Airlift pumps characteristics for shear-thinning non-Newtonian fluids: An experimental investigation on liquid viscosity impact

Shear-thinning non-Newtonian fluids are applied in a variety of chemical processing, wastewater, and food industries. However, handling and pumping these fluids, often possessing high viscosities, present significant challenges in these industrial settings. One effective solution to alleviate difficulties of pumping such fluids is through utilizing airlift pump technology. However, the use of this technology for these applications has not been sufficiently evaluated in the literature. In the present study, the operational performance of airlift pumps handling non-Newtonian fluids is experimentally investigated. A series of experiments is conducted using an airlift pump with a size of 31.75 mm to pump Xanthan Gum-water solutions with different concentrations of XG between 0.05 and 0.60 wt% (corresponding to viscosities ranging between 10 and 1000 cP) at a wide range of inlet air flow rates (6-140 SLPM). The impact of viscosity changes on the delivered liquid flow rate and pump efficiency is analyzed. In this analysis, high-speed imaging and capacitance sensor are used to evaluate the flow patterns and the instantaneous void fraction data needed to characterize the two-phase flow hydrodynamics. The effect of liquid viscosity on the time-series and the time-averaged void fraction data, their PDF distributions, flow pattern transition, and bubbles dynamic behavior is discussed. The results show that, on average, as liquid viscosity increases from 10.0 to 1000.0 cP, both delivered liquid flow rate and pumping efficiency reduce by 64.60% and 64.79%, respectively. However, the optimum performance points (i.e., maximum delivered liquid flow rate and pump efficiency) were found to occur around the same inlet air flow rates (in churn and slug flow patterns, respectively) regardless of the increase in liquid viscosity. Moreover, increasing the viscosity is found to significantly affect the instantaneous void fraction distributions and accelerate the slug-to-churn transition. Liquid viscosity shows a slight influence on average void fraction values; void fraction gradually rises as the viscosity increases from 20.0 to 1000.0 cP. Also, it is seen that Taylor bubbles and churn structures increase in length, while their velocity and frequency decline as the liquid viscosity increases.