Proceedings of the 8 th World Congress on Momentum, Heat and Mass Transfer (MHMT'23) Lisbon, Portugal – March 26 – 28, 2023 Paper No. ICMFHT 109 DOI: 10.11159/icmfht23.109 ICMFHT 109-1 Airlift Pumps with Annulus Risers: An Experimental Investigation Shahriyar G. Holagh 1* , Dana Fadlalla 1 , Marwan H. Taha 1 , Alexander Doucette 1 , Wael H. Ahmed 1 School of Engineering, University of Guelph, Guelph, N1G 2W1, ON, Canada *Ghazanfs@uoguelph.ca Abstract – Airlift pumps are used in many industries. In these pumps, the performance is strongly affected by the geometrical design conditions. In this study, the performance of an airlift pump is experimentally evaluated for both circular and annulus pump risers. An airlift pump operating under air-water two-phase flow conditions was tested using a dual pump injector and for a constant submergence ratio. Capacitance sensors are used to measure the instantaneous void fraction through the pump riser, while high-speed images are analyzed to identify the interfacial structures of the air-water two-phase flow patterns through the pump risers. The results show that the water flow rate and efficiency of the pump for both risers are strongly dependent on the flow-pattern. In the annulus riser, higher liquid flow rates and pump efficiency are achieved at low gas flow rates, where slug pattern exists, while for the circular riser, the pump performs better at higher gas flow rates. Also, void fraction was found to be higher in the annulus riser for the entire range of gas flow rate due to the smaller cross-sectional area and the faster gas phase velocity through this area. Moreover, in the annulus riser, the Taylor bubble exhibited rotational motion around the pipe axis while moving upward. The length of Taylor bubbles in the pump riser was found to be longer and move with higher velocity and frequency in the case of the annulus riser, which is contributing to the better pump performance at low air flow rates. Keywords: Airlift Pump; Annulus Riser; Performance; Efficiency; Void Fraction; Air-water 1. Introduction Airlift pumps are usually utilized for flow recirculation and aeration purposes in many industrial applications like aquaculture and sewage treatment, while they can be used to lift heavy and viscous liquids/mixtures such as hydrocarbons in oil and gas extraction or moving explosive and toxic liquids in chemical processing plants. An airlift pump is composed of a vertical pipe (i.e., riser) submerged into liquid tank and connected to a gas injector at the bottom, where gas is injected and leads to the creation of a gas-liquid mixture within the riser. The two-phase mixture has lower specific gravity; this, in turn, pushes the liquid phase upward, and pumping is accomplished. Having no moving mechanical components, these pumps offer low maintenance costs and more reliable operation while consuming less energy compared to conventional rotary pumps [1]. Literature review shows that both the lifted liquid flow rate vs. injected gas flow rate and efficiency (the ratio of the work used for lifting liquid to the work entering the system through isothermal expansion of the gas phase) curves of airlift pumps are influenced by operating and geometrical design conditions. Two-phase flow pattern within the riser, injected gas flow rate, void fraction, and working fluids are the most important operating conditions affecting their performance. On the other hand, geometrical aspects like submergence ratio (submerged length divided by the total riser length), riser diameter and length, injector design conditions (gas injection method and location) also strongly impact the pumps performance. Several studies have investigated altering the operating and geometrical conditions to improve the pump performance both experimentally and numerically. Generally, four common types of two-phase flow pattern (bubbly, stable and unstable slug, churn, and annular) have been observed in airlift pumps (Kassab et al. [2], [3], Hanifzadeh et al. [4], Ligus et al. [5], Charalampos et al. [6]). According to the literature, the pump performance is flow pattern dependent. That is, depending on the geometrical design, bubbly-slug transition [7], slug flow pattern [2] or slug-churn transition [8], [9] has been observed to give the highest efficiency, while slug-churn/churn flow patterns have been seen to result in the highest performance (i.e., increased liquid flow rate) [4]. Majority of the conducted studies have concentrated on the impact of operating and geometrical parameters on airlift pumps performance. According to the literature, the performance curve of airlift pumps is a function gas flow rate and pressure as well as submergence ratio and riser length and diameter [2], [10], [11]. In fact, lifted