Bubble Production Rate Research Articles

Modelling the ejection of primary aerosols during the fast pyrolysis of biomass anisotropic particles

A model for the fast pyrolysis of anisotropic biomass particles is presented which considers bubbling dynamics within the liquid intermediate phase (metaplast) and aerosol ejection from this phase. The model employs the population balance equation and the method of moments to estimate the production rate and resultant size distribution of aerosol ejections, incorporating a detailed CRECK reaction mechanism, and considers the effect of anisotropic biomass microstructure on the intraparticle transport of mass and energy. This study investigates the impact of particle size, heating rate (heat transfer coefficient), and lignocellulosic composition on aerosol ejection. The model predicts that, at high heating rates (convective heat transfer coefficient of 359 W/m2.K), aerosols can contribute over 20% to the heavy fraction yield in bio-oil for small particles (1 mm diameter, 4 mm length). The model can predict aerosol size distribution and surface area, indicating an average size of 20 μm for bubbles and 5 μm for aerosols during increased bubble production and aerosol ejection rates. These findings are consistent with prior experimental results and provide essential information for future modeling of extra-particle reactions of the aerosols as they progress through the reactor.

Bubble generation mechanisms in microchannel under microgravity and heterogeneous wettability

Advances in hybrid surfaces have revealed interesting opportunities for multiphase flow control under microgravity, as the surface tension force is dominant in this condition. However, a comprehensive investigation of bubble generation rates and slug flow parameters remains challenging. This research integrates hybrid wettability and modified dynamic contact angle models to address this important knowledge gap. Using the computational capabilities of the IsoAdvector multiphase method, we performed detailed simulations of complex multiphase flow scenarios with the OpenFOAM package. We then validated these simulation results through rigorous comparison with available experimental data, thereby strengthening the accuracy and reliability of our numerical simulations. Our comprehensive research demonstrates the profound effect of altering contact angle distribution patterns on several critical parameters. These results highlight the precise control that can be achieved through the strategic manipulation of these patterns, offering the possibility of adjusting factors such as bubble production rate, slug length, bubble diameter, the relationship of flow residence to bubble movement, bubble movement speed in the channel, and pressure drop. Interestingly, altering these patterns can also induce asymmetric behavior in bubbles under microgravity conditions, a phenomenon that has significant implications for various applications. Such insights are crucial for fields such as heat transfer in energy systems, reaction mechanisms in chemical processes, multiphase flow control in petrochemical industries, fluid dynamics in aerospace engineering, and cooling mechanisms in electronic devices. With the ability to modulate these fundamental parameters, we gain valuable insights into the design and optimization of microchannel systems. Consequently, this research presents a more efficient and innovative approach to multiphase flow control, promising improved operational performance, and efficiency in various engineering applications.

On the scalability of helium-filled soap bubbles for volumetric PIV

The scalability of experiments using PIV relies upon several parameters, namely illumination power, camera sensor and primarily the tracers light scattering capability. Given their larger cross section, helium-filled soap bubbles (HFSB) allow measurements in air flows over a significantly large domain compared to traditional oil or fog droplets. Controlling their diameter translates into scalability of the experiment. This work presents a technique to extend the control of HFSB diameter by geometrical variations of the generator. The latter expands the more limited range allowed by varying the relative helium-air mass flow rates. A theoretical model predicts the bubble size and production rate, which is verified experimentally by high-speed shadow visualization. The overall range of HFSB produced in a stable (bubbling) regime varies from 0.16 to 2.7 mm. Imaging by light scattering of such tracers is also investigated, in view of controversies in the literature on whether diffraction or geometrical imaging dominate the imaging regime. The light scattered by scaled HFSB tracers is imaged with a high-speed camera orthogonal to the illumination. Both the total energy collected on the sensor for a single tracer, as well as its peak intensity, are found to preserve scaling with the square of the diameter at object magnification of 10–1 or below, typical of PIV experiments. For large-scale volumetric applications, it is shown that varying the bubble diameter allows increasing both the measurement domain as well as the working distance of the imagers at 10 m and beyond. A scaling rule is proposed for the latter.Graphical abstract

Microbubble formation by flow focusing: role of gas and liquid properties, and channel geometry

Microfluidic flow focusing is a versatile method for the production of monodisperse microbubbles for biomedical applications involving ultrasound. Existing studies propose several theoretical models to predict bubble size and production rate as a function of the liquid and gas flow rate. Yet, they typically do not include physical fluid parameters such as density, viscosity and surface tension. Here, we present an exhaustive experimental and numerical investigation of the influence of physical properties of the gas and liquid, and of the channel geometry on bubble size and production rate. We find a particularly strong effect of (i) gas density on the production rate and (ii) liquid viscosity on the bubble size. We further discuss our findings within the context of existing theoretical models to reflect on gaps in our current understanding of the fluid mechanics of bubble formation by flow focusing.

