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The pressure oscillation and condensation behavior of steam bubbles at low steam mass flux are experimentally and theoretically studied in this work. Based on the synchronous measurement system of bubble behavior and pressure osci...
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The pressure oscillation and condensation behavior of steam bubbles at low steam mass flux are experimentally and theoretically studied in this work. Based on the synchronous measurement system of bubble behavior and pressure oscillation, it is found that the steam bubble condenses first and then expands and contracts, the water pressure reaches the maximum (about 13 kPa) when the bubble condenses to the minimum radius (about 1 mm). Subsequently, taking into account the movement of the bubble and the change of internal pressure during the bubble condensation process, a theoretical model of heat and mass transfer in the bubble condensation process is established, which shows that the steam bubble collapse is caused by heat transfer and the bubble internal pressure fluctuation. In the early condensation process of steam bubble, the bubble internal pressure continues to increase, meanwhile, the influence of bubble internal pressure on bubble condensation continues to increase. During the later expansion and contraction process of the bubble, the bubble internal pressure decreases first and then increases, the bubble behavior is mainly controlled by the bubble internal pressure.
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We analyse the controlled generation of bubbles of a given size at a determined bubbling rate in a co-flowing water stream forcing the gas flow. The temporal evolution of the bubble size, R(t), the air flow rate, Q(a)(t), and the ...
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We analyse the controlled generation of bubbles of a given size at a determined bubbling rate in a co-flowing water stream forcing the gas flow. The temporal evolution of the bubble size, R(t), the air flow rate, Q(a)(t), and the pressure evolution inside the bubble, p(b)(t), during the bubbling process are reported. To that aim, the temporal evolution of the bubble shape and the pressure inside the air feeding chamber, p(c)(t), where a harmonic perturbation is induced using a loudspeaker, are obtained from high-speed images synchronized with pressure measurements. A model is developed to describe the unsteady motion of the gas stream along the injection needle, coupled with the Rayleigh-Plesset equation for the growing bubble, allowing us to obtain p(b)(t). Thus, the minimum pressure amplitudes required inside the forming bubble to control their size and bubbling frequency are provided as a function of the gas flow rate, the liquid velocity, u(w), and the forcing frequency, f(f). Two different behaviors have been observed, depending on the liquid-to-gas velocity ratio, Lambda = u(w)/u(a). For small enough values of Lambda, the critical pressure amplitude is given by p(s) similar to rho(a) cu(a) St(f)(3), associated to a rapid pressure increase taking place during an interval of time of the order of the acoustic time. However, for larger values of Lambda, p(s) similar to rho u(w)(2) St(f)(3 )Lambda(-1/5)We(-1/4). Here rho and rho(a) are the liquid and gas densities respectively, c the speed of sound in air and St(f) = f(f)r(0)/u(w) and We = rho u(w)(2)r(o)/sigma the Strouhal and Weber numbers, where tau(o) denotes the outer radius of the injector. (C) 2020 Elsevier Ltd. All rights reserved.
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The present paper shows a novel approach in interpreting the standard deviation of pressure fluctuations in a fluidized bed with respect to the spectral analysis. Based on several realistic assumptions for a freely bubbling bed, t...
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The present paper shows a novel approach in interpreting the standard deviation of pressure fluctuations in a fluidized bed with respect to the spectral analysis. Based on several realistic assumptions for a freely bubbling bed, the physical model was proposed for the standard deviation of incoherent part of pressure fluctuations. Using the concept of energy dissipated in a fluidized bed the plausible explanation of linear dependence of standard deviation calculated from the total pressure signal on the excess gas velocity was given and verified experimentally. (C) 2004 Elsevier Ltd. All rights reserved.
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Gas holdups of large bubbles and small bubbles were measured by means of dynamic gas disengagement approach in the pressured bubble column with a diameter of 0.3 m and a height of 6.6 m.The effects of superficial gas velocity,liqu...
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Gas holdups of large bubbles and small bubbles were measured by means of dynamic gas disengagement approach in the pressured bubble column with a diameter of 0.3 m and a height of 6.6 m.The effects of superficial gas velocity,liquid surface tension * liquid viscosity and system pressure on gas holdups of small bubbles and large bubbles were investigated.The holdup of large bubbles increases and the holdup of small bubbles decreases with an increase of liquid viscosity.Meanwhile,the holdup of large bubbles decreases with increasing the system pressure.A correlation for the holdup of small bubbles was obtained from the experimental data.
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Industrial bubble column reactors use to operate at high pressure and temperature. However, few experimental investigations have been performed under such severe conditions. In this work the effects of high pressure (0.1-6 MPa) an...
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Industrial bubble column reactors use to operate at high pressure and temperature. However, few experimental investigations have been performed under such severe conditions. In this work the effects of high pressure (0.1-6 MPa) and high temperature (293-473 K) on the bubble shape and rising velocity in silicone oil and paraffin are experimentally investigated. The experiments are carried out in a stainless steel bubble column of 50 mm I.D with three pairs of high strength quartz windows. The bubble flow is visualized and recorded through high speed camera. New correlations for bubble aspect ratio E are proposed by use of the experimental data. The correlations are divided into three parts in terms of Weber number and Morton number. For We > 12, bubble aspect ratio is independent of Weber number, and is only related to Morton number. For We < 12 and Morton number larger than 3, bubble aspect ratio is only related to Reynolds number. For Morton number lower than 3, the aspect ratio could be expressed in terms of the Eotvos number and Reynolds number. Bubble rise velocity decreases with increasing pressure and decreasing temperature, which could be attributed to the variations of liquid viscosity, gas density, and bubble surface property. A modified correlation of Fan and Tsuchiya is recommended for bubble rise velocity valid at high temperature, high pressure and viscous liquids.
