fluids Article Two-Phase Flow Mass Transfer Analysis of Airlift Pump for Aquaculture Applications Rashal Abed 1 , Mohamed M. Hussein 1 , Wael H. Ahmed 1, * and Sherif Abdou 2   Citation: Abed, R.; Hussein, M.M.; Ahmed, W.H.; Abdou, S. Two-Phase Flow Mass Transfer Analysis of Airlift Pump for Aquaculture Applications. Fluids 2021, 6, 226. https://doi.org/ 10.3390/ﬂuids6060226 Academic Editors: Goodarz Ahmadi and Mehrdad Massoudi Received: 29 April 2021 Accepted: 11 June 2021 Published: 16 June 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁl- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 School of Engineering, University of Guelph, Guelph, ON N1G 2W1, Canada; rabed@uoguelph.ca (R.A.); husseinm@uoguelph.ca (M.M.H.) 2 FloNergia Inc., Burlington, ON L7L 4Y3, Canada; sherif.abdou@ﬂonergia.com * Correspondence: ahmedw@uoguelph.ca; Tel.: +1-(519)-824-4120 (ext. 53674) Abstract: Airlift pumps can be used in the aquaculture industry to provide aeration while concur- rently 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. Keywords: two-phase ﬂow; mass transfer; aeration; ﬂow patterns; airlift pump 1. Introduction Within the aquaculture industry, aeration and water circulation are among the most essential needs to maintain the proper dynamics of a lake [1]. Both of these processes assist in sustaining and prolonging the life of a body of water, while simultaneously improving the water quality, as well as the health and the production capacity of the farmed aquatic animal [2]. Water circulation is typically used to keep the water temperature consistent, reduce stratiﬁcation, increase nutrient solubility, and reduce the buildup of organic substances at the bottom of the tank [3]. In contrast, aeration, which is the addition of oxygen into the water, is used to support the aquatic life within the system by providing adequate aerobic conditions [1]. Airlift pumps are proven to be effective systems within this industry due to their ability to aerate and circulate water simultaneously. An aerator’s main function is to supply a pond with the proper concentration of dissolved oxygen in order to improve the energy efﬁciency of the oxygen transfer pro- cess [4]. A study testing the oxygen transfer within an airlift system concluded that if designed properly, an airlift pump can reach greater efﬁciencies for oxygen transfer than a diffused aeration system [5], eliminating the need for an added aeration device. Some important oxygen transfer parameters to evaluate the oxygenation occurring in the system are the standard oxygen transfer rate (SOTR) and the standard aeration efﬁciency (SAE). The SOTR can be deﬁned as the mass of oxygen that can be added to the body of water per unit time at standard conditions (20 ◦ C water, 0 mg/L initial DO concentration and 1 atm Fluids 2021, 6, 226. https://doi.org/10.3390/ﬂuids6060226 https://www.mdpi.com/journal/ﬂuids