Content Of Gas Bubbles Research Articles

Unsteady flow of bubble liquid in hydraulic systems of aircraft and helicopters

The subject of this work is the phenomenon of a water hammer in a liquid that contains a small volume of gas bubbles. Historically, this phenomenon began to be studied as the dynamics of gas bubbles (Rayleigh-Pleset equation). Today, thanks to progress in computer technology, this phenomenon is studied at the level of bubble deformation during hydraulic shock. Another approach is to consider the dynamics of a multiphase (two-phase) medium in the form of a bubbly liquid. After several assumptions, the main one being a relatively small gas content in the liquid, the model consists of two differential equations with respect to the shock wave propagation speed and the resulting pressure perturbations. The specified system of equations differs from the corresponding classical water hammer equations: they consider the convection of the velocity field. In addition, the friction of the liquid against the wall according to the Weisbach-Darcy model is considered. Because of the small content of gas bubbles, the Weissbach-Darcy friction is approximated in the same way as in a homogeneous liquid, i.e., in a certain sense, greater than the real friction. Maybe that is why more or less physical results are obtained only for small values of the dimensionless parameter responsible for the friction of the liquid against the wall. It concerns the non-contradiction of the assumptions and the results obtained on their basis. Thus, in the front region of the shock pulse, where the pressure increases, the radial velocity of the bubbles is negative; however, for relatively large values of the friction parameter, the maximum pressure disturbance moves from the center of the shock pulse. This contradicts the assumption about compression: after passing the maximum pressure, gas bubbles expand due to a decrease in pressure. The graphical dependence obtained in this study are compared with the results related to a homogeneous liquid. They agree, but the shock pulse in a bubbly liquid is not as concentrated in space as that in a homogeneous liquid. Its length is 10-12 times greater than the corresponding value in a homogeneous liquid. Research methods are purely theoretical. The well-known bubble liquid model is used as a single-speed model continuum. Differential equations are solved analytically, approximately (series expansion), and numerically. In addition, the original approach of obtaining an analytical solution of an autonomous system is used-finding the function of pressure disturbances from the velocity of propagation of the shock pulse (and vice versa). Conclusions. A simple one-dimensional hydraulic model of shock wave (impulse) propagation in a bubbly liquid is proposed. In contrast to classical ideas (solutions) about a water hammer, which consists of two waves of opposite directions of propagation, a shock pulse is a region of pressure disturbances in which the speed of motion of fluid particles is also variable – from the maximum value to almost zero.

Theoretical and Experimental Studies of Acoustic Reflection of Bubbly Liquid in Multilayer Media

Bubbly liquids are widely present in the natural environment and industrial fields, such as seawater near the ocean bottom, the multiphase flow in petroleum reservoirs, and the blood with bubbles resulting in decompression sickness. Therefore, accurate measurement of the gas content is of great significance for hydroacoustic physics, oil and gas resources exploration, and disease prevention and diagnosis. Trace bubbles in liquids can lead to considerable changes in the acoustic properties of gas–liquid two-phase media. Acoustic measurements can therefore be applied for trace bubble detection. This study derived the reflection coefficient of acoustic waves propagating in a sandwich layering model with liquid, bubbly liquid, and liquid. The influences of gas contents on the reflection coefficient at the layer interface were analyzed based on theoretical calculations. It was revealed that the magnitude of the reflection coefficient and the frequency interval between its valleys have a quantitative correlation with the gas contents. Thus, a novel means to detect the contents of trace bubbles was proposed by evaluating the reflection coefficients. The reflection features of a thin layer with bubbly liquid were then studied through experiments. It was validated by acoustical measurements and theories that the reflection coefficient is considerably sensitive to the change of gas contents as long as the gas content is tiny. With the increasing gas content, the maximum value of the reflection coefficient increases; meanwhile, the frequency intervals between the valleys become smaller. However, when the gas content is extensive enough, e.g., greater than 1%, the effect of the change of gas content on the reflection coefficient becomes inapparent. In that case, it is not easy to measure the gas content by the acoustic reflection signals with satisfying precision. This proposed method has potential applications for the detection of trace gas bubble content in several scenarios, e.g., decompression illness prevention and diagnosis.

Ultrasonic method for measuring of gas bubbles in liquids

The paper proposes to use an ultrasonic method to measure the content of gas bubbles in liquids. The task is relevant in various applications. Industrial ultrasonic analyzer STOK-101 was used to implement the method.

MATHEMATICAL MODELING OF LADLE FURNACE THERMAL CONDITIONS DURING GAS-BUBBLE MELT BLOWING. REPORT IV

A significant effect on heat transfer during copper fire refining in a ladle furnace is caused not only by forming and motion of gas bubbles in a melt, but also by the volume content of gas bubbles. The presented mathematical model analyzes the effect of melt gas fullness during blowing and gas temperature under the cover on an average temperature of the melt being refined.

