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1
Liu, Bendong, Chenxu Ma, Jiahui Yang, Desheng Li, and Haibin Liu. "Study on the Heat Source Insulation of a Thermal Bubble-Driven Micropump with Induction Heating." Micromachines 12, no. 9 (2021): 1040. http://dx.doi.org/10.3390/mi12091040.
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Thermal bubble-driven micropumps have the advantages of high reliability, simple structure and simple fabrication process. However, the high temperature of the thermal bubble may damage some biological or chemical properties of the solution. In order to reduce the influence of the high temperature of the thermal bubbles on the pumped liquid, this paper proposes a kind of heat insulation micropump driven by thermal bubbles with induction heating. The thermal bubble and its chamber are designed on one side of the main pumping channel. The high temperature of the thermal bubble is insulated by the liquid in the heat insulation channel, which reduces the influence of the high temperature of the thermal bubble on the pumped liquid. Protypes of the new micropump with heat source insulation were fabricated and experiments were performed on them. The experiments showed that the temperature of the pumped liquid was less than 35 °C in the main pumping channel.
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Heller, R., R. Jacob, D. Schönberner, and M. Steffen. "Hot bubbles of planetary nebulae with hydrogen-deficient winds." Astronomy & Astrophysics 620 (December 2018): A98. http://dx.doi.org/10.1051/0004-6361/201832683.
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Context. The first high-resolution X-ray spectroscopy of a planetary nebula, BD +30° 3639, opened the possibility to study plasma conditions and chemical compositions of X-ray emitting “hot” bubbles of planetary nebulae in much greater detail than before. Aims. We investigate (i) how diagnostic line ratios are influenced by the bubble’s thermal structure and chemical profile, (ii) whether the chemical composition inside the bubble of BD +30° 3639 is consistent with the hydrogen-poor composition of the stellar photosphere and wind, and (iii) whether hydrogen-rich nebular matter has already been added to the bubble of BD +30° 3639 by evaporation. Methods. We applied an analytical, one-dimensional (1D) model for wind-blown bubbles with temperature and density profiles based on self-similar solutions including thermal conduction. We also constructed heat-conduction bubbles with a chemical stratification. The X-ray emission was computed using the well-documented CHIANTI code. These bubble models are used to re-analyse the high-resolution X-ray spectrum from the hot bubble of BD +30° 3639. Results. We found that our 1D heat-conducting bubble models reproduce the observed line ratios much better than plasmas with single electron temperatures. In particular, all the temperature- and abundance-sensitive line ratios are consistent with BD +30° 3639 X-ray observations for (i) an intervening column density of neutral hydrogen, NH = 0.20-0.10+0.05 × 1022cm−2, (ii) a characteristic bubble X-ray temperature of TX = 1.8 ± 0.1 MK together with (iii) a very high neon mass fraction of about 0.05, virtually as high as that of oxygen. For lower values of NH, we cannot exclude the possibility that the hot bubble of BD +30° 3639 contains a small amount of “evaporated” (or mixed) hydrogen-rich nebular matter. Given the possible range of NH, the fraction of evaporated hydrogen-rich matter cannot exceed 3% of the bubble mass. Conclusions. The diffuse X-ray emission from BD +30° 3639 can be well explained by models of wind-blown bubbles with thermal conduction and a chemical composition equal to that of the hydrogen-poor and carbon-, oxygen-, and neon-rich stellar surface.
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Chen, Min, Kun Peng Jiang, Da Wei Jiang, Dong Dong Chen, and Yan Fang Zhao. "Thermal Bubble Nucleation in a Nanochannel: An Experiment Investigation." Applied Mechanics and Materials 597 (July 2014): 7–12. http://dx.doi.org/10.4028/www.scientific.net/amm.597.7.
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We investigated the nanoscale thermal bubble nucleation based on the principle of Coulter counter. With micro-nanofabrication technologies, a device was designed and fabricated, and a detection platform was set up which was used to investigate the thermal bubble nucleation of aqueous solution confined in a nanochannel with a cross size of about 100 nm×100 nm. Results show that with the temperature of the solution confined in the nanochannel increasing, the current through the channel increases first and then decreases, and vanishes after a fluctuating period. It can be found that the generating thermal bubbles can hinder the current flowing through the nanochannel. In addition, the shrinking and expanding of thermal bubbles’ volume correspond to the increase and decrease of the current. Finally, the thermal bubbles block the nanochannel entirely. Through the experiment results, our device can be applied to investigate the complex behaviors of thermal bubble produced in aqueous solution confined in nanochannels, effectively.
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Hung, P. K., P. H. Kien, and H. V. Hue. "Tracer Diffusion Mechanism in Amorphous Solids." Journal of Metallurgy 2011 (December 27, 2011): 1–11. http://dx.doi.org/10.1155/2011/861373.
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Tracer diffusion in amorphous solid is studied by mean of nB-bubble statistic. The nB-bubble is defined as a group of atoms around a spherical void and large bubble that represents a structural defect which could be eliminated under thermal annealing. It was found that amorphous alloys such as CoxB100−x (x=90, 81.5 and 70) and Fe80P20 suffer from a large number of vacancy bubbles which function like diffusion vehicle. The concentration of vacancy bubble weakly depends on temperature, but essentially on the relaxation degree of considered sample. The diffusion coefficient estimated for proposed mechanism via vacancy bubbles is in a reasonable agreement with experiment for actual amorphous alloys. The relaxation effect for tracer diffusion in amorphous alloys is interpreted by the elimination of vacancy bubbles under thermal annealing.
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Narezo Guzman, Daniela, Tomasz Frączek, Christopher Reetz, Chao Sun, Detlef Lohse, and Guenter Ahlers. "Vapour-bubble nucleation and dynamics in turbulent Rayleigh–Bénard convection." Journal of Fluid Mechanics 795 (April 13, 2016): 60–95. http://dx.doi.org/10.1017/jfm.2016.178.
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Vapour bubbles nucleating at micro-cavities etched into the silicon bottom plate of a cylindrical Rayleigh–Bénard sample (diameter $D=8.8$ cm, aspect ratio ${\it\Gamma}\equiv D/L\simeq 1.00$ where $L$ is the sample height) were visualized from the top and from the side. A triangular array of cylindrical micro-cavities (with a diameter of $30~{\rm\mu}\text{m}$ and a depth of $100~{\rm\mu}\text{m}$) covered a circular centred area (diameter of 2.5 cm) of the bottom plate. Heat was applied to the sample only over this central area while cooling was over the entire top-plate area. Bubble sizes and frequencies of departure from the bottom plate are reported for a range of bottom-plate superheats $T_{b}-T_{on}$ ($T_{b}$ is the bottom-plate temperature, $T_{on}$ is the onset temperature of bubble nucleation) from 3 to 12 K for three different cavity separations. The difference $T_{b}-T_{t}\simeq 16$ K between $T_{b}$ and the top plate temperature $T_{t}$ was kept fixed while the mean temperature $T_{m}=(T_{b}+T_{t})/2$ was varied, leading to a small range of the Rayleigh number $Ra$ from $1.4\times 10^{10}$ to $2.0\times 10^{10}$. The time between bubble departures from a given cavity decreased exponentially with increasing superheat and was independent of cavity separation. The contribution of the bubble latent heat to the total enhancement of heat transferred due to bubble nucleation was found to increase with superheat, reaching up to 25 %. The bubbly flow was examined in greater detail for a superheat of 10 K and $Ra\simeq 1.9\times 10^{10}$. The condensation and/or dissolution rates of departed bubbles revealed two regimes: the initial rate was influenced by steep thermal gradients across the thermal boundary layer near the plate and was two orders of magnitude larger than the final condensation and/or dissolution rate that prevailed once the rising bubbles were in the colder bulk flow of nearly uniform temperature. The dynamics of thermal plumes was studied qualitatively in the presence and absence of nucleating bubbles. It was found that bubbles enhanced the plume velocity by a factor of four or so and drove a large-scale circulation (LSC). Nonetheless, even in the presence of bubbles the plumes and LSC had a characteristic velocity which was smaller by a factor of five or so than the bubble-rise velocity in the bulk. In the absence of bubbles there was strongly turbulent convection but no LSC, and plumes on average rose vertically.
