It has been reported that the addition of microbubbles in a water flow enhances a cleaning efficiency of oil adhering to a channel wall. However, the enhancement mechanism of the cleaning effect has ...not been sufficiently understood yet. Experiments on the removal effects of water flows in a horizontal channel with and without microbubbles were therefore conducted to investigate the removal process by microbubbles. Silicone oil adhering to the bottom wall of the channel was used as dirt. The local thickness of the oil was measured during cleaning from micrographs of fluorescence intensity. The amount of oil removed by the water flow increased with increasing the Reynolds number. Adding microbubbles to the water flow increased the amount of removed oil. Microbubbles attached to the oil interface under turbulent conditions, and the bubbles grew by mass transfer through the gas-liquid interface and bubble coalescence. The detachment of bubbles grown on the oil interface led to oil peel-off, resulting in an improvement of cleaning effect.
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•The thickness of adhesion oil was measured using laser-induced fluorescence.•The presence of microbubbles was confirmed to enhance oil removal.•The removal rate was modeled as a superposition of shear and bubble effect terms.•Microbubbles adhering to oil can be grown by mass transfer and induce oil peeling.
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•The relationship of energy consumption with bubble diameter was constructed.•The phenol conversion in a sub-millimeter bubble-dominated WAO reactor can be well predicted.•The spatial ...distribution of variables (including temperature, etc.) were evaluated.•The initial bubble diameter lines between 0.2 ∼ 0.4 mm for the phenol WAO process.
The huge investment in equipment and energy consumption required for wet air oxidation (WAO) severely limits its industrial application due to harsh operating conditions with high temperatures and pressures. In this work, the energy consumption of phenol WAO was calculated considering gas compression, pumping, preheating and bubble generation. The relationship between energy consumption, bubble diameter and phenol conversion was constructed to evaluate the main influencing factors. It was found that sub-millimeter bubbles can effectively improve the WAO process by enhancing the oxygen mass transfer, resulting in a decrease in operating temperature and pressure. Considering the maximum conversion and minimum cost, the initial air bubble diameter for phenolic WAO is preferably between 0.2 ∼ 0.4 mm. The model was validated using experiments with a WAO reactor dominated by sub-millimeter air bubble, and good agreement was obtained between simulated results and plant data.
The article presents a model of bubble dynamics in lead and lead-bismuth coolants, implemented into the system thermohydraulic code HYDRA-IBRAE/LM. The article also contains the code validation ...results on the data of two experiments where the gas-lift effect was studied – at the CIRCE facility (Italy) and at the mock-up of a lead coolant reactor gas-lift probe (Russia). The article provides analytical estimates which show that as the injected gas flow rate increases, the increase in coolant flow rate decreases. It is shown that at low gas flow rates, the liquid flow rate is proportional to the gas flow rate to the power of 1/2, which was observed in the gas-lift probe mock-up experiment. As the injected gas flow rate increases, the degree decreases, as observed in the CIRCE experiments, until the dependence of the coolant flow rate on the gas flow rate is almost completely eliminated. These analytical evaluations are confirmed by the results of calculation and experimental simulations.
•Model of bubble dynamics in lead and lead-bismuth coolants is presented.•Simulation results on two facilities are performed.•Analytical estimates on the dependence of liquid flow rate on gas flow rate are shown.•Simulation results showed a good agreement with experimental data.
•A SVBG was designed to improve the microbubble generation efficiency.•The influence of geometric parameters on the flow structure of SVBG was studied.•The SVBG could shear the bubbles into ...micro-nano bubbles with size down to 780 nm.•The micro-nano bubble cavitation reactor displayed a superior DO value.
We designed a swirling-type venturi bubble generator (SVBG) by introducing a swirling flow field into the conventional venturi tube to improve the microbubble generation efficiency. The fan-shaped baffles were added at the entrance and the converging section was replaced by spiral channel to enhance swirling flow intensity so as to facilitate bubble breakup. The influence of geometric parameters on the flow structure of the SVBG was studied through numerical simulation. Then the optimized SVBG was installed at the downstream of the conventional venturi tube to construct a novel micro-nano bubble cavitation reactor. The manufactured cavitation reactor generated bubbles with size down to 780 nm. Moreover, the cavitation reactor exhibited a superior dissolved oxygen value, which was increased by 36.06% when compared with venturi tube, showing great promise for oxygen enrichment. The micro-nano bubble cavitation reactor presented can provide a more effective way to produce micro-nano bubbles.