Distributions of crystals and gas bubbles in reservoir ice during growth period

In order to understand the dominant factors of the physical properties of ice in ice thermodynamics and mechanics, in-situ observations of ice growth and decay processes were carried out. Two samplings were conducted in the fast and steady ice growth stages. Ice pieces were used to observe ice crystals and gas bubbles in ice, and to measure the ice density. Vertical profiles of the type and size of ice crystals, shape and size of gas bubbles, and gas bubble content, as well as the ice density, were obtained. The results show that the upper layer of the ice pieces is granular ice and the lower layer is columnar ice; the average crystal size increases with the ice depth and remains steady in the fast and steady ice growth stages; the shape of gas bubbles in the upper layer of ice pieces is spherical with higher total content, and the shape in the middle and lower layers is cylinder with lower total content; the gas bubble size and content vary with the ice growth stage; and the ice density decreases with the increase of the gas bubble content.

Plant-mediated transport and isotopic composition of methane from shallow tropical wetlands

The methane (CH4) content of gas bubbles in sediments and CH4 emission from plants in the Pantanal wetland of Brazil was examined across a depth gradient to ascertain the relative importance of plant-mediated CH4 emission versus ebullition. Sediment bubbles contained >50% CH4 at sites with water depths >1 m but often contained <50% CH4 in shallower waters. Previous work has shown that bubble % CH4 is related to ebullition rates, and therefore these patterns are suggestive of greater CH4 emission by ebullition from deeper waters compared to waters <1 m in depth. Stable isotope ratios of carbon and hydrogen in the CH4 showed evidence for significant CH4 oxidation but no apparent relation with water depth. Shallower waters typically contain rooted emergent plants with erect, vertical stems or petioles, whereas in waters deeper than ~1 m, emergent aquatic plants are limited to rooted forms with long stems that float at the water surface. Rooted emergent plants typical of deeper waters had low rates of CH4 emission (0.0–0.2 mg d−1 CH4 for individual plants) compared to species typical of inundation depths <1 m (1.6–7.5 mg d−1 CH4). These observations suggest that tropical savanna floodplains like the Pantanal with inundation depths >1 m have low rates of CH4 emission via rooted emergent and floating-leaf plants, in contrast to results from shallower rice fields and temperate wetlands in which plant-mediated transport dominates CH4 emission from vegetated waters.

Effective thermal conductivity of reservoir freshwater ice with attention to high temperature

AbstractA study on effective thermal conductivity (ETC) of natural ice in a reservoir with &lt;3% gas content and ∼300 mg L−1 dissolved matter content in the parent water was conducted in a laboratory. Ice sections were prepared to obtain the ice crystal structure, gas bubble content and ice density. Profiles of horizontal and vertical thermal conductivity of ice samples were determined with attention to relatively high temperature spanning 0 to –10°C. A detailed comparative analysis was conducted of the effects on ETC of direction, ice crystal structure, gas bubbles and temperature. Gas inclusions had little impact on the thermal conductivity of natural reservoir ice due to their quite low content (&lt;3%). At high ice temperature the ETC decreases remarkably as ice temperature approaches the melting point, as the ETC of sea ice does due to its brine volume at ice temperature approaching its melting point. The measured conductivities for temperatures higher than –4°C were less than expected from previous work on saline ice. Whether this was due to the measurement techniques or actual properties of the reservoir ice is not clear. The present findings could lead to better understanding of the thermal processes of ice in natural freshwater bodies.

Influences of gas bubble and ice density on ice thickness measurement by GPR

Lake ice thickness changes with regional hydrometeorology and is closely associated with global climate change. We tested the detection of ice thickness using ground penetrating radar (GPR) in the Hongqipao reservoir. Ice crystals, gas bubbles, ice density and ice thickness were also determined by concurrently drilling for validation. During the tests the gas bubble content was high in the upper and low in the bottom, ice density varied with the bubble content, and the ice thickness was not homogeneous. By comparisons between radar detected and in-situ measured ice thicknesses with theoretical analyses of the influence of gas bubble content on the dielectric constant, a three-layer model with snow, granular ice, and columnar ice was established and the transmission speed of radar wave within the ice was determined. Experience reveals that the equivalent dielectric constant can be used to evaluate the wave speed and the values at 1/3 ice cover depth can be used as equivalent values. Besides, the difference between the theoretical transmission time and the real detection time induced by large gas bubbles increases nonlinearly with the theoretical transmission time or ice thickness.

