Investigation of Cavitation Bubble Dynamics Considering Pressure Fluctuation Induced by Slap Forces

Cavitation erosion is induced by the penetrating pressure from implosion of cavitation bubbles nearby solid boundary. The bubble evolution and the subsequent collapse pressure are especially important to evaluate the erosion degradation of solid boundary materials. The bubble dynamics equation taking into account the influence of distance between bubble and solid boundary is formulated to investigate the effect of boundary wall on bubble evolution process. The pressure fluctuation induced by slapping forces is adopted to evaluate the bubble dynamic characteristics. Negative pressure period which reflects the effect of vibration velocity and gap clearance also has large influence on bubble dynamics. The effects of standoff distance, initial radius and negative pressure period on bubble evolution and collapsing shock pressure are discussed. Maximum bubble radius increases with standoff distance and initial radius, while shock pressure increases with distance and decreases with bubble initial radius, and both of them increase with negative pressure period.

Study on the Inter-Electrode Process of Aluminum Electrolysis (Ⅱ)—Digital Analysis of the Anode Gas Distribution Patterns on the Anode Surface Using A See-Through Cell

The evolution behavior of anode gas during aluminum electrolysis has been a hot spot of research for energy saving and process control. In the present work, the bubble evolution behavior during aluminum electrolysis was investigated using a lab-scale see-though cell. The bubble evolution characters on an 11 cm2 (bottom surface area) flat anode, an 11 cm2 slotted anode, and a 50 cm2 flat anode were investigated with statistical analysis, respectively. The results showed that bubbles tended to generate and adhere to certain regions on the anode surface due to the heterogeneity of the carbon material, and the adhering regions moved when current density was increased. The anode slot lowered the actual current density on the anode significantly by reducing the anode bubble coverage. Influenced by the group effect of bubbles, the 50 cm2 flat anode behavior constituted a lower bubble coverage rate, lower average bubble size, and lower actual current density than the 11 cm2 flat anode.

In-Situ TEM Annealing Observation of Helium Bubble Evolution in Pre-Irradiated FeCoNiCrTi0.2 Alloys

The FeCoNiCrTi0.2 high-entropy alloys fabricated by vacuum arc melting method, and the annealed pristine material, are face centered cubic structures with coherent γ’ precipitation. Samples were irradiated with 50 keV He+ ions to a fluence of 2 × 1016 ions/cm2 at 723 K, and an in situ annealing experiment was carried out to monitor the evolution of helium bubbles during heating to 823 and 923 K. The pristine structure of FeCoNiCrTi0.2 samples and the evolution of helium bubbles during in situ annealing were both characterized by transmission electron microscopy. The annealing temperature and annealing time affect the process of helium bubbles evolution and formation. Meanwhile, the grain boundaries act as sinks to accumulate helium bubbles. However, the precipitation phase seems have few effects on the helium bubble evolution, which may be due to the coherent interface and same structure of γ’ precipitation and matrix.