Rate Of Bubble Formation Research Articles

Experimental study on the effect of Tin-doped copper oxide capillary-porous surfaces on pool boiling heat transfer performance

The novel tin-doped copper oxide capillary-nano-porous surfaces were created using the easy and affordable sol-gel method. The pool's boiling incipience wall superheat on a capillary-nano-porous surface was lower than a non-coating surface. Bubble flow visualization investigation demonstrates that the coating's shape can significantly affect the processes involved in improving heat transmission. An investigation of the nano-porous surface's long-term stability was conducted using water. Repeated cycles of studies on created nano-porous surfaces revealed a little divergence in wall superheat and surface shape. The present study's tin-doped copper oxide coated surface (Sn-CuO-600) has a higher CHF (critical heat flux) and HTC (heat transfer coefficient). Heat transmission by boiling rises when a substantial quantity of bubbles are rapidly evacuated from the heating exterior. It is observed that a greater quantity of tiny, spherical bubbles are continually growing on the superhydrophilic Sn-CuO-600 surface. Compared to the plain copper surface, the Sn-CuO-600 surface experiences a significant reduction in bubble departure times. The rate of bubble formation is increased by superhydrophilic surfaces, which also reduce bubble dimensions and release times. Consequently, the Sn-CuO-600 surfaces exhibit superior heat transfer ability throughout boiling.

Bubble-mediated generation of airborne nanoplastic particles.

Micro- and nanoplastic particles have been detected in most environmental compartments. The presence of microplastics in the remote marine atmosphere and close to large lakes suggests bubble mediated water-air transfer as a source of airborne microplastics, however, quantitative estimates of plastic emission from surface waters remain uncertain. In this work, we elucidate the emission of submicron polystyrene nanospheres by bubble bursting in a laboratory setting from low salinity waters (salinity 0-1.0 g kg-1), polystyrene particle diameter (103, 147 and 269 nm), aqueous particle number concentrations in the range 4 × 107-2 × 109 cm-3, and bubble formation rate (0.88-3.35 L min-1 of air). Production of polystyrene aerosols was demonstrated using a scanning mobility particle sizer and confirmed by analysis of filter samples using pyrolysis gas chromatography coupled to mass spectrometry. We show that production of polystyrene aerosol particles scales linearly with the number concentration of plastic particles in the water. Our results suggest that small amounts (0.01 g kg-1) of salt increase polystyrene particle production. To the best of our knowledge this is the first study of bubble mediated water-air transfer of plastic particles as small as 100 nm.

A Scalable, Modular Degasser for Passive In-Line Removal of Bubbles from Biomicrofluidic Devices.

Bubbles are a common cause of microfluidic malfunction, as they can perturb the fluid flow within the micro-sized features of a device. Since gas bubbles form easily within warm cell culture reagents, degassing is often necessary for biomicrofluidic systems. However, fabrication of a microscale degasser that can be used modularly with pre-existing chips may be cumbersome or challenging, especially for labs not equipped for traditional microfabrication, and current commercial options can be expensive. Here, we address the need for an affordable, accessible bubble trap that can be used in-line for continuous perfusion of organs-on-chip and other microfluidic cultures. We converted a previously described, manually fabricated PDMS degasser to allow scaled up, reproducible manufacturing by commercial machining or fused deposition modeling (FDM) 3D printing. After optimization, the machined and 3D printed degassers were found to be stable for >2 weeks under constant perfusion, without leaks. With a ~140 µL chamber volume, trapping capacity was extrapolated to allow for ~5-20 weeks of degassing depending on the rate of bubble formation. The degassers were biocompatible for use with cell culture, and they successfully prevented bubbles from reaching a downstream microfluidic device. Both degasser materials showed little to no leaching. The machined degasser did not absorb reagents, while the FDM printed degasser absorbed a small amount, and both maintained fluidic integrity from 1 µL/min to >1 mL/min of pressure-driven flow. Thus, these degassers can be fabricated in bulk and allow for long-term, efficient bubble removal in a simple microfluidic perfusion set-up.

