Effect of viscosity on homogeneous–heterogeneous flow regime transition in bubble columns

Abstract

Experiments were performed in a cylindrical 0.14 m diameter bubble column with a metal perforated plate. Air and aqueous solutions of glycerol with viscosity 1-22 mPa s were the phases. Gas holdup was measured and plotted against the gas flow rate. The critical point where the homogeneous-heterogeneous regime transition begins was determined by the drift-flux plot of the primary data. The homogeneous regime stability was expressed by the critical values of the gas holdup and gas flow rate. The results show that moderate viscosity (3-22 mPa s) destabilizes the homogeneous regime and advance the transition. The results indicate that low viscosity (1-3 mPa s) could stabilize the homogeneous regime. The destabilizing effect of the column height proved previously for air-water system applies also to viscous batches.

Characterization of the localized hydrodynamic shear forces and dissolved oxygen distribution in sparged bioreactors

“…Unless the superficial gas velocity is kept very low, bubbles can no longer be considered as rising alone, since the proximity of other bubbles has the potential to affect both their motion and the dynamics of the liquid flow around them. The transition between the two regimes depends on the geometry of the reactor and viscosity of the medium, among other factors, with higher viscosities usually enhancing the transition (Ruzicka et al, 2003). In order to account for the changes in the continuous-phase hydrodynamics due to bubble-bubble interactions (Dhanasekharan et al, 2005), multiple bubbles were considered in our simulations.…”

Gas-Liquid Direct-Contact Evaporation: A Review

“…An augmentation of liquid viscosity is normally reported to favor the heterogeneous regime [59,75,80]. However, according to the experimental data of Ruzicka et al [81], such a trend is only to be expected for moderate viscosity values (3±22 mPa s); there exists a narrow viscosity range (1±3 mPa s) in which the opposite effect is actually observed. Experimental evidence of a shift in u trans towards slightly higher values upon an increase in liquid viscosity was recently reported by Mouza et al [82], who worked with water and aqueous glycerin solutions in a square column with porous spargers.…”

“…The former derives from the theory of linear stability and is limited to 2D columns, whereas the latter, based on an analogy with the Rayleigh-Benard instability of thermal layers in thermal convection, predicts a stabilizing effect of liquid viscosity on the homogeneous regime, a fact that was recently observed, but only for a narrow viscosity range [81]. Using the linear stability analysis, Thorat and Joshi [69] derived a theoretical equation for computing the transition gas holdup.…”

On the estimation of the regime transition point in bubble columns

“…Initially, different expressions were sought to represent u trans as a function of operating parameters chosen based on available experimental information about the relevant variables for regime transition and their respective effects [11,43,[55][56][57][58][59][60].…”