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The bubble departures from two neighboring brass nozzles (with inner diameter of 1.1 mm) in three liquids: distilled water, mineral, and synthetic engine oils were investigated. The numerical simulations were used for reconstructi...
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The bubble departures from two neighboring brass nozzles (with inner diameter of 1.1 mm) in three liquids: distilled water, mineral, and synthetic engine oils were investigated. The numerical simulations were used for reconstruction of liquid-flow around the departing bubbles. Bubble movements in liquid have been recorded using a high speed camera. The 2-D bubble paths have been reconstructed using: Laplacian of Gaussian filters, algorithm of detection of local extremes of image brightness and Kalman filter. It was shown that during alternative bubble departures bubble paths become repeatable. The dimensionless number (similar to Strouhal number) was proposed to describe oscillating liquid-flow generated by departing bubbles over the nozzle outlet. Such number was used for defining the hydrodynamic criterion of alternative bubble departures.
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The dynamics of bubble departures (at a frequency of ?=3 Hz) from a glass nozzle submerged in a tank filled with distilled water has been experimentally and theoretically studied. The volume of the system that supplies air to the ...
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The dynamics of bubble departures (at a frequency of ?=3 Hz) from a glass nozzle submerged in a tank filled with distilled water has been experimentally and theoretically studied. The volume of the system that supplies air to the nozzle (plenum chamber volume) and the air volume flow rate were changed in the experiment. The air pressure, bubble paths and liquid flow inside the nozzle were simultaneously recorded using a data acquisition system and a high-speed camera. It was shown that an increase in the plenum chamber volume leads to an increase in the intensity of the occurrences of chaotic changes in the subsequent waiting times. The analysis of the mechanism of the stability loss of the periodic bubble departures was based on changes in the time of the air pressure, the depth of the liquid penetration into the nozzle, the time of the bubble growth, the waiting time, and the bubble paths and their sizes, which is presented in this paper. The results of the analysis are compared with simulations that are based on the models of bubble growth and liquid flow inside the nozzle during the waiting time. It was shown that the air pressure rise, Δ_(Pl) during the waiting time is a non-linear function of the gas pressure after the bubble departure and the liquid velocity around the nozzle outlet. The nonlinearity of Δ_(Pl) increases when the plenum chamber volume increases, and it decreases when the air volume flow rate increases.
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This work is devoted to an experimental study of the effect of coalescence on the average diameter and velocity of gas bubbles in an inclined pipe. The measurements were carried out for agas flow rate of 3.3 and 5 mL/min at pipe i...
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This work is devoted to an experimental study of the effect of coalescence on the average diameter and velocity of gas bubbles in an inclined pipe. The measurements were carried out for agas flow rate of 3.3 and 5 mL/min at pipe inclination angles of 30-60°. The study of gas bubble diameters was performed using a shadow photography method. The values of the average diameter and velocity of the bubbles were obtained depending on the angle of inclination of the pipe. A map of regime parameters was constructed at which gas bubbles form a stable structure—a chain of bubbles with an equal diameter.
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In the paper the self-organising structure of bubble departures from nozzle outlets has been investigated. In the experiment, bubbles were generated from brass nozzles with inner diameters of 1.1 mm. They were submerged in a glass...
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In the paper the self-organising structure of bubble departures from nozzle outlets has been investigated. In the experiment, bubbles were generated from brass nozzles with inner diameters of 1.1 mm. They were submerged in a glass tank filled with distilled water. Three different nozzle arrangements have been considered. Correlation coefficients between signals from laser-phototransistor and pressure sensors have been calculated. It has been shown that self-organising structures of bubble departures are formed by alternative bubble departures. Their appearance significantly modifies the frequency of bubble departures and prevents departing bubbles from the vertical coalescence. When bubbles are emitted from three nozzles, the alternative bubble departures are created over each pair of neighbouring nozzles. In case of three nozzles arranged in the row, the alternative bubble departures appear on the left and right side of the central nozzle. When bubbles depart from three nozzles arranged in corners of the triangle, the appearance of alternative bubble departures over each pair of nozzles leads to appearing clockwise and counter-clockwise direction of bubble departures. It has been shown that the stability of alternative bubble departures depends on the distance between nozzles, their arrangement and the air volume flow rate. Numerical simulations show that the diagonal liquid flow (created when bubbles depart from neighbouring nozzles not at the same time) establishes 'the communication' between two bubble chains. Such 'communication' modifies conditions of liquid flow over the nozzles, the time between successive bubbles and finally, establishes the alternative bubble departures.