High-speed imaging of degassing kinetics of CO2–water mixtures

The exsolution of gas molecules from gas–liquid mixtures plays a significant role in a wide range of applications from industrial processes such as metal casting to subsurface flow of oil or geothermal waters. This study aims to improve the understanding of the conditions under which free gas bubbles start forming in CO2–water mixtures. The bubble point pressure was determined under various different conditions like the temperature and initial pressure of the mixture along with other parameters such as the bubble growth rate. A series of depressurization experiments at high pressure and temperature (up to 100 bar and 100 °C) is performed using a pressure cell that allows for visual monitoring of the degassing process. Bubble formation during the depressurization process is recorded using a high-speed camera paired with a uniform light source along with a pressure transducer and thermocouple. Image analysis allows for the determination of the bubble point pressure and rate of bubble formation. For CO2 in its gaseous state and at moderate temperatures, decent agreement between experimental results and the theoretical bubble point pressure is found, although significant deviations are observed at elevated temperatures. More pronounced differences in bubble point are observed for mixtures starting out at high pressures where CO2 is a supercritical fluid, which lead to lower than expected bubble point pressures.

Small bubbles formation and contribution to the overall gas holdup in large diameter columns of very high viscosity oil

A limited number of studies are available in literature on the small bubbles which create from gas-very high viscosity oils interaction and its contribution to the gas holdup in the system. The rate of small bubble formation has an important impact on heat and mass transfer in many chemical and industrial processes. The work presented in the current paper provides unique information on the formation of bubbles of millimetre diameter in high viscosity oil. A column of 290 mm diameter and Silicon oil of 330 Pa.s viscosity, were employed besides Electrical Capacitance Tomography and a high-resolution camera to investigate the characteristics of the small bubbles. Mechanism of bubble generation, effect of gas injection time and flowrate were studied. The average void fraction, total gas-liquid height, overall Probability Density Function (PDF) profile, small bubbles volume fractions and diameter were measured. Small bubbles generate from the eruption of large bubbles, at gas injection nozzles, coalescence of large bubbles, and at liquid bridges at transition to churn flow regime. Properties and concentration of the small bubbles are controlled by the location of the bubble generation, gas flowrate, and gas injection time. Small bubbles contribute by 6.6- 30% to the total gas holdup. Bubble diameter increased from 0.68 mm to 0.75 mm and decreased from 1.1 mm to 0.75 mm at the top and the bottom sections of the column respectively after 60 minof gas injection.

Heat-transfer characteristics of CO[formula omitted] boiling flow in the regenerative cooling channel of an Mg/CO[formula omitted] powder rocket engine for Mars missions

To solve the problem of thermal protection posed by the long working time of Mg/CO2 powder rocket engines, an experimental system is designed to study the heat-transfer characteristics of liquid CO2 in the regenerative cooling channel. How the heat flux, coolant temperature, mass flux, and back pressure influence the heat-transfer coefficient, the thermodynamic quality, and the gas-phase formation point of nearly saturated CO2 is studied. The heat-transfer coefficient is found to increase with increasing mass flux or decreasing inlet temperature. Higher heat flux increases the rate of bubble formation and promotes nucleate-boiling heat transfer, but it also intensifies the film boiling, thereby degrading the heat-transfer performance. Lower back pressure does not affect the heat-transfer performance in the nucleate-boiling region, but it worsens it in the film-boiling region. It is also found that the classical boiling-heat-transfer models do not predict the experimental heat-transfer coefficient well. Combined with experimental data, how reduced pressure affects heat transfer is considered, and a new empirical correlation formula is proposed for the heat-transfer coefficient of CO2 near saturation. The optimized model can successfully predict 90.23% of the experimental data, and the prediction accuracy is improved greatly. The present research provides a theoretical basis for designing a regenerative cooling scheme for an Mg/CO2 powder rocket engine.

Reversible Speed Regulation of Self-Propelled Janus Micromotors via Thermoresponsive Bottle-Brush Polymers.

