Microbubbles with slow rising speed, higher specific area and greater oxygen dissolution are desired to enhance gas/liquid mass transfer rate. Such attributes are very important to tackle challenges on the low efficiency of gas/liquid mass transfer that occurs in aerobic wastewater treatment systems or in the aquaculture industries. Many reports focus on the formation mechanisms of the microbubbles, but with less emphasis on the system optimization and assessment of the aeration efficiency. This work assesses the performance and evaluates the aeration efficiency of a porous venturi-orifice microbubble generator (MBG). The increment of stream velocity along the venturi pathway and orifice ring leads to a pressure drop (P_atm > P_abs) and subsequently to increased cavitation. The experiments were run under three conditions: various liquid velocity (Q_L) of 2.35–2.60 m/s at fixed gas velocity (Q_g) of 3 L/min; various Q_g of 1–5 L/min at fixed Q_L of 2.46 m/s; and free flowing air at variable Q_Ls. Results show that increasing liquid velocities from 2.35 to 2.60 m/s imposes higher vacuum pressure of 0.84 to 2.27 kPa. They correspond to free-flowing air at rates of 3.2–5.6 L/min. When the system was tested at constant air velocity of 3 L/min and under variable liquid velocities, the oxygen dissolution rate peaks at liquid velocity of 2.46 m/s, which also provides the highest volumetric mass transfer coefficient (K_La) of 0.041 min⁻¹ and the highest aeration efficiency of 0.287 kgO₂/kWh. Under free-flowing air, the impact of Q_L is significant at a range of 2.35 to 2.46 m/s until reaching a plateau K_La value of 0.0416 min⁻¹. The pattern of the K_La trend is mirrored by the aeration efficiency that reached the maximum value of 0.424 kgO₂/kWh. The findings on the aeration efficiency reveals that the venturi-orifice MBG can be further optimized by focusing on the trade-off between air bubble size and the air volumetric velocity to balance between the amount of available oxygen to be transferred and the rate of the oxygen transfer.

中文翻译：

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多孔文氏管微气泡发生器，用于水中的氧气溶解

期望具有缓慢的上升速度，更高的比表面积和更大的氧溶解度的微气泡以提高气/液传质速率。这些属性对于应对好氧废水处理系统或水产养殖业中发生的气/液传质效率低下的挑战非常重要。许多报告集中在微气泡的形成机理上，但很少强调系统优化和曝气效率评估。这项工作评估性能，并评估多孔文丘里孔微气泡发生器（MBG）的曝气效率。沿着文丘里通道和节流孔环的流速增加导致压降（P _atm > P _abs），然后增加空化。实验在以下三个条件下进行：在固定气体速度（Q _g）为3 L / min时，各种液体速度（Q _L）为2.35–2.60 m / s ；固定Q _L为2.46 m / s时，各种Q _g为1-5 L / min ；和自由流动的空气，其变量为Q _L s。结果表明，液体速度从2.35 m / s增加到2.60 m / s会产生0.84至2.27 kPa的更高真空压力。它们对应于以3.2–5.6 L / min的速度自由流动的空气。当系统以恒定的3 L / min的空气速度和可变的液体速度进行测试时，氧的溶解速率在液体速度为2.46 m / s时达到峰值，这也提供了最高的体积传质系数（K _La）为0.041 min ^-1，最高曝气效率为0.287 kgO ₂ / kWh。在自由流动的空气下，Q _L的影响在2.35至2.46 m / s的范围内显着，直到达到平稳段K _L a值为0.0416 min ^-1为止。K _L a趋势的模式反映在达到0.424 kgO ₂ / kWh最大值的曝气效率上。曝气效率的发现表明，通过关注气泡大小和空气体积速度之间的权衡以平衡要转移的可用氧气量和氧气速率之间，可以进一步优化文丘里孔MBG。转让。