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Tsai, Jr-Hung, and Liwei Lin. "Transient Thermal Bubble Formation on Polysilicon Micro-Resisters." Journal of Heat Transfer 124, no. 2 (2001): 375–82. http://dx.doi.org/10.1115/1.1445136.
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Transient bubble formation experiments are investigated on polysilicon micro-resisters having dimensions of 95 μm in length, 10 μm or 5 μm in width, and 0.5 μm in thickness. Micro resisters act as both resistive heating sources and temperature transducers simultaneously to measure the transient temperature responses beneath the thermal bubbles. The micro bubble nucleation processes can be classified into three groups depending on the levels of the input current. When the input current level is low, no bubble is nucleated. In the middle range of the input current, a single spherical bubble is nucleated with a waiting period up to 2 sec while the wall temperature can drop up to 8°C depending on the magnitude of the input current. After the formation of a thermal bubble, the resister temperature rises and reaches a steady state eventually. The bubble growth rate is found proportional to the square root of time that is similar to the heat diffusion controlled model as proposed in the macro scale boiling experiments. In the group of high input current, a single bubble is nucleated immediately after the current is applied. A first-order model is proposed to characterize the transient bubble nucleation behavior in the micro-scale and compared with experimental measurements.
7
Lin, Liwei, A. P. Pisano, and V. P. Carey. "Thermal Bubble Formation on Polysilicon Micro Resistors." Journal of Heat Transfer 120, no. 3 (1998): 735–42. http://dx.doi.org/10.1115/1.2824343.
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Thermal bubble formation in the microscale is of importance for both scientific research and practical applications. A bubble generation system that creates individual, spherical vapor bubbles from 2 to 500 μm in diameter is presented. Line shape, polysilicon resistors with a typical size of 50 × 2 × 0.53 μm3 are fabricated by means of micromachining. They function as resistive heaters and generate thermal microbubbles in working liquids such as Fluorinert fluids (inert, dielectric fluids available from the 3M company), water, and methanol. Important experimental phenomena are reported, including Marangoni effects in the microscale; controllability of the size of microbubbles; and bubble nucleation hysteresis. A one-dimensional electrothermal model has been developed and simulated in order to investigate the bubble nucleation phenomena. It is concluded that homogeneous nucleation occurs on the microresistors according to the electrothermal model and experimental measurements.
8
Zeng, Binglin, Kai Leong Chong, Yuliang Wang, et al. "Periodic bouncing of a plasmonic bubble in a binary liquid by competing solutal and thermal Marangoni forces." Proceedings of the National Academy of Sciences 118, no. 23 (2021): e2103215118. http://dx.doi.org/10.1073/pnas.2103215118.
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The physicochemical hydrodynamics of bubbles and droplets out of equilibrium, in particular with phase transitions, display surprisingly rich and often counterintuitive phenomena. Here we experimentally and theoretically study the nucleation and early evolution of plasmonic bubbles in a binary liquid consisting of water and ethanol. Remarkably, the submillimeter plasmonic bubble is found to be periodically attracted to and repelled from the nanoparticle-decorated substrate, with frequencies of around a few kilohertz. We identify the competition between solutal and thermal Marangoni forces as the origin of the periodic bouncing. The former arises due to the selective vaporization of ethanol at the substrate’s side of the bubble, leading to a solutal Marangoni flow toward the hot substrate, which pushes the bubble away. The latter arises due to the temperature gradient across the bubble, leading to a thermal Marangoni flow away from the substrate, which sucks the bubble toward it. We study the dependence of the frequency of the bouncing phenomenon from the control parameters of the system, namely the ethanol fraction and the laser power for the plasmonic heating. Our findings can be generalized to boiling and electrolytically or catalytically generated bubbles in multicomponent liquids.
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Voglar, Jure. "Physical Model of a Single Bubble Growth during Nucleate Pool Boiling." Fluids 7, no. 3 (2022): 90. http://dx.doi.org/10.3390/fluids7030090.
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A simplified physical model of a single bubble growth during nucleate pool boiling was developed. The model was able to correlate the experimentally observed data of the bubble’s growth time and its radius evolution with the use of the appropriate input parameters. The calculated values of separated heat fluxes from the heater wall, thermal boundary layer, and to the bulk liquid gave us a new insight into the complex mechanisms of the nucleate pool boiling process. The thermal boundary layer was found to supply the majority of the heat to the growing bubble. The heat flux from the thermal boundary layer to the bubble was found to be close to the Zuber’s critical heat flux limit (890 kW/m2). This heat flux was substantially larger than the input heater wall heat flux of 50 kW/m2. The thermal boundary layer acts as a reservoir of energy to be released to the growing bubble, which is filled during the waiting time of the bubble growth cycle. Therefore, the thickness of the thermal boundary layer was found to have a major effect on the bubble’s growth time.
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Arai, S., T. Kanagawa, T. Ayukai, and T. Yatabe. "Nonlinear and dissipation effects of pressure waves in water flows containing translational bubbles with a drag force." Journal of Physics: Conference Series 2217, no. 1 (2022): 012021. http://dx.doi.org/10.1088/1742-6596/2217/1/012021.
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Abstract Weakly nonlinear (i.e., finite but small amplitude) propagation of plane progressive pressure waves in compressible water flows uniformly containing many spherical bubbles is theoretically studied. Drag force acting bubbles and translation of bubbles are newly considered by introducing in momentum conservation equations in a two fluid model and the bubble dynamics equation for volumetric oscillations, respectively. Although these assumptions are the same as our previous paper, in this study, the energy conservation equation for each bubble describing a thermal conduction inside bubble is introduced. By using the method of multiple scales, the Korteweg–de Vries–Burgers equation for low-frequency long wave was derived from the set of basic equations in the two-fluid model. As a result, the dissipation effect was described by two types of terms, i.e., one was the second-order partial derivative owing to the liquid compressibility and the other was the term without differentiation owing to the drag force and the thermal conduction. Finally, we clarified that the dissipation owing to the drag force was smaller than that owing to the thermal conduction.
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Ge, Han, Kaichuang Wang, Jiawang Chen, Ronghua Zhu, Marisa Lazarus, and Dayun Yan. "Numerical Investigation of Air Entrapment Dynamics for High-Speed Thermal Spraying." Applied Sciences 12, no. 23 (2022): 12039. http://dx.doi.org/10.3390/app122312039.
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For thermal spraying, bubble entrapments are highly undesired, as this would lead to pores in the final coating and lower its adhesion quality. This understanding warrants an investigation of the process behind their formation. Nevertheless, the air entrapment process is difficult to study via experimental methods since molten droplets are always opaque and hard to visualize. Most numerical models are focused on air entrapment at the moment of impact, which could only explain the pores observed around the center of the splat. Here, in this paper, the air entrapment of a micron-sized molten nickel droplet impacting on a stainless-steel substrate is numerically studied. The results show that, besides the air entrapped during the high-speed impacting (impacting air bubbles/IM bubbles), bubbles may also be entrapped due to the fallback of the pointed-out finger on the edge during the spreading process (spreading air bubbles/SP bubbles). The number and size of the entrapped SP bubbles are related to the solidification rate and spreading rate. Therefore, both low (50 m/s) and high (200 m/s) impacting speeds could achieve an entrapped bubble ratio that is about 10% lower than that of a medium one (100 m/s). However, the formed coating is thick for low impacting speeds, and the low entrapped bubble ratio is obtained due to the cut-off of the peripherical fingers, which is actually unwanted.