Capillary driven fragmentation of large gas bubbles in turbulence

Bubble fragmentation drives up to 40% of the CO2 transfer from the atmosphere to the ocean. However, the small size bubble distribution, mainly responsible for gas dissolution, is still poorly understood. Combining experimental and numerical calculations, we find that capillary effects set small bubble production rate which physically explains the origin of their size distribution.

Eternal inflation and reheating in the presence of the standard model Higgs field

We study the details of eternal inflation in the presence of a spectator Higgs field within the framework of the minimal Standard Model. We have recently shown that in the presence of scalar field(s) which allow inflation only within a finite domain of field values, the universe reaches a steady state where the normalized distribution for the field(s) converges to a steady state distribution [1]. In this paper, we analyze this eternal inflation scenario with the renormalized Standard Model Higgs potential, since it also allows inflation in a finite domain, but turns over at high scales due to the running of the self-coupling, marking an exit from inflation. We compute the full steady state distribution for the Higgs using an integral evolution technique that we formulated in [1] and the fractal dimension of the universe. We then obtain a bound on the inflationary Hubble scale in order to have a large observable universe contained within the instability scale of $H\lesssim\mathcal{O}(10^9)$GeV depending on the top mass. Upon reheating of the universe, thermal fluctuations in the Higgs field could potentially pose another problem; however, we compute the rate of thermal bubble production and find that the probability of tunneling in the post-inflationary era is negligibly small even for very high reheat temperatures.

A Review and Analysis on Recent Advancements in Bubble Electrospinning Technology for Nanofiber Production.

Multiple applications of nanofiber in various segments of science and technology have sparked the interest of innovators to explore the innovative approaches for nanofiber production. The bubble electrospinning technique is the most versatile and simplest approach to scale up the production of nanofiber at the industrial level. Numerous patent applications have been filed with innovations and advancements in the field of bubble electrospinning technique. In present work, different patent applications in the field of bubble electrospinning technique, which represents the advancement in bubble electrospinning technology, are searched and analyzed using various paid and free patent databases. The patent search results are compiled, analyzed and individual innovations are studied in detail to bring all the advancements hitherto in the bubble electrospinning technology under the purview of one review article. The "bubble ws3 electrospin" syntax in the structured search (TAC) facility of the patseer® has revealed most relevant patents on advancement in bubble electrospinning. After applying the family patent filter to the search result (33 patents), ten patents are selected for detailed study. The gist of the invention from each of the patent application or granted patent is recapitulated in this paper, along with their mosaics. Definite number of inventions are available in the field of bubble electrospinning technique. Inventions, which are disclosed, might have their pros and cons with respect to ease of acceptance by the industrial fraternity for large-scale production depending upon simplicity or complexity of the instrument. There is a profound scope of innovation in the bubble electrospinning technology in the areas like bubble stabilization, size and production rate control and much more.

Generation and control of helium-filled soap bubbles for PIV

The operating regimes of an orifice-type helium-filled soap bubbles (HFSB) generator are investigated for several combinations of air, helium and soap flow rates to establish the properties of the production process and the resulting tracers. The geometrical properties of the bubbles, the production regimes and the production rates are studied with high-speed shadowgraphy. The results show that the bubble volume is directly proportional to the ratio of helium and air volume flow rates, and that the bubble production rate varies approximately linearly with the air flow rate. The bubble slip velocity is measured along the stagnation streamline ahead of a cylinder via particle image velocimetry (PIV), yielding the particle time response from which the neutral buoyancy condition for HFSB is inferred. The HFSB tracing capability approaches that of an ideal tracer (i.e., minimum slip and shortest response time) when the volume flow rate of helium is approximately one thousandfold the soap flow rate. This study provides guidelines for operating HFSB generation systems, intended for PIV experiments.Graphical abstract

Micropipette-Based Microfluidic Device for Monodisperse Microbubbles Generation.

