Effect of submergence ratio on the liquid phase velocity, efficiency and void fraction in an air-lift pump

• We examine the minimum air flow rate needed to induce the circulation of the liquid phase.
• Pump efficiency increases with increasing submergence ratio but beyond 75% it decreases.
• The minimum of superficial velocity ratio of the phases corresponds to optimal operating conditions of the air-lift pump.
• The evolution of void fraction with slip ratio for air-lift system is different when compared to others two phase upward flows.

The effects of submergence ratio and gas flow rate on the induced liquid flow rate, efficiency and void fraction have been investigated in an air-lift system. The experiments were conducted using a transparent riser pipe of 3.1 m length and 33 mm inner diameter. The evolution of liquid flow rate in function of air flow rate presents a first step of rapid growth followed by a constant liquid flow rate depending on the submergence ratio. These operating regimes have been linked to slug flow and churn flow correspondingly. It has been observed that the highest performance of the air-lift pump is related to the slug flow and slug to churn flow transition. The results also show that the minimum of superficial velocity ratio of the phases coincides with the maximum of pump efficiency. The maximum pump efficiency decreases for submergence ratios beyond 0.75. The behavior of void fraction, when the liquid is in circulation, is characterized by mean regular growth with an air flow rate accompanied by variations inherent to the dynamics of two-phase flow and is well represented using the drift-flux model. The results also show that the evolution of void fraction with slip ratio for air-lift system is different when compared to others two phase upward flows.

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