12
Yan, Shaohang, Tianwei Lai, Qi Zhao, et al. "Numerical Study on Single-Bubble Contraction–Rebound Characteristics in Cryogenic Fluids." Applied Sciences 12, no. 21 (2022): 10839. http://dx.doi.org/10.3390/app122110839.
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In cryogenic fluid storage and delivery, the rapid contraction and rebound of bubbles are prone to occur during bubble collapse due to the pressure saltation. With the contraction and rebound of bubbles, the pressure and temperature in the bubbles fluctuate greatly, which affects the service life of fluid machinery. During bubble contraction and rebound, there is an accompanied complex heat and mass transfer process. According to the thermal properties of cryogenic fluids, a single-bubble collapse model is proposed considering the temperature variations inside the bubble. In order to study the variation in temperature and pressure during bubble collapse in cryogenic fluids, the contraction and rebound of a single bubble in liquid hydrogen are investigated numerically under various operating pressures and supercooling degrees. The numerical results of the model indicate that there are periodic contraction and rebound of the bubble when the pressure rises suddenly. Furthermore, the periods and attenuation rates of bubbles in different media are studied and compared. For the most concerned pressure and temperature characteristics, the relationship between the peak pressure, the attenuation rate of the temperature and the dimensionless number is proposed.
13
Gvozdić, Biljana, Elise Alméras, Varghese Mathai, et al. "Experimental investigation of heat transport in homogeneous bubbly flow." Journal of Fluid Mechanics 845 (April 20, 2018): 226–44. http://dx.doi.org/10.1017/jfm.2018.213.
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We present results on the global and local characterisation of heat transport in homogeneous bubbly flow. Experimental measurements were performed with and without the injection of ${\sim}2.5~\text{mm}$ diameter bubbles (corresponding to bubble Reynolds number $Re_{b}\approx 600$) in a rectangular water column heated from one side and cooled from the other. The gas volume fraction $\unicode[STIX]{x1D6FC}$ was varied in the range 0 %–5 %, and the Rayleigh number $Ra_{H}$ in the range $4.0\times 10^{9}{-}1.2\times 10^{11}$. We find that the global heat transfer is enhanced up to 20 times due to bubble injection. Interestingly, for bubbly flow, for our lowest concentration $\unicode[STIX]{x1D6FC}=0.5\,\%$ onwards, the Nusselt number $\overline{Nu}$ is nearly independent of $Ra_{H}$, and depends solely on the gas volume fraction $\unicode[STIX]{x1D6FC}$. We observe the scaling $\overline{Nu}\,\propto \,\unicode[STIX]{x1D6FC}^{0.45}$, which is suggestive of a diffusive transport mechanism, as found by Alméras et al. (J. Fluid Mech., vol. 776, 2015, pp. 458–474). Through local temperature measurements, we show that the bubbles induce a huge increase in the strength of liquid temperature fluctuations, e.g. by a factor of 200 for $\unicode[STIX]{x1D6FC}=0.9\,\%$. Further, we compare the power spectra of the temperature fluctuations for the single- and two-phase cases. In the single-phase cases, most of the spectral power of the temperature fluctuations is concentrated in the large-scale rolls/motions. However, with the injection of bubbles, we observe intense fluctuations over a wide range of scales, extending up to very high frequencies. Thus, while in the single-phase flow the thermal boundary layers control the heat transport, once the bubbles are injected, the bubble-induced liquid agitation governs the process from a very small bubble concentration onwards. Our findings demonstrate that the mixing induced by high Reynolds number bubbles ($Re_{b}\approx 600$) offers a powerful mechanism for heat transport enhancement in natural convection systems.
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Leu, Tzong Shyng, and Yan Hao Liu. "Design and Fabrication of Thermocapillary Micro Bubble Pump." Advanced Materials Research 528 (June 2012): 23–26. http://dx.doi.org/10.4028/www.scientific.net/amr.528.23.
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In this paper, a novel MEMS-fabricated thermal bubble pump is proposed. By using thermocapillary effect in a microchannel loop, bubbles are designed to move only in one direction of the loop. Driving heater with a square-wave signal, bubble nucleates and grows asymmetrically above the heater. As soon as the heating pulse is turned off, an interesting phenomenon is found. Instead of bubble collapse, bubble moves toward growing direction. Continuous bubbles grow and move periodically when square-wave pulsing signals are applied. Thermocapillary pumping phenomena are achieved successfully in the experiments. By adjusting background temperature field, thermocapillary pumping phenomena can be sustained. Detailed mechanism for pumping force will be discussed in this paper.
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Ghiaasiaan, S. M., A. T. Wassel, and A. A. Pesaran. "Gas Desorption From Seawater in Open-Cycle Ocean Thermal Energy Conversion Barometric Upcomers." Journal of Solar Energy Engineering 112, no. 3 (1990): 204–15. http://dx.doi.org/10.1115/1.2930481.
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Gas desorption from warm and cold seawater under open-cycle ocean thermal energy conversion (OC-OTEC) conditions is addressed in this paper. The desorption process of dissolved O2, N2, and CO2 in the barometric upcomers of an OTEC plant is simulated mathematically. The model considers the growth of bubbles originating in the ocean and bubbles formed in the upcomers. Bubble growth is induced by gas mass transfer and water evaporation at the bubble-liquid interface, as well as by the decreasing hydrostatic pressure. Heterogeneous nucleation at pipe wall crevices and on suspended particles in the water stream is also modeled. Bubble coalescence due to turbulent shear and differential buoyancy is simulated. The results generated show the deaeration efficiency as a function of flow and geometric parameters. The calculations show that gas desorption in the barometric upcomers can be appreciable. Such desorption is enhanced by increasing the concentration of the incoming and/or the heterogeneously formed bubbles. Results of existing experiments are discussed and predictions are shown for the selected test conditions.
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Xin, Yalou, Yunling Jian, Hongfeng Yin, Yun Tang, Hudie Yuan, and Yuchi Liu. "The Influence of Alumina Bubbles on the Properties of Lightweight Corundum–Spinel Refractory." Materials 16, no. 17 (2023): 5908. http://dx.doi.org/10.3390/ma16175908.
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The use of a lightweight corundum–spinel refractory in working lining could reduce the thermal conductivity of industrial furnaces. In this study, bubble alumina was introduced to realize a lightweight Al2O3-MgAl2O4 refractory assisted by the reactive sintering of Al2O3 and MgO. The effects of alumina bubble content and sintering temperature on the phase compositions, microstructure and properties of the lightweight refractory were investigated. The results indicated that the overall performance of the lightweight Al2O3-MgAl2O4 refractory was mainly dominated by the content of alumina bubbles. The bulk density, compressive strength and thermal conductivity all decreased when the alumina bubble content increased from 10 to 30 wt%. Meanwhile, the sintering temperature also significantly affected the properties of the obtained refractory. It is worth noting that specimens fired at 1650 °C achieved a high refractoriness under load (RUL) of more than 1700 °C when alumina bubble content was less than 30 wt%, which was comparable to that of the dense Al2O3-MgAl2O4 refractory. The thermal conductivity of the obtained samples was remarkably decreased to no more than 2.13 W/(m·K). In order to overcome the trade-off between the light weight of the refractory and overall performance, it is feasible to adjust the content of alumina bubbles and raise the sintering temperature appropriately.