This work reports a reversible braking system for micromotors that can be controlled by small temperature changes (≈5 °C). To achieve this, gated‐mesoporous organosilica microparticles are internally loaded with metal catalysts (to form the motor) and the exterior (partially) grafted with thermosensitive bottle‐brush polyphosphazenes to form Janus particles. When placed in an aqueous solution of H2O2 (the fuel), rapid forward propulsion of the motors ensues due to decomposition of the fuel. Conformational changes of the polymers at defined temperatures regulate the bubble formation rate and thus act as brakes with considerable deceleration/acceleration observed. As the components can be easily varied, this represents a versatile, modular platform for the exogenous velocity control of micromotors.

Investigations of Hydrogen Evolution Reaction on Platinum in Alkaline Medium Using an Inverted Rotating Disc Electrode

Electrochemical energy storage and conversion using hydrogen has become important in the area of sustainable energy and development1. HER is one of the key reactions in alkaline water electrolysis and chlor-alkali industry2. Though water electrolysis is not a cost-effective method yet,it finds attention as it produces high purity hydrogen3.Platinum is a very active catalyst for HER.The mechanism of HER is believed to be a combination of three elementary steps, 1. the Volmer (V) step, where water molecules are reduced to produce adsorbed hydrogen, followed by either the Heyrovsky (H) step or the Tafel (T) recombination step. 2. In H step, a hydrogen molecule is formed by an electron transfer reaction between an adsorbed hydrogen and another water molecule to produce a hydrogen molecule in the desorbed state. 3. In T step,two adsorbed surface hydrogen next to each other react to form a hydrogen molecule by chemical desorption4.Until now, the published HER studies were restricted to Tafel slope analysis under a small over potential range and were conducted in a stationary electrode or a rotating disc electrode(RDE) set up. One difficulty in using RDE is the formation of gas bubbles which block the electrode surface. At small overpotentials, the bubble formation rate is very small and RDE is sufficient for performing HER. This restriction of small overpotential limits the experimental range and confidence in the model. Besides, using Tafel slope to determine the underlying mechanism is fraught with pitfalls, and it is desirable to fit the entire polarization data to the complete model.In this work, cathodic polarization of HER on inverted Pt disc electrode at different concentrations of KOH/NaOH are performed. In inverted RDE experimental arrangement,the electrode surface is faced upward and the gas bubbles from the electrode are released quickly.This expands the experimental range for HER studies. In all the experiments, sufficient NaClO4 was added so that the total concentration of anions/ cations was maintained to 1 M, and the solution resistance effects are minimized. MillQ water (Millipore) was used to prepare the solutions. A three electrode setup with Pt mesh as counter electrode and Ag/AgCl in 3 M NaCl as reference electrode was used. Prior to acquisition of polarization current at each cathodic potential, the electrode was activated to increase the catalytic activity and reproducibility. The experimental results are compared with model predicted results of VH, VHT and VT models and the best fit kinetic parameter values are determined. References A. Eftekhari, International Journal of Hydrogen Energy, 42 (16), 11053-11077 (2017).F. Safizadeh, E. Ghali, and G. Houlachi, International Journal of Hydrogen Energy, 40 (1), 256-274 (2015).A. Lasia, in Handbook of fuel cells: fundamentals technology and applications (eds W. Vielstich, A. Lamm, H. A. Gasteiger and H. Yokokawa), Vol. 2, p. 414-440, (2010).D. A. Harrington and B. E. Conway, Electrochimica Acta, 32 (12), 1703-1712 (1987).

Quantitative analysis of the stochastic approach to quantum tunneling

Recently there has been increasing interest in alternate methods to compute quantum tunneling in field theory. Of particular interest is a stochastic approach which involves (i) sampling from the free theory Gaussian approximation to the Wigner distribution in order to obtain stochastic initial conditions for the field and momentum conjugate, then (ii) evolving under the classical field equations of motion, which leads to random bubble formation. Previous work showed parametric agreement between the logarithm of the tunneling rate in this stochastic approach and the usual instanton approximation. However, recent work [1] claimed excellent agreement between these methods. Here we show that this approach does not in fact match precisely; the stochastic method tends to overpredict the instanton tunneling rate. To quantify this, we parameterize the standard deviations in the initial stochastic fluctuations by $\epsilon \sigma$, where $\sigma$ is the actual standard deviation of the Gaussian distribution and $\epsilon$ is a fudge factor; $\epsilon = 1$ is the physical value. We numerically implement the stochastic approach to obtain the bubble formation rate for a range of potentials in 1+1-dimensions, finding that $\epsilon$ always needs to be somewhat smaller than unity to suppress the otherwise much larger stochastic rates towards the instanton rates; for example, in the potential of [1] one needs $\epsilon \approx 1/2$. We find that a mismatch in predictions also occurs when sampling from other Wigner distributions, and in single particle quantum mechanics even when the initial quantum system is prepared in an exact Gaussian state. If the goal is to obtain agreement between the two methods, our results show that the stochastic approach would be useful if a prescription to specify optimal fudge factors for fluctuations can be developed.