Microbubbles have various applications including their use as carrier agents for localized delivery of genes and drugs and in medical diagnostic imagery. Various techniques are used for the production of monodisperse microbubbles including the Gyratory, the coaxial electro-hydrodynamic atomization (CEHDA), the sonication methods, and the use of microfluidic devices. Some of these techniques require safety procedures during the application of intense electric fields (e.g., CEHDA) or soft lithography equipment for the production of microfluidic devices. This study presents a hybrid manufacturing process using micropipettes and 3D printing for the construction of a T-Junction microfluidic device resulting in simple and low cost generation of monodisperse microbubbles. In this work, microbubbles with an average size of 16.6 to 57.7 μm and a polydispersity index (PDI) between 0.47% and 1.06% were generated. When the device is used at higher bubble production rate, the average diameter was 42.8 μm with increased PDI of 3.13%. In addition, a second-order polynomial characteristic curve useful to estimate micropipette internal diameter necessary to generate a desired microbubble size is presented and a linear relationship between the ratio of gaseous and liquid phases flows and the ratio of microbubble and micropipette diameters (i.e., Qg/Ql and Db/Dp) was found.

Acoustic emissions by marine algae during photosynthesis

Coastal underwater soundscapes typically contain signals from soniferous, biological processes. Identifying the sources that contribute to oftentimes acoustically complex soundscapes would facilitate a noninvasive, remote, and volumetrically integrative method to survey underwater ecological state, as has been demonstrated on land. To date the lack of knowledge on these sources has posed a challenge for extracting meaningful ecological information from underwater biological soundscape recordings. We have observed that photosynthesis by macroalgae is an acoustically active process, driven by oxygen bubbles separating from the algal surface and ringing at the Minnaert frequency. The resultant soundscapes correlate with benthic macroalgal cover across ecological gradients on shallow Hawaiian reefs during periods of daylight. Bubble size, production rate, and sound exposure level follow the concentration of dissolved oxygen, which in turn rises and falls with the availability of photosynthetically active radi...

Bubble nucleation on the surface of the primary heat exchanger in a domestic central heating system

The theoretical and experimental aspects of heterogeneous bubble nucleation are reviewed in the context of the micro bubbles present in a domestic gas fired wet central heating system. Such systems are mostly operated through the circulation of heated standard tap water through a closed loop circuit which often results in water supersaturated with dissolved air leading to micro bubble nucleation at the primary heat exchanger wall. This study will report the micro bubble nucleation in a standard domestic central heating system at typical operating conditions. Bubble nucleation rates have been calculated in the range of 0.3–4 bubbles/cm2 s with total system bubble production rates measured in the range of 784–6920 bubbles per second. Bubble nucleation rates have been calculated through the consideration of the heat exchanger surface under super saturation conditions. The lack of experimental research in this area is evident from the non-existence of experimental correlations developed for similar physical scenarios where low levels of super saturation predominate. Hence, the classical nucleation models are considered inadequate for adaptation to the present study. A correlation through the application of the model for non-classical heterogeneous nucleation is proposed, based on the experimental data of the present study.

Micro bubble formation and bubble dissolution in domestic wet central heating systems

16 % of the carbon dioxide emissions in the UK are known to originate from wet domestic central heating systems. Contemporary systems make use of very efficient boilers known as condensing boilers that could result in efficiencies in the 90-100% range. However, research and development into the phenomenon of micro bubbles in such systems has been practically non-existent. In fact, such systems normally incorporate a passive deaerator that is installed as a ‘default’ feature with no real knowledge as to the micro bubble characteristics and their effect on such systems. High saturation ratios are known to occur due to the widespread use of untreated tap water in such systems and due to the inevitable leakage of air into the closed loop circulation system during the daily thermal cycling. The high temperatures at the boiler wall result in super saturation conditions which consequently lead to micro bubble nucleation and detachment, leading to bubbly two phase flow. Experiments have been done on a test rig incorporating a typical 19 kW domestic gas fired boiler to determine the expected saturation ratios and bubble production and dissolution rates in such systems.

