Air Bubble Injection Research Articles

A high-efficiency mini-hydrocyclone for microplastic separation from water via air flotation

A mini-hydrocyclone was designed to remove microplastics from water through air flotation. The hydrocyclone geometry parameters were optimized through the combination of the orthogonal design method and numerical simulation. The performance of the optimized mini-hydrocyclone was experimentally evaluated. The experimental and numerical underflow pressure drop results showed a consistent trend in the considered flow range. The separation efficiency increased with increasing inlet flow rate, but increased, and then decreased, with the flow split ratio. The separation performance of microplastic in the entire size range could be improved through the injection of air bubbles into the water. The separation efficiency enhancement ranged from 5 % to 15 % within a split ratio range of 0.04 to 0.23. The separation efficiency increased rapidly with a low flow rate of air injection and remained high (> 92 %) with a further increase in the air flow rate. The concentration ratios of the hydrocyclone were all >7.8 owing to low flow split ratios. The maximum concentration ratio reached 9.7 at a feed flow rate of 0.45 m3/h, a split ratio of 0.1 and an air holdup of 5.4 %. The results demonstrated that the designed hydrocyclone with injected microbubbles can achieve high separation efficiency and concentration rate at the same time. The air flotation-induced increase in grade efficiency was mainly due to the density reduction effect of MP–bubble agglomerates, and the volume expansion effect was relatively small. The cyclonic air flotation technology can be applied to small-scale water treatment, such as separating microplastics in a washing machine.

Evaluations on effect of volume fraction of injected air on exergo-economic performance of a shell and tube heat exchanger

Increasing heat transfer rate in heat exchangers is one of the topics interested by researchers which leads to economic savings. Various methods have been proposed in this field which are categorized into two main groups of active and passive techniques. Despite numerous investigations were conducted in this regards, very rare investigations have probed these methods from the economic viewpoints. Present study was carried out to investigate the effect of volume fraction (VF) of air bubbles on exergo-economic performance of horizontal shell and helically coiled tube exchanger (HSHTE). The air bubbles were injected into shell side via especial method. Holes with certain properties were fabricated on a plastic pipe with diameter of 3 mm for injecting air bubbles. Both counter flow and parallel flow were considered in this investigation. Present study showed that air injection has significant effect on thermal efficiency, exergy destruction and economic performance of the HSHTE. It was found that increment of VF increases number of thermal units, first law efficiently and exergy destruction increase by 4.5, 2.4 and 12.5 times, respectably. Furthermore, best values of Net profit per unit transferred heat load (դ p ) was about 9.3 × 10 −5 ($/J) which presented up to 13% better financial performance in comparison with parallel flow.

Experimental study on entropic behavior of smooth pipe due to the simultaneous usage of spring turbulator and air bubble injection

Numerous investigations were conducted to enhance heat transfer in smooth tubes. They have used both active and passive methods. However, very rare investigations have reported the simultaneous usage of active and passive methods. Furthermore, the investigations on entropic behaviors are very rare too. Through present paper, effect of air bubble injection (as active method) together with spring wire turbulator (as the passive method) is probed. The pipe was subjected to a constant heat flux. Spring pitch and fluids flow rates were variable parameters of this study. Four flow levels of 2, 3, 4, and 5 were intended for water and air. The studied parameters were Nusselt number, cost-performance coefficient, and dimensionless exergy destruction. The flow patterns were also assessed. To calculate the Nusselt number and exergy destruction, ambient temperature, pipe surface temperature, water inlet, and outlet temperatures were measured. Results showed that reducing the induced rotational flow by the pitch, affects two-phase flow and leads significant changes flow pattern and two-phase flow motion model. Air bubble injection increased Nu by 40% and dimensionless exergy destruction by 36%.

Parametric study for hydraulic design of air-bubble injections to control scour around circular bridge piers

ABSTRACT Several countermeasure techniques have been presented to control bridge scour-induced failure. Air-bubble injection, a new method compatible with the environment, was introduced to combat destructive vortices that cause bridge piers to be scoured. Extensive experiments were conducted to determine the appropriate air-bubble injections for the least scours at a bridge pier. Two different clear-water flow intensities with air-bubble injections were assessed in different radial positions around and also on the upstream half of the bridge pier. The vertical position of air injections and air discharge were determined previously to be optimal. The long-term experiments revealed that the well-designed air-bubble injections reduced the local scour around the bridge pier. It was found that the complete air-bubble injection around the bridge pier is the best configuration and able to reduce the scour depth about 44% over the case with no air injection (non-protected pier). Moreover, the appropriate arrangement of bubble injections to lessen the scour depth is the nearest radial position of the injection to the bridge pier and with increasing the radial distance of injections to the pier, the bubble plumes move downstream by the main flow. The results indicate that bubble plumes would be effective in both flow intensity, u*/u*c = 0.7 and 0.9, as examined in the present study.

