Effect Of Air Bubbles Research Articles

A piezoelectric pump with composite vibrator for bubble resistance

Piezoelectric pumps, as microfluidic drive units, are widely used in microfluidic systems. Due to the fact that most piezoelectric pumps are driven by displacement, the introduction of air bubbles will produce a significant impact on their output performance. To minimize the adverse effect of air bubbles, a piezoelectric pump with composite vibrator (PPCV) is proposed. The composite vibrator consists of the active vibrator and the passive vibrator. By vibrating the passive vibrator in the pump chamber, it prevents bubbles retention. Multi-physics field simulation is established，which verifies the PPCV is feasible. Furthermore, a prototype is fabricated and experimentally investigated. At a voltage of 300 Vpp, the experimental results indicate a maximum output flow rate of 41.4 ml/min and a maximum output pressure of 18.7 kPa. After continuously entering 100 bubbles, the output performance of the PPCV decreases by less than 10 %, indicating that the PPCV owns excellent bubble resistance ability. The PPCV provides a new approach to microfluidic pumping devices.

Comparative experimental study of the effect of loading rate on the typical mechanical properties of bubble and clear ice cubes

Icing is a common liquid–solid phase change process that usually has negative effects. Bubbles will form in ice since air is significantly less soluble in ice than it is in water and these bubbles will affect the mechanical properties of ice cubes. To quantitatively investigate the effect of air bubbles on the mechanical strength of ice cubes, an experimental setup is built to explore the mechanical strength and modulus of clear and bubble ice cubes at different loading rates. The results show that even a low volume fraction of air bubbles in the ice cubes as low as 1.98% can have a significant effect on their mechanical properties. The weakening of tensile, compressive and bending strengths by air bubbles is almost less than 20%, while the weakening of shear strength by air bubbles reaches almost 60%. The effect of air bubbles on the four typical mechanical moduli does not exceed 20%. This research helps to optimize the de-icing technique and also provides methods and ideas for preparing ice.

Transformation of significant wave height and set-up due to entrained air bubbles effect in breaking waves

The transformation of wave height is of paramount significance in coastal engineering and the design of coastal structures. Considering the influence of air bubbles, this study devised an optimal dissipation model for accurately calculating changes in significant wave height (Hm0) and wave set-up for irregular waves undergoing breaking. Existing regular wave breaking models, which consider the effects of air bubbles, were adapted for direct application to irregular waves by deriving novel formulations. The proposed models leverage the probability of the fraction of broken waves. Hm0 was computed using the energy balance equation, while the wave set-up was calculated based on the momentum balance equation. A wide range of test scenarios, incorporating diverse scales (small and large) and experimental field data, was considered for validation. One of the proposed models, namely model-I (M-I), particularly demonstrated superior performance, manifesting lower error indices (P20), root-mean-square relative error (RMSRE), and Brier skill score (BSS) values in computing both Hm0 and wave set-up. Therefore, utilising M-I is strongly recommended for the precise estimation of Hm0 and set-up transformation.

Wave height distribution for plunging breakers induced by air bubbles

This study highlights the wave height distributions based on plunging breaking waves and air bubble effects in the surf zone. Wave height distributions predicted previously by different models have been reformulated in terms of air bubble effects. Some of the most commonly applied wave height distributions are judged using laboratory observations in a custom-built wave flume. Results have revealed a notable deviation from the Rayleigh distribution, with the proposed model demonstrating a closer match to experimental data, particularly for larger wave heights. Probability densities of larger wave heights are reduced significantly by entrained air bubbles, leading to measured wave heights below Rayleigh distribution predictions. In addition, the different wave height parameters derived from the proposed model exhibited good agreement with laboratory data compared to the Rayleigh distribution. Furthermore, theoretical analysis shows the scale parameter's dependence on the decay coefficient, aligning well with measurements and simplifying the proposed distribution to a one-parameter model. Again, based on the error analysis, the proposed model's results show good performance compared to others.