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Gago, Mauricio, Arkadi Kreter, Bernhard Unterberg, and Marius Wirtz. "Bubble Formation in ITER-Grade Tungsten after Exposure to Stationary D/He Plasma and ELM-like Thermal Shocks." Journal of Nuclear Engineering 4, no. 1 (2023): 204–12. http://dx.doi.org/10.3390/jne4010016.
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Plasma-facing materials (PFMs) in the ITER divertor will be exposed to severe conditions, including exposure to transient heat loads from edge-localized modes (ELMs) and to plasma particles and neutrons. Tungsten is the material chosen as PFM for the ITER divertor. In previous tests, bubble formation in ITER-grade tungsten was detected when exposed to fusion relevant conditions. For this study, ITER-grade tungsten was exposed to simultaneous ELM-like transient heat loads and D/He (6%) plasma in the linear plasma device PSI-2. Bubble formation was then investigated via SEM micrographs and FIB cuts. It was found that for exposure to 100.000 laser pulses of 0.6 GWm−2 absorbed power density (Pabs), only small bubbles in the nanometer range were formed close to the surface. After increasing Pabs to 0.8 and 1.0 GWm−2, the size of the bubbles went up to about 1 µm in size and were deeper below the surface. Increasing the plasma fluence had an even larger effect, more than doubling bubble density and increasing bubble size to up to 2 µm in diameter. When using deuterium-only plasma, the samples showed no bubble formation and reduced cracking, showing such bubble formation is caused by exposure to helium plasma.
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Bayazit, Baris B., D. Keith Hollingsworth, and Larry C. Witte. "Heat Transfer Enhancement Caused by Sliding Bubbles." Journal of Heat Transfer 125, no. 3 (2003): 503–9. http://dx.doi.org/10.1115/1.1565090.
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Measurements that illustrate the enhancement of heat transfer caused by a bubble sliding under an inclined surface are reported. The data were obtained on an electrically heated thin-foil surface that was exposed on its lower side to FC-87 and displayed the output of a liquid crystal coating on the upper (dry) side. A sequence of digital images was obtained from two cameras: one that recorded the response of the liquid crystal and one that recorded images of the bubble as it moved along the heated surface. With this information, the thermal imprint of the bubble was correlated to its motion and position. A bubble generator that produced FC-87 bubbles of repeatable and controllable size was also developed for this study. The results show that both the microlayer under a sliding bubble and the wake behind the bubble contribute substantially to the local heat transfer rate from the surface. The dynamic behavior of the bubbles corresponded well with studies of the motion of adiabatic bubbles under inclined plates, even though the bubbles in the present study grew rapidly because of heat transfer from the wall and the surrounding superheated liquid. Three regimes of bubble motion were observed: spherical, ellipsoidal and bubble-cap. The regimes depend upon bubble size and velocity. A model of the heat transfer within the microlayer was used to infer the microlayer thickness. Preliminary results indicate a microlayer thickness of 40–50 μm for bubbles in FC-87 and a plate inclination of 12 deg.
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Hauptmann, Marc, Steven Brems, Elisabeth Camerotto, et al. "Stroboscopic Schlieren Study of Bubble Formation during Megasonic Agitation." Solid State Phenomena 187 (April 2012): 185–89. http://dx.doi.org/10.4028/www.scientific.net/ssp.187.185.
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An important problem in megasonic cleaning is the nucleation process of bubbles, which act as the cleaning agents. A fundamental understanding of this nucleation process will help to optimize the cleaning parameters for future applications to achieve damage free cleaning. In this work, we use quantitative stroboscopic Schlieren imaging to study the interaction of nucleating bubbles with a travelling acoustic wave. The advantage of this method is that it is non-interfering, meaning that it does not disturb the bubble nucleation. It is revealed that nucleation mechanism is a 2 step process, where a regime of slow bubble growth due to rectified diffusion is subsequently followed by a transient cavitation cycle, where bubbles grow explosively. The latter is accompanied by broadband acoustic emission and enhanced thermal dissipation, leading to the occurrence of thermal convection visible in the Schlieren images.
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Novotný, František, Lenka Prokopová, and Daniela Bošová. "Glass Micro-Bubbles as Additional Thermal Insulation/Shielding for Translucent and Non-Transparent Materials." Key Engineering Materials 776 (August 2018): 140–46. http://dx.doi.org/10.4028/www.scientific.net/kem.776.140.
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Our research is based on innovative use of the hollow glass micro-spherical material "Glass micro-bubbles" 3MTM. We apply this material like a thin-layer additional thermal insulation/shielding for polycarbonate and steel matrices. 3 identical cargo container units with polycarbonate roof skylight are used for the research: A - without application, B - with inner application of Glass micro-bubble coating and C - with outside application of Glass micro-bubble coating.Observed parameters are translucence of daylight through layer of micro-glass bubbles on the skylight, the indoor temperature and humidity and the surface temperature of the outer and inner shell are measured.
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Edsall, Connor, Emerson Ham, Hal Holmes, Timothy L. Hall, and Eli Vlaisavljevich. "Effects of frequency on bubble-cloud behavior and ablation efficiency in intrinsic threshold histotripsy." Physics in Medicine & Biology 66, no. 22 (2021): 225009. http://dx.doi.org/10.1088/1361-6560/ac33ed.
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Abstract Objective. Histotripsy is a non-thermal focused ultrasound ablation method that destroys tissue through the generation of a cavitation bubble cloud. Previous work studying intrinsic threshold histotripsy has shown that dense bubble clouds can be formed by a single-cycle pulse when the negative pressure exceeds an intrinsic threshold of ∼25–30 MPa, with the ablation efficiency dependent upon the size and density of bubbles within the cloud. This work investigates the effects of frequency on bubble-cloud behavior and ablation efficiency in intrinsic threshold histotripsy. Approach. A modular transducer was used to expose agarose tissue phantoms to 500 kHz, 1 MHz, or 3 MHz, histotripsy pulses. Optical imaging was used to measure the bubble-cloud dimensions, bubble density, and bubble size. The effects of frequency on ablation efficiency were also investigated by applying histotripsy to red blood cell (RBC) phantoms. Main results. Results revealed that the bubble-cloud size closely matched theoretical predictions for all frequencies. The bubble density, which is a measure of the number of bubbles per unit area, was shown to increase with increasing frequency while the size of individual bubbles within the cloud decreased at higher frequencies. Finally, RBC phantom experiments showed decreasing ablation efficiency with increasing frequency. Significance. Overall, results demonstrate the effects of frequency on histotripsy bubble-cloud behavior and show that lower frequency generates more efficient tissue ablation, primarily due to enhanced bubble expansion.
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Mitchell, Katherine, Jungkyu Park, Alex Resnick, Hunter Horner, and Eduardo B. Farfan. "Phonon Scattering and Thermal Conductivity of Actinide Oxides with Defects." Applied Sciences 10, no. 5 (2020): 1860. http://dx.doi.org/10.3390/app10051860.