Acoustic spectrometry of bubbles in an estuarine front: Sound speed dispersion, void fraction, and bubble density.

Estuaries constitute a unique waveguide for acoustic propagation. The spatiotemporally varying three-dimensional front between the seawater and the outflowing freshwater during both flood and ebb constitutes an interfacial sound speed gradient capable of supporting significant vertical and horizontal acoustic refraction. The collision of these two water masses often produces breaking waves, injecting air bubbles into the water column; the negative vertical velocities of the denser saltwater often subduct bubbles to the bottom of these shallow waveguides, filling the water column with a bubbly mixture possessing a significantly lower effective sound speed. A field experiment was carried out in the mouth of Mobile Bay, Alabama in June 2021 to characterize estuarine bubble clouds in terms of their depth-dependent plume structure, frequency-dependent sound speed and attenuation, bubble size distribution, bubble number density, and void fraction. Results demonstrate that sound speed in the bubbly liquid consistently falls below the intrinsic sound speed of bubble-free water; specifically, the bubbly liquid 1.3 m below the surface in a front in this environment possesses effective sound speeds, void fractions, and bubble number densities of approximately 750 m/s, 0.001%, and 2 × 106 bubbles/m3, respectively.

Optical Properties of (PS-TiO2-Al2O3) Nanocomposite Films Injected with Air Nano Bubbles

In this work, the optical properties of (PS-TiO2-Al2O3) nanocomposites films prepared by casting method have studied. To use in different optical fields. The TiO2 and Al2O3 nano particles added with different weight percentages are (1,2, 3 and 4) wt% were injected air bubbles to generate Nano bubbles in the (PS-TiO2-Al2O3) nanocomposites. The results revealed that absorbance, absorption coefficient, extinction coefficient, and refractive index of the optical characteristics of nanocomposites for wavelength range (280-800) nm. Increase with increase TiO2 and Al2O3concentrations, while the Transmittance decreased with increase TiO2 and Al2O3 concentrations. Optical energy values gap from (3.62 – 1.50) eV, where the optical energy gap of produced films reduced as the number of TiO2 and Al2O3 nanoparticles increased.

Experimental study of heat transfer and pressure drop analysis of the air/water two-phase flow in a double tube heat exchanger equipped with dual twisted tape turbulator: Simultaneous usage of active and passive methods

In this paper, simultaneous use of active and passive methods for enhancing the thermal performance of a double-tube heat exchanger was investigated. This was done by injecting air bubbles into the working fluid and utilizing a dual twisted tape turbulator. Effects of these two procedures on the Nusselt number and pressure drop were evaluated when applied simultaneously. We further studied the effect of cold water flow rate on thermal parameter. The results indicated that the Nusslte number increases with the decrease of turbulator ratio and increases with the increase of bubble injection flow rate, cold water flow rate and the Reynolds number. The findings further showed that the simultaneous use of the two methods could increase the Nusselt number by 98–114%, 3–14%, and 20–39% compared to the cases with a simple tube heat exchanger, a turbulator-equipped heat exchanger (without bubble injection), and a heat exchanger with bubble injection (without turbulator), respectively.

Improvement of Thermal Performance of Coiled Tube Heat Exchanger Utilizing Air Bubble Injection Technique

The heat transfer enhancement in terms of temperature of a vertical helically coiled tube heat exchanger is carried out experimentally. The experiments were achieved in a heat exchanger with a 50 cm height and 15 cm internal diameter under four different cold and three hot water mass flow rates and four different airflow rates. At the same time, the temperature difference was taken invariant (ΔT=20°C). To avoid some uncertainties, the hot side temperature of the heat exchanger was measured via k-type thermocouples. The results showed that the increase of air injection flow rate improved heat transfer from the hot stream flowing in the coil to the shell’s cold stream. An intimate thermal mixing when air injected is clearly observed, which could be responsible for the heat exchanger’s thermal enhancement. Finally, the injected air pressure was noticed to be having only a minor effect on thermal performance improvement.

