Table 1: Experimental methods for characterizing (adapted from [1, 4]).

Method proposed byConceptAdvantagesDisadvantagesApplicabilityAccuracy

Zwietering [3]Visual observation of particles that do not rest at the vessel bottom for more than 1-2 secSimplicity, nonintrusiveNot applicable for opaque system, high uncertainty for high solid loading systems,
careful and skilled observation is necessary
13
Mersmann et al. [5]Visual observation of the height of the slurry compared to the total heightNonintrusive, SimplicitySmall particles suspended, come to the top of the tank, results in vanishing interface while larger particles are still resting at the bottom 15
Rewatkar et al. [6]Variation of impeller power consumption by increasing the amount of solid suspendedNonintrusive, can be used for opaque systemsRequires accurate measurement of power consumption, expensive for large scale vessels, the criteria are not clear 35
Rewatkar et al. [6]Variation of liquid phase mixing time by increasing amount of solid suspendedCan be used for opaque systemRequires accurate measurement of mixing time, not applicable for large-scale vessels, the criteria are not clear, in high solid loading or three-phase systems, accurate measurement of mixing time is challenging 35
Rewatkar et al. [6]Decrease in count rate recorded from radioactive tracer inside the vessel by increasing impeller speedNonintrusive can be used in opaque systemDecrease in recorded count rate could be because of tracer dispersion not just off-bottom suspension
The criteria are not clear
55
Musil et al. [7]Discontinuity in solid concentration close to the bottom of the vessel by increasing impeller speedCan be used in opaque systemIntrusive, accurate measurement of concentration is challenging 34
Chapman et al. [8]Peak in solid concentration measured close to the bottom of the vessel by increasing impeller speedCan be used in opaque systemIntrusive
accurate measurement of concentration is difficult
34
Buurman et al. [9]Use of Doppler effect at vessel bottomIndependent of material and scale, nonintrusiveApplying the technique is challenging, ultrasound sensor must be installed inside the vessel otherwise signals are scattered by wall 42
Micale et al. [10, 11]Change in the pressure recorded at the bottom of the vessel by increasing impeller speedIndependent of material, nonintrusiveProper selection of pressure recording port is important, method proposed to eliminate effect of dynamic pressure head is not accurate 23

Accuracy: 1: most accurate, 5: least accurate, Applicability: 1: easiest to apply, 5: most difficult to apply.