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•Gas fluidized bed with binary particle species were studied for coal beneficiation.•Binary systems with same mean diameter and same aerodynamic diameter were compared.•Effect of ...compositions in binary system on Umf and bed expansion was studied.•Bubble number, size and rise velocity were characterized from processed images.•A linear relationship between the bubble size and bubble rise velocity was found.
Fluidization behaviour of two binary particle systems, magnetite225-sand225 (M225-S225) particles with the same mean diameter (dp) and magnetite225-sand304 (M225-S304) particles with the same aerodynamic diameter (da) were observed in a two-dimensional fluidized bed. The number, size and rise velocity of gas bubbles in the binary fluidized bed were characterized by image analysis. A decreasing minimum fluidization velocity (Umf) with increasing sand volume fraction was found in the M225-S225 system while a nearly constant Umf was found in the M225-S304 system. Increasing trends of both bubble size and bubble rise velocity along the bed height were detected and a linear correlation between the bubble size and rise velocity was found for binary systems. The higher the fraction for one type of particles in the binary system is, the closer to the corresponding single-component system the hydrodynamic phenomena and bubble properties will be in both binary systems.
Subcooled boiling flow in a rod bundle geometry is an important phenomenon observed in the heat exchanger of heat transfer systems and reactor core of a nuclear power plant. However, experimental ...data on local two-phase flow parameters of rod bundle geometries in the subcooled boiling conditions are rare. In this study, an experiment was conducted to determine the distributions of the local two-phase parameters of a 4 × 4 rod bundle channel under a subcooled boiling water flow. The flow conditions were a mass flux range of 305 to 390 kg/m2s, a heat flux range of 190 to 274 kW/m2, and an inlet subcooling temperature of 20.5 to 25 °C at an inlet pressure of 200 kPa. The distributions of the void fraction, bubble velocity, interfacial area concentration (IAC), and Sauter mean diameter were measured with a four-sensor optical fiber probe (4S-OFP). The area-averaged bubble parameters were used to evaluate several drift-flux models and IAC correlations to assess their applicability to rod bundle channels.
•Experimentally investigated subcooled boiling flow in a 4 × 4 rod bundle channel.•Local bubble parameters are acquired to Mass flux, heat flux, and inlet subcooling.•Area-average bubble parameters are obtained from local bubble parameter data.•Existing interfacial area concentration (IAC) and drift-flux models are evaluated.
In the present study, flow boiling experiment using ITO transparent heating method and LBM simulation by improved Shan-Chen model are conducted to confirm Marangoni effect on the bubble departure and ...CHF in subcooled flow boiling heat transfer of pure water and CTAC/NaSal(1:1) solutions. Tests are performed with the same tube of d = 2.6 mm, inlet fluid temperature of Tin = 80 °C and outlet pressure of Pout = 101.3 kpa. With high speed camera and microlens, the bubble departure process and flow patterns are recorded at different mass velocities, concentrations and gravity direction. The improved Shan-Chen model with large density ratio(ρl/ρv = 36.55) is applied to simulate the bubble departure process with changing gravity direction and top wall temperature. The present results show that CHF of pure water is increased to approximately 131% by surfactant additives at 100 ppm(CMC), the dry spot at the bottom of bubble causes CHF in pure water and the slug bubble appearing is the main reason of CHF in CTAC/NaSal solution. Due to the solutal Marangoni effect, bubble group in CTAC/NaSal solution is adsorbed at the heating surface which increases the bubble departure diameter. For the first time, the failure of Marangoni effect on flow pattern at CHF is discovered due to the bubble adsorption.
•Investigate the bubble distribution in aerated emergent vegetated channels.•To explore the law of oxygen mass transfer in emergent vegetated channels.•The formula of oxygen transfer coefficient in ...emergent vegetated channel is obtained.