Effects of Increased Tooth Clearance on the Performance of a Labyrinth Seal With Oil-Rich Bubbly Laminar Flow

Abstract In recent years, multiphase pumps have become more and more popular because of the capability to simplify the process, reduce the footprint, and lower the cost. To compensate for the axial thrust force, an annular seal is normally used as a balance piston seal, and the labyrinth seal is one of the choices. A typical labyrinth seal consists of a surface with teeth and a smooth surface. The teeth are either on the rotor or the stator. To protect the machine, one side (either the teeth or the smooth surface) is made of a material that can be safely sacrificed during a rub. After the rub, the teeth clearance is increased. This paper studies the impact of the increased teeth clearance on the performance of the labyrinth seal under oil-rich bubbly flow conditions. The test fluid is a mixture of silicone oil (PSF-5cSt) and air with inlet gas volume fraction (GVF) up to 9%. Tests are conducted with pressure drop (PD) = 34.5 bars, rotor speed ω = 5 krpm, and radial tooth clearance Cr = 0.102 mm and 0.178 mm. Test results show that, for all test conditions (before and after injecting air bubbles into the oil flow), increasing Cr from 0.102 mm to 0.178 mm increases the mass flow rate by about 40% but barely changes the test seal's rotordynamic coefficients, i.e., the increased tooth clearance would not change the pump vibration performance.

Experimental Parametric Investigation to Reduce Drag of a Scaled Model of Bulk Carrier Using BDR/ALS Technique

Abstract The shipping business expects to develop energy-saving and drag-reducing techniques addressing the cost of shipping and environmental problems. It has been reported that for slow-moving vessels, frictional resistance accounts for up to 80% of the total resistance, needing urgent attention to reduce the same. To reduce frictional resistance, the air has been used as lubricant, which is injected below the moving body known as Bubble Drag Reduction or the Air Lubrication System. In this article, results obtained from experimental investigations into drag reduction of a 1:23 scaled model of an 8000-ton deadweight bulk carrier by injecting air bubbles below it are presented. Investigations were carried out for a speed range of 6–10 knots, and for each speed, the effect of six injection flow rates of .5–3.0 CFM were investigated. To investigate the effect of different sizes of injection holes, two types of injector units have been used: one with injection holes of 1 mm diameter and the other with injection holes of 2 mm diameter. The study carried out has many practical implications because it is easier to create bigger size holes which will reduce the power required to inject air, thereby increasing the efficiency of the entire technique. Introduction It is projected that crude oil prices will continue to increase in the future, forcing marine businesses to rely on researchers to develop energy-saving devices (ESD) and drag-reducing technologies. It has been reported that for slow-moving vessels such tankers, bulk carriers, very large crude carrier (VLCC), and ultra large crude carrier (ULCC), frictional resistance accounts for up to 80% of the total resistance, needing urgent attention to reduce the same (Lewis n.d.; Larsson & Raven 2010). Numerous technologies have been studied and applied in reducing the frictional drag (Brostow 2008; Abdulbari et al. 2013; Luo et al. 2015; Mohammad & Mousavi 2015; Sindagi et al. 2016). Based on further studies Sindagi et al. (2018a, 2018b, 2018c, 2018d) and Sindagi and Vijayakumar (2020), it is concluded that air lubrication has additional advantages over other technologies, such as it is environmentally friendly, the operation is quite easy, and it results in low operating costs and high energy savings. Moreover, with air lubrication, an 80% reduction in the drag of the flat plate was achieved by Merkle et al. (1983) and Madavan et al. (1984, 1985).

'Put a damper on' - rectify arterial line underdamping with an alternative to the air bubble injection method.

'Put a damper on' - rectify arterial line underdamping with an alternative to the air bubble injection method.

EXPERIMENTAL STUDY OF HEAT TRANFER AUGMENTATION USING AIR BUBBLE INJECTION AND (Al2O3 /WATER) NANOFLUID FLOW IN DOUBLE PIPE HEAT EXCHANGERS