Local defect resonance and nonlinearity of porosity air bubbles in solids

Acoustics of bubbles is quite developed field mainly due to multiple cavitation-related ultrasonic applications in liquids. New applications, which require detailed studies of ultrasound encounter with bubble in solid materials, have become apparent recently and are concerned with detectability of porosity in advanced solid materials based on layered technology, like composite and additive manufactured structures. To elucidate the transition from liquids to solids the present paper starts from theoretical similarity between both and proceeds to experimental study of the resonance acoustic effects of air bubbles in epoxy resin. The LDR frequencies are shown to be reciprocal to the bubble radius so that the latter can be evaluated if the frequency is known. The bubbles excited at the LDR frequencies and their subharmonics (superharmonic resonance) manifest extraordinary wide higher harmonic spectra that implies a nonlinear means for nondestructive testing of porosity in composites and other materials.

Mitigation Strategies to Reduce Detrimental Effects of Air Bubbles in Shaft Spillways: A Literature Review

Mitigation Strategies to Reduce Detrimental Effects of Air Bubbles in Shaft Spillways: A Literature Review

Air Bubble Effect on Heat Transfer Enhancement in 90° Ribbed Parallel Channels Based on Photovoltaic-Thermal Collector Cooling

The effect of entrained air bubbles on heat transfer enhancement inside 90° ribbed parallel channels has been experimentally studied to improve electrical efficiency inside future solar panels. In this work, the Reynolds number was measured from 200 to 600. The essential ratios of channel aspect, rib height, and rib pitch were all set to 0.4, 0.18, and 10, respectively. The volumetric flow fraction for all test conditions varied from 0.0 to 0.5. The overall heat transfer distributions on the surface were captured using an infrared thermography camera. The main finding showed that the average heat transfer rate and the thermal performance gained beyond 25–81% and 7–82% compared with the smooth wall. In addition, the volumetric flow fraction of 0.5 at the Reynolds number of 200 became the best.

Bioinspired construction of size adjustable hollow polydopamine microspheres for ultra-low dielectric polyimide composites

Polydopamine (PDA) has been extensively investigated due to its excellent adhesion ability and versatile chemical potential for secondary reactions. However, the potential application of hollow polydopamine microspheres (H-PDA) in the field of low-dielectric electronic packaging remains an unexplored area. Here, H-PDA microspheres with adjustable size were synthesized by a template-assisted approach, and the influence of size and content of H-PDA on the comprehensive performance of PI/H-PDA composites was explored in detail. The morphology observation revealed that the presence of H-PDA could be homogeneously dispersed in the PI matrix, and the PI/H-PDA composite containing 2 wt% H-PDA-800 achieved the lowest dielectric constant of 1.96 with a dielectric loss of 0.0123 at 1 MHz. It was attributed to the synergistic effects of nano-sized air bubbles from H-PDA and the dielectric confinement effect. Meanwhile, PI/H-PDA composites maintained high thermal stability (T5> 517 °C). In addition, the incorporation of H-PDA had a strengthening and toughening effect on PI composites, which can be explained by the sliding theory of macromolecular chains. This work offers a feasible strategy to obtain ultra-low dielectric constant of porous PI composites while maintaining good mechanical properties and thermal stability.

Monte-Carlo-based dynamic air–water cross-media channel for continuous-variable quantum key distribution

Cross-media and confidentiality are key features of next-generation optical communications. Quantum communication is regarded as a promising new form of secure communication. However, the cross-media transmission of quantum pulses tends to suffer from severe attenuation, which inevitably degrades the security of the whole system. In this paper, we consider the configuration of the continuous-variable quantum key distribution through an air–water cross-media channel that involves the lower-atmospheric channel, the underwater channel, and the air–water interface. We consider the effect of air bubbles in seawater, and the effect of the dynamic air–water interface as well. In particular, dynamic characteristics of light extinction and fluctuations caused by seawater and bubbles have been demonstrated with Monte Carlo (MC) simulations. Based on this MC-based model, we demonstrate the communication viability, and simulation results show that in clear seawater conditions with a wind speed of 5 m/s and a zenith angle of 15°, the receiver is able to achieve an effective secret key rate (10−4 bits/pulse) even at 9.71 m depth. Smaller zenith angles and lower wind speeds contribute to an increase in the interface secret key rate.

