Micro-fabricated electrolytic micro-bubblers

A phase-Doppler light-scattering method is used to measure, nonintrusively, liquid and bubble velocities and bubble size in vertical-upwards, dispersed, bubbly pipe flow. Bubble size measurements are also obtained with a video imaging technique. Optical distortion is eliminated, by using pipe material with index of refraction equal to that of water at room temperature, in combination with an index-of-refraction-matching box. Pure-liquid velocity and turbulence intensity test-measurements performed with the incorporation of this technique compare very well with existing data in pipe flow. Measurements of bubble velocity and size at two locations along the pipe are presented with emphasis on the near wall region. The experiments have been carried out at a Reynolds number of 12086 and a volumetric flow ratio of 2.7%. Bubble velocity fluctuation properties were found to be almost uniform in the core region. Bubble mean velocity was constant within one average bubble diameter from the wall and axial velocity fluctuations peaked at approximately half that distance. Velocity distributions near the wall were non-Gaussian and skewed towards lower values. The average bubble size was found to be in the range between 1200 μm and 1400 μm with standard deviations of the order of 500 μm. Smaller bubbles were found to be in the neighborhood of the wall.

A phase-Doppler light-scattering method is used to measure liquid and bubble velocities and bubble size in vertical-upwards, dispersed, bubbly pipe flow. The measurements are non-intrusive and therefore the possible physical effects of probe insertion are not present. Bubble size measurements are obtained with the phase-Doppler method and a video imaging technique which is also non-intrusive. Optical distortion is eliminated, by using pipe material with index of refraction equal to that of water in combination with an index-of-refraction-matching box. Pure-liquid velocity and turbulence intensity test-measurements compare very well with existing data in pipe flow. Measurements of bubble velocity and size at two locations along the pipe are presented with emphasis on the near wall region. The experiments have been carried out at a Reynolds number of 12086 and a volumetric flow ratio of 2.7%. Bubble velocity fluctuation properties were found to be almost uniform in the core region. Bubble mean velocity was constant within one average bubble diameter from the wall and axial velocity fluctuations peaked at approximately half that distance. Velocity distributions near the wail were non-gaussian and skewed towards lower values. The average bubble size was found to be in the range between 1200 μm and 1400 μm with standard deviations of the order of 500 μm. Smaller bubbles were found to be in the neighborhood of the wall.

The effects of twisted fin baffles on the microbubble formation from a venturi-type microbubble generator

Experimental bubble formation studies have been undertaken on air injection through a porous plate into fully developed turbulent salt-water flows in vertical rectangular channels of varying aspect ratio. This work was aimed at better understanding the effects of variables including pore size, channel size, channel pressure and gas-to-liquid mass flow ratio on the bubble size and bubble standard deviation. In this research, channel pressure was varied from 138–414 kPa (20–60 psi), the hydraulic channel diameter ranged from 1.82–10 mm which corresponded to aspect ratios from 10–1, mean porous plate pore sizes of 0.2 and 100 micron were used (media grade 0.2, 100) and liquid Reynolds numbers from 3400–30,000 were studied. Image processing techniques were used to measure bubble diameters from digital images taken of the bubbly flows which were back-lit via a high-intensity strobe light. The mean bubble diameters produced ranged from 106–1250 microns. Results show that the combined effects of channel pressure, channel geometry and flow rate on average bubble diameter can largely be captured by using wall shear stress at the air injection site whose calculation was based on previously published literature. Bubble diameter and standard deviation are reduced nonlinearly at higher wall shear stress and it is shown that for the bubbly flow regime the gas-to-liquid mass flow ratio has little effect on average bubble size over the conditions of this study.Copyright © 2013 by ASME

Experimental investigation of the thermal interactions of nucleation sites in flow boiling

Effects of pressure and fines content on bubble diameter in a fluidized bed studied using fast X-ray tomography

This paper describes the experiments designed to control bubble size during gas injection through porous media into liquid cross flow. A parametric study examined the effect of control variables on average bubble size and standard deviation. Results showed that for a given air and liquid flow rate, changing liquid channel height at the air injection site had the largest effect on bubble size and size distribution while varying porous media grade and electrolyte concentration had smaller, though significant, effects. In this study, the channel height was varied from 0.8 to 8 mm, porous media grade from 0.5 to 100 and salt concentration varied from zero to 3%. The resulting average bubble diameters were 0.085–2.5 mm.