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The nonlinear dynamics of self-organising bubble departures from twin nozzles in engine oils was analysed. Air bubbles were generated from twin brass nozzles with an inner diameter equal to 1 mm. The flow of bubbles in bubble chai...
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The nonlinear dynamics of self-organising bubble departures from twin nozzles in engine oils was analysed. Air bubbles were generated from twin brass nozzles with an inner diameter equal to 1 mm. The flow of bubbles in bubble chains was recorded using high-speed camera. The time series of air pressure oscillations and signal from laser-phototransistor identifying the presence of bubbles over the nozzles outlet were recorded simultaneously. The self-organising bubble departures were observed and their stability was analysed. It was found that self-organising bubble departures become unstable because of successive (during subsequent bubble departures) decrease of the mean air pressure in one of the nozzle air supply system. It was shown that instability of self-organising bubble departures leads to equalization of pressures in both nozzles air supply systems which causes that simultaneous bubble departures appear. In the present experiment, this process was repeated in a cyclic and chaotic way. It was shown that stable self-organising bubble departures are accompanied by periodic air pressure oscillations in one of the nozzles and chaotic air pressure oscillations in the second one.
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The chaotic properties of bubble paths in bubble chain have been analysed. The bubbles have been generated from a brass cylindrical nozzle with inner diameter equal to 1 mm and placed at the centre of the bottom of rectangular tan...
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The chaotic properties of bubble paths in bubble chain have been analysed. The bubbles have been generated from a brass cylindrical nozzle with inner diameter equal to 1 mm and placed at the centre of the bottom of rectangular tank (300 × 150 × 500 mm), which was filled with distilled water. Bubble departure diameter was about 5.5 mm. The mirrors system and high speed camera have been used for determining the 3D paths of subsequently departing bubbles. The chaotic changes of bubble path shapes have been observed. Bubble chains obtained for three different air volume flow rates have been analysed. The bubble departure frequencies were adequately 9.4 Hz, 11.6 Hz and 12.7 Hz. The method of Hurst exponent estimation for chaotic bubble paths has been proposed. The Hurst exponent has been calculated for bubble path projections on two orthogonal planes-parallel to the tank walls (shorter and wider). Obtained Hurst exponents confirm that bubble paths have deterministic chaos character. Also, sensitivity of the chaotic bubble paths on initial conditions and the structure of liquid flow around the bubble chain has been discovered. Proposed method allows us to detect anomalies of bubble paths. There has been discovered that predictability of bubble path projection varies depending on the plane which has been chosen for the projection. We can conclude that the method proposed in the paper is suitable for measurement of chaotic bubble path properties.
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Effect of alcohols on single-bubble sonoluminescence (SBSL) is studied for various aliphatic alcohols at two ultrasonic frequencies. SBSL intensity decreases as the alcohol concentration increases. The degree of SBSL quenching inc...
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Effect of alcohols on single-bubble sonoluminescence (SBSL) is studied for various aliphatic alcohols at two ultrasonic frequencies. SBSL intensity decreases as the alcohol concentration increases. The degree of SBSL quenching increases with the hydrocarbon chain lengths of the alcohols. In comparison with isomeric alcohols, greater quenching effects are obtained for less branched alkyl groups. At lower frequencies the SBSL is quenched by the aliphatic alcohols more significantly. All the results can be ascribed to the larger amount of the alcohols adsorbed at the bubble/water interface. The bubble size measured by a direct stroboscopic method is hardly affected by the low levels of alcohol used, although the SBSL intensity is quenched significantly.
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The motion of a single nitrogen gas bubble chain and the structure of water flow field surrounding the chain were experimentally studied. We developed a bubble generator that can control both the bubble diameter and the generation...