Demonstration of Sensor Monitoring of Lubricants

Due to the spread of carbon neutral, the effective use of lubricant has been drawing attention. Since the main component of lubricant is petroleum-derived hydrocarbon oil, reducing the amount used by 1 kg will reduce CO2 by approximately 3 kg. The value of CO2 reduction is very important. In order to reduce the amount of lubricant used, there is a movement to reduce the frequency of lubricant exchange or continue to use lubricant without exchanging it. However, it is known that lubricant-induced mechanical failures occur. For this reason, equipment condition monitoring using oil sensors has been spread. The color of the lubricant, also called machine blood, indicates the condition of the machine. The oil sensor measures contamination, which has a fatal effect on machine failure, and oxidation degradation, which is related to the performance of lubricant and the machine failure. Contamination includes water and wear debris, and oxidative degradation includes consumption of additives and oxidation of base oil. By digitizing the hue of wind turbine gear oil through color diagnosis using an oil sensor, the oil contamination and degradation is identified. Additives in the gear oil were quantified by liquid chromatography-mass spectrometry, and it was found that the color change of gear oil was highly correlated with the depletion of the extreme pressure additive. It is known that the depletion of the extreme pressure additive is correlated with the useful life of the gear oil. Using the technique, the remaining life diagnosis of the gear oil was shown. Demonstration in the gearbox with the oil sensor was succeeded by avoidance of the effects of air bubbles in the gear oil.

Estimation of air-bubble-induced wave height and set-up using representative wave approach

ABSTRACT This study aimed to investigate the possibility of modeling the wave height and set-up by using the representative wave method caused by air bubbles in irregular waves in the surf zone. Two regular wave-breaking models with air bubble effects were directly employed in the irregular waves and modified to obtain new irregular wave-breaking models. These models can be used to compute the root mean square (RMS) wave height and wave set-up based on the conservation laws of energy flux and momentum. Model I was solved analytically for a beach with a plane slope and numerically for a beach with an irregular slope for spilling and plunging breakers, separately. Additionally, model II was solved numerically for both slope types and breaking conditions. The modified models were calibrated and validated using a large amount of experimental data and a broad range of trial situations. These conditions included large-scale, small-scale, and field experiments. Finally, it was discovered that the modified models had excellent accuracy in computing the wave heights and set-ups. In terms of accuracy, Model I outperformed Model II for the computation of the RMS wave height and set-up of wave breakers in irregular waves.

Diversity Analysis of Multi-Aperture UWOC System Over EGG Channel With Pointing Errors

The existing single-aperture reception for underwater wireless optical communication (UWOC) is insufficient to deal with oceanic turbulence caused by the combined effect of temperature gradient and air bubbles. This paper analyzes the performance of multi-aperture reception for UWOC under channel irradiance fluctuations characterized by the mixture exponential–generalized gamma (EGG) distribution. We analyze the system performance by employing selection combining (SC) and maximum ratio combining (MRC) receivers. In particular, we derive the exact outage probability expression for the SC-based multi-aperture UWOC receiver and obtain an upper bound on the outage probability for the MRC-based multi-aperture UWOC receiver. With the help of the derived results, we analytically obtain the diversity order of the considered multi-aperture UWOC systems outperforming the single-aperture-based system by a factor of the number of multi-aperture elements. The simulation results validate the accuracy of derived analytical expressions and demonstrate that the low-complexity SC technique effectively improves the performance of the UWOC system under oceanic turbulence with pointing errors at a moderately high transmit power.

