Abstract
The dynamic behaviors of gas-liquid two-phase flow were simulated in a lab-scale intermittent bubble column by Euler-Euler two-fluid model coupled with the PBM (population balance model) using two different liquid phases, i.e., Newtonian fluid (water)/non-Newtonian fluid (activated sludge). When non-Newtonian fluid was used during intermittent aeration, some interesting results were obtained. Two symmetric vortexes existed in the time-averaged flow field; the vertical time-averaged velocity of the liquid phase decreased with increasing anaerobic time; the average gas holdup distribution was like a trapezoid with long upper side and short lower side and affected by the dynamic viscosity of the liquid phase. Compared with non-Newtonian fluid, the use of Newtonian fluid as the liquid phase led to a more complicated time-averaged flow field structure and vertical time-averaged velocity distribution, higher average gas holdup, and the asymmetric column-shaped gas holdup distribution with increasing anaerobic time. For different liquid phases, the instantaneous flow field, instantaneous vertical velocity, and instantaneous gas holdup distribution all periodically changed with anaerobic time; however, different from Newtonian liquid phase, non-Newtonian liquid phase had no periodic oscillating instantaneous horizontal velocity.
Highlights
The bubble column is widely used for study on wastewater treatment because of its low price, easy transport, and high mass transfer characteristics [1,2,3,4]. e bubble column is mainly researched by experiment and numerical simulation [5, 6]
[33] I was used for the modeling of the coalescence processes. e coalescence and breakage model described in this paper has been used to study the numerical simulation of a bubble column [5, 10, 22]. e number of cases, i 1 to 10, represents the 10 groups of bubbles [22]
When the anaerobic time was below 9 s as shown in Figures 3(a)–3(e), two approximately symmetric main vortexes existed in the bubble column, and their centers were located in the middle lower part of the bubble column. at complied with the time-averaged results from continuous aeration at low velocity given by Dıaz et al [22]
Summary
The bubble column is widely used for study on wastewater treatment because of its low price, easy transport, and high mass transfer characteristics [1,2,3,4]. e bubble column is mainly researched by experiment and numerical simulation [5, 6]. Wu [20] performed the gas-liquid numerical simulation of an anaerobic digester and considered the effect of non-Newtonian liquid His results showed that the low Reynolds number k-ε model was better than other turbulence models, and the gas-liquid mixing efficiency depended on the mixing mechanism and pumping cycle, but he used the drag force model for Newtonian fluid. Us, Euler-Euler two-fluid model coupled with PBM (EEPBM) was used in this paper for numerical simulation of gas-liquid two-phase flow in a lab-scale bubble column and analysis of dynamic behaviors of the fluids in a bubble column, such as gas holdup distribution, liquidphase flow field, and liquid phase velocity field, based on the comparison with the experiment [22] and verification of the mathematical model. Most liquid phases for numerical simulation of gas-liquid two-phase flow in a bubble column are Newtonian fluids, and there is a rare literature on dynamic behaviors of gas-liquid two-phase flow of Newtonian/nonNewtonian liquid phase in an intermittent aerating bubble column. us, Euler-Euler two-fluid model coupled with PBM (EEPBM) was used in this paper for numerical simulation of gas-liquid two-phase flow in a lab-scale bubble column and analysis of dynamic behaviors of the fluids in a bubble column, such as gas holdup distribution, liquidphase flow field, and liquid phase velocity field, based on the comparison with the experiment [22] and verification of the mathematical model. e drag force equation and intermittent aeration control of the non-Newtonian fluids were simulated by UDF (user-defined program). e research results provide references and guides for optimized design of the intermittent aerating bubble column for wastewater treatment
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