A Pilot Study Examining the Frequency and Quantity of Gas Embolization during Operative Hysteroscopy Using a Monopolar Resectoscope

Study Objective To assess baseline frequency of gas embolization during standard monopolar resectoscopic surgery. Design Prospective, nonrandomized, observational study (Canadian Task Force classification II-2). Setting Tertiary care medical center. Patients Eleven women and three controls. Intervention Operative hysteroscopy. Measurements and Main Results Echocardiography and serum studies were performed to detect bubble formation in the inferior vena cava, hepatic veins, and right heart. Gas bubbles were present in the hepatic veins or right heart in 10 patients and no controls. No patients had changes in coagulation profile and only one had clinical changes during surgery. Conclusion Gas bubbles can been detected by echocardiography in most patients undergoing resectoscopic surgery in the uterus. Clinical significance may relate to anatomic variations as well as to gas bubble content and volume.

Vertical profiles of CH4 concentrations, dissolved substrates and processes involved in CH4 production in a flooded Italian rice field

Vertical profiles were measured in soil cores taken from flooded rice fields in the Po valley during July and August 1990. Methane concentrations generally increased with depth and reached maximum values of 150–500 μM in 5–13 cm depth. However, the shape of the profiles was very different when studying different soil cores. The CH4 content of gas bubbles showed a similar variability which apparently was due to spatial rather than temporal inhomogeneities. Similar inhomogeneities were observed in the vertical profiles of acetate, propionate, lactate, and formate which showed maximum values of 1500, 66, 135, and 153, μM, respectively. However, maxima and minima of the vertical profiles of the different substates usually coincided in one particular soil core. Large inhomogeneities in the vertical profiles were also observed for the rates of total CH4 production, however, the percentage contribution of H2/CO2 to CH4 production was relatively homogeneous at 24 ± 7% (SD). Similarly, the H2 content of gas bubbles was relatively constant at 93.3 ± 9.6 ppmv when randomly sampled in the rice field at different times of the day. A small contribution (6%) of H2/CO2 to acetate production was also observed. Vertical profiles of the respiratory index (RI) for [2-14C] acetate showed that acetate was predominantly degraded by methanogenesis in 5–11 cm depth, but by respiration in the surface soil (3 cm depth) and in soil layers below 13–16 cm depth which coincided with a transition of the colour (grey to reddish) and the physical characteristics (porosity, density) of the soil. The observations indicate that the microbial community which degrades organic matter to CH4 is in itself relatively homogenous, but operates at highly variable rates within the soil structure.

Characterization of aluminium films deposited by ion-beam-assisted ultrahigh vacuum evaporation

Ion bombardment during deposition enables the microstructure and properties of thin films to be manipulated in a controlled manner. Aluminium films approximately 5 μm thick were deposited on oxidized silicon wafers at T≈250 °C by ultrahigh vacuum electron beam evaporation. For normalized energies E n in the range 0–200 eV (Al atom) -1 the influence of krypton and xenon ion bombardment during evaporation was investigated by X-ray diffraction, transmission electron microscopy, small angle X-ray scattering, scanning electron microscopy and thermal desorption spectroscopy. The results are discussed in terms of the change in texture, stress, grain size and content of gas bubbles. For 5 eV < E n<40 eV a characteristic tilt of the 〈111〉 fibre axis by approximately 20° away from the surface normal is observed. This tilt is attributed to an ion-assisted interface reaction during the beginning of the deposition process. For E n≈100–200 eV, a (111) “single crystal” texture develops with the crystal aligned to the ion beam direction. For E n>40 eV the average rare gas content saturates at about 1 at.% and 3 at.% for xenon and krypton respectively. The gas precipitates within smaller bubbles as high-density f.c.c. solid epitaxially oriented with the aluminium. The distribution of bubbles is rather inhomogeneous even within individual grains.

Apparatus and method for determining the quantity of gas bubbles in a liquid

A method and apparatus for measuring the quantity of bubbles in a gas/liquid mixture. An ultrasonic wave is launched into the mixture and the magnitudes of two reflected waves are measured and compared. The logarithm of the magnitudes of the reflected waves is a measure of the quantity of gas content. The method and apparatus are suitable for measuring gas bubble content repetitively in a mixture turbulently flowing through a conduit.

Hydroshock theory in a two-phase gas-liquid mixture in a slug flow regime

A study is made of the intensity of a hydroshock in a two-phase gas-liquid mixture in a slug flow regime in the case when a pipeline is shut off by a liquid slug. The intensity is studied as a function of the length of the shut-off section of the liquid slug, the content of gas bubbles in the liquid slugs, and the pipeline shut-off law, and with allowance for the shock-wave character of the process [1, 2]. The calculated data using the shock-wave theory agree well with the experimental data of [3] and, unlike the results of the linear theory of [3], make it possible to determine the intensity of the hydroshock not only in the case of weak waves, but also in the case of waves of moderate intensity.