 14°, and 90° were investigated, with the 8° Venturi exhibiting superior performance due to stable microbubble formation and effective coagulant dispersion, as confirmed by CFD analyses. Comparative tests with a conventional Flotest unit showed that achieving similar efficiencies required at least 30% saturated water. In contrast, the HC system delivered equivalent removal in continuous flow without external air saturation. These findings demonstrate the potential of HC as an integrated coagulation–flotation core and highlight its promise as a compact, energy-efficient, and scalable technology for natural organic matter removal in water treatment. Full article

In this paper, we analyse the effectiveness of microbubble technology in inactivating/reducing gram-negative, gram-positive, and radiation-resistant bacteria, including Escherichia coli, Bacillus subtilis, and Deinococcus radiodurans, respectively, in model water. Key water quality parameters such as dissolved oxygen, conductivity, pH, and total dissolved solids are recorded and presented to demonstrate their range in the current investigation. The study results indicate a reduction of 95% in E. coli, 100% in D. radiodurans, and 45% in B. subtilis following microbubble treatment. These findings suggest that ambient air microbubbles, generated using a low-cost, reagent-free, and eco-friendly venturi-type microbubble generator, represent a promising technique for reducing bacterial loads in water. Full article

Currently, the existing high-pressure water mist fire protection systems in cold storage facilities face challenges in achieving efficient atomization and uniform water mist distribution, which may limit their effectiveness in rapid cooling and flame suppression. The objective of this investigation is to improve the performance of high-pressure fine water mist nozzles by integrating a Venturi microbubble generator to improve mist atomization and distribution, particularly in the context of flames involving combustible polyurethane foam insulation materials. The gas–liquid two-phase flow characteristics within Venturi tubes were investigated through numerical simulations using ANSYS-Fluent 2022 R1 software. This study focused on critical parameters, including the water inlet pressure (1–9 MPa), pharynx diameter (8–12 mm), contraction angle (15–45°), and expansion angle (15–45°). The average water mist droplet diameters at 1, 3, and 9 MPa were 169.890, 150.002, and 115.606 μm, respectively, in the absence of the Venturi tube, according to the experimental results. A reduction of up to 16.7% was achieved by reducing the particulate sizes to 141.462, 139.142, and 109.525 μm using the Venturi tube. The fire-extinguishing time and water consumption were substantially reduced at higher pressures, such as 9 MPa. Under high-pressure conditions, the results indicated that the Venturi microbubble technology was significantly more effective in suppressing fires. The novelty of this study lies in the application of Venturi microbubble technology to improve fine water mist systems for fire protection in cold storage facilities. This enhanced system achieves better atomization, uniform water mist distribution, faster cooling, and more efficient flame suppression, making it a viable solution for improving fire protection in such environments. Full article

Due to their unique physical properties, microbubbles have received a lot of attention in waste treatment, aquaculture, and food processing. The demand for high-efficient and low power consumption microbubble generators has become a challenge today. Swirling flow has been widely proven to improve bubble formation. Numerous researchers have developed designs to produce swirl flow and strengthen the turbulence fluid flow. In this study, we present a swirl venturi microbubble generator with a 60° twisted baffle fin on the inlet section. The performance of the microbubble generator swirl venturi type was tested experimentally using parameters such as the distribution of bubble size, hydraulic power (L_w), and bubble-generating efficiency (η_b). A microbubble generator was installed in the transparent test pool with 672 L of water. A high-speed video camera was employed to visualize the flow behavior. The water and gas flow rates varied between 40 and 60 lpm and 0.1 and 0.5 lpm, respectively. The data were analyzed by MATLAB R2022b with the technique image processing method. The results showed that majority bubbles 100–300 µm were generated. An increased water flow rate (Q_L) will increase the hydraulic power by 22–27 W, while an enlargement of the gas flow rate (Q_G) would only enlarge it by 1 W. As the water flow rate increases, bubble-generating efficiency decreases. The lowest bubble-generating efficiency of 0.008% occurs at a Q_L 60 lpm and Q_G of 0.1 lpm. In conclusion, we can conclude that the microbubble generator swirl venturi type is an efficient device for generating microbubbles. Full article

