-Airlift pumps use buoyant forces to displace liquid in vertical pipes. In this paper, the performance of a new design of airlift pump has been investigated. This new design uses both axial and radial injectors to improve the pump performance. The behaviour of two-phase flow under different operating conditions of the pump is discussed. These include the effect of submergence ratio, air flow rate and void fraction on the pump efficiency. Flow visualization images are used to describe the two-phase flow patterns and their effect on the pump performance. It was clear from the present experiments that the pump operating at higher submergence ratios found to deliver higher water flow rates and better efficiencies. The void fraction was found to increase throughout the different flow patterns observed in the pipe riser while the water flow rate remained approximately constant.

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Airlift pumps can be used in the aquaculture industry to provide aeration while concurrently moving water utilizing the dynamics of two-phase flow in the pump riser. The oxygen mass transfer that occurs from the injected compressed air to the water in the aquaculture systems can be experimentally investigated to determine the pump aeration capabilities. The objective of this study is to evaluate the effects of various airflow rates as well as the injection methods on the oxygen transfer rate within a dual injector airlift pump system. Experiments were conducted using an airlift pump connected to a vertical pump riser within a recirculating system. Both two-phase flow patterns and the void fraction measurements were used to evaluate the dissolved oxygen mass transfer mechanism through the airlift pump. A dissolved oxygen (DO) sensor was used to determine the DO levels within the airlift pumping system at different operating conditions required by the pump. Flow visualization imaging and particle image velocimetry (PIV) measurements were performed in order to better understand the effects of the two-phase flow patterns on the aeration performance. It was found that the radial injection method reached the saturation point faster at lower airflow rates, whereas the axial method performed better as the airflow rates were increased. The standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) were calculated and were found to strongly depend on the injection method as well as the two-phase flow patterns in the pump riser.

Two-phase flow can be seen in petroleum, air conditioning systems, refrigeration systems, pumping technologies and power generation [1]. Two-phase flow is characterized by different flow pattern such as bubble flow, churn flow, slug flow, and annular flow behaviour[2]. Void fraction can be defined as the volumetric ratio between the gas phase to the total mixture. One of the most widely used techniques to determine void fraction is the electrical impedance by placing two electrodes on either side of the pipe and measuring the impedance between these two probes [3]. In this technique the capacitance change is related to the variation of the dielectric constants of the two phases within the sensor [4]. Minimizing the error in the capacitance readings will prove helpful in accurately identifying the flow pattern passing through the sensor. The void fraction time signal for air-water two-phase mixture will be evaluated for different two-phase flow patterns by the use of a capacitance sensor. The experimental setup consists of a Flonergia airlift pump, and controlled through mass flow meters to be able to create the different flow patterns within the vertical pipe. A concave designed sensor was mounted on the vertical pipe and connected to a DAQ system where the data is collected using LabVIEW. To ensure accurate readings from the capacitance sensor, a calibration of the sensor was performed by taking time signals of two cases: 1. Vertical column full of liquid, 2. Vertical column full of air. This provides the two points on a linear calibration curve between void fraction and the capacitance signals. For each air-water capacitance signal, 50000 samples are collected at a sample rate of 1000 Hz to obtain the time signal for each case. It was determined that the average air signal was 401.5 and the average water signal was 412.93. By taking the maximum root mean square from each signal and dividing the value by the range, the error in each reading was less than 1 %. The three flow regimes that were evaluated were bubbly flow, slug flow, and churn flow. The void fraction that were determined for each flow rate were 1.6% for an air flow rate of 0.5LPM, 14% for 3.5 LPM and 21% for 15 SLPM. It was observed that as the airflow rates increased, the void fraction also increased and the flow patterns change for bubble to slug and to churn flow. The next steps will be to evaluate the time signal for each flow pattern to understand the structure of the bubble that will be passing through the capacitance sensor. Evaluating the time signal will give a better understanding of the flow pattern that is in operation. In addition, the void fraction for a range of flow conditions can be compared with flow visualization to accurately determine the flow pattern.