Optimizing the Air Dissolution Parameters in an Unpacked Dissolved Air Flotation System

Due to the various parameters that influence air solubility and microbubble production in dissolved air flotation (DAF), a multitude of values that cover a large range for these parameters are suggested for field systems. An unpacked saturator and an air quantification unit were designed to specify the effects of power, pressure, temperature, hydraulic retention time, and air flow on the DAF performance. It was determined that a pressure of 621 kPa, hydraulic retention time of 18.2 min, and air flow of 8.5 L/h would be the best controlled parameters for maximum efficiency in this unit. A temperature of 7 °C showed the greatest microbubble production, but temperature control would not be expected in actual application. The maximum microbubble flow from the designed system produced 30 mL of air (±1.5) per L of water under these conditions with immediate startup. The maximum theoretical dissolved air volume of 107 mL (±6) was achieved at a retention time of 2 h and a pressure of 621 kPa. To isolate and have better control over the various DAF operational parameters, the DAF unit was operated without the unsaturated flow stream. This mode of operation led to the formation of large bubbles at peak bubble production rates. In a real-world application, the large bubble formation will be avoided by mixing with raw unsaturated stream and by altering the location of dissolved air output flow.

Bursting bubble aerosols

AbstractWe depict and analyse the complete evolution of an air bubble formed in a water bulk, from the time it emerges at the liquid surface, up to its fragmentation into dispersed drops. To this end, experiments describing the drainage of the bubble cap film, its puncture and the resulting bursting dynamics determining the aerosol formation are conducted on tapwater bubbles. We discover that the mechanism of marginal pinching at the bubble foot and associated convection motions in the bubble cap, known as marginal regeneration, both drive the bubble cap drainage rate, and are responsible for its puncture. The resulting original film thickness $h$ evolution law in time, supplemented with considerations about the nucleation of holes piercing the film together culminate in a determination of the cap film thickness at bursting ${h}_{b} \propto {R}^{2} / \mathscr{L}$, where $R$ is the bubble cap radius of curvature, and $\mathscr{L}$ a length which we determine. Subsequent to a hole nucleation event, the cap bursting dynamics conditions the resulting spray. The latter depends both on the bubble shape prescribed by $R/ a$, where $a$ is the capillary length based on gravity, and on ${h}_{b} $. The mean drop size $\langle d\rangle \ensuremath{\sim} {R}^{3/ 8} \hspace{0.167em} { h}_{b}^{5/ 8} $, the number of drops generated per bubble $N\ensuremath{\sim} \mathop{ (R/ a)}\nolimits ^{2} \mathop{ (R/ {h}_{b} )}\nolimits ^{7/ 8} $ and the drop size distribution $P(d)$ are derived, comparing well with measurements. Combined with known bubble production rates over the ocean, our findings offer an adjustable parameter-free prediction for the aerosol flux and spray structure caused by bubble bursting in this precise context.

Recent Patents on Micro- and Nano-Bubble Applications and Potential Application of a Swirl-type Generator

Bubbles are widely used for various purposes, such as product cleaning, medical treatments, food processing, and fishery operations. There are several ways to produce smaller bubbles, such as using venturi tube cavitation, pressure discharge, ultrasonic waves, and swirl flows.?? In a number of recent patents, micro/nano-bubbles generated by a swirl flow have been used in several applications because this method involves low cost and simple design and provides high performance as well as the ability to generate very small bubbles. In recent years, the controllable bubble size generator, which enables the bubble size to be changed according to the sequence of operations, has been devised, and this swirl-type generator can be used to vary the bubble size and production rate. The swirl-type generator, which is operated using air and water as fluids, makes bubbles that are divided into smaller bubbles by means of the shear stress produced by the swirl flow. In the present paper, micro/nano-bubble applications and technology mentioned in recent patents are reviewed, and the applicability of the swirl-type generator was discussed. Various applications in six fields, i.e., industry, fishery, medicine, agriculture, home amenity, and miscellanea, were surveyed and introduced for the novel inventions, methods, techniques and design centered on the recent patents using the fine bubble characteristic properties such as electrical charges, suspended floating particles, and large surface area volume ratio. The present article analyzes and compares recent patents involving the use of micro/nano-bubbles and gives the extension/vector of the micro/nano-bubble utilization in profitable business prospects. Keywords: bubble generator, micro-bubble, nano-bubble, swirl flows, ultrasonic waves, industry, fishery, medicine, home amenities, agriculture