Flow and heat transfer characteristics of submerged impinging air-water jets

Flow and heat transfer characteristics of submerged impinging water jets were experimentally investigated. Air was mixed with water using a venturi tube installed before a pipe nozzle. The effects of the volumetric air fraction (β = 0.0–0.7) and jet impingement distance (L/D = 2–8) were studied at a water jet Reynold number, Rew, of 24,000. The air-water flow in the pipe nozzle and impinging air-water jet was recorded using a high-speed camera. An infrared thermal imaging camera measured local heat transfer on the impingement surface. Results show that heat transfer depends strongly on the volumetric air fraction. Impingement distance also affects the behavior of air bubbles in the water jet. Air bubbles can increase the heat transfer on the impingement region by increasing turbulence intensity in the jet with small air bubbles or an intermittent effect of large air bubbles impinging on the surface. Impinging jets where L/D = 4 with β = 0.3 and L/D = 2 with β = 0.2 give the highest heat transfer enhancement, about ∼47% compared to the case of β = 0.0.

Effect of air bubbles on the membrane filtration of rhodamine B.

Effect of air bubbles on the membrane filtration of a basic dye, rhodamine B (RB), using a hydrophilic PTFE membrane filter (pore size: 0.20μm) was studied. The air bubbles were generated by vigorously mixing the aqueous solution containing 0.05% (v/v) of 1-butanol with a shaft generator of a homogenizer. RB being far smaller than the pore size of the membrane filter could not be rejected without air bubbles, but it was rejected by the membrane filter in the presence of air bubbles. The rejection ratio increased with increasing the rotation speed of the shaft generator because of the increase in the amount of air bubbles and therefore the increase in the surface area of air bubbles for the adsorption of RB. On the other hand, another basic dye, methylene blue (MB), was negligibly rejected in the same condition. Dynamic surface tension measurement of aqueous solutions containing different amounts of dye indicated that RB strongly adsorbed to the air-water interface, while MB hardly adsorbed. The results obtained in the present study strongly suggest the potential usefulness of air bubbles for the selective microfiltration of dissolved organic molecules or ions.

Entrainment and Enrichment of Microplastics in Ice Formation Processes: Implications for the Transport of Microplastics in Cold Regions.

Sea ice can serve as a temporary sink for microplastics (MPs), and thus, it too can function as a secondary source of and transport medium for MPs. This study aimed to explore the effect of various MP properties and environmental characteristics on the entrainment and enrichment of MPs in ice under varying turbulence conditions. It was found that high rotation speed in freshwater distinctively enhanced the entrainment of hydrophobic MPs in ice, this being attributable to the combined effects of frazil ice and air bubbles. The hydrophobic nature of these MPs caused them to be attracted to the water/air or water/ice interface. However, in saline water, high turbulence inhibited the entrainment of all of the MP types under study. The ice crystals formed a loose structure in saline water instead of congealing, and this allowed the exchange of MPs between ice and water, leading to the rapid expulsion of MPs from the ice. The enrichment factors of all the MPs under study increased in calm saline water compared to in calm freshwater. The results revealed that the entrainment and enrichment of MPs in ice can be critical pathways affecting their fate in cold regions.

Computer vision-based measurement of wave force on the rectangular structure

Measurement of the wave force acting on the structure is normally achieved by the traditional load cells. In this study, a non-contact computer vision (CV)-based method is proposed, which can conveniently acquire the wave pressure and force without installing pressure sensors or load cell mounted on the structure. Based on the velocity field measured by the Optical Flow technique, the pressure field is successfully computed by solving the Poisson pressure equation, and the wave force is further determined by integrating the pressure over the surfaces of the structure. The proposed method is verified by conducting a series of laboratory experiments of wave interacting with the rectangular structure. The accuracy of the method is validated by comparing with the results measured by pressure sensors. It indicates that the CV obtained pressure and wave forces generally agree well with the sensor measured results, including the time history of wave force and the peak wave force, and the reasons for the deviation and error are also discussed. The effects of wave height and wave period on the pressure field and wave force are studied, and it is found that the Keulegan–Carpenter number is an important parameter determining the peak wave force. Finally, the limitations existed in this method are noted, including the two-dimensional simplification and air bubble effects, which need to be addressed in the future.