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In the present study, we examine the effect of point defects and fission gases on thermal transport in representative actinide oxides used in modern reactors. In particular, oxygen interstitials and Kr/Xe fission gas bubbles are of primary focus. Reverse non-equilibrium molecular dynamics is employed to investigate thermal transport in UO2 and PuO2 with oxygen interstitials at the defect concentrations of 0.1%, 1%, and 5%. The results show that any alteration to the lattice structures of these fuels reduce their thermal conductivities significantly. For the largest UO2 structure simulated in the present study, for example, 0.1% oxygen interstitials decreased the thermal conductivity by 18.6%. For the case of the effect of fission gas bubbles, serious modification to phonon dispersion in oxide fuels is caused by the presence of a single fission gas bubble, resulting in a large temperature drop in their temperature profiles. The average interfacial thermal resistance across a fission gas bubble (comprised of 30 Kr and/or Xe atoms) is estimated to be 2.1 × 10−9 Km2/W.
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Dhillon, Navdeep S., Dilipkumar Choudhary, Jayden Maree, Victor Inhelder, and Jazmin Guadarrama. "Controlled generation of a vapor bubble representative of nucleate boiling conditions using transient focused laser heating." Journal of Applied Physics 133, no. 2 (2023): 024702. http://dx.doi.org/10.1063/5.0134203.
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Nucleate boiling is a phenomenon of significant importance in a broad range of industries. Increasing boiling performance parameters could lead to more efficient power plants and better electronics thermal management. However, difficulties associated with studying this extremely complex phenomenon have prevented a meaningful progress in the area of boiling heat transfer enhancement. In this paper, we implement a laser-based controlled bubble generation technique to enable accurate phenomenological studies of the boiling process. We present details of the transient focused-laser heating mechanism used to nucleate a microscale vapor embryo on the boiling surface. We present high-speed optical imaging data showing how this vapor embryo grows into a bubble using electrically applied background heat flux. Unlike the currently available artificial bubble generation approaches, which either generate unphysical bubbles or are extremely difficult to implement, we show that the laser-nucleated controlled single bubble demonstrates bubble ebullition characteristics closely representative of naturally occurring bubbles in nucleate pool boiling.
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STOREY, BRIAN D., and ANDREW J. SZERI. "Mixture segregation within sonoluminescence bubbles." Journal of Fluid Mechanics 396 (October 10, 1999): 203–21. http://dx.doi.org/10.1017/s0022112099005984.
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This paper concerns a relaxation of the assumption of uniform mixture composition in the interior of sonoluminescence bubbles. Intense temperature and pressure gradients within the bubble drive relative mass diffusion which overwhelms diffusion driven by concentration gradients. This thermal and pressure diffusion results in a robust compositional inhomogeneity in the bubble which lasts several orders of magnitude longer than the temperature peak or light pulse at the main collapse of the bubble. This effect has important consequences for control of sonoluminescence, gas dynamics, sonochemistry, and the physics of light production.
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Lin, Liwei, and Albert P. Pisano. "Thermal bubble powered microactuators." Microsystem Technologies 1, no. 1 (1994): 51–58. http://dx.doi.org/10.1007/bf01367761.
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Weerasinghe, Asanka, Brian D. Wirth, and Dimitrios Maroudas. "Thermal expansion of plasma-exposed tungsten." Journal of Applied Physics 132, no. 18 (2022): 185102. http://dx.doi.org/10.1063/5.0123280.
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We report results from a systematic analysis of thermal expansion of plasma-exposed tungsten based on molecular-dynamics simulations using models of tungsten with distributions of helium (He) bubbles in the tungsten matrix. We distinguish between two approaches of filling the bubbles with He, where the amount of He in the bubble can or cannot vary with temperature. In the former case, the thermal expansion coefficient decreases monotonically with the porosity and He content of the tungsten matrix, while in the latter case, the thermal expansivity increases monotonically with increasing porosity and He content. The latter condition, where the He content in the bubble is determined at the implantation temperature and remains constant with varying temperature in the tungsten matrix, is consistent with He species transport in tungsten used as a plasma-facing component (PFC) in nuclear fusion reactors and implies the development of biaxial compressive thermal strains in the PFC material that contribute to accelerating the growth of a nanostructure on PFC tungsten surfaces. Our analysis advances the fundamental understanding of thermal expansion in PFC tungsten and contributes to the development of a thermophysical property database for properly incorporating effects of realistic heat loads into modeling the dynamical response of PFC tungsten under fusion reactor operating conditions.
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Zhang, Jing, Lingxin Zhang, and Jian Deng. "Numerical Study of the Collapse of Multiple Bubbles and the Energy Conversion during Bubble Collapse." Water 11, no. 2 (2019): 247. http://dx.doi.org/10.3390/w11020247.
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This paper investigates numerically the collapses of both a single cavitation bubble and a cluster consisting of 8 bubbles, concerning mainly on the conversions between different forms of energy. Direct numerical simulation (DNS) with volume of fluid (VOF) method is applied, considering the detailed resolution of the vapor-liquid interfaces. First, for a single bubble near a solid wall, we find that the peak value of the wave energy, or equivalently the energy conversion rate decreases when the distance between the bubble and the wall is reduced. However, for the collapses of multiple bubbles, this relationship between the bubble-wall distance and the conversion rate reverses, implying a distinct physical mechanism. The evolutions of individual bubbles during the collapses of multiple bubbles are examined. We observe that when the bubbles are placed far away from the solid wall, the jetting flows induced by all bubbles point towards the cluster centre, while the focal point shifts towards the solid wall when the cluster is very close to the wall. We note that it is very challenging to consider thermal and acoustic damping mechanisms in the current numerical methods, which might be significant contributions to the energy budget, and we leave it open to the future studies.
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Mohammadein, S. A., and A. F. Abu-Bakr. "The growth of vapour bubble in a superheated liquid between two phase turbulent flow." Canadian Journal of Physics 88, no. 5 (2010): 317–24. http://dx.doi.org/10.1139/p10-022.
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In this paper, the growth of a vapour bubble in superheated water for two-phase turbulent flow is studied. The growth problem is formulated by mass and momentum equations under physical assumptions between two finite boundaries. The analytical solution is obtained in terms of the vapour bubble radius. The bubbly growth is affected by thermal diffusivity, superheating, and the Péclet number. The fact that the scale of the bubble is larger than the scale of the turbulence in the mixture surrounding the growing bubble is considered. The previous models of growth for laminar flow are obtained as a special cases of the present model for some values of the parameters a, b, n, and φ0, respectively.
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Yasui, Kyuichi. "Multibubble Sonoluminescence from a Theoretical Perspective." Molecules 26, no. 15 (2021): 4624. http://dx.doi.org/10.3390/molecules26154624.
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In the present review, complexity in multibubble sonoluminescence (MBSL) is discussed. At relatively low ultrasonic frequency, a cavitation bubble is filled mostly with water vapor at relatively high acoustic amplitude which results in OH-line emission by chemiluminescence as well as emissions from weakly ionized plasma formed inside a bubble at the end of the violent bubble collapse. At relatively high ultrasonic frequency or at relatively low acoustic amplitude at relatively low ultrasonic frequency, a cavitation bubble is mostly filled with noncondensable gases such as air or argon at the end of the bubble collapse, which results in relatively high bubble temperature and light emissions from plasma formed inside a bubble. Ionization potential lowering for atoms and molecules occurs due to the extremely high density inside a bubble at the end of the violent bubble collapse, which is one of the main reasons for the plasma formation inside a bubble in addition to the high bubble temperature due to quasi-adiabatic compression of a bubble, where “quasi” means that appreciable thermal conduction takes place between the heated interior of a bubble and the surrounding liquid. Due to bubble–bubble interaction, liquid droplets enter bubbles at the bubble collapse, which results in sodium-line emission.
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Uchida, Tsutomu, Ike Nagamine, Itsuka Yabe, et al. "Dissolution Process Observation of Methane Bubbles in the Deep Ocean Simulator Facility." Energies 13, no. 15 (2020): 3938. http://dx.doi.org/10.3390/en13153938.
