Papers by Keyword: Gas Bubble

Abstract: In this paper, a case study is performed for the possibility of using water ethanol mixture in predicting the bubble behavior in multiphase flow. The study compares the concept of formation of foam at the surface of the mixture with the procedure of producing aluminum foam by direct gas injection. Material properties such as kinematic viscosity, density and surface tension on the foaming process will be studied experimentally, while the foam bubble size will be studied by means of digital image processing. Finally the path of the bubble from the nozzle to the liquid surface shall be simulated by means of computational fluid dynamics software and verified experimentally by the usage of a speed camera. Acquirement of this practical knowledge can improve the effectiveness of the real foaming process of the aluminum and aluminum alloys. Simultaneously, it helps to understand main basic features of the formed metal foams. The study is meant to define the best parameters for the foaming process for water-ethanol mixture. Such results are to be compared to their corresponding parameters for the direct injection foaming method for aluminum. The main aim to be able to correlate the 2 processes, in means to decreasing time and cost required to produce aluminum metal foam through test trials, usually causing the waste of material, fuel and energy. Furthermore, the quality and quantity evaluation of the created foam is presented. The effect of the flow rate of the quality of foams can be observed experimentally. The theoretical calculation can reproduce the bubble dynamics observed experimentally.

Abstract: Semi-solid die casting technology has great advantages at defects control and has been successfully used to produce high quality aluminum alloy components for several years. In this process, semi-solid metal with high apparent viscosity and low plunger velocity are used to avoid surface turbulence which is the main source of entrapped gas in conventional die casting processes. But, entrapped gas still has other sources, such as melting, pouring, surface flooding and confluence weld. Solution heat treatment is always used to strengthen semi-solid die castings. The entrapped gas leads to blister defects, which directly decreases the acceptance rate of semi-solid die castings. So, the entrapped gas is still a serious issue in semi-solid die casting process. We studied the floating behavior of entrapped gas bubble in semi-solid metal. Two floating models were established for gas bubbles with different sizes. These models were used to analyze the possibility of entrapped gas escaping from semi-solid metal in casting practice. The results showed that entrapped gas from feed billet could not escape from the semi-solid metal in the casting process of impeller, which was proved by experiment results. These results emphasized the importance of clean melt and semi-solid metal. Some advices were given at last for avoiding or removing the entrapped gas in semi-solid die casting process.

Abstract: The basic behavior during underwater electrical discharge up to 10 kJ stored energy is investigated through both numerical analysis and optical-observation experiments. Since the authors have been investigating the use of underwater exploding phenomena for food processing and other applications, it is necessary to know the whole process which may affect the quality of the samples recovered. In the present investigation, the propagation of underwater shock wave was measured using a high-speed camera and compared with the numerically simulated results using LS-DYNA. Also, the motion of gas bubble, which is induced quite after the propagation of the shock wave, was measured and compared with the numerical simulation using the same code. The pressure of the bubble is not such high as the shock wave, but it is known that the impulse is not possible to be ignored due to its relatively long duration of the pressurization. Through a series of optical-observation experiments, it is confirmed that the numerical simulation is potentially possible to predict the whole phenomena for processing foods and other materials.

Abstract: A detailed analysis is provided to discuss the effects of acoustic driving frequency and amplitude on bubble radial oscillation based on a revised bubble dynamical model. Numerical study demonstrates that 3 types of bubble radial oscillation can be achieved according to different driving signal frequency; driving signal amplitude affects oscillation differently due to its value, and a certain critical value of acoustic signal amplitude was found where the oscillation is becoming chaotic.

Abstract: To analyze the radial oscillation of forced acoustic gas bubble in liquid, a revised model including the effect of compressibility is mathematically formulated. Based on proposed model, the effects of fluid viscosity and temperature are discussed respectively. Numerical study demonstrates that gas bubble oscillation may change from nonlinear chaos into linear one due to the augmentation of fluid viscosity. Meanwhile, the stable oscillation may diverge with a sensible rise in temperature.

Abstract: Aiming at the cutting bed settling problems in horizontal section during drilling process, a novel additive FGC for cuttings transport is applied. The experimental results show that the wettability was converted to amphiphobic and the cuttings preferentially attached to gas bubbles after FGC adsorption on the cuttings’ surface. The surface area of the cuttings is increased and the density of it is reduced, making cuttings more easily to be driven by liquid and settlement decrease. Tested by the horizontal simulation device, the cuttings transport effect is good and most of cuttings can be circulated to the outlet position by drilling fluid.

Abstract: Electro-chemical discharge machining (ECDM) is one of nontraditional processes for micro-fabrication of non-conductive materials. A high applied voltage is preferable to form a gas film and to generate discharge in the film. However, accumulation of discharge heat often causes cracks of the surface because non-conductive materials have low heat conductivity. In this study, the effect of ultrasonic vibration and the electrolyte level on the performance of gravity-feed drilling by ECDM was investigated. Ultrasonic vibration was applied to a glass plate. A tungsten rod as a tool electrode was fed by gravity. Ultrasonic vibration changed the discharge behavior and improved electrolyte circulation. Although high amplitude ultrasonic vibration caused very dense and wide current pulses consistently during machining process, it decreased removal rate significantly. In addition, electrolyte levels affect single bubble size and the resistance in the electrolyte. Low electrolyte level will cause higher resistance, and higher temperature of the tool electrode and workpiece. A high bias current flew at a low electrolyte level without ultrasonic vibration. In this case, removal rate decreased and surface integrity was improved.

Abstract: Gas bubbles entrapped in polymer intermediate layer often lead to voids which are severe defects of adhesive bonding qualities. Although the empirical method had been used for a long time to eliminate the bubbles, theoretic analysis considering the bubble behavior during bonding process is more preferable because of the better universality. The interrelationships between processing parameters and bubble deformation were investigated. A theoretic model describing those interrelationships was developed reasonably using gas diffusion theory to predict the bubble behavior. The mathematic equations of this model were deduced and the solution was obtained with some proper simplifications. Experiments under different conditions were carried out and the experimental results were contrasted with the theoretical predictions. It was obvious that when choosing temperatures and pressures carefully, the model could predict the bubble behavior accurately.

Abstract: Various processing methods exist for applying agitation to a molten metal during solidification to obtain metal slurries suitable for semi-solid metal processing. . In this paper, a new technique to achieve semi-solid metal structure using agitation during solidification is reported. The technique applies a new medium and means to efficiently create semi-solid metal structures. The results of a systematic study showing the feasibility and the necessary conditions to achieve the structure are discussed.