Iron normally exists in the form of ferrous ion (Fe²⁺) in primary ore deposits of valuable metals. To remove iron from hydrometallurgical leaching solution or suspension by precipitation, ferrous ion should be oxidized to ferric ion (Fe³⁺) first. Due to the low oxidation rate of Fe²⁺ by the traditional oxygen oxidation method, industry has to use more agitating barrels, steam, and compressed gas, as well as a larger workshop area, which dramatically increases the equipment investment and operation costs. In this study, a strengthened oxygen oxidation method for Fe²⁺ using a homemade venturi jet microbubble generator is proposed. Microbubbles of air, oxygen, or oxygen-enriched air can be formed in the leaching solution or suspension, which can greatly improve the dissolved oxygen content in the solution and increase the gas-liquid contact area, thereby accelerating the oxygen oxidation rate of Fe²⁺ to Fe³⁺ and realizing the rapid iron removal of the leaching solution or suspension. By measuring the residual concentration of Fe²⁺ in the solution after oxidation reaction, it was found that the pump power, solution temperature, pH, concentration of Cu²⁺, and solution flow rate had great effects on the oxidation performance of the produced microbubble. By analyzing the images of the microbubbles and measuring the dissolved oxygen content in the solution, it is confirmed that the accelerated oxidation reaction rate of Fe²⁺ using the new proposed method was mainly due to the increase of the dissolved oxygen amount in the solution. Moreover, this method can significantly increase the purification depth of iron ion, expand production capacity, and decrease energy consumption. Full article

Microbubble generators are of considerable importance to a range of scientific fields from use in aquaculture and engineering to medical applications. This is due to the fact the amount of sea life in the water is proportional to the amount of oxygen in it. In this paper, experimental measurements and computational Fluid Dynamics (CFD) simulation are performed for three water flow rates and three with three different air flow rates. The experimental data presented in the paper are used to validate the CFD model. Then, the CFD model is used to study the effect of diverging angle and throat length/throat diameter ratio on the size of the microbubble produced by the Venturi-type microbubble generator. The experimental results showed that increasing water flow rate and reducing the air flow rate produces smaller microbubbles. The prediction from the CFD results indicated that throat length/throat diameter ratio and diffuser divergent angle have a small effect on bubble diameter distribution and average bubble diameter for the range of the throat water velocities used in this study. Full article

Microbubbles with slow rising speed, higher specific area and greater oxygen dissolution are desired to enhance gas/liquid mass transfer rate. Such attributes are very important to tackle challenges on the low efficiency of gas/liquid mass transfer that occurs in aerobic wastewater treatment systems or in the aquaculture industries. Many reports focus on the formation mechanisms of the microbubbles, but with less emphasis on the system optimization and assessment of the aeration efficiency. This work assesses the performance and evaluates the aeration efficiency of a porous venturi-orifice microbubble generator (MBG). The increment of stream velocity along the venturi pathway and orifice ring leads to a pressure drop (P_atm > P_abs) and subsequently to increased cavitation. The experiments were run under three conditions: various liquid velocity (Q_L) of 2.35–2.60 m/s at fixed gas velocity (Q_g) of 3 L/min; various Q_g of 1–5 L/min at fixed Q_L of 2.46 m/s; and free flowing air at variable Q_Ls. Results show that increasing liquid velocities from 2.35 to 2.60 m/s imposes higher vacuum pressure of 0.84 to 2.27 kPa. They correspond to free-flowing air at rates of 3.2–5.6 L/min. When the system was tested at constant air velocity of 3 L/min and under variable liquid velocities, the oxygen dissolution rate peaks at liquid velocity of 2.46 m/s, which also provides the highest volumetric mass transfer coefficient (K_La) of 0.041 min⁻¹ and the highest aeration efficiency of 0.287 kgO₂/kWh. Under free-flowing air, the impact of Q_L is significant at a range of 2.35 to 2.46 m/s until reaching a plateau K_La value of 0.0416 min⁻¹. The pattern of the K_La trend is mirrored by the aeration efficiency that reached the maximum value of 0.424 kgO₂/kWh. The findings on the aeration efficiency reveals that the venturi-orifice MBG can be further optimized by focusing on the trade-off between air bubble size and the air volumetric velocity to balance between the amount of available oxygen to be transferred and the rate of the oxygen transfer. Full article