Predictors of Bubble Formation and Type Obtained With Pneumatic Dissection During Deep Anterior Lamellar Keratoplasty in Keratoconus

To identify predictors of bubble formation and type during big-bubble deep anterior lamellar keratoplasty (BB-DALK) performed in keratoconus at different stages of severity. Retrospective Cohort Study. Setting: University Magna Græcia (Catanzaro, Italy); Study Population: Consecutive keratoconus patients undergoing BB-DALK from September 2014 to February 2019. Keratometric astigmatism, mean keratometry value (K-mean), highest keratometry value (K-max), thinnest point, anterior segment optical coherence tomography (AS-OCT)-based stage of ectasia. Rate of bubble formation and type; number and fate of micro-/macroperforation; conversion to mushroom keratoplasty (MK); comparison of parameters in patients with bubble formation vs failure and in type 1 vs type 2 bubble; areas under the curves (AUC) of preoperative parameters for distinguishing between bubble types. Pneumatic dissection succeeded in 113 of 155 eyes (72.9%), with 100 type 1 bubbles (88.4%), 11 type 2 (9.8%), and 2 mixed-type (1.8%). Microperforations were managed conservatively in type 1 bubbles; macroperforations occurring in both types of bubbles required conversion to MK. Preoperative K-mean and K-max values were significantly higher in eyes in which bubble formation succeeded (respectively, P= .006 and P < .013). Type 1 bubbles formed in eyes with significantly lower age, K-mean, and AS-OCT stages and higher pachymetric values (always P < .029). Age had the highest diagnostic power for discrimination between bubble types, followed by AS-OCT stage, pachymetry, K-mean, and astigmatism (respectively, AUC= 0.861, 0.779, 0.748, 0.700, 0.670). Older age and advanced stages of keratoconus were predictors of type 2 bubble formation during BB-DALK that was associated with an increased risk of complications.

Solvent role on covalent organic framework thin film formation promoted by ultrasound

The present study reports the formation of thin films from covalent organic framework (COF) via ultrasound using different solvents. The morphology of the resulting films was correlated to the rate of bubble formation and the maximum bubble size, through derivations from the Rayleigh-Plesset equation. Solvents were chosen according to their different characteristics, such as polarizability, ability to disperse solutes, and bonding hydrogen bond. A very thin and organized film was obtained after exfoliation of the COF by sonication in polar solvents, such as ethanol, while rougher three-dimensional films were obtained from hexane. Our investigation revealed that there is a strong correlation (Pearson’s r > 0.9) between the bubble formation capacity of a solvent, the respective polar HSP and COF film topography formed as a result of the ultrasound processing.

Real-time magnetic resonance imaging of fluidized beds with internals

The effect of internals on the fluidization dynamics in three-dimensional (3D) cylindrical fluidized beds was studied using real-time magnetic resonance imaging. Instantaneous snapshots of particle velocity and particle position were acquired for gas velocities U below and above the minimum fluidization velocity Umf. Below Umf, we found local fluidization and gas bubbling in areas adjacent to an inserted horizontal tube, likely caused by the gas locally exceeding Umf as it flows around the insert. Above Umf, the presence of the insert in the bed affected the fluidization dynamics. The wake region above the insert exhibited a lower average particle velocity and reduced velocity fluctuations as well as a substantially reduced number and size of gas bubbles as compared to a reference bed without internals. The extent of this wake region was found to be approximately as wide as the insert, and it extended from the top of the insert to the free surface of the bed. Moreover, the presence of internals also affected the regions below the insert by showing an increased rate of bubble formation directly below the inserted tube. The present work can provide relevant information on the design of fluidized beds with internals. Moreover, the data gathered in this work can be used to validate the accuracy of 3D numerical models of gas-solid systems.

