Extending the application of electrical resistance tomography using linear probes in fluid mixing diagnosis
G. Forte1, 2*, P.J. Clark1, O. Wale3, J.F. Hall4, N. Zumaeta4 M.J.H. Simmons2 & E.H. Stitt1
1 Johnson Matthey Technology Centre, Billingham, TS23 4LB, UK
2 School of Chemical Engineering, University of Birmingham, Edgbaston, B15 2TT, UK
3 Johnson Matthey Technology Centre, Sonning, RG4 9NH, UK
4 Johnson Matthey, Environmental Catalytic Technologies, Royston, SG8 5HE, UK
Electrical Resistance Tomography (ERT) has been widely employed to investigate mixing in stirred tanks either employing a cylindrical electrode cage or a linear probe. This paper reviews the use of the linear probe for mixing studies in stirred vessels; it has been used to determine mixing times on pilot and full scale vessels to support scale up of mixing processes. This technique is shown to be able to distinguish different mixing regimes within multiphase systems and to provide at least qualitative information on the dispersion of the gas and suspension of the solids. This work aims to explore in more detail the response of the probe, enabling identification of its potential and limitations in detecting complex phenomena such as turbulence. The length and time scales of the measurement are similar or longer than those of the Kolmogorov scales of turbulence. It is thus reasonable to hypothesize that turbulence and convective flows may play a significant role in influencing the observed macro-scale electrical properties of the system, resulting in an increase in the apparent conductivity of the fluid.
In studies using suspended dense conducting particles we have observed that accounting for the liquid conductivity profile allows improved observations of the effect of the particle addition on the conductivity and consequently their distribution over the height of the tank. This may prove a more reliable way to assess the distribution of conducting solids and measure cloud height for these very conductive systems.
Keywords Electrical Resistance Tomography ERT, stirred tank, three-phase mixing, turbulence
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