In order to clarify the microscopic flow structure, the ultrasonic Doppler method was applied to the measurement of two-phase bubbly flow in vertical pipe (i.d.50mm). Liquid flow structure might strongly be influenced by the characteristic of the injected bubbles, i.e. bubbles’ size and void fraction. In this study, a bubble generator was newly designed with the purpose to control the bubble size and void fraction, independent of liquid main-flow rate. The experiment was performed at z/d = 66 from the bubble generator. Liquid flow rates were of the Reynolds numbers ranging from Rem = 3700 to 6200. The gas flow rate was constant at JG = 0.00348(m/s) at the measurement position. By analyzing the bubbles’ picture, it was confirmed that bubble size distribution and average bubble size were almost constant if the liquid flow rate were changed. The ultrasonic Doppler method has the capability of measuring the instantaneous velocity profiles of both phases at the same time. By processing the data based on pattern recognition, the recorded data can be classified to several groups. Using this method, the authors have tried to measure the bubbly flow in rectangular channel. In the present study, the application of this method to bubbly flow in circular pipe was satisfactory to obtain the liquid velocity distribution in bubbly flow and surrounding bubbles. From these results, it was clarified that velocity profile in bubbly flow in circular pipe has a maximum value near the pipe wall. Furthermore, velocity profiles around the bubble are influenced by leading bubbles.

This paper presents a comprehensive study based on multiphase-seepage and wellbore multiphase-flow theories. It establishes a model for calculating the rate of gas intrusion that considers various factors, including formation pore permeability, bottomhole pressure difference, rheology of the drilling fluid, and surface tension. Experiments were conducted to investigate the mechanism of gas intrusion under shut-in conditions, and the experimental results were employed to validate the reliability of the proposed method for calculating the gas intrusion rate. Furthermore, this research explores the transportation rates of single bubbles and bubble clusters in drilling fluid under shut-in conditions. Additionally, empirical expressions were derived for the drag coefficient for single bubbles and bubble clusters in the wellbore. These expressions can be used to calculate gas transportation rates for various equivalent radii of single bubbles and bubble clusters. The initial bubble size of intrusive gas, the transportation speed of intrusive gas in the wellbore, the rate of gas intrusion, and variations in the wellbore pressure after gas intrusion were analyzed. Additionally, a method was developed to calculate the rising velocity of bubble clusters in water based on experimental results. The study reveals that the average bubble size in the bubble cluster is significantly smaller than the size of single bubbles generated from the orifice. When the viscosity of the drilling fluid is low, the transportation velocity of the bubble cluster exhibits a positive correlation with the average bubble diameter. When the average bubble diameter exceeds 1 mm, the bubble velocity no longer varies with changes in the bubble-cluster diameter. The research results provide theoretical support for wellbore pressure prediction and pressure control under shutdown conditions.

