Effect of fine particles on gas hold-up in three-phase sparged reactors

The dual effect of viscosity on bubble column hydrodynamics

“…The increase in the gas holdup at low viscosities and its consequent decrease at higher viscosities is in qualitative agreement with the findings from other authors (see, for example, refs. (Bach and Pilhofer, 1978;Eissa and Schügerl, 1975;Godbole et al, 1982;Khare and Joshi, 1990;Olivieri et al, 2011;Rabha et al, 2014;Ruzicka et al, 2003)). An interesting discussion concerning the contribution of the "coalescence-induced" bubbles to the gas holdup structure in highly viscous liquid phases, was proposed by Yang et al (2010), to whom the reader should refer.…”

“…In addition, they observed that, for CMC solutions, the gas holdup first increases up to, approximately, μ L =2.23 -4.75 mPa s, then it decreases (7.81 < μ L < 52.29 mPa s, depending on U G ), and finally becomes roughly constant (μ L > 52.29 mPa·s). Khare and Joshi (Khare and Joshi, 1990) (d c =0.20 m, H c =3.0 m, sieve plate, d 0 =2.0 mm) studied the influence of viscosity on the gas holdup using aqueous solutions of glucose: as a result, they observed that the gas holdup first increases up to μ L =4 mPa s and then it decreases for 4 < μ L < 10 mPa·s. Ruzicka et al (Ruzicka et al, 2003) (d c =0.14 m, H 0 =0.2 -0.8 m, perforated plate, d 0 =0.5 mm) summarized the influence of the viscosity over the gas holdup as follows: with increasing liquid viscosity the gas holdup increases for μ < 3 mPa·s and it decreases for 3 < μ < 22 mPa s. Olivieri et al (2011) (d c =0.12 m, H c =2 m, H 0 =0.8 m, needle sparger, d 0 =0.4 mm) investigated the effect of the liquid viscosity using several aqueous solutions of Alginate within the viscosity range 1-117 mPa s: they reported an increase in the gas holdup up to μ L =4.25 mPa s and, then, a decrease at higher viscosities.…”

“…When increasing the viscosity, the tendency to coalescence prevails, creating large bubbles rising the column at a higher velocity, thus reducing the gas holdup. In particular, the "dual effect of the viscosity" was clearly observed in some experimental investigations (Bach and Pilhofer, 1978;Eissa and Schügerl, 1975;Godbole et al, 1982;Khare and Joshi, 1990;Olivieri et al, 2011;Rabha et al, 2014;Ruzicka et al, 2003), but it is not clear whether it also applies to larger bubble columns (see, for example, the fluid dynamics phenomena behind Eq. (1)) and what the reasons are behind this behavior.…”

“…(1)) and what the reasons are behind this behavior. At present, Godbole et al (1982) and Khare and Joshi (1990) are the only investigators who studied the dual effect in a large-diameter bubble column, but they only focused on the gas holdup.…”

New Approaches for Theoretical Estimation of Mass Transfer Parameters in Both Gas-Liquid and Slurry Bubble Columns

“…reported many gas holdup correlations developed on the basis of atmospheric data and they do not incorporate any influence of gas density. In the case of liquid mixtures, Bach and Pilhofer (1978), Godbole et al (1982) and Khare and Joshi (1990) determined that gas holdup does not decrease if the viscosity of water is increased by adding glycerol, carboxymethyl cellulose (CMC) or glucose but passes through a maximum. Wilkinson et al (1992) assumes that this initial increase in gas holdup is due to the fact that the coalescence rate in mixtures is lower than in pure liquids.…”