“Invisible” QCD axion rolling through the QCD phase transition

Visible matter in the current Universe is a consequence of the phase transition of the strong force, quantum chromodynamics (QCD). This phase transition has occurred at the Universe temperature around Tc≃165 MeV while it was expanding. Strongly interacting matter particles are quarks above Tc, while they are pions, protons and neutrons below Tc. The spin degrees of freedom 37 (u and d quarks and gluons) just above Tc are converted to 3 (pions) after the phase transition. This phase transition might have been achieved mostly at supercooled temperatures. The supercooling was provided by the expansion of the Universe. We obtain the effective bubble formation rate α(T)≈104−5 MeV and the completion temperature of the phase change (to the hadronic phase), Tf≃126 MeV. During the phase transition, the scale factor R has increased by a factor of 2.4. This provides a key knowledge on the energy density of “invisible” QCD axion at the full hadronic-phase commencement temperature Tf, and allows for us to estimate the current energy density of cold dark matter composed of “invisible” QCD axions.

Results of viscobubble deep anterior lamellar keratoplasty after failure of pneumatic dissection

AimTo report the outcomes of bubble formation obtained by means of intrastromal injection of ophthalmic viscoelastic device (OVD) after failure of pneumatic dissection for deep anterior lamellar keratoplasty (DALK).MethodsDALK was...

Effect of optimized infusion process on the safety of outpatient infusion

Objective To explore the effect of optimal infusion flow on the safety of outpatient infusion based on the law of bubble precipitation. Methods A total of 488 infusion outpatients who were treated in the First Hospital of Zibo from January to March 2016 were selected by convenient sampling method. All the selected patients were divided into observation group (250 cases from outpatient infusion room 1) and control group (238 cases from outpatient infusion room 2) . The control group was treated according to the conventional infusion regimen, and the observation group was treated with the optimized infusion regimen. Bubble formation rate during infusion process, infusion safety and nursing satisfaction were compared between the two groups. Results The bubble formation rate was 18.40% in the observation group and 30.25% in the control group. The difference was statistically significant (χ2=6.229, P<0.001) . The bubble timely treatment rate was 100.00%, which was significantly higher than 53.36% in the control group (χ2=78.443, P<0.001) . The peak time of bubble precipitation in the observation group and the control group was (56.30±9.73) min and (40.55±5.81) min respectively, there was a significant difference between the two groups (t=10.903, P<0.001) . The satisfaction score of the observation group was (13.19±0.93) , significantly higher than that of the control group (9.40±1.06) (t=4.652, P=0.010) . Conclusions The optimized infusion care program can ensure the safety of outpatient infusion and improve the satisfaction of patients, which has clinical guiding significance. Key words: Veins; Safety; Infusion; Bubble; Outpatient clinic

Pulsed laser deposition of amorphous molybdenum disulfide films for efficient hydrogen evolution reaction

At high current density during the hydrogen evolution reaction (HER) process, the active layer for most of MoS2-based electrocatalysts suffers from pulverizations and easily drops-off due to a high rate of bubble formation and strong stirring. Herein, a facile pulsed laser deposition (PLD) method is used to fabricate amorphous molybdenum disulfide (MoS2) films on gold-coated carbon cloth (Au/CC) for HER test. Because of the strong anchoring interaction between MoS2 catalysts and the Au/CC substrate during the underlying laser ablation process, remarkable stability with 5000 continuous HER cycles has been achieved in the acid media. Furthermore, the as-obtained MoS2 catalyst shows a small Tafel slope of 48 mV decade−1, an onset overpotential of 132 mV and the overpotential of 180 mV at a current density of 10 mA cm−2. These results demonstrate that PLD is a very promising technique for making the film electrodes for application in electrocatalytic process.

