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Experimental investigation of mixing phenomena in a gas stirred liquid bath

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Abstract

Mixing phenomena in a room temperature water bath, agitated by injecting air through a straight circular nozzle fitted axially at the bottom of the vessel, were characterized by experimentally measuring mixing time(t mix) by electrical conductivity technique. It was found thatt mix defined at 99.5 pct homogenization did not depend on location and size of conductivity probe, location of tracer injection, and the amount of tracer injected. tpet decreased with increasing gas flow rate and bath height, but decreasing nozzle diameter. Visual observations of the two-phase plume and flow conditions in the bath revealed that the plume swirled above a certain gas flow rate which enhanced the mixing rates in the bath. The transitions in Int mix vs In εb curves were found to correspond to onset of swirling; εb is the rate of buoyancy energy input per unit bath volume. Systematic analysis of experimental data revealed that a fraction of gas kinetic energy contributed to mixing in the bath. It was a function of bath height, being negligible at lower bath heights and almost 1 at larger bath heights. Further, it was experimentally found thatt mix decreased with increasing bath height only up to a certain value, beyond which it started increasing. Visual observations of the bath revealed that the height at whicht mix started increasing corresponded to a transition in which the bath was converted into a bubble column. The experimental data, for a particular bath height, were fitted into two separate straight lines of the formt mix =cε −n wherec andn are empirical constants and ε is the rate of energy input per unit bath volume.

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Abbreviations

a :

empirical constant defined by Eq. [3]

c 1c2 :

empirical constants defined by Eqs. [7] and [8], respectively

D :

bath diameter (m)

d n :

nozzle diameter (mm)

g :

acceleration due to gravity (m/s2)

H :

bath height (m)

h :

defined by Eq. [6] (m)

n, n1 :

empirical constants defined by Eqs. [3], [7], and [8],

n 2 :

respectively

Patm :

atmospheric pressure (N/m2)

Q :

gas flow rate (Nm3/s)

s :

standard error (dimensionless)

T L :

liquid temperature (K)

t mix :

mixing time (s)

u LP :

average liquid velocity inside plume (m/s)

V L :

bath volume (m3)

V p :

plume volume (m3)

x :

fraction of gas kinetic energy contribution to mixing (dimensionless)

Y :

degree of mixing (dimensionless)

ε:

rate of energy dissipation per unit bath volume (kg/ms3)

ε b :

rate of buoyancy energy per unit bath volume (kg/ms3)

ε bc :

it corresponds to transition in Int mix vs In εb plots (kg/ms3)

ε bs :

it corresponds to onset of swirling motion of plume (kg/ms3)

ε k :

rate of gas kinetic energy per unit bath volume (kg/ms3)

θ c :

plume cone angle (deg)

p G :

gas density (kg/m3)

p L :

liquid density (kg/m3)

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Authors and Affiliations

  1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, 02139, Cambridge, MA

    G. G. krishna Murthy (Postdoctoral Fellow)

  2. Department of Metallurgical Engineering, Indian Institute of Technology, 208016, Kanpur, India

    S. P. Mehrotra (Professors) & A. Ghosh (Professors)

Authors
  1. G. G. krishna Murthy
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  2. S. P. Mehrotra
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  3. A. Ghosh
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Formerly Graduate Student in the Department of Metallurgical Engineering at the Indian Institute of Technology, Kanpur, India

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Murthy, G.G.k., Mehrotra, S.P. & Ghosh, A. Experimental investigation of mixing phenomena in a gas stirred liquid bath. Metall Trans B 19, 839–850 (1988). https://doi.org/10.1007/BF02651408

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