Effect of Air Bubble on Liquid Crystal Alignment

Effect of Air Bubble on Liquid Crystal Alignment

Dielectric constant of ice in natural rivers

Ground-penetrating radar (GPR) is a non-contact measurement method widely used to determine ice thickness, which is an important hydrological parameter of rivers in winter. The accuracy of GPR measurements of ice thicknesses is highly dependent on the dielectric constant value of ice. Research on the dielectric constant of ice has mainly focused on pure ice; however, pure ice is not commonly found in natural rivers. In fact, hydrodynamic and meteorological factors, as well as boundary conditions, affect ice in natural rivers, which can be treated as a mixture of pure ice, air bubbles, sediment, and pure water. Therefore, the dielectric constant of ice in natural rivers often differs from the theoretical value of pure ice, a fact that has often been neglected in prototype measurements. During eight years of prototype monitoring in the Heilong River and Yellow River (China), it was found that variations in the dielectric constants of ice in the two rivers produced errors in the GPR ice thickness measurements. In this study, we measure the dielectric constant of ice at 158 measurement points across more than 20 river sections, and we present a recommended range of values for the dielectric constant. Regarding media, such as air bubbles, sediment, and water in natural river ice, we analyze sand (both dry and wet) in ice-bound sediment and the effects of air bubbles, sediment, and water upon the ice's dielectric constant. Using temperature and voltage measuring rods installed in the ice, we demonstrate that the water content in the ice differs significantly according to the freeze-up and breakup periods. The present study recommends guidelines including suitable timing, ice-condition, and dielectric-constant reference values for GPR-based ice thickness measurements to improve the measurement accuracy. Thus, this work can serve as a reference for future applications in similar rivers.

Physical-Layer Security for UAV-Assisted Air-to-Underwater Communication Systems with Fixed-Gain Amplify-and-Forward Relaying

We analyze a secure unmanned aerial vehicle-assisted two-hop mixed radio frequency (RF) and underwater wireless optical communication (UWOC) system using a fixed-gain amplify-and-forward (AF) relay. The UWOC channel was modeled using a mixture exponential-generalized Gamma distribution to consider the combined effects of air bubbles and temperature gradients on transmission characteristics. Both legitimate and eavesdropping RF channels were modeled using flexible α-μ distributions. Specifically, we first derived both the probability density function (PDF) and cumulative distribution function (CDF) of the received signal-to-noise ratio of the system. Based on the PDF and CDF expressions, we derived the closed-form expressions for the tight lower bound of the secrecy outage probability (SOP) and the probability of non-zero secrecy capacity (PNZ), which are both expressed in terms bivariate Fox’s H-function. To utilize these analytical expressions, we derived asymptotic expressions of SOP and PNZ using only well-known functions. We also used asymptotic expressions to determine the suboptimal transmitting power to maximize energy efficiency. Furthermore, we investigated the effect of levels of air bubbles and temperature gradients in the UWOC channel, and studied the nonlinear characteristics of the transmission medium and the number of multipath clusters of the RF channel on the secrecy performance. Finally, all analyses were validated using a simulation.

Influence of micron-sized air bubbles on sonochemical reactions in aqueous solutions exposed to combined ultrasonic irradiation and aeration processes

Sonochemical reactors are promising for wastewater treatment applications. However, the combination of ultrasonic irradiation and aeration processes raises questions regarding the extent to which entrained air bubbles influence sonochemistry. In this study, the effect of micron-sized air bubbles (20 and 70 µm, 0.1–5.0 vol%) on sonochemical activity, based on KI dosimetry, was tested in a horn-type reactor (20 kHz). Bubbles were generated using the pressurization–depressurization method. The results showed that low bubble concentrations increased sonochemical yields but higher concentrations tended to decrease the yields. Compared with the bubble-free case, 20-μm bubbles enhanced sonochemistry at all concentrations, while 70-μm bubbles inhibited sonochemistry at the highest concentration (5.0 vol%). Two regimes, acoustic attenuation and nucleus introduction, were identified as inhibiting and enhancing sonochemical effects, respectively, and their dependence on bubble characteristics was examined. These results are significant as investigation into these regimes will allow a deeper understanding of the key factors controlling sonochemistry in the presence of micron-sized air bubbles and could be used to design sonoreactors equipped with aerators.