The effects of operating conditions including a novel downcomer geometry on the gas/air entrainment rate, Qa
, were investigated for a local vertical confined plunging liquid jet reactor (CPLJR) as an alternative aeration process that is of interest to Kuwait and can be used in various applications, such as in wastewater treatment as an aerobic activated sludge process, fermentation, brine dispenser, and gas–liquid reactions. Operating conditions, such as various downcomer diameters (Dc
= 45−145 mm), jet lengths (Lj
= 200–500 mm), nozzle diameters (dn
= 3.5–15 mm), and contraction angles (Ɵ
=20–80°), were investigated. A newly designed downcomer with various mesh openings/pores (Dm
= 0.25ʺ (6.35 mm)–1ʺ (25.4 mm)) was also investigated in the current study. The air entrainment results showed that these were the primary parameters for the measured air entrainment rate in confined systems. The highest gas entrainment rates were achieved when the ratio of the downcomer diameter (Dc
) to the nozzle diameter (dn
) was greater than approximately 5, as long as the liquid superficial velocity was sufficient to carry bubbles downward. Furthermore, a downcomer with mesh openings (Dm
) less or equal to 0.5ʺ (12.7 mm) provided a higher entrainment rate than that of conventional downcomer (without a mesh).
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