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Gas–liquid flow and bubble coalescence and breakup behavior were studied in a top blown-rotary agitated reactor for steelmaking. Several important models of bubble coalescence and breakup mechanisms were considered and compared, and water model experiment was carried out to verify and optimize the mathematical models. The influence of different operating parameters including paddle arrangement, stirring speed and top blowing flow rate on the bubble size and distribution was revealed. The results show that the predicted bubble size and distribution present a good agreement with the experimental results using the improved Luo–Laakkonen combination model. As the position of the stirring paddle moves from the center to the side wall, the bubble distribution in the reactor becomes more uniform, and the bubble size gradually decreases. With the increase in the paddle rotation speed, the bubble size decreases. However, this effect begins to weaken when the paddle rotation speed exceeds 150 r/min. Increasing the top blowing flow rate will increase the bubble size in the reactor, but it has a weak effect on bubble dispersion. When the top blowing rate exceeds 2.0 m3/h, the bubble size in the bath is basically not less than 5 mm.

Ideal two-dimensional (2D) semiconductors with high mobility comparable to three-dimensional (3D) Si or GaAs are still lacking, hindering the development of high-performance 2D devices. Here in this work, using first-principles calculations and considering all the electron-phonon couplings, we show that monolayer BX (X = P, As, Sb) with honeycomb lattices have intrinsic phonon-limited carrier mobility reaching record-high values of 1200-14000 $cm^2V^{-1}s^{-1}$ at room temperature. Despite being polar and the band edges located at the K point with multiple valleys, these three systems unusually have small carrier scattering rates. Detailed analysis shows that, both the intravalley scattering and the intervalley scattering between two equivalent K points are weak, which can be understood from the large mismatch between the electron bands and phonon spectrum and suppressed electron-phonon coupling strength. Furthermore, we reveal the general trend of mobility increase from BP to BAs and to BSb and conclude that: smaller effective masses, larger sound velocities, higher optical phonon energies, heavy atomic masses, and out-of-plane orbitals tend to result in small match between the electron and phonon bands, small electron-phonon coupling strengths, and thus high mobility. Our work demonstrates that 2D semiconductors can achieve comparable carrier mobility to 3D GaAs, thus opening doors to 2D high-performance electronic devices., 25 pages, 8 figures