Heat transfer control by using jet discharge in reattachment region downstream of a backward-facing step
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Many measurement schemes have been developed to study the resonant characteristics of a bubble near a surface. The desire is to be able to measure the free field characteristics of such a bubble. For experimental
investigations, a trade off must be made between the size of the apparatus and the free field measurement. Thus
there is a need to study the effect of surface interference on the resonant characteristics of a bubble. Additionally, recent works have shown that Xanthan gel is a suitable alternative to sea water when studying linear bubble dynamics. The use of Xanthan gel allows for a bubble to be freely suspended, doing away with the need to mechanically hold the bubble in place. An experiment to study the resonance frequency of an acoustically driven, freely suspended bubble near a surface in Xanthan gel is described. The resonance frequency of the bubble was generally found to not be effected by surface interference for a bubble placed more than 25 bubble radii away from a surface.. Moreover, mechanically suspending a bubble in place was found not to have any discernable effect on its resonance characteristics.
Free surface
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The objective of the present experimental work is the study of local heat transfer performance over a target plate under impingement of inline and staggered jet arrays by a liquid crystal thermograph technique. Three jet-to-target spacings Z (= z/d) of 3, 6, and 9 with inline and staggered jet arrays were considered at jet Reynolds numbers Re = 1500, 3000, and 4500 in three different exit-flow orientations. The results show that the local heat transfer rates are characterized by obvious periodic-type variation of Nusselt number distributions. The downstream peaks are diminished with increasing cross-flow effect. The best heat transfer performance is obtained with the cross flow exiting from both ends of the impingement channel. The inline jet array produces relatively higher local and overall heat transfer rates than those of the staggered jet array. Additionally, in the present results of 3 ≤ Z ≤ 9, higher heat transfer rates are found for the system with a smaller jet-to-plate spacing.
Heat transfer enhancement
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Bubble loading is the ratio of the weight of the solid particles to the bubble’s surface, and it has an effective role in the flotation efficiency. This paper investigates bubble loading an industrial processing circuit through considering the important role of the bubble diameter in calculating bubble loading, and the effect of the aeration rate and frother dosage on the bubble diameter. The ratio of the weight of solid particles to the bubble volume was estimated to be in the range of 8 to 24 g/L. Although increasing the aeration could result in increasing the weight of the particles attached to the bubbles, the bubble loading was reduced by increasing the aeration rate due to its impact on the bubble diameter and the percentage of bubble surface coverage. For example, when the aeration rate was increased from 45 to 146 m3/h, the bubble loading decreased from 23 to 12 g/L. By increasing the frother dosage from 70 to 150 mL/min, the bubble loading increased from 16 to 19 g/L.
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Aspect ratio (aeronautics)
Momentum (technical analysis)
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The objective of the present experimental work is the study of local heat transfer performance over a target plate under impingement of inline and staggered jet arrays by a liquid crystal thermograph technique. Three jet-to-target spacings Z (= z/d) of 3, 6, and 9 with inline and staggered jet arrays were considered at jet Reynolds numbers Re = 1500, 3000, and 4500 in three different exit-flow orientations. The results show that the local heat transfer rates are characterized by obvious periodic-type variation of Nusselt number distributions. The downstream peaks are diminished with increasing cross-flow effect. The best heat transfer performance is obtained with the cross flow exiting from both ends of the impingement channel. The inline jet array produces relatively higher local and overall heat transfer rates than those of the staggered jet array. Additionally, in the present results of 3 Ј Z Ј 9, higher heat transfer rates are found for the system with a smaller jet-to-plate spacing.
Heat transfer enhancement
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Three-dimensional direct numerical simulation on a single bubble rising by buoyancy in viscous liquids was carried out with the level set method.The effect of initial bubble shape on the bubble dynamics was studied numerically with Etvs number Eo=1-103 and Morton number Mo=10-10-102,and the influencing mechanism was explained in detail.The bubble shape and rise velocity predicted by the simulation agree with a well-known bubble regime phase diagram in literature.In addition,a phase map was also established at high Eo to provide quantitative analysis on the transition of final bubble topology from spherical-cap to toroidal bubble.The numerical results show that the final shape and rise velocity are not affected by the initial bubble shape at low Eo(Eo52),while the final bubble state appears to be the spherical-cap and toroidal bubble and is influenced by initial bubble shape at high Eo and low Mo.The bubble is easier to become a toroidal bubble and the temporal fluctuation of bubble rise velocity is stronger when the aspect ratio of the initial bubble is greater.
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Using a model that with or without considering the interaction between bubbles through the radiated pressure waves, numerical simulations of cavitation bubbles have been performed in order to study the effect of the bubble–bubble interaction on radial pulsations of bubbles. Comparing the results obtained by with or without considering the bubble–bubble interaction, it is suggested that the suppression or enlargement property of expansion ratios of bubbles due to the bubble–bubble interaction largely depends on the ultrasound parameters, the ambient bubble radii, the distances between bubbles and the number of bubbles (in multi-bubble environment, the last two aspects can be expressed using the coupling strength). The frequency response curve of expansion ratio decreases and shifts to left due to the bubble–bubble interaction and the larger the coupling strength is, the more the left-shifting is.
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This paper describes the theory and experiments involve in the capture of bubbles onto a patterned surface. Guided by surface free energy, bubbles can automatically attach to the energetically favorable locations (bubble-traps) and align into bubble arrays. Bubble capturing potential φbc is proposed as the quantity to evaluate the surface’s “affinity” for bubbles. A bubble-trap can therefore be viewed as an area with locally maximum positive φbc. Two types of bubble-traps are proposed and evaluated. Type I bubble-traps are hydrophobic patterns on a hydrophilic flat surface. Type II bubble-traps are concave conic pits surrounded by a hydrophilic flat surface. Simulation of bubble capturing potential φbc explains the bubble-capturing behavior for both cases and predicts a better performance for type II bubble-traps. Experiments agree well with the theoretical prediction and suggest promising applications.
Conic section
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Downstream processing
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In order to study preferably the effects of the bubble on electro-flotation,the features and characteristic equation of the bubble were discussed.At the same time,the key factors of the bubble on electro-flotation were researched deeply and the collision probability between the particle and the bubble was also established.The results show that there is an obvious influence of the electrode material on the hydrogen bubble diameters in the acidic medium,but the effects are unconspicuous in the neutral and alkaline medium.pH of the medium has greater impacts on the diameters of the hydrogen bubble and oxygen bubble.The effects of electrode diameters and current densities have less influences on the bubble diameters,but the dispersivity of parts diameters of the bubble becomes stronger.The diameters of the hydrogen bubble for the maximal bubble contents increase with the increase of the temperature,but the distribution range of diameters has no obvious changes.The diameters of the bubble decrease with the increase of current density,and the collision probability between the particle and the bubble can get the maximum as the current density attains a certain number.
Particle (ecology)
Number density
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