Investigation of the effect of viscosity on slug flow in airlift tubular membranes in search of a sludge surrogate

Abstract

The behaviour of three different liquid-gas slug flows (water, carboxymethyl cellulose and activated sludge) in a vertical tube was studied using a high speed camera (HSC). Experiments were performed using different flow rates and two tube diameters (6.3 and 9.9 mm). The observed difference in behaviour of the ascending gas slugs can be explained by the difference in viscosity of the fluids (Newtonian and non-Newtonian). Moreover, it was observed that the degree of coalescence of gas slugs is lower for non-Newtonian liquids and they behave like a succession of slugs without actually coalescing into a single larger gas slug. Finally, gas slug rising velocities were also extracted, but no subsequent difference in the rising velocities of the different fluids was found.

The use of electrical resistance tomography for the characterization of gas holdup inside a bubble column bioreactor containing activated sludge

“…Because of the necessity of fluid transparency for the application of many measuring techniques and difficulties of working with real activated sludge systems, previous researchers have instead used surrogates such as water, xanthan gum solutions, yeast suspensions, and carboxylmethyl cellulose (CMC) solutions in their experiments [6,[14][15][16][17]. But the representativeness of these surrogates is questionable.…”

Heat-and-mass transfer relationship to determine shear stress in tubular membrane systems

“…The parameter C TB depends on the velocity profile of the liquid upstream of the rising bubble, k TB is a constant function of the Froude number, g, is the gravity acceleration, q L and q G are the liquid and gas densities, respectively. Previous efforts [5,22] estimated the values of C TB and k TB as 1.077 ± 0.014 and 0.277 ± 0.068 respectively (error range corresponds to the 95% confidence interval of the estimated parameters). Hydrodynamic models of slug flow have already been reported in literature [23][24][25][26].…”

“…Zheng and Che [28,29] proposed the addition of a semi-empirical correction factor (C) to Eq. (22), to take into consideration the buoyancy forces (i.e. gas rises faster than liquid) and the slug length.…”

“…(60) and (61). This correction factor should consider the fact that the hydraulic diameter changes in the falling film zone (thickness of the boundary layer), and that the slug flow Reynolds number ($1800-3000) is either in the laminar or transition regime [22]. The correction factor is a function of the Reynolds number as defined by Eq.…”

Electrical resistivity tomography used to characterize bubble distribution in complex aerated reactors: Development of the method and application to a semi-industrial MBR in operation

“…However, the application of such methods requires specific fluid characteristics such as transparency or electrochemical properties and cannot be operated in presence of activated sludge. On the other hand, the impact of rheology on bubble size, shape and preferential flow path have been reported [4,11] and should not be neglected. Braak et al [12] compared hydrodynamics between air/water and air/mixed liquor flows.…”