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To investigate the temperature dependency of the methane bubble dissolution rate, buoyant single methane bubbles were held stationary in a countercurrent water flow at a pressure of 6.9 MPa and temperatures ranging from 288 K to 303 K. The 1 to 3 mm diameter bubbles were analyzed by observation through the pressure chamber viewport using a bi-telecentric CCD camera. The dissolution rate in artificial seawater was approximately two times smaller than that in pure water. Furthermore, it was observed that the methane bubble dissolution rate increased with temperature, suggesting that bubble dissolution is a thermal activation process (the activation energy is estimated to be 9.0 kJ/mol). The results were different from the expected values calculated using the governing equation for methane dissolution in water. The dissolution modeling of methane bubbles in the mid-to-shallow depth of seawater was revised based on the current results.
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Yasui, Kyuichi. "Production of O Radicals from Cavitation Bubbles under Ultrasound." Molecules 27, no. 15 (2022): 4788. http://dx.doi.org/10.3390/molecules27154788.
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In the present review, the production of O radicals (oxygen atoms) in acoustic cavitation is focused. According to numerical simulations of chemical reactions inside a bubble using an ODE model which has been validated through studies of single-bubble sonochemistry, not only OH radicals but also appreciable amounts of O radicals are generated inside a heated bubble at the violent collapse by thermal dissociation of water vapor and oxygen molecules. The main oxidant created inside an air bubble is O radicals when the bubble temperature is above about 6500 K for a gaseous bubble. However, the concentration and lifetime of O radicals in the liquid water around the cavitation bubbles are unknown at present. Whether O radicals play some role in sonochemical reactions in the liquid phase, which are usually thought to be dominated by OH radicals and H2O2, should be studied in the future.
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Schönberner, Detlef, Ralf Jacob, René Heller, and Matthias Steffen. "Analysis of the X-ray spectrum of the hot bubble of BD+30°3639." Proceedings of the International Astronomical Union 12, S323 (2016): 109–13. http://dx.doi.org/10.1017/s1743921317001223.
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AbstractWe developed a model for wind-blown bubbles with temperature and density profiles based on self-similar solutions including thermal conduction. We constructed also heat-conduction bubbles with chemical discontinuities. The X-ray emission is computed using the well-documented CHIANTI code (v6.0.1). These bubble models are used to (re)analyse the high-resolution X-ray spectrum of the hot bubble of BD+30°3639, and they appeared to be much superior to constant temperature approaches.We found for the X-ray emission of BD+30°3639 that temperature-sensitive and abundance-sensitive line ratios computed on the basis of heat-conducting wind-blown bubbles and with abundances as found in the stellar photosphere/wind can only be reconciled with the observations if the hot bubble of BD+30°3639 is chemically stratified, i.e. if it contains also a small mass fraction (≃ 3 %) of hydrogen-rich matter immediately behind the conduction front. Neon appears to be strongly enriched, with a mass fraction of at least about 0.06.
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Toporkov, D. Yu. "Сollapse of weakly-nonspherical cavitation bubble in acetone and tetradecane". Multiphase Systems 13, № 3 (2018): 23–28. http://dx.doi.org/10.21662/mfs2018.3.003.
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Collapse of a weakly-spherical cavitation bubble in acetone and tetradecane is studied. The bubble radius is 500 μm, the temperature and pressure of the liquid are 293 K and 15 bar in the case of acetone and 663 K and 50 bar in the case of tetradecane. A hydrodynamic model is used in which the compressibility of the liquid, the nonstationary thermal conduction of the vapor and the liquid, and nonequilibrium heat and mass transfer on the bubble surface, as well as imperfection of the vapor, are considered. Realistic wide-range equations of state are used. It has been found that converging shock waves appear in the bubbles during its collapses in acetone and tetradecane. The maximum values of the thermodynamic parameters are comparable. A comparison of the evolution of the bubble sphericity perturbation and motion of the shock wave in the bubble allows suggesting that tetradecane is a more favorable medium for the realization of a near-spherical cumulation in a bubble than acetone.
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Kuriki, Hiroki, Yoko Yamanishi, Shinya Sakuma, Satoshi Akagi, and Fumihito Arai. "Local Ablation of a Single Cell Using Micro/Nano Bubbles." Journal of Robotics and Mechatronics 25, no. 3 (2013): 476–83. http://dx.doi.org/10.20965/jrm.2013.p0476.
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We have successfully produced mono-dispersed microgas bubbles less than around 10 µm in diameter in an electrically induced ultrasonic field. The discharged output power and conductive area of the micro-electrode are controlled by glass shell insulation around the copper micro-wire. A small space between the wire and glass tip, a “bubble reservoir,” contributes to the stabilization of the electric discharge and directional bubble generation. The directionally dispensed bubbles can be used for processing soft materials such as biological cells. For the present study, the cell membrane has successfully been processed with resolution of a few µm order and without any thermal collateral damage.
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Baddour, R. E. "Computer simulation of ice control with thermal-bubble plumes — line source configuration." Canadian Journal of Civil Engineering 17, no. 4 (1990): 509–13. http://dx.doi.org/10.1139/l90-058.
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Thermal-bubble plumes in a freshwater environment are studied to determine their ice control capabilities. A computer model is developed to optimize the operation of thermal-bubble installations when designed to control ice. Steady-state and transient simulations of ice control are presented. It is conceivable to fully computerize the operation of thermal-bubble installations by combining data acquisition, data analysis, computer simulation, and control automation. Key words: ice control, ice management, thermal-bubble plume, computer simulation.
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Zhang, Wei Hao, and Guo Zhong Li. "Preparation and Application of the Vesicant in Gypsum." Advanced Materials Research 306-307 (August 2011): 934–37. http://dx.doi.org/10.4028/www.scientific.net/amr.306-307.934.
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Gypsum and vesicant were used to manufacture foamed gypsum by physical foaming. The effect of different components of vesicant on the properties of bubbles and gypsum slurry were confirmed in the experiments. The changes of dry bulk density and thermal conductivity of foamed gypsum were studied in the conditions of adding bubbles. The results showed that the comprehensive performance was better when adding150ml bubble to 300g gypsum, compared with blank sample, the dry bulk density and thermal conductivity of the samples decreased by 38%, 36% respectively, the dry bulk density was 812 Kg/m3 and the thermal conductivity was 0.18 W/m•K.
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d’Agostino, Luca, Fabrizio d’Auria, and Christopher E. Brennen. "A Three-Dimensional Analysis of Rotordynamic Forces on Whirling and Cavitating Helical Inducers." Journal of Fluids Engineering 120, no. 4 (1998): 698–704. http://dx.doi.org/10.1115/1.2820726.
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This paper investigates the linearized dynamics of three-dimensional bubbly cavitating flows in helical inducers. The purpose is to understand the impact of the bubble response on the radial and tangential rotordynamic forces exerted by the fluid on the rotor and stator stages of whirling turbomachines under cavitating conditions. The flow in the inducer annulus is modeled as a homogeneous inviscid mixture, containing vapor bubbles with a small amount of noncondensable gas. The effects of several contributions to the damping of the bubble dynamics are included in the model. The governing equations of the inducer flow are written in “body-fitted” orthonormal helical Lagrangian coordinates, linearized for small-amplitude perturbations about the mean flow, and solved by modal decomposition. The whirl excitation generates finite-speed propagation and resonance phenomena in the two-phase flow within the inducer. These, in turn, lead to a complex dependence of the lateral rotordynamic fluid forces on the excitation frequency, the void fraction, the average size of the cavitation bubbles, and the turbopump operating conditions (including, rotational speed, geometry, flow coefficient and cavitation number). Under cavitating conditions the dynamic response of the bubbles induces major deviations from the noncavitating flow solutions, especially when the noncondensable gas content of the bubbles is small and thermal effects on the bubble dynamics are negligible. Then, the quadratic dependence of rotordynamic fluid forces on the whirl speed, typical of cavitation-free operation, is replaced by a more complex behavior characterized by the presence of different regimes where, depending on the whirl frequency, the fluid forces have either a stabilizing or a destabilizing effect on the inducer motion. Results are presented to illustrate the influence of the relevant flow parameters.