Utilization of hydrogen in electroflotation of silica

In this study the hydrogen bubble electroflotation of 3–15 μm diameter silica particles was investigated. Experiments were conducted to determine the influence of current density, solids concentration, mechanical agitation and the presence of dissolved gases on the rate of hydrogen gas production. It was found that approximately 98% of the theoretical hydrogen production resulted in gas bubbles. There was a very small increase in the hydrogen bubble production rate with the introduction of mechanical agitation, while the opposite trend was observed for the degassed electrolyte solution. Hydrogen gas production was found to be largely independent of the concentration of the suspended solids. Batchwise flotation experiments were also undertaken to determine the influence of particle diameter and solids concentration on flotation recovery. The experimental results were inputted into a recovery model, based largely on the work of Koh and Schwarz [1], that was applied to gain insight into the factors that influence the fractional coverage of the bubble surface by the particles. From the analysis it was found that, for this study at least, flotation recovery was controlled by either the bubble–particle aggregate rise velocity being greater than zero or the bubble–particle aggregate projected area being less than that of just the bubble.

Dynamics in space and time of four testate amoebae ( Difflugia spp.) co-existing in the zooplankton of a reservoir in southern China

We studied a long time series of the dynamics in space and time of four species of Difflugia (thecamoebae) that co-exist in the pelagic plankton of Liuxihe Reservoir, an oligo-mesotrophic impoundment in southern China, during 8–9 months (“summer” form March to November), and retreat to the benthos during the rest of the year (“winter”). We discuss the reasons for the winter retreat, and suggest that predator evasion may be involved, although temperature-linked physiological effects (like the rate of gas bubble production) appear more probable. Clear diel vertical migration of Difflugia was not observed, but patchiness was common. We found no evident lake edge-effects in the spatial pattern either, but the abundances were strongly influenced by trophic conditions and increased by up to one order of magnitude in the upstream, eutrophic sections of the reservoir.

Evaluation of a steady-state test of foam stability

We have evaluated a steady-state test of foam stability, based on the steady-state height of a foam produced by a constant velocity of gas flow. This test is mentioned in the book by Bikerman [Foams, Springer, Berlin, 1973] and an elementary theory was developed for it by Verbist et al. [J. Phys. Condens. Matter 8 (1996) p. 3715]. For the study, we used an aqueous solution of the cationic surfactant dodecyl trimethylammonium bromide, C12TAB, at a concentration of two times the critical micelle concentration (2 cmc). During foam generation, bubbles collapse at the top of the column which, in turn, eventually counterbalances the rate of bubble production at the bottom. The resulting balance can be described mathematically by an appropriate solution of the foam drainage equation under specified boundary conditions. Our experimental findings are in agreement with the theoretical predictions of a diverging foam height at a critical gas velocity and a finite foam height in the limit of zero velocity. We identify a critical liquid fraction below which a foam is unstable as an important parameter for characterizing foam stability. Furthermore, we deduce an effective viscosity of the liquid which flows through the foam. Currently unexplained are two experimental observations, namely sudden changes of the steady-state foam height in experiments that run over several hours and a reduction in foam height once an overflow of the foam from the containing vessel has occurred.

Experimental comparison between acoustic and pressure signals from a bubbling flow

Experiments were performed on both the acoustic and pressure signals produced by bubbles formed from an underwater nozzle. The data were analyzed by a comprehensive set of spectral and nonlinear-dynamical techniques. As air flow rates increase, it is well known that such flows became chaotic. However, the present study of both acoustic and pressure signals showed that chaos could appear in different regimes and was manifested in different ways in the acoustic and pressure signals. The use of different time delays for the chaotic analysis of acoustic and pressure signals were found necessary. The acoustic signals offer data primarily on the bubble size while the pressure signals offer data primarily on the bubble production rate. The present results suggest that chaos can appear in the bubble size and bubble production rate independently.

Sound generation on bubble coalescence following detachment

A system in which bubbles coalesced on formation was used to probe one mechanism by which bubbles create sound. The aim was to determine in which situations sound is produced and to predict its amplitude. A set of carefully co-ordinated high-speed video and acoustic timeseries showed that needle-formed bubbles generated loud bubble-acoustic emissions at the instant of coalescence of secondary bubbles with the primary bubble. As the air flow rate increased, the size and number of secondary bubbles increased, and the sound amplitude also increased. On coalescence, the sound pressure always rose initially. A dimensionless scaling found that the sound amplitude emitted scaled with the volume of the secondary bubble. This scaling was shown to be consistent with the sound-emission mechanism being the equalization of pressures in the coalescing bubbles. The trend in amplitude with bubble production rate was well predicted by the scaling.