Experimental study and analytical modeling of an alkaline water electrolysis cell

A traditional alkaline aqueous electrolyzer is investigated by using a 3-electode structure that enables the reaction resistance of each individual electrode to be accurately monitored. Combining experimental observations with resistance-based model analysis, we establish a quantitative relationship between current density and key voltage losses, including losses due to thermodynamics, kinetics, ohmic, and mass transport. These results demonstrate that the oxygen evolution reaction and bubble effects play crucial roles in determining electrolyzer performance. By varying the distance between electrodes, 2 effective OH− conductivities in 0.4M KOH are found to be 0.1333 and 0.9650 second cm−1, depending on bubble formation and release rate at the electrode interface. Moreover, bubble coverage on electrode surface achieves a steady state of 96% when current density is above 0.1 A cm−2. In the study of various electrolyte concentrations, all the model predictions show good agreement with experimental results, confirming its ability to capture actual cell performance. This newly presented empirical resistance-based model provides a practical framework to simulate complicated electrolysis reactions, serving as a comprehensive guide for continuous improvement of water electrolysis.

On the relationship of drop entrainment with bubble formation rates in oil mist filters

Abstract A comparative investigation was conducted on bubble formation and drop entrainment rates from oil mist filters in steady state operation, in order to establish a firm link between the two mechanisms. Rates were measured as a function of key filter operating parameters at different points of the filter surface, using wettable glass microfiber media as typical representatives of this application. Also, data for the thickness of the drainage film were obtained along the rear filter surface. For a given set of operating conditions, the bubble formation rate, the entrainment rate and the thickness of the oil film were found to increase roughly in proportion between the top and the bottom of the (vertically installed) filter. Bubble formation rates increased roughly tenfold along that path, from typically about 500–5000 bubbles per s and cm2, while entrainment rose from about 1000–3000 small drops per s and cm2. The drop size was narrowly confined to between about 1 and 2 µm, regardless of vertical position on filter surface and operating conditions. Both rates increased systematically with oil loading rate, but were relatively independent of the airflow velocity. The average number of fragment drops per bubble was on the order of 1, independent of oil loading rate. Independent measurements of bubble fragmentation on a free oil surface also gave an average fragment-to-bubble ratio close to unity for small bubbles (≤3 mm), but showed an increase ∼d2 for larger bubbles. Overall, these measurements lend strong support to the contention that bubbling is the dominant mechanism of entrainment from the type of oil mist filter media investigated.

Control of Accumulation of Cu(I) in Copper Sulfate Electroplating Plating Solution

Formation and accumulation of Cu(I) in copper sulfate electroplating solutions were discussed. By electrolysis, the accumulation of Cu(I) in the plating solutions was also confirmed in the laboratory. Accumulation rate and amount will depends on the current density and electrolysis time and the dissolved gases. Cu(I) is held in an aqueous solution as a complex with PEG, and gradually it is consumed by oxidation or disproportionation reaction. In the plating solutions using a nano bubble water, formation and accumulation rate of Cu(I) was different by gas species dissolved. Our results indicate the possibility for control of Cu(I) in the plating solutions.

Micro-explosion of liquid intermediates during the fast pyrolysis of sucrose and organosolv lignin

A new methodology has been proposed to describe of the dynamics of bubble formation during pyrolysis of Organosolv lignin and sucrose (surrogates for biomass) using fast speed visualization (125fps) with mathematical modeling. The model uses a population balance to predict overall rates of bubble birth and death, bubble bursting, and aerosol ejection. The experimental studies were performed on a uniquely modified CDS Analytical Pyroprobe 5000 to visualize the formation of bubbles within the liquid intermediate phase at heating rates close 100°C/s. Experimentally, we observed that bubbles follow a log-normal distribution versus bubble size within the liquid intermediate phase for both materials. This distribution function changes over time due to increased viscosity from solidification reactions that generate char and the changes in the rate of bubble formation. Micro-explosion intensity was used to estimate aerosol ejection intensity. The model predicts aerosol ejection yields of 21.18% w/w from Organosolv lignin and 17.40% w/w from sucrose during pyrolysis with an average droplet size of 10μm.