In the present work, an experimental study on how to increase the heat transfer coefficient (HTC) in double pipe heat exchanger (DPHE) use of a variety of Al2O3 Nano-dispersion concentrations mixed in water as base fluid with air bubble injection for counter flow arrangement under turbulent flow conditions with (Re) Reynold number range from (6000 t0 45000) . The thermal performance of (DPHE) has been enhanced with the use of two techniques. The first, is represented by adding nanoparticles to hot water (inner pipe) raising the (HTC) inside the inner tube. Increase the volume concentration cause increase in the viscosity of the nanofluid leading to increase in friction factor .Secondly is represented by Air bubble injection in outer pipe with cold water to enhance the (HTC). The mobility of air bubbles inside the water from down to up by the force of the buoyancy, and the movement of these air bubbles results in significant mixture and turbulence within the water. The variations of number of thermal units (NTU), exergy loss, dimensionless exergy and (Nu) are evaluated. The investigated parameters were cold water volume flow rates (8, 10, 12 and14) l/min, flow in outer tube. Also, three different volume flow rates of air (12, 16 and 20) l/min mixed with water in outer tube. The volume flow rates of hot water remains constant at (8 l/min) flow in inner pipe with three volumetric concentrations of given nanofluid. The results showed that the air bubble injection throughout the tube gave maximum enhancement in heat transfer characteristics followed by the no air bubble injection. Since the enhancement in heat transfer characteristics varies linearly with the volumetric concentration of Nanofluids, Nanofluids with 0.3% of Al2O3 nanoparticles gave more enhancements in (HTC) than the case without nanofluid. The Nusselt number increased about (8% - 45%).

On the Influences of Air Bubbles on Water Flow in a Two-Dimensional Channel

As an inevitable trend for the sustainable development of the global economy, saving energy and reducing emissions are key goals for the entire world. The use of air bubbles to reduce viscous friction is one of the most effective approaches to achieve this goal, as it may significantly reduce the frictional drag of ships. However, the injection of air bubbles will change flow characteristics near the wall due to the significant differences in density and viscosity between air and water. In addition, parameters such as bubble size, bubble surface tension, bubble number and bubble position also affect the flow near the wall, resulting in significant diversity and instability in two-phase flow. To clarify the mechanism of these effects, a two-dimensional channel flow with air bubbles is studied using Computational Fluid Dynamics (CFD). The interactions between bubbles and water and between bubbles and wall are studied, and the detailed characteristics of bubbles moving in fully developed flow are considered. This study shows that the velocity gradient is the main factor influencing wall shear stress, and the presence of bubbles has a marked impact on the local velocity gradient distribution of the nearby flow. It is also found that shorter distance between a bubble and the wall enhances the flow interaction and leads to more significant perturbations of wall shear stress.

High‐Speed 3D Imaging of Multiphase Systems: Applying SCAPE Microscopy to Analog Experiments in Volcanology and Earth Sciences

AbstractMultiphase suspensions are complex systems where microscopic interactions between suspended bubbles, particles, and liquids can significantly alter bulk behavior. Observing the internal mechanics of such suspensions can help constrain the dynamics of natural multiphase flows. To capture these internal processes at high speed and in three dimensions, we propose the use of Swept Confocally Aligned Planar Excitation (SCAPE) microscopy in analog experiments. This imaging technique, developed for neuroscience and biology, uses a sweeping light sheet to illuminate and image fluorophores within a sample. We performed experiments using water and various oils as the liquid phases, glass or PMMA particles for solids, and air or CO2 for gas, which we imaged at rates >50 volumes per second, over a volume size of ∼1 × 1 × 0.4 mm. We focused on three case studies: (1) bubble nucleation, growth, and rise in sparkling water, where we found that bubble detachment from angular PMMA particles left residual bubbles that also grew and detached, generating more bubbles compared to smooth particles; (2) flow of immiscible liquids (water droplets suspended in canola oil) in a porous matrix of PMMA beads, which highlighted the importance of pore and throat sizes on droplet velocities; and (3) injection of air bubbles into concentrated suspensions of glass beads or crushed PMMA particles in a refractive‐index‐matched liquid, which revealed particle motion and strong alterations of the bubble shape. We conclude that SCAPE microscopy is a powerful tool to study the dynamics of multiphase systems.

The Effect of Injected Air Bubble Size on the Thermal Performance of a Vertical Shell and Helical Coiled Tube Heat Exchanger

In the present study, the effect of injecting air bubble size on the thermal performance of a vertical counter-current shell and coiled tube heat exchanger is experimentally investigated. The experiments were accomplished in ... | Find, read and cite all the research you need on Tech Science Press

Thermo-hydraulic study in a shell and tube heat exchanger using rod inserts consisting of wire-nails with air injection: Experimental study

