Controllable Generation of a Submillimeter Single Bubble in Molten Metal Using a Low-Pressure Macrosized Cavity
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GAS bubbles injected into a liquid are used in a variety of industrial applications and experimental research such as metallurgy, chemistry, food science, biology, and of course, the physics of the multiphase flows. Regardless of the purpose for bubble injection, the typical tasks are to determine or control an amount of gas, number, and size of bubbles being injected into the liquid phase. These tasks are usually accomplished by employing application-specific methods of bubble generation, detection, and characterization. In the case when fluid is a nontransparent and chemically aggressive (e.g., corrosive liquids at high temperature), the practical implementation can be a complex task requiring costly solutions. The optimal choice of the gas injection method, allowing predefined generation of the gas amount with acceptable accuracy, may significantly simplify system design and lower the cost of a facility. Available in literature, experimental approaches, where millimeter or submillimeter gas bubble injection into a liquid is realized, can be divided into two categories: (1) techniques allowing mass production of the bubbles and (2) those where a single bubble can be produced. There are many methods where generated ALEXANDER KONOVALENKO, PER SKO¨LD, PAVEL KUDINOV, SEVOSTIAN BECHTA, and DMITRY GRISHCHENKO are with the Nuclear Power Safety Division, Royal Institute of Technology (KTH), Albanova, 10691 Stockholm, Sweden. Contact email: [email protected] Manuscript submitted June 9, 2016. Article published online January 31, 2017. 1064—VOLUME 48B, APRIL 2017
bubbles have broad size distribution and a few where size is accurately controlled. As an example of a bubble mass production technique, Fujikawa et al. proposed a micro-air-bubble generation device based on a rotating porous plate.[1] The method allows generation of 10 to 30 lm in size air bubbles dispersed in water. The authors validated the predicted mean bubble radius against experimental observations. In another experimental study, a conventional gas injection into liquid through the orifice was analyzed for the effect of different geometries of the orifice.[2] Importantly, these studies demonstrated that a slit-like shape is an energetically efficient orifice geometry for submillimeter bubble generation where slit length does not affect the resulting bubble size. The microfluidic flow-focusing devices became of interest to researchers in many studies because of advances and availability of nanofabrication technologies. The micrometer in size channels for the gas and fluid phases can be easily fabricated. With a good reproducibility, the formation and pinch-off the bubbles below 50 lm can be studied.[3] The effect of flow-focusing geometry of the device has been studied in Reference 4. An overview of the recent advances in development of the energy efficient fluidic oscillators can be found in Reference 5. The variety of single-bubble generation techniques is limited in comparison with the multiple bubble production, in particular, for the case when size and detachment time of s
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