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This study aims at controlling air pressure fluctuation in a chamber from which liquid is being drained continuously by using a submerged micro-hole. In practical applications, this test chamber is used to simulate the commercial ...
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This study aims at controlling air pressure fluctuation in a chamber from which liquid is being drained continuously by using a submerged micro-hole. In practical applications, this test chamber is used to simulate the commercial ink cartridge of a thermal bubble inkjet printhead. The chamber air pressure drops owing to liquid being drained from the chamber, and it rises again as bubbles are generated and detached from a submerged micro-hole connecting liquid and the atmosphere. The chamber air pressure fluctuation can be controlled in a designated range that depends on factors such as physical properties of liquid used in the chamber, micro-hole diameter, and liquid drain rate. In this study, both distilled water and 10% wt. isopropanol solution are tested with micro-hole diameter ranging from 60 to 1200 μm. To simulate practical ink injection rates, the liquid drain rate ranges from 0.006 to 0.10 ml/s. For conditions tested in this study, our measured results show that the chamber air pressure variation and detached bubble volume depend mainly on micro-hole diameter and physical properties of liquid, and only slightly on liquid drain rate. Two correlations are proposed to obtain both the detached bubble volume and chamber air pressure fluctuation from physical properties of liquid and micro-hole diameter.
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Bubble formation at multiple orifices with a common gas plenum was studied experimentally. Gas pressure fluctuations in the plenum were measured and different model of bubble formation were identified. Main attention was paid to r...
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Bubble formation at multiple orifices with a common gas plenum was studied experimentally. Gas pressure fluctuations in the plenum were measured and different model of bubble formation were identified. Main attention was paid to regular synchronous modes because of their importance in formation of uniform gas-liquid mixtures. Factors affecting the interactions among orifices on both the gas and liquid sides were identified.
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The diameter of bubbles generated from submerged orifices is closely related to the air pressure, which consists of static and dynamic pressures. It has been proven that switching the air supply from a steady to oscillatory flow c...
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The diameter of bubbles generated from submerged orifices is closely related to the air pressure, which consists of static and dynamic pressures. It has been proven that switching the air supply from a steady to oscillatory flow can improve the dynamic pressure and thus lead to smaller bubbles. To complement the control strategy for bubble size optimization, this study proposes an approach to enhance static pressure by introducing a Y-junction shunting configuration under an oscillatory air supply. A model of gas pressure as a function of the shunting ratio was developed and validated experimentally. A positive correlation was observed between the shunting ratio and static pressure. The bubble size first decreased and then increased as the shunting ratio increased from 0 to 3.0. The smallest bubbles were obtained at a shunting ratio of 1.5 with a diameter reduction of 26% compared with no shunting. By segregating the bubble formation process, the bubble diameter at detachment continuously decreases over the shunting ratio. However, the number of coalesced bubbles first decreased and then increased, and the underlying mechanism is discussed. The findings indicated that the shunting air supply could facilitate bubble size optimization when the shunting ratio was appropriately controlled.
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Water sonolysis generates hydrogen through acoustic cavitation. In this work, based on a model for a reactive acoustic bubble, correlations between the sonochemical production of hydrogen and the maximum temperature and pressure r...
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Water sonolysis generates hydrogen through acoustic cavitation. In this work, based on a model for a reactive acoustic bubble, correlations between the sonochemical production of hydrogen and the maximum temperature and pressure reached in the bubble at the violent collapse have been made. The computational analysis has been performed for more than 800 points obtained by combining various cavitation parameters, i.e., frequency, acoustic intensity, liquid temperature, and ambient bubble radius. The simulation results showed that hydrogen production rate progressed linearly with the bubble temperature and pressure rise up to plateaus, which begin at 3500 ± 200 K and 100 ± 10 atm. Analyzing the progress of $$\text {H}^{{\cdot }}$$ H · and $$^{{\cdot }} $$ · OH ( $$\text {H}_{2}$$ H 2 precursors) as function of bubble temperature and pressure showed very similar evolutions as those obtained for $$\text {H}_{2}$$ H 2 with the same optimums at 3500 ± 200 K and 100 ± 10 atm. Consequently, in addition to the quench of hydrogen formation at very high bubble temperatures through the reaction $$\text {H}_{2}+\,^{{\cdot }}{\hbox {OH}}\rightarrow \text {H}_{2}\hbox {O}+\text {H}^{{\cdot }}$$ H 2 + · OH → H 2 O + H · , the existing optimum temperature and pressure for $$\text {H}_{2}$$ H 2 production may also be due the hard consumption of their precursors ( $$^{{\cdot }}$$ · OH and $$\text {H}^{{\cdot }})$$ H · ) above 3500 K and 100 atm.
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The effect of pressure on gas holdup was investigated experimentally with gas-liquid systems, of nitrogen-water, and carbon dioxide-water, in a bubble column with diameter of 45 mm. Single nozzles of 1.4, and 4.0 mm in diameter we...
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The effect of pressure on gas holdup was investigated experimentally with gas-liquid systems, of nitrogen-water, and carbon dioxide-water, in a bubble column with diameter of 45 mm. Single nozzles of 1.4, and 4.0 mm in diameter were used as gas disperser. When the 4.0 mm nozzle was used, no effect of pressure on gas holdup was observed. When single nozzle of 1.4 mm with nitrogen as the gas phase, gas holdup increased with pressure. But when carbon dioxide was used as the gas phase, gas holdup showed a maximum at pressure of 0.6 MPa. The gas holdup at 1.1 MPa was approximately the same value as that at atmospheric pressure. To explain these phenomena by the behavior of bubbles in the column, bubble size near the wall and bubble frequency at the center of column were measured.
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