Recently, air bubbles injection with utilizing insets inside the tubes for enhancing heat transfer performance in shell and tube heat exchanger STHEs has achieved a great interest. In this study, air was injected by the simple method in tube sides where wired nails-circular rod inserts (WNCR) are presented with water tube side flow rate TSFR changed from 14 LPM to 18 LPM and water shell side flow rate is kept constant at a typical value of 18 LPM. Two configurations of inserts with different distance between the nails (10 cm and 5 cm) are employed with three different air volumetric flow rates AVFR of 1, 2, and 3 LPM. Effects of inserts only, inserts in conjunction with air injection, and air injection only on thermal parameters (i.e. number of transfer units NTU, effectiveness ε, and overall heat transfer coefficient U) and hydraulic performance (indicated in pressure drop Δp) are studied and discussed. Moreover, exergy efficiency and thermal hydraulic parameter are also presented and studied. Results indicated that inserts are more pronounced than air injection for all performance parameters. Moreover, the second type (insert B) of inserts has more influence than the first one (insert A). Percentage enhancements in performance parameters are within the ranges of 31%–131% for insert A, 43%–177% for insert B, 33%–143% for injection with insert A, 44%–184% for injection with insert B, 2%–19% for air injection only with insert A, and 1%–23% for insert B. Finally, air injection only gives a small effect on heat exchanger performance parameters (less than 5%) for performance parameters such as NTU, Δp, and thermal hydraulic parameter.

Experimental investigation of heat transfer and exergy loss in heat exchanger with air bubble injection technique

The main aim of this study is to evaluate thermal performance and exergy analysis of a shell-and-tube heat exchanger with a new technique called air bubble injection. The study has been carried out with different parameters such as flow rate, fluid inlet temperature, and different air injection techniques. The air has been injected at different locations such as the inlet of pipe, throughout the pipe, and in the outer pipe of the heat exchanger. Based on the results, the performance of the heat exchanger enhances with an increase in the flow rate and the fluid inlet temperature. The exergy loss and dimensionless exergy loss increase with a rise in the flow rate. The maximum and dimensionless exergy losses are obtained at a maximum flow rate of 3.5 l min−1. With the air bubble injection in the heat exchanger, it has been observed that the temperature difference increases, which leads to an increase in the exergy loss. The injecting air bubbles throughout the tube section shows that minimum dimensionless exergy is 27.49% concerning no air injection.

Experimental investigation of heat transfer enhancement in heat exchanger due to air bubbles injection

The present work experimentally investigated air bubbles injection on heat transfer enhancement and pressure drop of turbulent flow in two helical coils heat exchanger. The experience is accomplished for turbulent flow with Reynolds number (Re) of (9000 to 50000) for hot water and constant mass flow rate of cold water 0.0331 kg/s .Air bubbles injection in hot water in the range of (1.5, 2.5, and 3.5) lit/min. Experimental results represented by Nusselt number(NU), effectiveness (ε), number of thermal units (NTU) and exergy losses. It was evinced that, the presence of air bubbles in hot water causes enhanced in Nusselt number from (64 to 126) % and increased the friction factor from (66 to 85) % in the Reynolds number range from (9000 to 50000). Bubbles injection has a positive effect on enhanced heat transfer and negative effect of increased friction factor and this represent by thermal enhancement factor which was increased about (1.13 to 1.29) in mass flow rate of hot water of 0.0163 kg/s by using values of air bubbles from (1.5 to 3.5) lit/min. A quantity of number of thermal units (NTU) and effectiveness (ε) appreciably enhanced due to air bubbles. Furthermore, exergy loss with air bubbles was higher than without air bubble injection.

Thermal and exergy analysis of air- nanofluid bubbly flow in a double-pipe heat exchanger

Heat exchangers are among the most applied energy systems and increasing their performance can contribute to resolving current energy and environmental issues. Of the active and passive methods of heat transfer enhancement, air bubble injection and using nanofluids, respectively, were selected for this research. Experiments were conducted to study energy, exergy and hydrodynamic performances of a vertical double pipe heat exchanger under the effects of the combined method applied in the annulus side. Finally, multi-objective optimization based on artificial neural network metamodeling and genetic algorithm was carried out to find the best performance on the basis of heat exchanger effectiveness and exergy performance. Results indicate a promising potential in performance enhancement of the combined method.

HEAT TRANSFER AUGMENTATION APPROACH IN DOUBLE PIPE HEAT EXCHANGER

In recent years researchers are focussing in augmenting the heat transfer rate of heat exchangers because it is crucial in engineering applications. The double pipe is the commonly used heat transfer equipment in industries due to its easy manufacturing, maintenance and compactness. Researchers had made a lot of efforts to enhance the thermal performance of the double pipe. In this paper, the modifications have done on double pipe heat exchanger using discontinuous helical turbulators, with open-cell porous foam, air bubble injection etc. for the heat transfer enhancement and the various methods the double pipe went through has discussed in details. In this present article reviewed the correlations of Nusselt number, Reynolds number and ΔP in Double pipe heat exchanger for heat transfer augmentation.