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Guerrero, M. A., X. Fang, Y. H. Chu, J. A. Toalá, and R. A. Gruendl. "Revealing the Location of the Mixing Layer in a Hot Bubble." Proceedings of the International Astronomical Union 12, S323 (2016): 114–18. http://dx.doi.org/10.1017/s1743921317002320.
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AbstractThe fast stellar winds can blow bubbles in the circumstellar material ejected from previous phases of stellar evolution. These are found at different scales, from planetary nebulae (PNe) around stars evolving to the white dwarf stage, to Wolf-Rayet (WR) bubbles and up to large-scale bubbles around massive star clusters. In all cases, the fast stellar wind is shock-heated and a hot bubble is produced. Processes of mass evaporation and mixing of nebular material and heat conduction occurring at the mixing layer between the hot bubble and the optical nebula are key to determine the thermal structure of these bubbles and their evolution. In this contribution we review our current understanding of the X-ray observations of hot bubbles in PNe and present the first spatially-resolved study of a mixing layer in a PN.
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D'Agostino, Luca, Christopher E. Brennen, and Allan J. Acosta. "Linearized dynamics of two-dimensional bubbly and cavitating flows over slender surfaces." Journal of Fluid Mechanics 192 (July 1988): 485–509. http://dx.doi.org/10.1017/s0022112088001958.
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The present work investigates the dynamics of two-dimensional, steady bubbly flows over a surface and inside a symmetric channel with sinusoidal profiles. Bubble dynamics effects are included. The equations of motion for the average flow and the bubble radius are linearized and a closed-form solution is obtained. Energy dissipation due to viscous, thermal and liquid compressibility effects in the dynamics of the bubbles is included, while the relative motion of the two phases and viscous effects at the flow boundaries are neglected. The results are then generalized by means of Fourier synthesis to the case of surfaces with slender profiles of arbitrary shape. The flows display various flow regimes (subsonic, supersonic and super-resonant) with different properties according to the value of the relevant flow parameters. Examples are discussed in order to show the effects of the inclusion of the various energy dissipation mechanisms on the flows subject to harmonic excitation. Finally the results for a flow over a surface with a Gaussian-shaped bump are presented and the most important limitations of the theory are briefly discussed.
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TEMKIN, S. "Radial pulsations of a fluid sphere in a sound wave." Journal of Fluid Mechanics 380 (February 10, 1999): 1–38. http://dx.doi.org/10.1017/s0022112098003401.
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This paper presents analytical results for the temperature and pressure fluctuations in a droplet or bubble pulsating in a sound wave, the related damping coefficients, as well as the corresponding sound attenuation coefficients for dilute suspensions. The study is limited to small-amplitude motions but includes the effects of compressibility and heat conduction in the fluid outside the particle. Results are obtained for both average and surface values of the particle's temperature and pressure fluctuations that are applicable to droplets in gases and liquids, and to gas bubbles in liquids. In the latter instance, it is found that the bubble's response exhibits a clear resonant peak at the isothermal natural frequency, that acoustic radiation is the dominant dissipation mechanism near resonance, and that the disturbances produced by the bubble in the liquid significantly reduce the thermal damping at most frequencies. Similar conclusions apply for droplets in liquids, except that the effects of resonance are significantly diminished.
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Li, Jiaqi, Daniel Kang, Kazi Fazle Rabbi, et al. "Liquid film–induced critical heat flux enhancement on structured surfaces." Science Advances 7, no. 26 (2021): eabg4537. http://dx.doi.org/10.1126/sciadv.abg4537.
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Enhancing critical heat flux (CHF) during boiling with structured surfaces has received much attention because of its important implications for two-phase flow. The role of surface structures on bubble evolution and CHF enhancement remains unclear because of the lack of direct visualization of the liquid- and solid-vapor interfaces. Here, we use high-magnification in-liquid endoscopy to directly probe bubble behavior during boiling. We report the previously unidentified coexistence of two distinct three-phase contact lines underneath growing bubbles on structured surfaces, resulting in retention of a thin liquid film within the structures between the two contact lines due to their disparate advancing velocities. This finding sheds light on a previously unidentified mechanism governing bubble evolution on structured surfaces, which has notable implications for a variety of real systems using bubble formation, such as thermal management, microfluidics, and electrochemical reactors.
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BRENNER, MICHAEL P. "Cavitation in linear bubbles." Journal of Fluid Mechanics 632 (July 27, 2009): 1–4. http://dx.doi.org/10.1017/s0022112009008167.
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Recent work has developed a beautiful model system for studying the energy focusing and heating power of collapsing bubbles. The bubble is effectively one-dimensional and the collapse and heating can be quantitatively measured. Thermal effects are shown to play an essential role in the time-dependent dynamics.
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SMEULDERS, D. M. J., and M. E. H. VAN DONGEN. "Wave propagation in porous media containing a dilute gas–liquid mixture: theory and experiments." Journal of Fluid Mechanics 343 (July 25, 1997): 351–73. http://dx.doi.org/10.1017/s0022112097005983.
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The influence of a small amount of gas within the saturating liquid of a porous medium on acoustic wave propagation is investigated. It is assumed that the gas volumes are spherical, homogeneously distributed, and that they are within a very narrow range of bubble sizes. It is shown that the compressibility of the saturating fluid is determined by viscous, thermal, and a newly introduced Biot-type damping of the oscillating gas bubbles, with mean gas bubble size and concentration as important parameters. Using a super-saturation technique, a homogeneous gas–liquid mixture within a porous test column is obtained. Gas bubble size and concentration are measured by means of compressibility experiments. Wave reflection and propagation experiments carried out in a vertical shock tube show pore pressure oscillations, which can be explained by incorporating a dynamic gas bubble behaviour in the linear Biot theory for plane wave propagation.
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Shimabukuro, Hayato, Yi Mao, and Jianrong Tan. "Estimation of H ii Bubble Size Distribution from 21 cm Power Spectrum with Artificial Neural Networks." Research in Astronomy and Astrophysics 22, no. 3 (2022): 035027. http://dx.doi.org/10.1088/1674-4527/ac4ca3.
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Abstract The bubble size distribution of ionized hydrogen regions probes information about the morphology of H II bubbles during reionization. Conventionally, the H II bubble size distribution can be derived from the tomographic imaging data of the redshifted 21 cm signal from the epoch of reionization, which, however, is observationally challenging even for upcoming large radio interferometer arrays. Given that these interferometers promise to measure the 21 cm power spectrum accurately, we propose a new method, which is based on artificial neural networks, to reconstruct the H II bubble size distribution from the 21 cm power spectrum. We demonstrate that reconstruction from the 21 cm power spectrum can be almost as accurate as being directly measured from the imaging data with fractional error ≲10%, even with thermal noise at the sensitivity level of the Square Kilometre Array. Nevertheless, the reconstruction implicitly exploits the modeling in reionization simulations, and hence the recovered H II bubble size distribution is not an independent summary statistic from the power spectrum, and should be used only as an indicator for understanding H II bubble morphology and its evolution.