The average large gas bubble size in slurry bubble columns is estimated using a spectral analysis method applied to measured pressure time series. A pressure time series measured in a bubble column consists of local pressure fluctuations and global pressure fluctuations. The local pressure fluctuations arise from the liquid velocity fluctuations induced by the large gas bubbles and by the changes in gas holdup. The standard deviation of these local pressure fluctuations is a measure of the average large bubble size. The coherence between the pressure time series measured at the sparger and at any other location in the column is used to separate the local pressure fluctuations from the global pressure fluctuations. The global pressure fluctuations are measured instantaneously throughout the column and form the coherent part of the pressure time series. The local pressure fluctuations, which are absent at the sparger, form the incoherent part of the pressure time series. In a 2‐D bubble column, a clear correlation is demonstrated between the incoherent standard deviation of the pressure time series and the average large gas bubble size obtained from video imaging. A good agreement is also found between this correlation and the 3‐D model proposed by Krishna et al. for predicting the average large bubble size in 3‐D (slurry) bubble columns. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Micro bubbles measuring tens of micrometers or less in diameter have recently been paid much attention. Swirl type, pressurizing dissolution, and perforated plate methods have been proposed for micro bubble generation. The swirl type method can generate micro bubbles even under low-pressure power in a simple structure. This study examined the effect of the swirl chamber inlet diameter on the bubble diameter in a swirl type micro bubble generator. The swirl chamber inlet diameter was varied in the range of 15-90 mm and the effect was examined. In order to clarify the effect of enlarged inlet diameter, the micro bubbles diameter was measured under changing water supply pressure and air flow rate, the behavior of air column in the swirl chamber was visualized, and the velocity distribution around outlet of swirl chamber was measured. As a result, when the swirl chamber inlet diameter was enlarged, the outflow form changed from an axial outflow to a radial outflow. The average bubble diameter could also be reduced. An average bubble diameter of 28 μm could be realized under the conditions of swirl inlet diameter of 90 mm and water supply pressure of 0.1 MPa gage.

Helium bubble evolution and hardening in 316L by post-implantation annealing

In this paper the liquid jet gas pump as an important gas-liquid contactor is investigated on bubble sizes. Its internal mixed effect is influenced by gas holdup, bubble size distribution and interfacial area. To improve the mixed effect, experiment investigations have been carried out in a modified down-flow liquid jet gas pump with special emphasis on gas distribution. The mixing tube and diffuser are made of transparent Perspex for visual observation. Bubble diameters in the diffuser have been measured by photographic and capillary method at different operating conditions. Under the same Reynolds number of orifice, about 80% of the bubble diameters range from 0.6 mm to 1.3 mm, which has no obvious effect on the gas-liquid flow rate ratio. The average bubble diameter increases by the decrease of Orifice Reynolds number at the same gas-liquid flow rate ratio (lower gas-liquid rate ratio), the maximal bubble size can reach 3 mm. With the decrease of gas-liquid flow rate ratio, gas gathers together in the wall and the stream appears non uniform, the sampling test shows that the bubble diameters have a small diminution. It is found experimentally that the bubble diameters are strongly dependent on Orifice Reynolds number and the bubble distribution is affected by gas-liquid flow rate ratio

Investigation of condition-induced bubble size and distribution in electroflotation using a high-speed camera

Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical properties. Recent studies have shown that methane gas and hydrate can coexist in gas hydrate–bearing sediments. Accurate calibration and understanding of the fundamental processes regarding such coexisting gas bubble dynamics is essential for geophysical characterization and hazard mitigation. We conducted high-resolution synchrotron imaging of methane hydrate formation from methane gas in water-saturated sand. While previous hydrate synchrotron imaging has focused on hydrate evolution, here we focus on the gas bubble dynamics. We used a novel semantic segmentation technique based on convolutional neural networks to observe bubble dynamics before and during hydrate formation. Our results show that bubbles change shape and size even before hydrate formation. Hydrate forms on the outer surface of the bubbles, leading to reduction in bubble size, connectivity of bubbles, and the development of nano-to micro-sized bubbles. Interestingly, methane gas bubble size does not monotonously decrease with hydrate formation; rather, we observe some bubbles being completely used up during hydrate formation, while bubbles originate from hydrates in other parts. This indicates the dynamic nature of gas and hydrate formation. We also used an effective medium model including gas bubble resonance effects to study how these bubble sizes affect the geophysical properties. Gas bubble resonance modeling for field or experimental data generally considers an average or equivalent bubble size. We use synchrotron imaging data to extract individual gas bubble volumes and equivalent spherical radii from the segmented images and implement this into the rock physics model. Our modeling results show that using actual bubble size distribution has a different effect on the geophysical properties compared to the using mean and median bubble size distributions. Our imaging and modeling studies show that the existence of these small gas bubbles of a specific size range, compared to a bigger bubble of equivalent volume, may give rise to significant uncertainties in the geophysical inversion of gas quantification.