In the case of increasingly serious river pollution worldwide, aeration in channels is an effective way to solve water pollution. However, traditional aeration research is aimed mainly at nonvegetated channels, and there is relatively little research in vegetated channels. Aeration contributes to the absorption of pollutants by vegetation, so studying the mass transfer of dissolved oxygen in vegetated channels is of great significance. This paper innovatively studies the variation law and formula of the oxygen mass transfer coefficient in vegetated channels through an experiment and theoretical analysis. Through flume experiments, this study examines the bubble size and oxygen transfer coefficient under different vegetation densities and establishes a formula to simulate the oxygen transfer coefficient under different vegetation densities. The results show that vegetation has little effect on bubble diameter, and the main effect on bubble diameter is the aeration rate. The existence of vegetation significantly increases the mass transfer of oxygen, and the higher the vegetation density is, the greater the oxygen transfer coefficient transfer is. At the same time, a formula predicting the oxygen transfer coefficient is proven, and the simulation results are good, in which the coefficient of determination (R2) was 0.9535 and the mean absolute error (MAE) reached 0.0857. This study provides a theoretical basis for the selection and layout of aeration systems in vegetated channels.
•The algorithm is applied to various flow patterns without pre-classification.•The method is suitable to analyze inhomogeneous and fluctuating two-phase flows.•The effects of flow direction and ...maldistribution are quantified with key features.•Measured key features are compared to a flow pattern map for the same test channel.•The maximum bubble diameter model is used to validate the measured bubble sizes.
High-resolution photographs of the air-water flow in a transparent cross-corrugated channel are analyzed using digital image processing. Gas-liquid distribution is controlled via several inlet nozzles. Flow direction is varied between upward, downward, and horizontal flow.
The image analysis algorithm is applied to a wide range of void fractions and flow patterns including bubbly, intermediate and film flow. Large bubble clusters are separated using edge detection. Local film and bubbly flow are identified with texture analysis. The method is suitable for locally inhomogeneous two-phase flow which is difficult to analyze visually.
Objective and reproducible results are obtained by measuring features in the processed images: Mean and maximum bubble diameter, and the ratio of local film flow are determined. For non-uniform gas injection, expansion of two-phase flow across channel width is measured. Impact of flow direction and maldistribution on two-phase flow is demonstrated by calculating differences of the features. Uncertainties of image processing results are quantified. Bias is discussed based on visual analysis of the photographs in a previous study.
Models for maximum bubble diameter and local film flow ratio, used to model flow pattern transitions in a previous study, are verified: For uniform two-phase distribution, models generally agree with measured values.
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•Bubbles were generated on submerged capillaries in a leaky-dielectric liquid under non-uniform electric field.•The reinforcing effect of electrohydrodynamic on the formation bubbles ...was confirmed.•Mechanisms of the electrohydrodynamic on growing bubble were analysed systematically.•Dynamic behaviors of growth bubble were quantitatively analyzed.
In this paper, the dynamic behaviors of bubbles in ethanol were investigated with a needle-ring electrode rig in the presence of a direct current (DC) electric field. High-speed photography was used to capture the bubble dynamic characteristics under various electric field strengths. The obtained results show that the applied electric field accelerates the bubble formation speed and release frequency, but restricts the bubble release diameter. Meanwhile, high electric field strength causes the bubble shape being squeezed in horizontal direction and stretched in vertical direction, respectively. Quantitatively, the evolutions of the bubble non-dimensional size parameter δ reflect that producing the bubbles whose width are smaller than those of orifice is to judiciously control the electric field strength, which is not closely related to the capillary model. The bubble aspect ratio χ and the non-dimensional contact angle θb/θs depend primarily on electric field strength and show a desirable corresponding relationship with the bubble deformation and the triple-phase contact line, respectively. Furthermore, by combining the bubble evolution with the dimensionless Eötvös number (Eo), Weber number (We) and electrical Bond number (BoE), the main forces work on the bubble and surrounding liquid are evaluated and elaborated.
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