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Green, Samuel, Jonathan Mackey, Thomas J. Haworth, Vasilii V. Gvaramadze, and Peter Duffy. "Thermal emission from bow shocks." Astronomy & Astrophysics 625 (April 29, 2019): A4. http://dx.doi.org/10.1051/0004-6361/201834832.
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The Bubble Nebula (or NGC 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved O star BD+60°2522. The young dynamical age of the nebula and significant space velocity of the star suggest that the Bubble Nebula might be a bow shock. We ran 2D hydrodynamic simulations to model the interaction of the wind of the central star with the interstellar medium (ISM). The models cover a range of possible ISM number densities of n = 50−200 cm−3 and stellar velocities of v* = 20−40 km s−1. Synthetic Hα and 24 μm emission maps predict the same apparent spherical bubble shape with quantitative properties similar to observations. The synthetic maps also predict a maximum brightness similar to that from the observations and agree that the maximum brightness is at the apex of the bow shock. The best-matching simulation had v* ≈ 20 km s−1 into an ISM with n ∼ 100 cm−3, at an angle of 60° with respect to the line of sight. Synthetic maps of soft (0.3−2 keV) and hard (2−10 keV) X-ray emission show that the brightest region is in the wake behind the star and not at the bow shock itself. The unabsorbed soft X-rays have a luminosity of ∼1032−1033 erg s−1. The hard X-rays are fainter: ∼1030−1031 erg s−1, and may be too faint for current X-ray instruments to successfully observe. Our results imply that the O star creates a bow shock as it moves through the ISM and in turn creates an asymmetric bubble visible at optical and infrared wavelengths and predicted to be visible in X-rays. The Bubble Nebula does not appear to be unique; it could simply be a favourably oriented, very dense bow shock. The dense ISM surrounding BD+60°2522 and its strong wind suggest that it could be a good candidate for detecting non-thermal emission.
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Charee, Wisan, Viboon Tangwarodomnukun, and Chaiya Dumkum. "Bubble Formation in the Underwater Laser Ablation of Silicon." Applied Mechanics and Materials 835 (May 2016): 144–48. http://dx.doi.org/10.4028/www.scientific.net/amm.835.144.
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Thermal damage of workpiece material induced by laser machining process can be reduced by using the underwater technique. This method requies the whole workpiece to be submerged in water while a laser beam strikes the work surface for ablation. Though water can cool the workpiece during the ablation, the dynamic features of water can adversely interfere the laser beam. The vapor bubbles created in water can scatter the laser beam and in turn attenuate the laser intensity at the work surface so as the ablation performance. In this paper, the bubble formation caused by laser machining of silicon in water was investigated and analyzed. The shadowgraph technique associated with the high speed camera was used to capture and measure the vapor bubble in water. The bubble size was found to increase with the laser pulse energy. After a number of laser pulses irradiated on the workpiece surface, the bubble was broken up into small ones which can significantly disturb the laser beam so as the ablation performance.
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Kappagantu, Ramana, and Elvis Dominguez. "Simulating vibro-acoustic damping of bubbles in fluids." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 266, no. 2 (2023): 962–71. http://dx.doi.org/10.3397/nc_2023_0115.
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Bubbles in fluids are common occurrence due to impurities, thermal or flow variations. They are sometimes considered detrimental to the flow and more importantly surrounding structural integrity. On the other hand, bubbles were used positively towards damping vibrations in fluid filled structures [1] and as barriers or curtains in the removal of plastic waste from water ways [2] and also in noise attenuation from offshore windfarms [3]. In the latter two cases, engineers hypothesized these curtains help marine life from sound pollution from surrounding machinery and ships. In this paper the authors discuss two cases to study the effect of bubble size and bubble density. In the first experiment a curtain of air bubbles was introduced in a water body and sound transmission loss (STL) through this curtain was studied. In a second experiment, a stainless-steel tank filled with liquid mercury is infused with helium bubbles and the vibration levels were monitored.
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Delale, Can F. "Thermal Damping in Cavitating Nozzle Flows." Journal of Fluids Engineering 124, no. 4 (2002): 969–76. http://dx.doi.org/10.1115/1.1511163.
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Recent investigations of bubbly cavitating nozzle flows using the polytropic law for the partial gas pressure have shown flow instabilities that lead to flashing flow solutions. Here, we investigate the stabilizing effect of thermal damping on these instabilities. For this reason we consider the energy equation within the bubble, assumed to be composed of vapor and gas, in the uniform pressure approximation with low vapor concentration. The partial vapor pressure is fixed by the vapor saturation pressure corresponding to the interface temperature, which is evaluated by assuming the thin boundary layer approximation within the liquid. Consequently, the partial gas pressure is evaluated by its relation to the heat flux through the interface in the uniform pressure approximation. The model is then coupled to the steady-state cavitating nozzle flow equations replacing the polytropic law for the partial gas pressure. The instabilities found in steady cavitating nozzle flows are seen to be stabilized by thermal damping with or without the occurrence of bubbly shock waves.
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Guo, Lei, Shu Sheng Zhang, and Lin Cheng. "Study for Bubble Dynamics of Nucleate Boiling in Narrow Channels." Advanced Materials Research 123-125 (August 2010): 499–502. http://dx.doi.org/10.4028/www.scientific.net/amr.123-125.499.
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Two different types of channels are investigated which have I- and Z-shaped cross-sections with a width of 2mm. Using the numerical simulation method, the influence of wall contact angle to the process of bubble generating and growth up is studied, and the relationship between different channel shapes and pressure drop is also investigated. In the calculation process, the effects of gravity, surface tension and wall adhesion are taken into account. It is found that wall contact angle has a great influence to the morphology of bubbles. The smaller the wall contact angle is, the rounder the bubbles are, and the shorter the bubbles take to departure from the wall, otherwise, the bubbles are more difficult to depart. The variation of contact angle also has effect upon the heat transfer coefficient, the greater the wall contact angle is, the larger bubble-covered area is, thus the wall thermal resistance gets higher, and the heat transfer coefficient becomes lower. The role of surface tension in the process of boiling heat transfer is much larger than the gravity in narrow channels. The generation of bubbles dramatically disturbs the boundary layer, and the bubble bottom micro-layer can enhance the heat transfer. The heat transfer coefficient of Z-shaped channels is larger than that of I-shaped channels, while the pressure drop of the former is obviously higher.
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Hayes, Brandon, Lawrence Smith, Heiko Kabutz, et al. "Rapid Fabrication of Low-Cost Thermal Bubble-Driven Micro-Pumps." Micromachines 13, no. 10 (2022): 1634. http://dx.doi.org/10.3390/mi13101634.
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Thermal bubble-driven micro-pumps are an upcoming actuation technology that can be directly integrated into micro/mesofluidic channels to displace fluid without any moving parts. These pumps consist of high power micro-resistors, which we term thermal micro-pump (TMP) resistors, that locally boil fluid at the resistor surface in microseconds creating a vapor bubble to perform mechanical work. Conventional fabrication approaches of thermal bubble-driven micro-pumps and associated microfluidics have utilized semiconductor micro-fabrication techniques requiring expensive tooling with long turn around times on the order of weeks to months. In this study, we present a low-cost approach to rapidly fabricate and test thermal bubble-driven micro-pumps with associated microfluidics utilizing commercial substrates (indium tin oxide, ITO, and fluorine doped tin oxide, FTO, coated glass) and tooling (laser cutter). The presented fabrication approach greatly reduces the turn around time from weeks/months for conventional micro-fabrication to a matter of hours/days allowing acceleration of thermal bubble-driven micro-pump research and development (R&D) learning cycles.