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The motion of a single nitrogen gas bubble chain and the structure of water flow field surrounding the chain were experimentally studied. We developed a bubble generator that can control both the bubble diameter and the generation frequency independently. Experimental conditions of bubble Reynolds number and bubble distance divided by bubble diameter were from 300 to 650 and from 6.5 to 300, respectively. We discuss the interaction effects on the motion of each bubble rising in a chain, as compared to the effects of a single rising bubble. The bubble trajectories and the surrounding water flow fields in the state of bubbles rising in a chain were investigated using a high-speed digital video camera and an analog single-lens-reflex camera. We observed two important physical phenomena. First, bubbles passed through a nearly identical path in the case of low frequency of bubble production. On the contrary, at a height of approximately 50 turn from the nozzle, the bubbles in the case of high frequency deviated and scattered from this path due to bubble-bubble interaction. Second, with higher bubble production frequency, coherent bubble chain and the characteristic structure of the surrounding water flow called "liquid jet" were observed near the nozzle. The direction of liquid jet flow differed from the bubble trajectory. We theoretically investigated the relation of coherent bubble chain and liquid jet by applying the conservation of liquid momentum. (c) 2005 Elsevier Ltd. All rights reserved.
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This paper explores when will occur and collapse in Bitcoin bubbles by applying generalized sup augmented Dickey-Fuller test method proposed by Phillips et al. (Testing for multiple bubbles: historical episodes of exuberance and c...
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This paper explores when will occur and collapse in Bitcoin bubbles by applying generalized sup augmented Dickey-Fuller test method proposed by Phillips et al. (Testing for multiple bubbles: historical episodes of exuberance and collapse in the S&P 500. Singapore Management University, Working Paper, No. 04-2013, 2013). The results show that there are six explosive bubbles in China and five bubbles in U.S. market, mostly occur in the period of huge surges in Bitcoin price. This is consistent with the bubble model originated by Blanchard and Watson (Bubbles, rational expectations and financial markets. NBER Working Paper, No. 945 1982) that certain asset price is decomposed into fundamental and the bubble components. In particular, exogenous shocks, including foreign or domestic economic events lead to the origination of bubbles. Serious financial crisis may trigger long-term and large-scale bubbles, while relative not persistence (short-term) bubbles are caused by domestic particular components. It can be inferred that Bitcoin can be used as a hedge against market specific risk. Finally, Bitcoin bubbles would collapse due to the administrative intervention by economic authorities. Thereby, government should lead public expectation to keep the confidence to authority and reduce the speculation behavior to stabilize the asset price and financial market.
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Mass transfer rates, k_L, of single carbon dioxide bubbles contaminated with alcohols in vertical pipes of 12.5,18.2 and 25.0 mm diameters were measured to investigate effects of the carbon chain length of the alcohols on k_L. Fou...
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Mass transfer rates, k_L, of single carbon dioxide bubbles contaminated with alcohols in vertical pipes of 12.5,18.2 and 25.0 mm diameters were measured to investigate effects of the carbon chain length of the alcohols on k_L. Four straight-chain alcohols, i.e. 1-pentanol, 1-heptanol, 1-octanol and 1-decanol, were used. A wide range of bubble diameter, d, covered ellipsoidal and Taylor bubbles. Effects of the alcohol concentration, C_(sol), on k_L were also investigated to make clear the values of C_(sol) corresponding to fully-contaminated conditions. As a result, the following conclusions were obtained. (1) The k_L of bubbles contaminated with alcohols decrease with increasing C_(sol), and they become constant at high C_(sol), i.e. bubbles in the latter C_(sol) ranges are fully-contaminated from the point of view of mass transfer. On the other hand, the rising velocities decrease with increasing C_(sol) due to the reduction of surface tension even when k_L are independent of C_(sol). (2) The k_L of ellipsoidal bubbles fully-contaminated with alcohols decrease with increasing the carbon chain length, whereas the reduction rate of k_L becomes smaller and smaller as the carbon chain length increases. The k_L of fully-contaminated ellipsoidal bubbles can be expressed by accounting for the adsorption constant of alcohol in an available k_L correlation. (3) The increase in the carbon chain length also decreases k_L of fully-contaminated Taylor bubbles, whereas the effect of carbon chain length on k_L becomes smaller with increasing d.
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