A Study on the Effect ofNozzle Type on the Hydrodynamics of Ejector-Induced Cocurrent Upflow Bubble Column

Bubble columns as gas-liquid cocurrent contactors have gained a considerable attention
due to various advantages they offer. The effectiveness of gas distributors in the bubble
columns determines the mass transfer efficiency of the column. Ejector is one of the most
widely used devices as the gas distributors in the bubble columns. Although empirical
correlations for the ejectors have been reported in literature, no study based on the
principle of fluid mechanics has been carried out on the effect of ejector geometry on its
important hydrodynamic characteristics. A better understanding of the ejectors is essential
for an improved design of the ejector itself and the bubble column.
In the present work, the experimental setup consists of an ejector integrated with upflow
bubble column and a gas-liquid separator at the top of the column. Experimental
investigations have been carried out on the effect of ejector nozzle geometry on the
hydrodynamics of cocurrent upflow bubble column. Gas entrainment rate, gas hold-up,
pressure drop and energy dissipation for water-air system are studied and reported.
Experiments have been conducted using convergent and orifice nozzles with different
types and sizes.
It is found experimentally that nozzle with smaller nozzle diameter develops higher
vacuum and entrains more air as the suction fluid, for a given flow rate of water as the
motive fluid. This also means that nozzle with smaller nozzle diameter gives higher gas
hold-up and dissipates more energy to create intense mixing between the two phases. In
terms of nozzle type, orifice nozzles present higher vacuum level than convergent nozzles
for the same nozzle diameter. The pressure drop across the nozzle and the air entrainment
rate have been modeled and analyzed by applying Bernoulli's principle. Predicted values
of air entrainment rate as a function of water flow rate through the nozzle by the
theoretical model developed show good agreementwith experimental values. Gas hold-up
data has also been analyzed using drift flux model. The analysis agrees well with the
previous works.