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In this paper, a new method for determination of void fraction in surface aeration process is presented and discussed. The proposed method is based on the image processing technique. The experimental setup has been designed to create various surface aeration conditions in the water. Void fraction has been calculated for the wide range of water height, impeller immersion depth and rotational speed. Experiments have been performed in an open cubic tank with side length of 60 cm, equipped with one Rushton disk turbine. Moreover, the void fraction has been measured with level gauge method. The results showed that the image processing technique provides more accurate results than the level gauge measurements for void fraction calculation in surface aeration especially in low void fraction aeration. In addition, the experimental data revealed that increase in impeller immersion depth and rotational speed increase void fraction and oxygen transfer rate in surface aeration process.

This paper reports tests on a lab-scale surface aeration vessel was equipped with a Rushton turbine to examine its performance in terms of standard aeration efficiency (SAE), mixing time, and void fraction characteristics. These characteristics were investigated by tests using variations of rotor speed, impeller immersion depth, and water level. Results showed that variation of impeller immersion depth had a greater effect on the SAE compared to variation of water level. Moreover, the SAE increased with rotor speeds up to about 150 to 200 rpm and then decreased. In addition, void fraction improved by impeller immersion depth and rotor speed enhancement; however, mixing time and power number were reduced as rotor speed increased. According to the response surface methodology statistical optimizations, optimum values for rotor speed, impeller immersion depth, and water level were 168.90 rpm, 25 mm, and 30 cm, respectively, to achieve the maximum value of SAE.

A novel 3D model was developed to study the effects of process parameters on the friction stir welding (FSW) of Al-SiC composites with regards to residual stresses and peak temperatures. An arbitrary Lagrangian-Eulerian formulation and remeshing were employed to account for large plastic deformations. The thermal history of the workpiece was used to define a coupled thermo-mechanical model. Al-SiC sheets were welded via the FSW method, and the resulting residual stress profiles were consistent with the results for the same test cases obtained via the developed model. The maximum magnitudes of the residual stresses were then used to quantitatively validate the model with the experimental results. The results show that at different transverse speeds, the rotation rates had dissimilar effects on the residual stresses of the post-welded sheets. The effect was dependent on whether the peak temperatures achieved in each case exceeded the Al-SiC precipitate dissolution temperature. This was further confirmed with the temperature distribution profiles obtained by the same model.